Tubewell energy audit

TUBEWELL ENERGY
AUDIT MANUAL
NATIONAL ENERGY CONSERVATION CENTRE
ENERCON

Contents
1 INTRODUCTION.................................................................................................................1
1.1 Background..................................................................................................................................1
1.2 Water Requirement of Different Crops.............................................................................1
1.2.1 Kharif Crops...............................................................................................................................................................2
1.2.2 Rabbi crops.................................................................................................................................................................5
1.3 Ground Water in Pakistan......................................................................................................7
1.3.1 Quantity .......................................................................................................................................................................7
1.3.2 Quality ..........................................................................................................................................................................7
1.4 Tubewells in Pakistan..............................................................................................................7
1.5 Tubewell Energy Efficiency...................................................................................................8
1.6 Organization of the Manual................................................................................................10
2 CENTRIFUGAL PUMP..................................................................................................... 11
2.1 Types of Pumping System...................................................................................................11
2.1.1 Horizontal Shaft Centrifugal Pump...............................................................................................................11
2.1.2 Turbine (Vertical Shaft) Pump .......................................................................................................................12
2.1.3 Submersible Pump...............................................................................................................................................12
2.2 Components of Centrifugal Pump....................................................................................13
2.2.1 Impeller.....................................................................................................................................................................14
2.2.2 Shaft............................................................................................................................................................................14
2.2.3 Casing.........................................................................................................................................................................14
2.3 Pumping System Terminology..........................................................................................15
2.3.1 Head............................................................................................................................................................................15
2.3.2 Static Head...............................................................................................................................................................16
2.3.3 Friction head (hf)..................................................................................................................................................17
2.3.4 Pump Performance Curve.................................................................................................................................17
2.3.5 Pump Suction Performance (NPSH).............................................................................................................18
2.3.6 Best Efficiency Point............................................................................................................................................22
2.3.7 Pump Curves for Multiple Impeller Sizes ..................................................................................................23
2.4 Pump Speed Selection ..........................................................................................................24
2.5 How to Select a Centrifugal Pump ...................................................................................25
3 OPERATING CHARACTERISTICS OF TUBEWELL COMPONENTS .................... 27
ENERCON, The National Energy Conservation Centre
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3.1 Well.............................................................................................................................................. 29
3.1.1 Parts of Tubewell .................................................................................................................................................29
3.1.2 Draw Down .............................................................................................................................................................30
3.2 Pumps......................................................................................................................................... 31
3.3 Diesel Engines/Tractors...................................................................................................... 35
3.4 Electric Motors........................................................................................................................ 36
3.5 Transmission ........................................................................................................................... 38
3.6 Piping.......................................................................................................................................... 40
4 PERFORMANCE TESTING OF TUBEWELL COMPONENTS..................................43
4.1 Pumpset..................................................................................................................................... 43
4.2 Diesel Engine............................................................................................................................ 45
4.3 Electric Motor.......................................................................................................................... 46
4.3.1 Load Test.................................................................................................................................................................46
4.3.2 Stator Resistance..................................................................................................................................................47
4.3.3 No Load Test...........................................................................................................................................................47
4.4 Transmission ........................................................................................................................... 47
4.5 Pump........................................................................................................................................... 48
4.6 Piping System .......................................................................................................................... 49
4.7 Well.............................................................................................................................................. 49
5 INSTRUMENTSANDEQUIPMENT FORTUBEWELLENERGYAUDITS...........56
5.1 Water Flow Meter ................................................................................................................ 57
5.2 Pressure Module..................................................................................................................... 58
5.3 Multimeter................................................................................................................................ 58
5.4 Energy/Electric Power Analyzer ..................................................................................... 59
5.5 Tachometer............................................................................................................................... 59
5.6 Fuel Weighing System ................................................................................................... 60
5.7 Electric Well Sounder......................................................................................................... 60
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5.8 Diesel Engine Compression Tester..................................................................................61
5.9 Smoke Tester/Flu Gas Analyzer....................................................................................61
5.10 Thermocouple Thermometer............................................................................................62
5.11 Friction Torque Tester.........................................................................................................62
5.12 Tool Kit.......................................................................................................................................62
5.13 Accessories Kit ........................................................................................................................63
5.14 First Aid Kit...............................................................................................................................63
6 AUDIT METHODOLOGY......................................................................................... 64
6.1 Calibration of Instruments .................................................................................................64
6.2 Audit Procedure......................................................................................................................64
6.2.1 General Information:..................................................................................................................................64
6.2.2 Tube Well General Information .....................................................................................................................64
6.2.3 Safety Aspects....................................................................................................................................................64
6.2.4 Test Feasibility Review...............................................................................................................................65
6.2.5 Guidelines for Tube Well Energy Audit ..........................................................................................65
6.3 Energy Audit Performa ........................................................................................................73
6.4 Manpower/Time Frame ......................................................................................................73
7 DATA ANALYSIS AND DIAGNOSIS OF TUBE WELL PROBLEMS....................... 74
7.1 Calculations...........................................................................................................................74
7.1.1 Discharge..................................................................................................................................................................74
7.1.2 Head............................................................................................................................................................................75
7.1.3 Water Power.......................................................................................................................................................78
7.1.4 Pump Set Efficiency.......................................................................................................................................78
7.1.5 Piping Efficiency ..............................................................................................................................................78
7.1.6 Overall Efficiency ............................................................................................................................................79
7.1.7 Estimated Motor Efficiency..............................................................................................................................79
7.1.8 Estimated Engine Efficiency ............................................................................................................................79
7.1.9 Estimated Transmission Efficiency ..............................................................................................................80
7.1.10 Estimated Pump Efficiency.........................................................................................................................80
7.1.11 Friction Loss in Stuffing Box......................................................................................................................81
7.1.12 Voltage and Current Imbalance................................................................................................................81
7.2 Diagnosis of Tube well Problems.....................................................................................81
7.2.1 Cavitation.................................................................................................................................................................82
7.2.2 Variations in Total System Head....................................................................................................................85
7.2.3 Diesel Engine.........................................................................................................................................................86
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7.2.4 Pump..........................................................................................................................................................................86
7.2.5 Transmission..........................................................................................................................................................86
7.2.6 Piping System...................................................................................................................................................86
7.2.7 Well............................................................................................................................................................................87
7.3 Format for Audit Report...................................................................................................... 87
8 BEST PRACTICES FOR ENERGY EFFICIENT IRRIGATION AND TRACTOR
FUEL EFFICIENCY ....................................................................................................................93
8.1 Crop and Irrigation System Water Requirements..................................................... 93
8.1.1 Crop Evapotranspiration ..................................................................................................................................93
8 . 1 . 2 Irrigation F r e q u e n c y ............................................................................................................................93
8.1.3 Net Irrigation Requirement.............................................................................................................................94
8.1.4 Gross Irrigation Requirement.........................................................................................................................94
8.2 Water Requirement of Different Crops.......................................................................... 95
8.3 Irrigation Methods................................................................................................................. 96
8.3.1 Surface Irrigation .................................................................................................................................................96
8.3.2 High Efficiency Irrigation Systems (HEIS) ................................................................................................97
8.4 Tractor Fuel Efficiency......................................................................................................... 99
8.4.1 Fuel Efficiency Factors for Tractor Selection...........................................................................................99
8.4.2 Proper Gear Selection.........................................................................................................................................99
8.4.3 Ballasting Tractors for Fuel Efficiency......................................................................................................100
8.4.4 Tire Inflation.........................................................................................................................................................100
84.5 Tractor Maintenance to Conserve Energy...............................................................................................101
8.4.6 Efficient Soil Tillage Systems ........................................................................................................................101
ANNEX I : IRRIGATION PUMP SET EFFICIENCY IN DEVELOPING COUNTRIES –
FIELD MEASUREMENTS IN PAKISTAN
ANNEX II : UNIT CONVERSION TABLE
ANNEX III : PUMP PERFORMANCE CURVES
ANNEX IV : EFFICIENCY OF DIFFERENT MOTOR CLASSES
ANNEX V : FRICTION LOSS DATA FOR DIFFERENT PIPE SIZES
ANNEX VI : FILLED TUBEWELL ENERGY AUDIT REPORTS
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Exhibits
Exhibit 1.1 Typical Field in Punjab Being Irrigated.........................................................................................................1
Exhibit 1.2: Typical Irrigated Rice Field in Pakistan .......................................................................................................2
Exhibit 1.3: A Maize Crop Near Okara Ready for Harvesting ......................................................................................2
Exhibit 1.4: Typical Irrigated Cotton Field in Punjab......................................................................................................3
Exhibit 1.5: Furrow Irrigated Sugarcane Field ..................................................................................................................4
Exhibit 1.6: Typical Wheat Field in Punjab (Pakistan)...................................................................................................5
Exhibit 1.7: Typical Tubewell in Punjab ...............................................................................................................................7
Exhibit 2.1: Centrifugal Pump.................................................................................................................................................11
Exhibit 2.2Turbine Pump .........................................................................................................................................................12
Exhibit 2.3: Submersible Pump..............................................................................................................................................13
Exhibit 2.4: Components of Centrifugal Pumps..............................................................................................................13
Exhibit 2.5: Double Shroud Pump Impeller......................................................................................................................14
Exhibit 2.6: Volute Casing.........................................................................................................................................................15
Exhibit 2.7: Pump Static Head................................................................................................................................................16
Exhibit 2.8: Static Suction Head and Static Discharge Head .....................................................................................17
Exhibit 2.9: Pump Performance Curve ...............................................................................................................................17
Exhibit 2.10: Pump Operating Point....................................................................................................................................17
Exhibit 2.11: Reason of Cavitation........................................................................................................................................18
Exhibit 2.12: Available Net Pressure Suction Head (NPSH)......................................................................................20
Exhibit 2.13: Pump Operation Point....................................................................................................................................22
Exhibit 2.14: Family of Pump Performance Curves......................................................................................................23
Exhibit 2.15: Performance Curves for Different Impeller Sizes ..............................................................................24
Exhibit 2.16: Pump Selection..................................................................................................................................................25
Exhibit 3.1: Energy Input-Output of a Diesel Engine Operated Pumping System...........................................28
Exhibit 3.2: Borehole of a Horizontal Shaft Tubewell..................................................................................................29
Exhibit 3.3: Parts of Tubewell ................................................................................................................................................29
Exhibit 3.4: Pump Draw Down...............................................................................................................................................30
Exhibit 3.5: Pump and Well Characteristic Curves........................................................................................................32
Exhibit 3.6: Characteristic Curve of Centrifugal Pump................................................................................................33
Exhibit 3.7: Diesel Engine Performance Curves of Continuous Rated Power of 51 HP/38 kW................36
Exhibit 3.8: Motor Efficiency Vs. Load Level....................................................................................................................38
Exhibit 4.1: Energy Input-Output and Efficiency of a Water Pumping System ................................................43
Exhibit 4.2: Total Dynamic Head- Horizontal Shaft Centrifugal Pump ................................................................51
Exhibit 4.3: Field Head – Deep Well Turbine Pump......................................................................................................52
Exhibit 4.4: Motor Efficiency vs Power Factor................................................................................................................53
Exhibit 4.5: Observation Well to Measure Static and Pumping Water Levels for Uncased Well..............54
Exhibit 4.6: Pumping Situation Depicting No Well Problem.....................................................................................54
Exhibit 4.7: Pumping Situation Depicting Pump Installed at High Level Causing High Suction Lift.....54
Exhibit 4.8: Pumping Situation Depicting Plugged Strainer Causing High Suction Lift ........................55
Exhibit 5.1: Ultrasound Flow Meter.....................................................................................................................................57
Exhibit 5.2: Ultrasound Flow Meter Kit..............................................................................................................................57
Exhibit 5.3: Multimeter..............................................................................................................................................................58
Exhibit 5.4: Power Analyzer....................................................................................................................................................59
Exhibit 5.5: Tachometer............................................................................................................................................................59
Exhibit 5.6: Fuel Weighing System.......................................................................................................................................60
Exhibit 5.7: Electric Well Sounder........................................................................................................................................60
Exhibit 5.8: Diesel Engine Compression Tester..............................................................................................................61
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Exhibit 5.9: Smoke Tester ........................................................................................................................................................61
Exhibit 5.10: Thermocouple Thermometer .....................................................................................................................62
Exhibit 5.11: First Aid Kit.........................................................................................................................................................63
Exhibit 6.1: Typical Name Plates of Motor and Pump.................................................................................................65
Exhibit 6.2: Typical Capacitor Bank of Electric Tubewell..........................................................................................66
Exhibit 6.3: Ultrasonic Flow Meter in Installed Position............................................................................................66
Exhibit 6.4: Power Analyzer Readings ...............................................................................................................................66
Exhibit 6.5: Flow Meter Readings.........................................................................................................................................67
Exhibit 6.6: XY Method (Flow Trajectory Method) for Flow Measurement ......................................................67
Exhibit 6.7 : Scale in Position to take X Reading............................................................................................................68
Exhibit 6.8: Free Zone Measurement..................................................................................................................................68
Exhibit 6.9: Electrical Readings.............................................................................................................................................69
Exhibit 6.10: Motor Speed Measurement..........................................................................................................................70
Exhibit 6.11: Motor Temperature Measurement...........................................................................................................70
Exhibit 6.12: Depth of Pump Installation..........................................................................................................................71
Exhibit 6.13: Length of Horizontal Line.............................................................................................................................72
Exhibit 6.14: Height above Ground......................................................................................................................................72
Exhibit 6.15: Water Depth Measurement .........................................................................................................................72
Exhibit 8.1: Surface Irrigation................................................................................................................................................97
Exhibit 8.2: Rain Gun System..................................................................................................................................................97
Exhibit 8.3: Centre Pivot System...........................................................................................................................................98
Exhibit 8.4: Drippers ..................................................................................................................................................................98
Exhibit 8.5: Bubbler....................................................................................................................................................................98
Exhibit 8.6: Micro-tubes............................................................................................................................................................99
Exhibit 8.7Impact of Tyre Inflation on Fuel Efficiency..............................................................................................101
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Tables
Table 1.1:Water Requirement of Different Crops.............................................................................................................2
Table 1.2: Power Rating of Tubewells ...................................................................................................................................8
Table 1.3: Utilization Pattern of Tubewells.........................................................................................................................8
Table 3.1: Recommended Well Case and Pumping Pipe Size for Various Flow Rates...................................30
Table 3.2: Drawdown in Tubewells in the Indus Basin..............................................................................................31
Table 3.3: Typical NEMA B Design Motor, 10-20 hp; 85% Efficiency...................................................................37
Table 3.4: Effect of Voltage Variation on Induction Motor Performance............................................................38
Table 3.5: Equivalent Length of Straight Pipe for Valves and Fittings (m) ........................................................41
Table 3.6: Increase in Friction Loss Due to Aging of Pipe..........................................................................................42
Table 4.1: Smoke Ratings as Per Bosch-Bacharak Smoke Test................................................................................45
Table 5.1: Instruments & Methods for Tubewell Energy Audit...............................................................................56
Table 7.1: Motor Efficiency Estimation ..............................................................................................................................79
Table 7.2: Engine Efficiency Estimation.............................................................................................................................80
Table 7.3: Common Problems with Centrifugal Pumps and Their Causes.........................................................83
Table 8.1: Water Requirement of Different Crops under Various Irrigation Options...................................95
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1 INTRODUCTION
1.1 Background
Agriculture is a major sector of the economy of Pakistan as well as one of the major
consumers of commercial energy. At present, irrigation pumps and farm tractors are
large consumers of energy in the agriculture sector. It is very important that all
segments of our economy, including agriculture, make the most efficient use of
available energy resources.
1.2 Water Requirement of Different Crops
The agriculture of Pakistan is
characterized by two main
cropping seasons, namely, the
Kharif (summer crops) from
April to September; and Rabi
(winter crops) from October to
March. Wheat is the main crop
of Rabi season, while rice,
maize, sugarcane and cotton
are considered the major crops
of Kharif. Mono cropping,
sequence cropping, mixed
cropping, inter-cropping and
relay cropping systems are
practiced by growers (farmers), especially those with small holdings, to maximize crop
production per unit area. The cropping pattern is largely determined by water availability
and the climatic conditions as adaptation of crops.
Water requirement of different crops has been reproduced in the Table 1.1.
Crop Water Requirement (Under Flood Irrigation)
Acre Inches Cubic Meter Liters
Wheat 16 1,645 1,644,000
Cotton 22 2,262 2,261,600
Maize (Autumn) 13 1,336 1,336,400
Exhibit 1.1 Typical Field in Punjab Being Irrigated
1

Maize (Spring) 20 2,056 2,056,400
Sugarcane 64 6,579 6,579,200
Rice 64 6,579 6,579,200
Table 1.1:Water Requirement of Different Crops
1.2.1 Kharif Crops
1.2.1.1 Rice
Rice is one of the leading cash and foreign
exchange earning food crops of the world,
including Pakistan. It requires a constant
and plentiful supply of irrigation water. It
needs 46 acre inches as soaking dose 4-6
days before transplanting, 1-2 acre inches
at the time of transplanting and 3-4 acre
inches 7-10 days after transplanting to
maturity of the crop. The reproductive
stages from penicle initiation to flowering
and grain formation are the critical stages.
Any stress at this stage will affect the yield
and grain quality. However, rice requires
over all 60-70 acre inches irrigation water
on the basis of varieties.
1.2.1.2 Maize
Maize is also one of the cereal crops. It
is very efficient water user. It needs
large quantities of irrigation water for
high yield, because drought conditions
lead to lower yields and lower quality
grains. Maize requires 6-8 irrigations.
First irrigation 3-4 weeks after sowing,
remaining may be given at 10-15 days
interval. The grain formation is critical
growth stage. It is not important grain
crop in Sindh, but is grown mostly as
fodder crop and very rare as for grain.
Exhibit 1.2: Typical Irrigated Rice Field
in Pakistan
Exhibit 1.3: A Maize Crop Near Okara Ready for
Harvesting
2

1.2.1.3 Sorghum (Jowar)
The major area of sorghum in Pakistan lies in Punjab, but the yield per hectare is higher in
Sindh. The sorghum plants are drought resistant, but 3-4 irrigations (30-35,50-60 and 70-
80 days after sowing) are compulsory for better yield.
1.2.1.4 Millet (Bajra)
The area under millet crop is highly variable, because it is dependent on the amount and
time of the rainfall. It is mostly confined to the desert and mountain (Thar, Cholistan and
Kohistan) area. 3-4 irrigations are sufficient for better yield, as recommended for sorghum.
1.2.1.5 Mungbean (Green gram)/Mash (Black gram)/Arhar (Pigeonpea or Red gram)
It does not require much irrigation due to short duration and drought tolerant crop.
However, 3-4 irrigations are sufficient for getting good yield. Flowering and seed
development stages are very critical.
1.2.1.6 Cowpea
This crop is grown as pulse, vegetable, fodder and green manure crop, hence is of economic
importance, especially in Sindh. Irrigation requirements are same as of mungbean crop.
1.2.1.7 Cotton
Cotton is alone fiber crop of Pakistan. It
is also most important cash and foreign
exchange earning crop. It requires 7-8
irrigations (at least 80 cm) to get an
acceptable yield. The first irrigation is to
be given 35-40 days after sowing (DAS)
and subsequent irrigations should be
applied at 15 days interval. The most
critical stages for irrigation are early
flowering to first boll opening and
maturity.
1.2.1.8 Sunflower
Sunflower has gained higher popularity
and acreage, among the new oilseed crops introduced for boosting edible oil production.
The important features of this crop are short growing period, high yield potential and wide
Exhibit 1.4: Typical Irrigated Cotton Field in
Punjab
3

range of growing season viz. autumn, spring and winter. It fits well in different cropping
patterns, low irrigation water requirements, wide adaptability to soil and moisture
conditions. Its seed contains high oil (over 40%) of good edible quality and meal of good
quality free from toxic compounds. 3 irrigations are necessary. The 1st irrigation should
be given 30-35 DAS, 2nd at start of flowering and 3rd just after petal fall.
1.2.1.9 Sugarcane
Sugarcane is also one of the major
crops. The highest acreage is in
Punjab but yield is higher in Sindh.
The crop requires 30-33 irrigations
at 15 days interval during winter and
weekly in summer (a total of 96 acre
inches).
1.2.1.10 Soybean
It requires 5-7 irrigations from
sowing to maturity. Irrigation at pod
filling stage is very necessary, drought at this stage will reduce yield drastically.
1.2.1.11 Groundnut (Peanut)
This crop requires 30 acre inches during 5-7 irrigations. The first irrigation should be given
25-30 DAS and subsequent at 15-20 days intervals. The critical stage is seed development.
1.2.1.12 Sesame
The sesame is cultivated throughout Pakistan as irrigated as well as un-irrigated crop. It
requires 3-4 (21 acre inches) irrigation at 30 days interval.
1.2.1.13 Caster
Caster is grown under arid conditions, mostly as rainfed crop. Under irrigated conditions, it
needs 5-7 (20 acre inches) irrigation at 30 days interval.
1.2.1.14 Guar (Cluster bean)
It is a very important drought resistant Kharif legume of Barani and irrigated areas.
However, if irrigation is available, then 20-25 cm per hectare, in the course of 2-3
irrigations increase the yield.
Exhibit 1.5: Furrow Irrigated Sugarcane Field
4

1.2.1.15 Moth
Moth is also important drought tolerant crop, cultivated as rainfed. Irrigated crop requires
2-4 irrigations.
1.2.1.16 Sesbania (Janter or Danicha)
This crop is widely grown in all over Pakistan as main Kharif fodder and as green manure
crop. It adds about 80 kg/ha nitrogen in the soil, therefore also used as rotation crop for
maintaining the soil fertility. This crop requires 4-6 irrigations. First 2-3 irrigations at
weekly and following should be applied fortnightly.
1.2.2 Rabbi crops
1.2.2.1 Wheat
Wheat is a staple food of more than one
third of the world population. The major
area in Pakistan lies in Punjab, but the
yield per hectare is slightly higher in
Sindh. 5-6 irrigations (21 acre inches) are
sufficient, for normal wheat crop, under
optimum soil conditions. First irrigation
should be given 3-4 weeks after sowing.
Out of all stages, crown root initiation
(CRI) is the most important stage for
irrigation, in view of nutrient availability
and root development. Other critical
stages are tillering, heading, milky and
dough 21, 50, 80 and 100 days after
sowing (DAS) respectively.
1.2.2.2 Barley
Barley is drought tolerant crop. It does not require much irrigation. However, 3-4
irrigations are recommended for maximum yield per unit area. First irrigation is to be
given at 35 DAS. The irrigation at actively tillering increases the yield.
1.2.2.3 Gram (Chickpea)
About 81% of gram area in Pakistan lies in Punjab followed by NWFP and Sindh, but the
yield is highest in Sindh. No irrigation is required if planted after rice as Dobari crop. In
Exhibit 1.6: Typical Wheat Field in Punjab
(Pakistan)
5

case of irrigated crop, only one irrigation is required at pre-flowering stage. Heavy pre-
sowing irrigation is better than light pre-sowing irrigation.
1.2.2.4 Lentil (Masoor)
One irrigation at pre-flowering is adequate, but in light soil, it requires two irrigations.
However, no irrigation is required for Dobari or Bosi crop.
1.2.2.5 Grasspea (Matter)
Two irrigations are sufficient under irrigated conditions, but no irrigation is required for
Dobari or Bosi crop.
1.2.2.6 Rapeseed and Mustard
3-4 irrigations may be given to Toria and Sarsoon, 1-2 irrigations to Jambho or Taramira at
25-30 days intervals. Seed development stage is critical for irrigation. No irrigation is
required for Dobari or Bosi crop.
1.2.2.7 Safflower
It is sensitive to heavy irrigations, especially in later growth stages. However, 56 irrigations
are required under irrigated conditions.
1.2.2.8 Linseed
4-5 irrigations are enough. First irrigation 30 DAS and subsequent doses at 20-25 days
intervals should be given. No irrigation is required, when it is grown as Dobari crop.
1.2.2.9 Lucerne (Alfalfa)
Lucerne is very important leguminous fodder, grown as a subsequent crop. 2 light
irrigations in a week after sowing are helpful. It requires 10-15 irrigations in year, with an
interval of 7-10 days during summer and 15-20 days in winter months. The yields are
decreased with delay in irrigations.
1.2.2.10 Berseem
First 2 irrigations should be light and within a week. The following irrigations should be
given at 10-15 days intervals.
1.2.2.11 Senji
It is one of the fodder crops, needs 2-3 irrigations during entire cropping period.
6

1.3 Ground Water in Pakistan
1.3.1 Quantity
The Indus Basin is formed by alluvial deposits carried by the Indus and its tributaries and is
underlain by an unconfined aquifer covering about 15 million acres in surface area. In the
Punjab about 79% of the area and in Sindh about 28% of the area is underlain by fresh
groundwater, which is mostly used as supplemental irrigation water and pumped through
tube wells. Some groundwater is saline and water from the saline tube wells is generally
put into drains and, where this is not possible, it is discharged into the large canals for use
in irrigation after diluting with the fresh canal water. In KPK abstraction in excess of
recharge in certain areas such as Karak, Kohat, Bannu and D.I. Khan has lowered the water
table and resulted in the contamination from underlying saline water. Whereas in
Balochistan, the Makran coastal zone and several other basins contain highly brackish
groundwater.
1.3.2 Quality
The quality of groundwater ranges from fresh (salinity less than 1000 mg/l TDS) near the
major rivers to highly saline farther away, with salinity more than 3000 mg/l TDS. The
general distribution of fresh and saline groundwater in the country is well known and
mapped as it influences the options for irrigation and drinking water supplies. In the
country some 14.2 million acres are underlain with groundwater having salinity less than
1000 mg/l TDS, 4.54 million acres with salinity from 1000 to 3000mg/l TDS and 10.57
million acres with salinity more than 3000 mg/l TDS.
1.4 Tubewells in Pakistan
According to 2010-11 Statistics of
Agricultural Machinery, there were
954,320 tubewells and surface pumps in
the country. Distribution of diesel and
electric tubewells was 777,379 (81%)
and 176,941 (19%) respectively. The
average annual growth rate of tubewell
population is 6.91%.
Exhibit 1.7: Typical Tubewell in Punjab
7

Power rating profile of the tubewells in Pakistan is provided in following table:
Less Than 10 hp 10 to 15 hp 16-20hp 20-25 hp 25 and Above
Electric 50% 12% 16% 12% 10%
Diesel 76% 1% 11% 4% 8%
Table 1.2: Power Rating of Tubewells
Utilization pattern of the tubewells in Pakistan has been provided in following table
Province Total
Number
of
Tubewell
Average use Renting out time
Days per
Year
Hours per
Day
Number of
Tubewell
Average
Hours
rented per
year
Average
Hourly rate
(Rs.)
Punjab
Electric 61931 183 6 22174 619 110
Diesel 771642 124 5 143308 315 114
Sindh
Electric 3349 151 7 513 468 112
Diesel 43691 123 6 6502 311 111
KPK
Electric 9829 152 4 2350 43 106
Diesel 11020 108 5 2583 380 122
Baluchistan
Electric 10659 227 7 681 532 120
Diesel 9552 189 5 611 259 121
Pakistan
Electric 85,868 184 6 25,718 597 110
Diesel 834,905 125 5 153,004 316 114
Table 1.3: Utilization Pattern of Tubewells
1.5 Tubewell Energy Efficiency
Agriculture sector accounts for 13% of national electricity consumption, amounting 9,686
GWh annually. The estimated annual consumption of diesel (for irrigation purposes) is
8

58,100 tons of diesel (Pakistan Energy Year Book 2013). Furthermore, overall average
efficiency of 5 to 7 percent for diesel tubewells and 20 to 30 percent for electric
tubewells in Pakistan is estimated with potential for achieving overall efficiencies of
10 and 35 percent for diesel and electric tubewells, respectively. Improvement of
irrigation pumpset efficiencies will not only conserve valuable energy supplies but
also reduce pumping costs leading to lower cost of crop production.
A successful energy conservation program requires a proper framework and baseline for
identifying and evaluating energy conservation opportunities. Energy cannot be saved
until it is known how it is being used and where its efficiency can be improved. In most
cases, the establishment of this baseline requires a comprehensive and detailed survey of
energy uses and losses. This survey is generally known as an Energy Audit. Findings of
Tubewell Energy Audit Program conducted by Enercon in 1990s have been reproduced in a
research paper attached to this manual as Annex I.
Conducting an energy audit does not, however, constitute in itself an energy conservation
program. A number of other conditions must also be met. First, there must be a will to
save energy. Second, economically viable alternatives must be available. Third, financing
must be available and fourth, the farmer must be committed to continuing the energy
rationalizing efforts.
The overall efficiency of a pumping plant depends upon the efficiencies of the power unit,
transmission element, pump, piping system and the well. Instrumentation including
electric power analyzers, fuel metering equipment, flow meters and pressure transducers,
etc. is used in the evaluation of energy efficiency of the tubewell components as well as
determining the causes of low efficiency.
The test results are analyzed using basic computations and existing support material
(exhibits, charts, calculators, computers, etc). The analysis results are used to build an
energy balance. From this balance, it is determined how efficiently each component of
the tubewell is actually operating and whether there is room for improvement. Finally,
the costs and benefits of selected options are assessed.
This manual is designed primarily to assist field engineers in carrying out tubewell energy
audits and can also be used as a reference for university students taking courses on water
pumping for irrigation and drainage.
9

1.6 Organization of the Manual
• Including this introductory chapter, this manual is divided into eight chapters.
• Given that water pump is the heart of any tubewell, Chapter 2 provides a brief
introduction about the centrifugal pump types, its important terminology, components
and selection.
• Chapter 3 provides brief review of the basic operating characteristics of tubewell
components such as electric motors, diesel engines, transmission elements,
pumps, piping and the well. An intimate knowledge of these operating characteristics is
necessary for tubewell engineers involved in selection; installation, operational
management and energy conservation programs.
• Chapter 4 discusses data requirements and types of tests for performance testing
and trouble shooting of tubewell components.
• Instruments and equipment for tubewell audits are discussed in Chapter 5.
• Tubewell energy audit methodology and data analysis are discussed in Chapters 6 and
7, respectively.
• Chapter 8 provides brief overview of On Farm Energy Efficiency by covering Best
Practices for Energy Efficient Irrigation and Tractor Fuel Efficiency.
• Relevant engineering information is given in the annexures.
10

2 CENTRIFUGAL PUMP
Pump is heart of any liquid handling system. For Irrigation Purposes, centrifugal pumps
have universal adoption, being the most common type of irrigation pumps.
A centrifugal pump operates in the following manner:
1. Liquid is forced into an impeller either by vacuum created at the eye the impeller.
2. The vanes of impeller pass kinetic energy to the liquid, thereby causing the liquid to
rotate. The liquid leaves the impeller at high velocity.
3. The impeller is surrounded by a volute casing or in case of a turbine pump a stationary
diffuser ring. The volute or stationary diffuser ring converts the kinetic energy into
pressure energy.
In this chapter, a brief introduction has been provided about the centrifugal pump types,
important terminology, components and selection.
2.1 Types of Pumping System
There are three major types of centrifugal pumps being used for irrigation purpose in
Pakistan
2.1.1 Horizontal Shaft Centrifugal Pump
The pump is usually placed near the water level in a dug well. The pump and the motor are
in the same plane. In Pakistan, horizontal shaft centrifugal pumps are usually being used
where the required head ranges between 30 ft to 110 ft with usual power rating ranging
between 5 to 30 hp. This is the most popular type of Pump for Tubewells, hence the major
focus of the manual is on Horizontal Shaft Centrifugal Pump. Typical configuration of the
centrifugal pump is presented in the Exhibit 2.1.
Exhibit 2.1: Centrifugal Pump
11

2.1.2 Turbine (Vertical Shaft) Pump
A turbine pump is a particular type of centrifugal pump that is mainly used to pump water
from deeper wells as compared to horizontal shaft centrifugal pump. A turbine pump
consists of a pump shaft, a rotating device known as an impeller, and a motor or an engine.
A turbine pump may consist of multiple semi-open or enclosed impellers, also known as
"stages." A metal plate called shroud supports the vanes of the impeller in an open or semi-
open impeller, whereas in an enclosed impeller, the shroud encloses the impeller vanes.
The motor on this type of pump is usually placed well above the water level. In Pakistan,
turbine pumps are usually being used where the required head ranges between 75 ft to 160
ft with usual power rating ranging between 20 to 30 hp. Typical configuration of the
Turbine pump is presented in the following Exhibit 2.2.
Exhibit 2.2Turbine Pump
2.1.3 Submersible Pump
A submersible pump has a hermetically sealed motor close-coupled to the pump body. The
whole assembly is submerged in the fluid to be pumped. This pump is particularly suited for
lower water table areas. The main advantage of this type of pump is that it prevents pump
cavitation, a problem associated with a high elevation difference between pump and the
fluid surface. In Pakistan, usually submersible pumps are being used where the required
12

head is more than 150 ft . Typical configuration of the Turbine pump is presented in the
following Exhibit 2.3.
Exhibit 2.3: Submersible Pump
2.2 Components of Centrifugal Pump
The main components of a centrifugal pump are shown in following Exhibit and described
below:
Exhibit 2.4: Components of Centrifugal Pumps
• Rotating components: an impeller coupled to a shaft
• Stationary components: casing, casing cover, and bearings
13

2.2.1 Impeller
An impeller is a circular metallic disc with a built-in passage for the flow of fluid. Impellers
are generally made of bronze, polycarbonate, cast iron or stainless steel. As the
performance of the pump depends on the type of impeller, it is important to select a
suitable design and to maintain the impeller in good condition.
The number of impellers determines the number of stages of the pump. A single stage
pump has one impeller and is best suited for low head (= pressure) service. A two-stage
pump has two impellers in series for medium head service. A multi-stage pump has three
or more impellers in series for high head service.
Impellers can be classified on the basis of:
• Major direction of flow from the rotation axis: radial flow, axial flow, mixed flow
• Suction type: single suction and double suction
• Shape or mechanical construction
Closed impellers have vanes enclosed by shrouds (=
covers) on both sides (Exhibit 2.5). They are generally
used for water pumps as the vanes totally enclose the
water. This prevents the water from moving from the
delivery side to the suction side, which would reduce
the pump efficiency. In order to separate the
discharge chamber from the suction chamber, a
running joint is necessary between the impeller and
pump casing. This joint is provided by wearing rings,
which are mounted either over extended
portion of impeller shroud or inside the
cylindrical surface of pump casing. A disadvantage of closed impellers is the higher risk of
blockage.
2.2.2 Shaft
The shaft transfers the torque from the motor to the impeller during the startup and
operation of the pump.
2.2.3 Casing
The main function of casing is to enclose the impeller at suction and delivery ends and
thereby form a pressure vessel. The pressure at suction end may be as little as one-tenth of
Exhibit 2.5: Double Shroud Pump Impeller
14

atmospheric pressure and at delivery end may be twenty times the atmospheric pressure
in a single-stage pump. For multi-stage pumps the pressure difference is much higher. The
casing is designed to withstand at least twice this pressure to ensure a large enough safety
margin. A second function of casing is to provide a supporting and bearing medium for the
shaft and impeller. Therefore the pump casing should be designed to
• Provide easy access to all parts of pump for inspection, maintenance and repair
• Make the casing leak-proof by providing stuffing boxes
• Connect the suction and delivery pipes directly to the flanges
• Be coupled easily to its prime mover (i.e. electric motor) without any power loss.
For Irrigation pumps, volute casing is used. Volute casing (Exhibit 2.6) has impellers that
are fitted inside the casings. One of the main purposes is to help balance the hydraulic
pressure on the shaft of the pump. However, operating pumps with volute casings at a
lower capacity than the manufacturer’s recommended capacity can result in lateral stress
on the shaft of the pump. This can cause increased wearing of the seals, bearings, and the
shaft itself. Double-volute casings are used when the radial force becomes significant at
reduced capacities.
Exhibit 2.6: Volute Casing
2.3 Pumping System Terminology
2.3.1 Head
Pressure is needed to pump the liquid through the system at a certain rate. This pressure
has to be high enough to overcome the resistance of the system, which is also called “head”.
The total head is the sum of static head and friction head:
15

2.3.2 Static Head
Static head is the difference in height between the source and destination of the pumped
liquid (see Exhibit 2.7). Static head is independent of flow
rate.Thestaticheadatacertainpressuredependsontheweightoftheliquidandcanbecalculatedw
iththisequation:
𝐻𝑒𝑎𝑑𝑖𝑛𝐹𝑒𝑒𝑡 =
𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒(𝑝𝑠𝑖) × 2.31
𝑆𝑝𝑒𝑐𝑖𝑓𝑖𝑐𝐺𝑟𝑎𝑣𝑖𝑡𝑦𝑜𝑓𝑡ℎ𝑒𝐹𝑙𝑢𝑖𝑑𝐵𝑒𝑖𝑛𝑔𝑃𝑢𝑚𝑝𝑒𝑑
Exhibit 2.7: Pump Static Head
Static head consists of (Exhibit 2.8):
1. Total suction head (hS): resulting from lifting the liquid relative to the pump center line.
The hSis positive if the liquid level is above pump centerline, and negative if the liquid
level is below pump centerline (also called “suction lift)
2. Total discharge head (hd): the vertical distance between the pump centerline and the
surface of the liquid in the destination tank.
16

Exhibit 2.8: Static Suction Head and Static Discharge Head
2.3.3 Friction head (hf)
This is the loss needed to overcome that is caused by the resistance to flow in the pipe and
fittings. It is dependent on size, condition and type of pipe, number and type of pipe fittings,
flow rate, and nature of the liquid. The friction head is proportional to the square of the flow
rate.
In most cases the total head of a system is a combination of static head and friction head.
2.3.4 Pump Performance Curve
The head and flow rate determine the
performance of a pump, which is
graphically shown in Exhibit 2.9as the
performance curve or pump
characteristic curve. For the
calculation of the efficiency of the
pumping system, these two
parameters are of the prime
importance. The Exhibit 2.9 shows a
typical curve of a centrifugal pump
where the head gradually decreases with
increasing flow. As there instance of a
system increases, the head will also
increase. This causes the flow rate
to decrease and will eventually
reach zero. A zero flow rate is only
acceptable for a short period
without causing to the pump to
burnout.
The rate of flow at a certain head is
called the duty point. The pump
performance curve is made up of
many duty points. The pump
operating point is determined by
the intersection of the system
curve and the pump curve as shown in Exhibit.
Flow
Head
Static
Head
Pump
performance
curve
S
Exhibit 2.9: Pump Performance Curve
Exhibit 2.10: Pump Operating
Point
17

2.3.5 Pump Suction Performance (NPSH)
Cavitation or vaporization is
the formation of bubbles
inside the pump. This may
occur when at the fluid’s local
static pressure becomes lower
than the liquid’s vapor
pressure (at the actual
temperature) as shown in
Exhibit 2.11. A possible cause
is when the fluid accelerates
around a pump impeller.
Vaporization itself does not
cause any damage. However,
when the velocity is decreased
and pressure increased, the
vapor will evaporate and
collapse.
This has three undesirable effects:
1. Erosion of vane surfaces, especially when pumping water-based liquids
2. Increase of noise and vibration, resulting in shorter seal and bearing life
3. Partially choking of the impeller passages, which reduces the pump performance and
can lead to loss of total head in extreme cases.
To characterize the potential for boiling and cavitation, the difference between the total
head on the suction side of the pump - close to the impeller, and the liquid vapor pressure
at the actual temperature, can be used.
Suction Head
The suction head in the fluid close to the impeller can be expressed as the sum of
the static and the velocity head:
ℎ 𝑠 =
𝑃𝑠
γ� +
𝑉𝑠
2
2𝑔
� Equation 2.1
where
Exhibit 2.11: Reason of Cavitation
18

hs = suction head close to the impeller
ps = static pressure in the fluid close to the impeller
γ = specific weight of the fluid
vs = velocity of fluid
g = acceleration of gravity
Liquids Vapor Head
The liquids vapor head at the actual temperature can be expressed as:
ℎ 𝑣 =
𝑃𝑣
γ� Equation 2.2
where
hv = vapor head
pv = vapor pressure
It is worth mentioning that the vapor pressure in fluids depends on temperature. Water,
our most common fluid, starts boiling at 20 oC if the absolute pressure in the fluid is 2.3
kN/m2. For an absolute pressure of 47.5 kN/m2, the water starts boiling at 80 oC. At an
absolute pressure of 101.3 kN/m2 (normal atmosphere), the boiling starts at 100 oC.
Net Positive Suction Head - NPSH
The Net Positive Suction Head - NPSH - can be expressed as the difference between the
Suction Head and the Liquids Vapor Head and expressed like
𝑁𝑃𝑆𝐻 = ℎ 𝑠 − ℎ 𝑣 Equation 2.3
or, by combining equation 2.1 and 2.2:
𝑁𝑃𝑆𝐻 =
𝑃𝑠
γ� +
𝑉𝑠
2
2𝑔
� −
𝑃𝑣
γ� s
Available NPSH - NPSHa
The Net Positive Suction Head made available the suction system for the pump is often
named NPSHa. The NPSHa can be determined during design and construction, or
determined experimentally from the actual physical system.
19

Exhibit 2.12: Available Net Pressure Suction Head (NPSH)
For a common application - where the pump lifts a fluid from an open tank at one level to
an other, the energy or head at the surface of the tank is the same as the energy or head
before the pump impeller and can be expressed as:
ℎ 𝑜 = ℎ 𝑠 + ℎ𝑙 Equation 2.4
where
h0 = head at surface
hs = head before the impeller
hl = head loss from the surface to impeller - major and minor loss in the suction pipe
In an open tank the head at surface can be expressed as:
ℎ 𝑜 =
𝑃𝑜
γ� =
𝑃𝑎𝑡𝑚
γ� Equation 2.5
For a closed pressurized tank the absolute static pressure inside the tank must be used.
The head before the impeller can be expressed as:
ℎ 𝑠 =
𝑃𝑠
γ� +
𝑉𝑠
2
2𝑔
� + ℎ 𝑒 Equation 2.6
where
he = elevation from surface to pump - positive if pump is above the tank, negative if the
pump is below the tank
Transforming Equation 2.4 with Equation 2.5 and 2.6:
20

𝑃𝑎𝑡𝑚
γ� =
𝑃𝑠
γ� +
𝑉𝑠
2
2g
� + ℎ 𝑒 + ℎ1 Equation 2.7
The head available before the impeller can be expressed as:
𝑃𝑠
γ� +
𝑉𝑠
2
2g
� =
𝑃𝑎𝑡𝑚
γ� − ℎ 𝑒 − ℎ𝑙 Equation 2.8
or as the available NPSHa:
𝑁𝑃𝑆𝐻 𝑎 =
𝑃𝑎𝑡𝑚
γ� − ℎ 𝑒 − ℎ𝑙 −
𝑃𝑣
γ� Equation 2.9
Available NPSHa - the Pump is above the Tank
If the pump is positioned above the tank, the elevation - he - is positive and
the NPSHa decreases when the elevation of the pump increases.
At some level the NPSHa will be reduced to zero and the fluid starts to evaporate.
Available NPSHa - the Pump is below the Tank
If the pump is positioned below the tank, the elevation - he - is negative and the
NPSHa increases when the elevation of the pump decreases (lowering the pump).
It's always possible to increase the NPSHa by lowering the pump (as long as the major and
minor head loss due to a longer pipe don't increase it more). This is important and it is
common to lower the pump when pumping fluids close to evaporation temperature.
Required NPSH - NPSHr
The NPSHr, called as the Net Suction Head as required by the pump in order to prevent
cavitation for safe and reliable operation of the pump.
The required NPSHr for a particular pump is in general determined experimentally by
the pump manufacturer and a part of the documentation of the pump.
21

Exhibit 2.13: Pump Operation Point
The available NPSHa of the system should always exceeded the required NPSHr of the pump
to avoid vaporization and cavitation of the impellers eye. The available NPSHa should in
general be significant higher than the required NPSHr to avoid that head loss in the suction
pipe and in the pump casing, local velocity accelerations and pressure decreases, start
boiling the fluid on the impeller surface.
Pumps with double-suction impellers has lower NPSHr than pumps with single-suction
impellers. A pump with a double-suction impeller is considered hydraulically balanced but
is susceptible to an uneven flow on both sides with improper pipe-work.
To prevent cavitation, centrifugal pumps must operate with a certain amount of pressure at
the inlet i.e. net positive suction head (NPSH). NPSHR is typically included on pump
performance curves. If the NPSHA is sufficiently above the NPSHR, then the pump should
not cavitate. A common rule in system design is to ensure that NPSHA is 25% higher than
NPSHR for all expected flow rates. When oversized pumps operate in regions far to the
right of their design points, the difference between NPSHA and NPSHR can become
dangerously small.
2.3.6 Best Efficiency Point
An important characteristic of the head/flow curve is the best efficiency point (BEP). At the
BEP, the pump operates most cost-effectively in terms of both energy efficiency and
maintenance. Operating a pump at a point well away from its BEP may accelerate wear in
bearings, mechanical seals, and other parts. In practice, it is difficult to keep a pump
operating consistently at this point because systems usually have changing demands.
22

However, keeping a pump operating within a reasonable range of its BEP lowers overall
system operating costs.
Manufacturers use a coverage chart to describe the performance characteristics of a family
of pumps. This type of chart, shown in Exhibit 2.14, is useful in selecting the appropriate
pump size for a particular application. The pump designation numbers in Exhibit2.14 refer
to the pump inlet size, the pump outlet size, and the impeller size, respectively. There is
significant overlap among these various pump sizes, which is attributable to the availability
of different impeller sizes within a particular pump size.
Exhibit 2.14: Family of Pump Performance Curves
2.3.7 Pump Curves for Multiple Impeller Sizes
Once a pump has been selected as roughly meeting the needs of the system, the specific
performance curve for that pump must be evaluated. Often, impellers of several different
sizes can be installed with it, and each impeller has a separate, unique performance curve.
Exhibit2.15 displays performance curves for each size of impeller. Also illustrated are iso-
efficiency lines, which indicate how efficient the various impellers are at different flow
conditions. Sizing the impeller and the pump motor is an iterative process that uses the
curves shown in Exhibit 2.15 to determine pump efficiency and performance over its
anticipated operating range.
23

Exhibit 2.15: Performance Curves for Different Impeller Sizes
2.4 Pump Speed Selection
Pump speed is usually an important consideration in system design. The pump speed is
perhaps best determined by evaluating the effectiveness of similar pumps in other
applications. In the absence of such experience, pump speed can be estimated by using a
dimensionless pump performance parameter known as specific speed. Specific speed can
be used in two different references: impeller specific speed and pump suction specific
speed. The impeller specific speed (Ns) is used to evaluate a pump’s performance using
different impeller sizes and pump speeds.
Specific speed is an index that, in mechanical terms, represents the impeller speed
necessary to generate 1 gallon per minute at 1 foot of head. The equation for impeller
specific speed is as follows:
𝑁𝑠 =
𝑛�𝑄
𝐻
3
4�
where
Ns = specific speed
n = pump rotational speed (rpm)
Q = flow rate (gpm)
24

H = total head per stage (ft)
For standard impellers, specific speeds range from 500 to 10,000. Pumps with specific
speed values between 2,000 and 3,000 usually have the highest efficiency.
2.5 How to Select a Centrifugal Pump
The data required to size and
source a pump include 1) system
flow demands and 2) the
system’s resistance curve. To
determine the system curve, the
required data include the system
configuration, the total pipe
length, the pipe size, and the
number of elbows, tees, fittings,
and valves.
A designer can use these data—
along with known fluid
properties and the head
available from the suction
source—to estimate the system’s
head loss and its NPSHA at the pump suction.
At this point, the designer must review the manufacturers’ data to find pumps that can
meet system requirements. This process requires repeated evaluations of many different
pump characteristics, including the BEP, pump speed, NPSHR, and pump type. Using the
expected system operating range, a designer must evaluate the family of performance
curves, similar to that shown in Exhibit, for each pump manufacturer to identify pumps
that meet the service needs.
The next step is to evaluate the performance curves of each pump selected. Each pump
usually has a range of performance curves for each impeller size offered with that pump. In
Exhibit, a 4x1.5-6 pump is used as an example.
The design point is just below the curve for the 6-inch impeller. For this particular pump
size, at these operating conditions, the pump efficiency is 74%, and the 5-hp motor appears
strong enough to meet service requirements. The pump’s BEP is just slightly to the right of
Exhibit 2.16: Pump Selection
25

the design point and the NPSHR is 6 ft. If the NPSHA is more than 7.5 ft, or at least 25%
higher than the NPSHR, the 4x1.5-6 pump should be suitable.
26

3 OPERATING CHARACTERISTICS OF TUBEWELL
COMPONENTS
A tubewell consists of the following major components:
Well Majority of pumps are installed on drilled wells which may be
cased or un-cased. Public tube wells are generally cased and
gravel packed. Coir, cement, brass and PVC strainers are in
common use. Coir and cement strainers are widely used by
farmers on private tubewells because of low initial cost.
Pump Majority of pumps installed in Pakistan are the horizontal
shaft (dug well) centrifugal pumps. Turbine and submersible
turbine pumps constitute a small percentage and have been
installed in the deep water zones of the country.
Prime mover Electric motors, high and slow speed stationary diesel engines
and tractors are the common power units used for irrigation
water pumping.
Transmission Electric motors are usually direct coupled to the pumps. Flat
belt drives are common for transmitting power from diesel
engines. In some cases high speed diesel engines are directly
coupled to the pumps and belts are used for transmitting power
from electric motors.
Piping Galvanized iron pipes of 50 to 75 mm (2 to 3 in) diameter
and steel pipes of 75 to 150 cm (3 to 6 in.) diameter' are
commonly used on tube wells in Pakistan. Bends and pipes
fabricated from sheet steel arc also common.
Each component of the tubewell has distinct operating characteristics. The energy
efficiency of a tubewell depends on the degree of matching amongst the components and
their individual efficiencies. Energy input output view of a water pumping system is shown
in Exhibit 3.1. Operating characteristics of the various tubewell components are briefly
described in the following sections.
27

Exhibit3.1:EnergyInput-OutputofaDieselEngineOperatedPumpingSystem
28

3.1 Well
The crust of earth is normally porous. Absorption of water w h i c h f a l l s on the
ground surface infiltrates through the crust and fills its pores. If a hole is drilled into the
zone of saturation or a pipe with holes is installed, water will appear in it and will stand
corresponding to the level of water contained in the formation. A saturated formation
capable of yielding sufficient quantity of water is called an aquifer. This water can move
freely under a p r e s s u r e gradient and is available for pumping. A tube well is a type of
water well in which a long 100–200 mm (5 to 8 inch) wide stainless steel tube or pipe is
bored into an underground aquifer. The lower end is fitted with a strainer, a pump at the
top lifts water for irrigation. The required depth of the well depends on the depth of the
water table.
Exhibit 3.2: Borehole of a Horizontal Shaft
Tubewell
3.1.1 Parts of Tubewell
A complete tube-well means:
1. A borehole vertical drilled up to
designed depth
2. Installation of requisite well assembly
i.e., housing pipe, blind pipe, slotted pipe
or strainers, bail plug and other
accessories.
3. Placing of suitable gravel pack (in case of
gravel, packed tube-wells)/ Placing of suitable
sand pack (in case of sand packed tube-wells).
Exhibit 3.3: Parts of Tubewell
29

Housing pipe: It is the pipe provided in upper portion of the tube-well in which pump and
motor assembly is accommodated. Slotted pipe or screen: The screen or slotted pipe should
be provided against the required thickness of aquifer in order to allow ground water to be
pumped into the tube-well. The housing pipe, blind pipe and slotted pipe to be used in the
tube-well may preferably be of seamless mild steel. Gravel packing: The term gravel
packing is used to the placing of uniform gravel adjacent to the well screen. Use of cage
type wire wound Strainer/Brass Strainer: These strainers are used in fine sandy formation.
Column pipe: It is G. I. pipe directly connected with pump motor assembly, acts as delivery
pipe, which is brought above top of housing pipe, and provided with a 90° bend and a
sluice valve for controlling discharges
Department of Agriculture and private contractors offer tubewell digging services.
Pumping Rate
in LPM
Size of well
casing (in cm)
Size of pumping pipe (in
cm)
113-226 10 5
226-302 12.5 7.5
302-378 15 8.25 to 1
378-567 15 10
567-945 20 12.5
945-1512 20 15
Table 3.1: Recommended Well Case and Pumping Pipe Size for Various Flow Rates
3.1.2 Draw Down
The difference in the static and
pumping water levels in the well is
called drawdown. Drawdown in a
pumped well consists of head loss
in the formation around the well
(aquifer loss)and the head loss
which takes place in entrance to the
well itself(well loss) as shown in
Exhibit3.4. Aquifer loss is a function
of aquifer characteristics, geometry
of well and boundary conditions
while well loss is primarily a
function of open area of well Exhibit 3.4: Pump Draw Down
30

strainer, slot size, slot velocity, frictional and convergence losses. Diameter of wells varies
from15 to 60cm for drilled wells and from 1.5 to 5 m for open wells.
Data on drawdown per unit discharge (specific capacity) from tubewells having different
diameters, lengths and types of strainers, etc in the lndus Basin is presented in Table 3.2
These drawdowns arc common during the first 3 to 5 years. Once the strainers are
affected by incrustation, yield begins to fall and drawdown starts increasing thus reducing
efficiency of the well
Designed
Capacity
of
tubewell
(ft3/s)
Type of
Strainer
Range of
Open
Area
(%)
Dia of
Strainer
(in)
Effective
Well Dia
(in)
Range of
length of
strainer
(ft)
Range of
depth of
bore (ft)
Type of
Formation
Drawdown
per ft3/s
(ft)
3 Slit type
brass of
iron
5 to 8 10 22 120-150 200-
350
Med-Sand 4 to 6
3 -Do- Do 10 18 -Do- -Do- -Do- 6
2 -Do- -Do- 8 12-18 120 200-
250
-Do- 6-8
2 -Do- -Do- 8 12-18 120 200-
250
-Do- 6-8
2 Coir
String
10-15 10 10 120 200-
250
-Do- 6-8
2 -Do- 10-15 8 8 100-120 -Do- Med-fine
sand
8-10
1 to 2 -Do- 10 - 15 6 6 100 200 -Do- 10-12
Table 3.2: Drawdown in Tubewells in the Indus Basin
3.2 Pumps
Centrifugal pumps are commonly used on tubewells. Characteristics of a turbine pump
and well have been combined in Exhibit 3.5.
The head discharge curves of both the pump and well intersect at the operating point. The
head discharge curve of the well (well curve) is determined with the help of a test
pump. After the yield characteristics and desired discharge rate have been determined, a
pump with the desired characteristics is selected and permanently installed at the well.
System head tends to increase due to lowering of water table and aging of pipes resulting in
the shift of operating point to the left. A properly selected pump should, therefore,
31

operate a little to the right of the peak efficiency point on the pump efficiency curve
when new.
Exhibit 3.5: Pump and Well Characteristic Curves
Among the more important factors affecting the operation of a centrifugal pump are
the suction conditions. Abnormally high suction lifts (low Net Positive Suction Head)
beyond the suction rating of the pump, usually cause serious reduction in capacity and
efficiency, and often lead to serious trouble from vibration and cavitation.
Typical characteristic curves of a centrifugal pump are shown in Exhibit 3.6. Pump
performance curves of various pump models available is Pakistan’s market have been
regenerated in the Annex II.
32

Exhibit 3.6: Characteristic Curve of Centrifugal Pump
The mathematical relationships between these several variables are known as the
affinity laws and can be expressed as follows:
With impeller diameter kept constant:
Q1
Q2
=
N1
N2
Law 1a
H1
H2
= �
N1
N2
�
2
Law 1b
33

BHP1
BHP2
= �
N1
N2
�
3
Law 1c
With speed kept constant:
Q1
Q2
=
D1
D2
Law 2a
H1
H2
= �
D1
D2
�
2
Law 2b
BHP1
BHP2
= �
D1
D2
�
3
Law 2c
Q1 = Capacity and H 1 = head at N 1 rpm. or with impeller dia. D1
Q2 = Capacity and H 2 =head at N 2 rpm or with impeller dia. D2
Law 1a applies to Centrifugal, Angle Flow, Mixed Flow, Propeller, Peripheral, Rotary and
Reciprocating pumps.
Law 1b and 1c apply to Centrifugal, Angle Flow, Mixed Flow, Propeller, and Peripheral
Pumps.
Law 2a, 2b and 2c apply to Centrifugal pumps only.
Where complete rating charts such as those shown in Exhibit 3.6 are not available, pump
performance at other than manufacturer's specified points can be estimated using the
affinity laws. However, this is true for Law 2 only under certain defined conditions.
Calculated head-discharge characteristic using Law 1 agrees very closely to the test
performance curves. The use of Affinity Law 1, therefore, to calculate performance when
the speed is changed and the impeller diameter remains constant, is quite accurate
approximation.
When the impeller of a pump is reduced in diameter, the design relationships are changed,
and in reality a new design results. The discrepancy is small for low specific speed pumps
and more pronounced for higher specific speed pumps. Law 2, therefore, must be used with
great deal of caution.
When the affinity laws are used for calculating speed or diameter changes, it is important
to consider the effect of suction lift on the characteristic for the increased velocity in the
suction line and pump may result in cavitation that may substantially alter the
characteristic curve of the pump.
34

Characteristic curves for various models of a famous make of centrifugal pumps are
given in Annexure II.
3.3 Diesel Engines/Tractors
According to 2010-11 Statistics of Agricultural Machinery, there were 954,320 tubewells
and surface pumps in the country. Distribution of diesel and electric tubewells was 777,379
(81%) and 176,941 (19%) respectively. Locally made and imported high speed diesel
engines and tractors constitute the power units for diesel tubewells.
The performance of a typical diesel engine under various conditions of load and speed is
shown in Exhibit 3.7. For a diesel engine there is no sharp limit of power output at any
speed and the color or exhaust smoke is a good guide for loading of an engine in good
condition. A manufacturer may publish test curves showing a favorable output at all
speeds but such a curve could not be compared with another test unless the exhaust
conditions of smoke were same.
Manufacturers specifications typically give only the maximum power output of an engine.
Engines for intermittent use are rated at approximately 80 to 90 percent of the maximum
power. For engines under continuous operation such as those installed on tubewells and
tractors, the rating is approximately 60 percent of the maximum. To prevent the
purchaser from abusing the engine, a throttle stop or governor is often installed. Small
intake valves, to limit the mass of air induced into the engine, can also accomplish this
purpose. Some manufacturers may advertise and deliver engines setup for maximum
power. Naturally, an attempt to develop maximum power for extended periods will
greatly shorten the life of the engine.
Close examination of Exhibit 3.7 will indicate that a diesel engine can be operated at
reasonably high efficiency for a wide range of loads by changing the speed. For
example the engine whose performance is shown in Exhibit 3.7 can deliver 28hp to 45hp
at specific diesel consumption of 0.221 kg/kWh with speed changing from 1200 to 2200
rpm. The fuel consumption will, however, vary from a high of 0.220 kg/kWh at 2400 rpm
speed to a low of 0.210 kg/kWh at 1800 rpm. Therefore, proper throttle setting and the
selection of appropriate engine and pump pulleys can greatly improve fuel efficiency
especially when the engine is partially loaded.
35

Exhibit 3.7: Diesel Engine Performance Curves of Continuous Rated Power of 51 HP/38 kW1
Although diesel engines can be operated at high efficiencies at varying loads, a grossly
oversized engine results in high pumping cost due to high investment and maintenance
costs.
3.4 Electric Motors
The electric motors employed for irrigation water pumping are mainly 3-phase
squirrel cage induction motors. The losses in an induction motor are caused by a variety
of imperfections. These losses can be grouped under no-load and operating losses. The
relative magnitude of these losses for a typical motor in the 7.5 to 15 kW (10 to 20
hp} range are given in Table 3.3.
Losses %
Primary I2R Losses (Stator) 5.6
Secondary I2R Losses (Rotor) 2.7
Iron Core Losses 3.0
Friction and Windage 1.4
1Curve 1 - Maximum rating (ISO Fuel Stop Power), Curve 2 - Intermittent rating, Curve 3 - Continuous rating
36

Stray Losses 2.3
Losses Sub-Total 15.0
Useful Power 85.0
Table 3.3: Typical NEMA B Design Motor, 10-20 hp; 85% Efficiency
Efficiency of induction motors varies with the degree of loading (Exhibit 3.8). While the
efficiency of electric motors does not vary greatly within the half to full load range,
overloaded motors have shorter lives and more expensive to maintain. On the other hand
under loaded motors increase the cost per kilowatt of power used and cause unnecessary
loading of the supply grid due to low power factors.
Voltage variation can have a significant effect on the motor efficiency (Table 3.4). It also
has severe effects on other motor parameters and tends to reduce motor life. As
summarized in Table 3.4, voltage variation effect is especially ad verse when the voltages
are higher than rated and should be avoided or controlled to the extent possible. Voltage
imbalance among the three phases has an even more serious effect on motor operation and
should be strictly controlled. A 5 percent voltage imbalance, for example, can increase
motor losses by 33 percent.
Effect of Voltage Change
Operating
Characteristics
90% Voltage 110% Voltage 120% Voltage
Starting and
maximum running
Torque
Decrease 19% Increase 21% Increase 44%
Synchronous Speed No Change No Change No Change
Percentage Slip Increase 23% Decrease 17% Decrease 30%
Full load speed Decrease 0.5-1% Increase 1% Increase 0.5-1%
Staring Current Decrease 10-12% Increase 10-12% Increase 25%
Full load Current Increase1-5% Increase 2-11% Increase 15-35%
Temperature rise
at full load
Increase 6-12% Increase 4-23% Increase 30-80%
Standard NEMA design B Motors
Efficiency
Full Load Increase 0.5-1% Decrease 1-4% Decrease 7-10%
0.75% Load Increase 1-2% Decrease 2-5% Decrease 6-12%
37

Power Factor
Full Load Increase 8-10% Decrease 10-15% Decrease 10-30%
Table 3.4: Effect of Voltage Variation on Induction Motor Performance
Exhibit 3.8: Motor Efficiency Vs. Load Level
Performance data for various efficiency classes of electric motors is given in Annexure III.
3.5 Transmission
Flat belt drives between diesel engines and pumps are common. Electric motors are usually
connected to pumps through flexible couplings. Flat and v-belt drives are also used.
38

Belts are simple, economical and trouble free method of transmitting power. Cush ion
action, quiet operation, flexibility of space requirements, lubrication-free and reliable
operation arc the main advantages of belt drives. Proper pulley alignment, belt joints
and tension arc, however, prerequisites for satisfactory operation of belt drives.
In its simplest form, the formula for power transmitted by a flat belt is
𝑃 = 𝑆 =×
(𝑇1 − 𝑇2)
1000
where
P = Power transmitted by belt, kW
S = belt speed, m/s
T1 = tension at the tight side, N
T2 = tension at the slack side, N
Flat belts are tightened to certain recommended tension ratios. Taking into
consideration the centrifugal tension and incorporating tension ratio R, above equation can
be rewritten as:
𝑃 =
𝑆(𝑇1 − 𝑇𝑐)�1 − 1
𝑅� �
1000
where
T = centrifugal tension, N
R = tension ratio= (T1-Tc)/(T2-Tc)
With fixed center or manually adjusted drives and 180 deg arc, belts are installed at
R=2 and the tension restored when R reaches 3.
Various factors influence the length of service of a flat belt. A reduction in pulley diameter
or an increase in belt thickness will cause a marked reduction in the service life of the
belt. Specifically, a 50 percent reduction in pulley diameter will reduce the service life
to 1/32 of its former value, while only a 20 percent increase in belt thickness will
reduce life by 66 percent. To obtain a reasonable length ,of service with small pulleys, the
thickness of belt or the tension must be reduced. A well-designed belt drive working under
normal conditions should operate without slip. Creep, however, is inevitable with all
types of belting but with good belts seldom reaches one percent. Poor maintenance of
flat belt drives can lead to excessive slip and hence loss of power, overheating of drive
components and short belt life.
39

The nature of drive between the prime mover and pump affects the efficiency of pumping
system. In comparison with direct drives which have transmission efficiency of nearly 100
percent, efficiency of v-belt drives ranges from 90 to 95 per cent and for flat belt drives
from 80 to 95 percent.
3.6 Piping
The flow of water is basic to all hydraulics. Friction losses incident to water flow may
seriously affect the performance of pumps. The most critical part of a system involving
pumps is the suction piping. A centrifugal pump that lacks proper pressure or flow patterns
at its inlet will not respond properly or perform to its maxi mum capability.
A significant portion of the head against which many pumps operate is due largely to the
friction losses created by the flow. A basic understanding of the nature of these losses and
an accurate means of estimating their magnitude is therefore essential.
It is well established that friction losses in either laminar or turbulent flow of in
compressible fluids in pipe lines can be expressed by the basic formula:
ℎ = 𝑓 ×
𝐿
𝐷
×
𝑉2
2𝑔
where
h = friction head loss, m
f = friction factor
L = length of pipe, m
D = average internal diameter of pipe, m
v = average velocity in pipe, m/s
g = acceleration due to gravity, m/s2
Extensive theoretical and empirical studies carried out by leading hydraulic laboratories
of the world have resulted in a simple method for determining friction factor "f" as a
function of relative pipe roughness and/or Reynold Number of flow. Exhibits based on
a comprehensive analysis of mass of experimental data on pipe friction have been
compiled and are available in hydraulic handbooks for quick reference. Friction loss
data for pipe size common in Pakistan is reproduced in Annex IV.
Piping for tubewells consist or straight pipes as well fittings such as valves, elbows,
reducers/enlarges, tees, etc. The resistance to flow caused by a fitting may be computed
from the equation:
40

ℎ = 𝐾
𝑉2
2𝑔
where
h = frictional head loss, m
v = average velocity, m/s
K = resistance coefficient of the fitting
Wide differences in the values of K are found in the published literature. For convenience,
friction loss in fittings is often expressed as an equivalent length of straight pipe. This
presentation is simple to use on complicated piping layouts involving an assortment of
different fittings. Equivalent length of straight pipe for various fittings is reproduced in
Table 3.5.
Table 3.5: Equivalent Length of Straight Pipe for Valves and Fittings (m)
Pipes deteriorate with age. In general, the flow carrying capacity of a pipe line decreases
with age due to roughening of the interior surface caused by corrosive products, etc. The
effect corresponds to a variation in friction factor due to increasing relative roughness.
Precise estimates of the effect of aging on pipe friction arc not available. Approximate data
presented in Table 3.6 may be used with caution and discretion.
Age of Pipe in Years Multiplier for use with Values Given in Annex 3
Small Pipes 4’’ -10’’ Large Pipes 12’’-60’’
New 1.00 1.00
5 1.40 1.30
10 2.20 1.60
15 3.60 1.80
41

20 5.00 2.00
25 6.30 2.10
30 7.25 2.20
35 8.10 2.30
40 8.75 2.40
45 9.25 2.60
50 9.60 2.86
55 9.80 3.26
60 10.00 3.70
65 10.05 4.25
70 10.10 4.70
Table 3.6: Increase in Friction Loss Due to Aging of Pipe
42

4 PERFORMANCE TESTING OF TUBEWELL
COMPONENTS
The energy input-output and efficiency
of a pumping system are presented in
Exhibit 4.1. In cases where efficiency of
the pumpset is of interest, the electric
energy (or energy in fuel) and water
horsepower need only be measured.
However.a complete analysis requires
determination of efficiencies of all
components in the system. Data
requirements and types of tests for
performance testing and trouble
shooting of tubewell components are
discussed in this chapter.
4.1 Pumpset
Pumpset efficiency refers to the
efficiency at which the prime mover,
transmission and pump combination
converts energy (electricity or fuel) into
mechanical work done on water. The
following data is required to calculate
pumpset efficiency:
• Electric power input to the motor
or rate of diesel consumption by
the engine.
• Pump discharge.
• Total dynamic head.
Electric power input to the motor can be
measured using a wattmeter. Fuel
consumption by diesel engine can be
measured by timing the period
required to consume a known quantity
of fuel or a fuel flow meter may be
used.
Exhibit4.1:EnergyInput-OutputandEfficiencyofaWaterPumpingSystem
43

Several methods of measuring pump discharge of tubewells are available. These include
ultrasonic flow meter, impeller meters; orifice plates and trajectory coordinate method (X-
Y Method) etc.
Total dynamic head developed by a pump (Exhibit 4.1) is made up of the following:
• Static discharge head
• Static suction lift
• Head loss in the delivery pipe
• Head loss in the suction pipe
• Velocity head of discharge
Total dynamic head developed by a horizontal shaft centrifugal pump can be calculated
from measurements of pressures immediately before and after the pump and velocities of
flow in the suction and discharge pipes. Velocities of flow in discharge and suction pipes
can be calculated from discharge and internal diameters of discharge and suction pipes,
respectively. With reference to Exhibit 4.1, total dynamic head developed by the pump is:
𝐻 =
𝑃𝑑
𝛾
−
𝑃𝑠
𝛾
+
𝑉𝑑2
2𝑔
−
𝑉𝑎2
2𝑔
where
H = Total dynamic head, m
Pd = Pressure reading on gauge in discharge pipe, Pa
Ps = Pressure reading on gauge in suction pipe, Pa
Vd = Velocity or water in discharge pipe, m/s
Va = Velocity or water in suction pipe, m/s
g = Acceleration due to gravity, m/s2
The method of head determination described above applies specifically to pumping units
installed so that both suction and discharge flanges of the pump and adjacent piping are
located so as to be accessible for installation of gauges for testing the pump. In this case
the pump is charged with the head losses in the pump itself and all other head losses are
rightfully charged against the piping system.
The installation of turbine pumps is invariably such that it is not possible to obtain
pressures at the suction and discharge of the submerged basic pumping unit. Therefore,
the method of head determination and testing must necessarily vary from the practice
used for horizontal pumps. The only fair method of head determination is one that will
permit checking of pump performance in the field. The method is briefly described below.
With reference to Exhibit 4.2, the total dynamic head determined by this method is called
"Field Head" for it can be obtained by field measurements. In this method, all velocity,
entrance and friction losses at the suction of the pump are charged against the pump. Also
44

all exit losses from pump discharge as well as all column friction losses arc charged against
the pump. This makes the efficiency of the pump appear lower than it really is.
However, when not charged to the pump it makes field checking of turbine pump
performance impractical.
4.2 Diesel Engine
The two parameters needed to evaluate the efficiency of an engine are the rate of fuel
consumption and brake power. Simultaneous measurements of fuel consumption and
brake power can be made using a fuel flow meter and a dynamometer. Measurement of
fuel consumption is relatively easy. However, field measurement of power output of the
engine is not generally practical. Dynamometers are inherently big and heavy thus posing
transport problems. In addition, coupling of the dynamometer with the stationary
engines installed in difficult to reach positions makes the use of dynamometers nearly
impossible. Under these conditions the only alternative solution is to estimate engine
efficiency from indirect measurements such as compression pressure, color of smoke,
operating temperature, etc.
Low engine compression pressure, poor atomization of fuel, wrong injection timing, low
engine operating temperature, etc., all lead to part of the fuel not being fully oxidized and
to the production of smoke. Color of the exhaust gases is a fair indicator of the
combustion efficiency of the engine and thus can be used to estimate the efficiency
of the engine.
Color of the exhaust may be classified as clear, light, medium, dark and very dark. A
smoke tester may be used instead of visual observation. Smoke ratings are expressed in
arbitrary units for the particular smoke meter brand. For the Bosch-Bacharak Smoke
Test (ASTM D2156), Bosch l, Bosch 2, Bosch 3, Bosch 4 and Bosch 8 correspond to clear,
light, medium ,dark and very dark smoke, respectively.
Color of Smoke (Bosch Number) Diesel Engine Efficiency,
%
Clear (Bosch Number 1) 30
Light (Bosch Number 2) 28
Medium (Bosch Number 3) 25
Dark (Bosch Number 4) 21
Very Dark (Bosch Number 5) 16
Table 4.1: Smoke Ratings as Per Bosch-Bacharak Smoke Test
The slow and high speed diesel engines installed on tubewells operate under these
conditions and their efficiency can be estimated from the color of exhaust. Tractor
45

engines are lightly loaded when used for pumping water and efficiency estimates based
on exhaust color may be in significant error.
Part load operation, inefficient combustion, low compression pressure, excessive friction
and defective cooling system lead to low engine efficiencies. Following tests may be
carried out for trouble shooting the causes of low efficiency:
• Smoke test for inefficient combustion
• Compression test to detect low compression pressure in the combustion
chamber
• Temperature of coolant entering and leaving the cooling system.
The other method of gathering information about the combustion performance of the
engine is emission analyzer. The instrumental methods include instruments used for non-
continuous or continuous sampling using extractive samples and in-situ type instruments
that require no sampling system. The instrument contains sensors of oxygen, carbon
dioxide, carbon monoxide, nitrogen, sulfur dioxide, sulfur trioxide, nitric oxide, nitrogen
dioxide, hydrogen sulfide, and hydrocarbons. Emission analyzers are found in many
different price brackets. The cheapest portable multi-gas analyzers are commonly found
under $5000. Portable units with improved sample conditioning and added program
functionality are often found in the $5000 to $25,000 price range.
4.3 Electric Motor
A number of methods have been employed around the world to measure, approximate, or
otherwise determine motor efficiency. Some of these methods are listed below:
• Brake Test
• Dynamometer Test
• Duplicate machine Test
• Equivalent Circuit Calculation Method
• Input Measurement and Segregation of Loss Method. These methods,
however, are applicable to motors on a test bench only.
Determination of the efficiency of a motor in service on a tubewell is extremely difficult for
reasons outlined for the diesel engines. An adaptation of IEEE Standard 112-2004 for the
field testing of motors involves decoupling the motor from the pu1np. Three
measurements required in this procedure are:
4.3.1 Load Test
Voltage, current, power input and shaft speed of the motor under actual load.
46

4.3.2 Stator Resistance
With the motor turned off, stator resistance between phases.
4.3.3 No Load Test
Voltage, current and power input to the motor load and turned on ..
Motor efficiency can also be approximately estimated from motor power factor which is an
easily measured quantity. Both the efficiency and power factor are dependent on the load
on the motor. Efficiency-power factor relationship for a popular brand of 3-phase
induction motors is shown in Exhibit 4.3. Correction for efficiency loss due to voltage or
current imbalance may be applied to refine the estimate. This method of efficiency
estimation requires the measurement of power input, power factor and line voltages and
currents.
Percent load on the motor can be calculated from the motor output and rated capacity.
Overloading can also be checked by measuring motor temperature as motors run hot when
over loaded.
Measurement of line voltages can help in the detection of low or unbalanced voltage. Low
motor voltage at the motor may be caused by overload, poor connections and small lead-in
wires. Motors run hot due to unbalanced voltage. Unbalance may be present in the supply
or caused by the motor coil unbalance.
Current imbalance is a common problem arriving from unbalanced supply voltage and sub-
standard rewinding of motors. This leads to wastage of electrical energy. More important is
the fact that motors with large current imbalance are more prone to burnouts due to
fluctuations in supply voltage.
4.4 Transmission
Transmission efficiency of direct couplings is nearly 1OO percent and need not be
measured. Energy is lost in belt drives mainly due to slip. Continuous deformation
and flapping of belt adds to energy loss but is difficult to measure. For simplicity,
efficiency of belt drives can be estimated from slip using the following equation:
𝜂 𝑡𝑟 = 100 + (1 − 𝑆) × 0.95
ηtr = efficiency of belt transmission, %
S = belt slip
0.95 = correction factor
47

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