Lab Manual

Electro-Mechanical Systems

SZABIST

School of Mechatronics Engineering
Laboratory Manual
For

ME2402 Electro-...
TABLE OF CONTENTS

Safety Rules and operating Procedures

I

Laboratory Safety information

II

Guidelines for Laboratory ...
Lab Manual

13.

Electro-Mechanical Systems

SZABIST

Study of 3 phase Transformer connections

Appendix

LABORATORY PRACT...
10.
Get your circuit diagram approved by the staff member and connect up the circuit strictly as per
the approved circuit ...
Lab Manual

Electro-Mechanical Systems

SZABIST

22.
At the time of starting a motor, the ammeter connected in the armatur...
GUIDELINES FOR LABORATORY NOTEBOOK
The laboratory notebook is a record of all work pertaining to the experiment. This
reco...
Lab Manual
Electro-Mechanical Systems
are often given to illustrate the treatment of the experimental data in obtaining th...
TROUBLE SHOOTING HINTS
1. Be Sure that the power is turned ON
2. Be sure the ground connections are common
3. Be sure the ...
Lab Manual

Electro-Mechanical Systems

SZABIST

9
EXPERIMENT NO 1

DATE:

LOAD TEST ON D.C. SHUNT MOTOR
AIM:
To conduct load test on D.C motor and to obtain performance cha...
Lab Manual

Electro-Mechanical Systems

SZABIST

PRECAUTIONS:
1.The motor field rheostat should be kept at minimum resista...
Lab Manual

Electro-Mechanical Systems

SZABIST

LOAD TEST ON DC SHUNT MOTOR
TABULAR COLUMN
Sl.No.

VL
V

IL
A

Speed(N)
R...
Lab Manual

Electro-Mechanical Systems

EXPERIMENT NO 2

SZABIST

DATE:

LOAD TEST ON D.C. SERIES MOTOR
AIM:
To conduct lo...
5. Apply load in steps and note down the corresponding reading till the rated current is reached.
`

GRAPH:
1.Output power...
Lab Manual

Electro-Mechanical Systems

SZABIST

LOAD TEST ON DC SERIES MOTOR
TABULAR COLUMN
Sl.No.

VL
V

IL
A

Speed(N)
...
Lab Manual

Electro-Mechanical Systems

EXPERIMENT NO 3

SZABIST

DATE:

SPEED CONTROL OF DC SHUNT MOTOR
AIM:
To control t...
2. Field rheostat should be kept at minimum resistance minimum position.
PROCEDURE:
ARMATURE CONTROL METHOD:
1. Connect as...
Lab Manual

Electro-Mechanical Systems

SZABIST

SPEED CONTROL OF DC SHUNT MOTOR
TABULAR COLUMS
ARMATURE CONTROL METHOD
SL...
Lab Manual

Electro-Mechanical Systems

SZABIST

23
EXPERIMENT NO 4

DATE:

OCC & LOAD TEST ON SEPERATELY EXCITED DC
GENERATOR
AIM:
To conduct OCC and load test of a separate...
Lab Manual

Electro-Mechanical Systems

SZABIST

PROCEDURE
OCC TEST
1. Connect as per the circuit diagram
2.Close the DPST...
OPEN CIRCUIT CHARACTERISITICS AND LOAD
CHARACTERISTICS OF SEPARATELY EXCITED DC GENERATOR
TABULAR COLUMNS
OPEN CIRCUIT CHA...
Lab Manual

Electro-Mechanical Systems

SZABIST

LOAD CHARACTERISTICS OF SEPARATELY EXCITED DC
GENERATOR
TABULAR COLUMNS
T...
Load
SL.NO. Current
IL
Amps
1
2
3
4
5
6

MODEL CALCULATION:
Ia = IL
Eg = VL + Ia Ra

Load
Voltage
VL
Volts

Armature Ia Ra...
Lab Manual

Electro-Mechanical Systems

SZABIST

29
EXPERIMENT NO 5

DATE:

OCC AND LOAD TEST ON DC SHUNT GENERATOR
OPEN CIRCUIT CHARACTERISTICS
AIM:
To obtain the OCC of the...
Lab Manual
Electro-Mechanical Systems
SZABIST
State P,Z,A are constants the above equation are written as Eg= KфN. I f the...
b) LOAD TEST ON SELF EXCITED DC GENERATOR
AIM:
To conduct the direct load test on the given self excited DC generator to p...
Lab Manual
Electro-Mechanical Systems
SZABIST
From the above equation, the terminal voltage(VL),Is the no; load induced EM...
8. Once the experiment is completed the load on the generator is gradually decreased, the various
rheostats are brought ba...
Lab Manual

Electro-Mechanical Systems

SZABIST

OPEN CIRCUIT CHARACTERISITICS AND LOAD TEST ON
DC SHUNT GENERATOR
TABULAR...
OPEN CIRCUIT CHARACTERISITICS AND LOAD TEST ON
DC SHUNT GENERATOR
TABULAR COLUMNS
To find Armature Resistance Ra:
SL.NO. A...
Lab Manual

Electro-Mechanical Systems

Load
SL.NO. Voltage
VL
Volts

Load
Current
IL
Amps

Field
Current
If
Amps

Armatur...
In a D.C. series generator the field winding is connected in series with the armature winding. In
this case the armature c...
Lab Manual
Electro-Mechanical Systems
SZABIST
6. After the experiment is completed the load on the generator is gradually ...
Lab Manual

Electro-Mechanical Systems

SZABIST

LOAD TEST ON DC SERIES GENERATOR
TABULAR COLUMNS
To find Armature Resista...
Lab Manual

Electro-Mechanical Systems

EXPERIMENT NO 7

SZABIST

DATE:

LOAD TEST ON SINGLE PHASE TRANSFORMER
AIM:
To con...
PRECAUTIONS:
1.The autotransformer should be kept at minimum voltage position.
2.Before switching off the supply the varia...
Lab Manual

Electro-Mechanical Systems

SZABIST

LOAD TEST ON SINGLE PHASE TRANSFORMER
TABULAR COLUMN
mf1 =
SL.NO Primary
...
Lab Manual

Electro-Mechanical Systems

SZABIST

47
EXPERIMENT NO 8

DATE:

OPEN CIRCUIT AND SHORT CIRCUIT TESTS ON
SINGLE PHASE TRANSFORMER
AIM:
To conduct OC and SC tests o...
Lab Manual

Electro-Mechanical Systems

SZABIST

49
PRECAUTIONS:
1. The autotransformer should be kept at minimum voltage position.
2. Before switching off the supply the var...
Lab Manual

Electro-Mechanical Systems

ISC(RO1COSф0 + XO1 Sin ф0 )
% Regulation at lag = ___________________________ X
V1...
OPEN CIRCUIT AND SHORT CIRCUIT TESTS ON SINGLE PHASE
TRANSFORMER
TABULAR COLUMNS
OPEN CIRCUIT TEST:
VO
Volts

IO
Amps

Wat...
Lab Manual

Electro-Mechanical Systems

SZABIST

PREDETERMINATION OF EFFICIENCY AT DIFFERENT LOADS:
(i)
At Unity Power Fac...
Lab Manual

Electro-Mechanical Systems

EXPERIMENT NO 9

SZABIST

DATE:

SWINBURNE’S TEST
AIM:
To predetermine the efficie...
Lab Manual

Electro-Mechanical Systems

SZABIST

PRECAUTIONS:
1. The field rheostat must be kept in minimum resistance pos...
VIVA QUESTIONS:
1.

What is the purpose of Swinburne’s test?

2.

What are the constant losses in a DC machine?

3. What a...
Lab Manual

Electro-Mechanical Systems

SZABIST

SWINBURNE’S TEST
TABULAR COLUMNS
(i)
VO
Volts

(i)
SL.NO

Motor on No Loa...
PREDETERMINATION OF LOSSES AND EFFICEINCY AT DIFFERENT
LOADS:
(i)
As a Motor:
SL.
NO

Load
Voltage
VL
Volts

Load
Current
...
Lab Manual

Electro-Mechanical Systems

SZABIST

61
EXPERIMENT NO 10

DATE:

SEPARATION OF IRON LOSSES IN DC MACHINE
AIM:
To separate the no load losses in a DC Machine as ir...
Lab Manual

Electro-Mechanical Systems

SZABIST

63
PROCEDURE:1. Connections are made as per the circuit diagram.
2. The DC supply is switched ON and the motor is started usi...
Lab Manual

Electro-Mechanical Systems
SEPARATION OF IRON LOSSES IN DC MACHINE

SZABIST

TABULAR COLUMNS

To find Armature...
Lab Manual

Electro-Mechanical Systems

SZABIST

EXPERIMENT NO 11

DATE:

HOPKINSON’S TEST
AIM:
To conduct the Hopkinson’s...
versa. The motor is started with no load. Then the field of one is weakened and the other is strengthened so
that the form...
Lab Manual

Electro-Mechanical Systems

SZABIST

FORMULAE:
1. Armature Cu loss of generator = (Ifg + Ig)2 Ra Watts
2. Arma...
HOPKINSON’S TEST
TABULAR COLUMNS
Motor
Vm
Volts

Generator
Im
Amps

Ifm
Amps

Vg
Volts

Ig
Amps

Ifg
Amps

Armature
Cu Los...
Lab Manual

Electro-Mechanical Systems

SZABIST

71
EXPERIMENT NO 12

DATE:

SUMPNERS TEST
AIM:
To predetermine the efficiency of the transformer at any desired load and powe...
Lab Manual

Electro-Mechanical Systems

SZABIST

PROCEDURE:
1.
2.
3.
4.
5.

Connect as per the circuit diagram.
Close the ...
SUMPNER’S TEST
TABULAR COLUMNS
TFR.1
Current
I1
A

TFR.2
Current
I2
A

TFR.1
Voltage
V1
V

TFR.2
Voltage
V2
V

TFR.1
W1

T...
Lab Manual

Electro-Mechanical Systems

SZABIST

75
Lab Manual

Electro-Mechanical Systems

SZABIST

EXPERIMENT NO 13

DATE:

STUDY OF THREE PHASE TRANSFORMER CONNECTIONS
AIM...
advantage of stabilizing the primary neutral by connecting it to the neutral of the generator is that it
eliminates distor...
Lab Manual

Electro-Mechanical Systems

SZABIST

DELTA/DELTA CONNECTION:
This connection is for low voltage transformer. T...
Lab Manual

Electro-Mechanical Systems

SZABIST

PROCEDURE:
1.
2.
3.
4.

Connections are given as per the circuit diagram....
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Load Test on DC Shunt Motor
Load Test on DC Series Motor
Speed Control of DC Shunt Motor
OCC and Load Test on Separately Excited DC Generator
OCC and Load Test on DC Shunt Generator
Load Test on DC series Generator
Load Test on Single phase Transformer
OC & SC Test on Single phase Transformer
Swinburne’s Test
Separation of iron losses in DC Machine
Hopkinson’s Test
Sumpner’s Test on Single phase Transformer
Study of 3 phase Transformer connections

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Ems-lab-manual

  1. 1. Lab Manual Electro-Mechanical Systems SZABIST School of Mechatronics Engineering Laboratory Manual For ME2402 Electro-Mechanical System Fourth Semester Year: ________ 1
  2. 2. TABLE OF CONTENTS Safety Rules and operating Procedures I Laboratory Safety information II Guidelines for Laboratory Notebook III Sl.No 1. Troubleshooting Hints Experiment Name Load Test on DC Shunt Motor IV Page No 2. Load Test on DC Series Motor 3. Speed Control of DC Shunt Motor 4. OCC and Load Test on Separately Excited DC 5. Generator OCC and Load Test on DC Shunt Generator 6. Load Test on DC series Generator 7. Load Test on Single phase Transformer 8. OC & SC Test on Single phase Transformer 9. Swinburne’s Test 10. Separation of iron losses in DC Machine 11. Hopkinson’s Test 12. Sumpner’s Test on Single phase Transformer
  3. 3. Lab Manual 13. Electro-Mechanical Systems SZABIST Study of 3 phase Transformer connections Appendix LABORATORY PRACTICE SAFETY RULES 1. SAFETY is of paramount importance in the Mechatronics Engineering Laboratories. 2 .Electricity NEVER EXECUSES careless persons. So, exercise enough care and attention in handling electrical equipment and follow safety practices in the laboratory. (Electricity is a good servant but a bad master). 3 .Avoid direct contact with any voltage source and power line voltages. (Otherwise, any such contact may subject you to electrical shock) 4. Wear rubber-soled shoes. (To insulate you from earth so that even if you accidentally contact a live point, current will not flow through your body to earth and hence you will be protected from electrical shock) 5. Wear laboratory-coat and avoid loose clothing. (Loose clothing may get caught on an equipment/instrument and this may lead to an accident particularly if the equipment happens to be a rotating machine) 6 .Girl students should have their hair tucked under their coat or have it in a knot. 7. Do not wear any metallic rings, bangles, bracelets, wristwatches and neck chains. (When you move your hand/body, such conducting items may create a short circuit or may touch a live point and thereby subject you to electrical shock) 8. Be certain that your hands are dry and that you are not standing on wet floor. (Wet parts of the body reduce the contact resistance thereby increasing the severity of the shock) 9. Ensure that the power is OFF before you start connecting up the circuit.(Otherwise you will be touching the live parts in the circuit) 3
  4. 4. 10. Get your circuit diagram approved by the staff member and connect up the circuit strictly as per the approved circuit diagram. 11. Check power chords for any sign of damage and be certain that the chords use safety plugs and do not defeat the safety feature of these plugs by using ungrounded plugs. 12. When using connection leads, check for any insulation damage in the leads and avoid such defective leads. 13. Do not defeat any safety devices such as fuse or circuit breaker by shorting across it. Safety devices protect YOU and your equipment. 14. Switch on the power to your circuit and equipment only after getting them checked up and approved by the staff member. 15. Take the measurement with one hand in your pocket. (To avoid shock in case you accidentally touch two points at different potentials with your two hands) 16. Do not make any change in the connection without the approval of the staff member. 17. In case you notice any abnormal condition in your circuit ( like insulation heating up, resistor heating up etc ), switch off the power to your circuit immediately and inform the staff member. 18. Keep hot soldering iron in the holder when not in use. 19. After completing the experiment show your readings to the staff member and switch off the power to your circuit after getting approval from the staff member. 20. While performing load-tests in the Electro Mechanical System Laboratory using the brakedrums: i. ii. iii. Avoid the brake-drum from getting too hot by putting just enough water into the brakedrum at intervals; use the plastic bottle with a nozzle (available in the laboratory ) to pour the water.(When the drum gets too hot, it will burn out the braking belts) Do not stand in front of the brake-drum when the supply to the load-test circuit is switched off. (Otherwise, the hot water in the brake-drum will splash out on you) After completing the load-test, suck out the water in the brake-drum using the plastic bottle with nozzle and then dry off the drum with a sponge which is available in the laboratory.(The water, if allowed to remain in the brake-drum, will corrode it) 21. the correct rating of the fuse/s to be connected in the circuit after understanding correctly the type of the experiment to be performed: no-load test or full-load test, the maximum current expected in the circuit and accordingly use that fuse-rating.(While an over-rated fuse will damage the equipment and other instruments like ammeters and watt-meters in case of over load, an under-rated fuse may not allow one even to start the experiment)
  5. 5. Lab Manual Electro-Mechanical Systems SZABIST 22. At the time of starting a motor, the ammeter connected in the armature circuit overshoots, as the starting current is around 5 times the full load rating of the motor. Moving coil ammeters being very delicate, may get damaged due to high starting current. A switch has been provided on such meters to disconnect the moving coil of the meter during starting. This switch should be closed after the motor attains full speed. Moving iron ammeters and current coils of wattmeters are not so delicate and hence these can stand short time overload due to high starting current. No such switch is therefore provided on these meters. Moving iron meters are cheaper and more rugged compared to moving coil meters. Moving iron meters can be used for both a.c. and d.c. measurement. Moving coil instruments are however more sensitive and more accurate as compared to their moving iron counterparts and these can be used for d.c. measurements only. Good features of moving coil instruments are not of much consequence for you as other sources of errors in the experiments are many times more than those caused by these meters. 23. Some students have been found to damage meters by mishandling in the following ways: i. ii. Keeping unnecessary material like books, lab records, unused meters etc. causing meters to fall down the table. Putting pressure on the meter (specially glass) while making connections or while talking or listening somebody. STUDENTS ARE STRICTLY WARNED THAT FULL COST OF THE METER WILL BE RECOVERED FROM THE INDIVIDUAL WHO HAS DAMAGED IT IN SUCH A MANNER. Copy these rules in your Lab Record. Observe these yourself and help your friends to observe.. I have read and understand these rules and procedures. I agree to abide by these rules and procedures at all times while using these facilities. I understand that failure to follow these rules and procedures will result in my immediate dismissal from the laboratory and additional disciplinary action may be taken. Signature Date Lab 5
  6. 6. GUIDELINES FOR LABORATORY NOTEBOOK The laboratory notebook is a record of all work pertaining to the experiment. This record should be sufficiently complete so that you or anyone else of similar technical background can duplicate the experiment and data by simply following your laboratory notebook. Record everything directly into the notebook during the experiment. Do not use scratch paper for recording data. Do not trust your memory to fill in the details at a later time. Organization in your notebook is important. Descriptive headings should be used to separate and identify the various parts of the experiment. Record data in chronological order. A neat, organized and complete record of an experiment is just as important as the experimental work. 1. Heading: The experiment identification (number) should be at the top of each page.Your name and date should be at the top of the first page of each day's experimental work. 2. Object: A brief but complete statement of what you intend to find out or verify in the experiment should be at the beginning of each experiment 3. Diagram: A circuit diagram should be drawn and labeled so that the actual experiment circuitry could be easily duplicated at any time in the future. Be especially careful to record all circuit changes made during the experiment. 4. Equipment List: List those items of equipment which have a direct effect on the accuracy of the data. It may be necessary later to locate specific items of equipment for rechecks if discrepancies develop in the results. 5. Procedure: In general, lengthy explanations of procedures are unnecessary. Be brief. Short commentaries along side the corresponding data may be used. Keep in mind the fact that the experiment must be reproducible from the information given in your notebook. 6. Data: Think carefully about what data is required and prepare suitable data tables. Record instrument readings directly. Do not use calculated results in place of direct data; however, calculated results may be recorded in the same table with the direct data. Data tables should be clearly identified and each data column labeled and headed by the proper units of measure. 7. Calculations: Not always necessary but equations and sample calculations
  7. 7. Lab Manual Electro-Mechanical Systems are often given to illustrate the treatment of the experimental data in obtaining the results. SZABIST 8. Graphs: Graphs are used to present large amounts of data in a concise visual form. Data to be presented in graphical form should be plotted in the laboratory so that any questionable data points can be checked while the experiment is still set up. The grid lines in the notebook can be used for most graphs. If special graph paper is required, affix the graph permanently into the notebook. Give all graphs a short descriptive title. Label and scale the axes. Use units of measure. Label each curve if more than one on a graph. 9. Results: The results should be presented in a form which makes the interpretation easy. Large amounts of numerical results are generally presented in graphical form. Tables are generally used for small amounts of results. Theoretical and experimental results should be on the same graph or arrange in the same table in a way for easy correlation of these results. 10. Conclusion: This is your interpretation of the results of the experiment as an engineer. Be brief and specific. Give reasons for important discrepancies. 7
  8. 8. TROUBLE SHOOTING HINTS 1. Be Sure that the power is turned ON 2. Be sure the ground connections are common 3. Be sure the circuit you build is identical to your circuit diagram (Do a node by node check) 4. Be sure that the supply voltages are correct 5. Be sure that the equipment is set up correctly and you are measuring the correct parameters 6. If steps I through 5 are correct then you probably have used a component with the wrong value or one that doesn’t work. It is also possible that the equipment does not work (although this is not probable) or the protoboard you are using may have some unwanted paths between nodes. To find your problem you must trace through the voltages in your circuit node by node and compare the signal you expect to have. Then if they are different use your engineering judgment to decide what is causing the different or ask your lab assistant
  9. 9. Lab Manual Electro-Mechanical Systems SZABIST 9
  10. 10. EXPERIMENT NO 1 DATE: LOAD TEST ON D.C. SHUNT MOTOR AIM: To conduct load test on D.C motor and to obtain performance characteristics APPARATUS REQUIRED: Sl.No. 1. 2.` 3. 4. Apparatus Voltmeter Ammeter Rheostat Tachometer Type MC MC Digital Range (0-300)V (0-20)A 230 ohm/1.5A Quantity 1 1 1 1 Fuse Rating: 125% of rated current 125*17/100=21.25 ≈ 20 A THEORY: The shunt motor has a definite no load speed hence it does not run away when load is suddenly thrown off provided the field circuit remains closed. The drop in speed from no-load to full load is small hence this motor is usual referred to a constant speed motor. The efficiency curve is usually of the same shape for all electric motors and generators. The shape of efficiency curve and the point of maximum efficiency can be vary considerable by the designer, though it is advantageous to have an efficiency curve which is fairly flat. So that there is little change in efficiency between load and 25% overload and to have the maximum efficiency as near to the full load as possible. From the curves it is observed that is certain value of current is required even when output is zero. The motor input under no-load conditions goes to meet the various losses, occurring within the machine. As compared to other motors a shunt motor is said to have a lowest starting torque. But this should not be taken off mean that is shunt motor is incapable of starting heavy load. Actually it means that series and compound motor as capable of starting heavy load with les excess of current inputs over normal values then the shunt motor and the consequently the depreciation on the motor will be relatively less.
  11. 11. Lab Manual Electro-Mechanical Systems SZABIST PRECAUTIONS: 1.The motor field rheostat should be kept at minimum resistance position. 2. The motor should be started at no load condition. 3. The motor should be cooled by circulating water throughout the experiment. PROCEDURE: 1. Connect as per the circuit diagram 2.Close the DPST switch 3. Start the motor using three point starter 4.Adjust the field rheostat till the motor reaches its rated speed. 5. Note down the no load reading of voltmeter, ammeter, speed and spring balance reading. 6.Apply load in steps and note down the corresponding reading till the rated current is reached. ` GRAPHS: 1.Output power Vs efficiency 2. Output power Vs current 3. Output power Vs torque 4. Output power Vs speed 5.Speed Vs torque RESULT: Thus the load test on D.C shunt motor was performed and the respective graphs were drawn. VIVA QUESTIONS 1.Why should the field rheostat be kept in the position of minimum resistance? 2.What is the loading arrangement used in a dc motor? 3.How can the direction of rotation of a DC shunt motor be reversed? 4.What are the mechanical and electrical characteristics of a DC shunt motor? 5.What are the applications of a DC shunt motor? 11
  12. 12. Lab Manual Electro-Mechanical Systems SZABIST LOAD TEST ON DC SHUNT MOTOR TABULAR COLUMN Sl.No. VL V IL A Speed(N) RPM S1 Kg S2 Kg S1 ̃~ S2 Kg Torque N-m Output Power W Input Power W Efficiency η % 1 2 3 4 5 6 7 8 MODEL CALCULATION: Input power =VL*IL Watts Output power = 2лNT/ 60 Watts Torque T= (S1~S2)*9.81*R N-m, where R is the radius of the brake drum in metre Output power Efficiency η = x 100 Input power 13
  13. 13. Lab Manual Electro-Mechanical Systems EXPERIMENT NO 2 SZABIST DATE: LOAD TEST ON D.C. SERIES MOTOR AIM: To conduct load test on D.C series motor and to obtain performance characteristics APPARATUS REQUIRRED; Sl.no Apparatus 1. Voltmeter 2. Ammeter 3. Tachometer Type MC MC Digital Range (0-300)V (0-20)A Quantity 1 1 1 Fuse Rating: 125% of rated current 125*17/100=21.25≈ 20 A THEORY: The drop in speed with increased load is much prominent in series motor than in a shunt motor hence a series motor is not suitable for application requiring a substantially constant speed. For a given current input a starting torque developed by a series motor is greater than that developed by a shunt motor. Hence series motors are used where huge starting torques are necessary that means for cranes and traction purpose. In addition to huge starting torque there is another unique characteristics of series motor which makes this especially desirable for traction work that means when a load comes on a series motor it response by decreasing its speed and supplies the increased torque with a small increase in current. On the other hand a shunt motor under the same condition would hold its speed nearly constant and would supply the required increased torque with a large increase of input current. PRECAUTIONS: 1. The motor should be started with some load 2. The motor should be stopped with some load. PROCEDURE: 1. Connect as per the circuit diagram 2. Close the DPST switch 3. Start the motor using two point starter 4. Note down the reading of voltmeter, ammeter, speed and spring balance reading. 15
  14. 14. 5. Apply load in steps and note down the corresponding reading till the rated current is reached. ` GRAPH: 1.Output power Vs efficiency 2. Output power Vs current 3. Output power Vs torque 4. Output power Vs speed 5.Speed Vs torque RESULT: Thus the load test on D.C series motor was performed and the respective graphs were drawn. VIVA QUESTIONS 1.Why a DC series motor should not be stared without load? 2. Why a DC series motor has a high starting torque? 3.Compare the resistances of the field windings of DC shunt and series motor? 4.What are the applications of DC series motor? 5. Comment on the Speed – Torque characteristics of a DC series motor.
  15. 15. Lab Manual Electro-Mechanical Systems SZABIST LOAD TEST ON DC SERIES MOTOR TABULAR COLUMN Sl.No. VL V IL A Speed(N) RPM S1 Kg S2 Kg S1 ̃~ S2 Kg Torque N-m Output Power W Input Power W Efficiency η % 1 2 3 4 5 6 7 8 MODEL CALCULATION: Input power =VL*IL Watts Output power = 2лNT/ 60 watts Torque T= (S1~S2) *9.81*R N-m, where R is the radius of the brake drum in metre. Output power Efficiency η = x 100 Input power 17
  16. 16. Lab Manual Electro-Mechanical Systems EXPERIMENT NO 3 SZABIST DATE: SPEED CONTROL OF DC SHUNT MOTOR AIM: To control the speed of DC shunt motor by 1. Armature control method 2. Field control method APPARATUS REQUIRRED: Sl.no Apparatus 1. Voltmeter 2.` Ammeter 3.` Ammeter 4. Rheostat 5 Tachometer Type MC MC MC Range (0-300)V (0-5)A (0-2)A 250 ohm/1.5A Digital Quantity 1 1 1 2 1 Fuse Rating: 40% of rated current 40*17/100=6.8≈10 A THEORY: Flux Control method The speed of the DC motor is inversely propositional to the flux per pole, when the armature voltage is kept constant. By decreasing the flux the speed can be increased and vice – versa. Hence the main flux of field control method the flux of a DC motor can be changed by changing field current with help of a shunt field rheostat. Since shunt field current is respectively small shunt field rheostat has to carry only a small amount of current which means I 2R losses is small so that rheostat is small in size .This method is very efficient. Armature Control method This method is used when speed below the no load speed are required.As the supply voltage is normally constsnt the voltage across the armature is varied by inserting a variable rheostat in series with the armature circuit. As conductor resistance is increased potential difference across the armature is decreased, herby decreasing the armature speed. F or a load of constant torque speed is approximately propositional to the potential difference across the armature. PRECAUTIONS: 1. Armature rheostat must be kept at maximum resistance position. 19
  17. 17. 2. Field rheostat should be kept at minimum resistance minimum position. PROCEDURE: ARMATURE CONTROL METHOD: 1. Connect as per the circuit diagram 2.Close the DPST switch 3. Start the motor using three point starter 4.By keeping the field current(If) as constant value, adjust the armature rheostat and note down the corresponding armature voltage and motor speed. 5.Repeat the step four till the motor reaches the rated speed. FLUX CONTROL METHOD: 1. Connect as per the circuit diagram 2.Close the DPST switch 3. Start the motor using three point starter 4.By keeping the armature voltage as constant value, adjust the field rheostat and note down the corresponding field current and motor speed. GRAPHS: 1.Field current Vs speed 2. Armature voltage Vs speed RESULT: Thus the speed of DC shunt motor was controlled by 1.Armature control method 2. Field control method and the respective graphs were drawn. VIVA QUESTIONS: 1.How does the speed of a DC shunt motor vary with armature voltage and field current? 2. Compare the resistance of the armature and field winding. 3.What is the importance of speed control of DC motor in industrial application? 4.Which is of the two method of speed control is better and why? 5.Why is the speed of DC shunt motor practically constant under normal load condition?
  18. 18. Lab Manual Electro-Mechanical Systems SZABIST SPEED CONTROL OF DC SHUNT MOTOR TABULAR COLUMS ARMATURE CONTROL METHOD SL.NO. Field Current If = 0.6 A Armature Speed N Voltage Va RPM V Field Current If = 0.5 A Armature Speed N Voltage Va RPM V 1. 2. 3 4 5 6 FIELD CONTROL METHOD SL.NO. Armature Voltage Va= 180 V Field Current Speed N If RPM A Armature Voltage Va = 170 V Field Current Speed N If RPM A 1. 2. 3 4 5 6 21
  19. 19. Lab Manual Electro-Mechanical Systems SZABIST 23
  20. 20. EXPERIMENT NO 4 DATE: OCC & LOAD TEST ON SEPERATELY EXCITED DC GENERATOR AIM: To conduct OCC and load test of a separately excited DC generator and to plot the internal and external characteristics. APPARATUS REQUIRRED; Sl.No Apparatus 1. Voltmeter 2.` Ammeter 3.` Ammeter 4. Rheostat 5. Rheostat 4. Tachometer Type MC MC MC Range (0-300)V (0-5)A (0-2)A 250 ohm/1.5A 1200ohm/0.8A Quantity 1 1 1 1 1 1 Fuse Rating: 125% of rated current 125*17/100=21.25≈ 20 A THEORY: Due to residual magnetism in the poles some EMF is generated even when If = 0. Hence the curve starts a little way up. The slight curvature at the lower end is due to magnetic inertia. It is seen that in the first part of the curve is practically straight. Hence the flux and the consequently the generated EMF is directly proportional to the exciting current. However at the higher flux densities where it is small iron path reluctance becomes appreciable and straight. Field windings are connected parallel to the armature and it is called dc shunt generator. Due to residual magnetism some initial emf and hence some current will be generated. This current while passing into the field coils will strengthen the magnetism of poles. This will increase pole flux which will further increase the generated emf. Increased emf and flux proceeds till equilibrium reached. This reinforcement of emf and flux proceeds till equilibrium reached at some point. PRECAUTIONS: 1. Field rheostat of motor should be kept at minimum resistance position. 2. Field rheostat of the generator should be kept at minimum resistance position.
  21. 21. Lab Manual Electro-Mechanical Systems SZABIST PROCEDURE OCC TEST 1. Connect as per the circuit diagram 2.Close the DPST switch 3. Start the motor using three point starter 4.By keeping the field current(If) as constant value, adjust the armature rheostat and note down the corresponding armature voltage and motor speed. 5. Adjust the potential divider of the generator and note down the ammeter and voltmeter readings. 6. Bring back the potential divider to minimum voltage position and switch off supply LOAD TEST 1. Connect as per the circuit diagram 2.Close the DPST switch 3. Start the motor using three point starter 4.By keeping the field current(If) as constant value, adjust the armature rheostat and note down the corresponding armature voltage and motor speed. 5. Adjust the potential divider of the generator and by varying the load until its maximum and note down the ammeter and voltmeter readings . 6. Bring back the potential divider to minimum voltage position and switch off supply GRAPHS: 1.Field current Vs Generated voltage 2. Load current Vs Load voltage RESULT: Thus an OCC and LOAD characteristics of a separately excited generator was performed and the respective graphs were drawn. VIVA QUESTIONS: 1. What is the principle of generator? 2. What is meant by residual magnetism? 3. What is critical field resistance? 4. What is meant by saturation? 5. What are the reasons for the drooping load characteristics? 25
  22. 22. OPEN CIRCUIT CHARACTERISITICS AND LOAD CHARACTERISTICS OF SEPARATELY EXCITED DC GENERATOR TABULAR COLUMNS OPEN CIRCUIT CHARACTERISTICS: SL.NO. Field If Amps 1 2 3 4 5 6 7 8 9 Current Generated Eg Volts Voltage
  23. 23. Lab Manual Electro-Mechanical Systems SZABIST LOAD CHARACTERISTICS OF SEPARATELY EXCITED DC GENERATOR TABULAR COLUMNS To find Armature Resistance Ra: SL.NO. Armature Current Armature Voltage Armature Resistance Ia (Amps) Va (Volts) Ra = Va/Ia (Ohms) 1 2 3 4 Average Ra LOAD CHARACTERISTICS: 27
  24. 24. Load SL.NO. Current IL Amps 1 2 3 4 5 6 MODEL CALCULATION: Ia = IL Eg = VL + Ia Ra Load Voltage VL Volts Armature Ia Ra Current Volts Ia = IL Amps Generated Voltage Eg = VL + Ia Ra Volts
  25. 25. Lab Manual Electro-Mechanical Systems SZABIST 29
  26. 26. EXPERIMENT NO 5 DATE: OCC AND LOAD TEST ON DC SHUNT GENERATOR OPEN CIRCUIT CHARACTERISTICS AIM: To obtain the OCC of the given self excited DC generator and hence to determine 1.critical field resistance 2.critical speed 3.OCC at the specified speed NAME PLATE DETAILS: DC generator DC Motor Rated current Rated voltage Power rating Rated speed Rated current Rated voltage Power rating Rated speed APPARATUS REQUIRRED; Sl.No. Apparatus 1. Voltmeter 2.` Ammeter 3.` Ammeter 4 Rheostat 5. Rheostat 6 Tachometer Type MC MC MC Digital Range (0-300)V (0-20)A (0-2)A 1200 ohm/0.8A 250 ohm/1.5A Quantity 2 1 1 1 1 1 Fuse Rating: 125% of rated current 125*17/100=21.25≈ 20 A THEORY: A DC generator requires an excitation circuit to generate an induce voltage depending on whether excitation circuit consumes power for the armature of the machine or from separately require power supply. Generators may be classified as self excited or separately excited generators respectively. The induced emf in DC generators is given by the equation PфZN/60A volts.
  27. 27. Lab Manual Electro-Mechanical Systems SZABIST State P,Z,A are constants the above equation are written as Eg= KфN. I f the speed of the generator also maintained constant then Eg = Kф but the flux is directly proportional to the current Hence Eg =K2If.From the above equation it is clear that the induced emf is directly propositional to the field current when speed maintained constant,. The plot between the induced emf and the field current is known as open circuit characteristics of the DC generator. The typical shape of the characteristics is shown in fig. The induced emf when the field current is zero is known as residual voltage. This emf is due to the presence of a small amount of flux detained. In the field poles of the generator called residual flux. Once the OCC is obtained parameters such as critical field resistance, critical speed and the maximum voltage to which the machine can build up can be determined. If required the OCC at a different speeds can also be obtained. .Critical speed is minimum speed below which the generator shunt fails to excite. PRECAUTIONS: 1. Remove the fuse carriers before wiring and start wiring as per the circuit diagram. 2. Keep the motor field rheostat at minimum resistance position and generator field rheostat at maximum position 3. The SPST switch is kept open at the time of starting the experiment. 4. Fuse calculations. As the test is a no-load test the required fuse ratings are 20% of motor rated current. 5. Replace the fuse carriers with appropriate fuse wires after the circuit connections are checked by the staff-in-charge. PROCEDURE 1. The circuit connections are made as per the circuit diagram in the shown figure. 2. Keeping the motor field rheostat in its minimum position generator field maximum position; and the starter in its of position, the main supply is switched ON to the circuit. 3. The motor is started using the three point starter by slowly and carefully moving the starter handle from its OFF to ON position. 4. The motor to brought to its rated speed by adjusting its rheostat and checked with the help of a tachometer. 5. With the SPST switch open, the residual voltage is noted. 6. Now the SPST switch is closed and the Generator field Rheostat is varied in step and at each step the field current (If) and the corresponding induced EMF (Eg) are recorded in the tabular column. This procedure is continued unit generator voltage reaches 120% of its rated value the machine is maintained constant. 7. After the experiment is completed the various rheostats are brought back to their original position in sequence and then main supply is switched off. RESULT: The magnetization characteristics curve is drawn and the value of built up voltage is obtained from graph. Critical resistance and critical speed are determined from the graph. 31
  28. 28. b) LOAD TEST ON SELF EXCITED DC GENERATOR AIM: To conduct the direct load test on the given self excited DC generator to plot. 1. External characteristics(Or load characteristics) 2. Internal characteristics(Or total characteristics) NAME PLATE DETAILS: DC generator DC Motor Rated current Rated voltage Power rating Rated speed Rated current Rated voltage Power rating Rated speed Excitation: Excitation: * Voltage * Current APPARATUS REQUIRED: Sl.No Apparatus 1. Voltmeter 2. Ammeter 3. Ammeter 4 Rheostat 5. Rheostat 6 Tachometer *Voltage * Current Type MC MC MC Digital Range (0-300)V (0-20)A (0-2)A 1200 ohm/0.8A 250 ohm/1.5A Quantity 2 1 1 1 1 1 THEORY: A DC generator works on the principle of Faraday’s Law of Electromagnetic induction, which says that, “Whenever a conductor is moved in magnetic field , an EMF is generated in it”. “ The magnitude of induction EMF is directly proportional to the rate of change of flux” . The voltage equation for a DC shunt generator is given; by VL=Eg-IaRa; Under No Load Condition; Since Ia,Is negligibly small,
  29. 29. Lab Manual Electro-Mechanical Systems SZABIST From the above equation, the terminal voltage(VL),Is the no; load induced EMF(Eg), as the load on the generator increases , the load current and hence the armature current increases due to armature reaction the induced EMF in the armature decreases. Also increased armature current causes increase in IaRa drop. Hence the terminal voltage decreases with increase load. The plot between the terminal voltage (VL) and load current (IL) is known as the external of load characteristics. The plot between the induced EMF (Eg) and the armature current (Ia) is known as the internal or total characteristics. The type of graph of internal and external characteristics is shown in model graph. PRECAUTIONS: (Not to be included in the record) 1. Remove the fuse carriers before wiring and start wiring as per the circuit diagram. 2. Check the positions of the various rheostats as specified below; *Motor field rheostat is kept at minimum resistance position *Generator field rheostat is kept at maximum resistance position 3. The DPST switch on the load side is kept open at the time of starting the experiment. 4. Fuse calculation. As this is a load test, the required fuse rating are • • 120% of the motor rated current for supply side DPST. 120% of the generator rated current for load side DPST. 5. Replace the fuse carriers with appropriate fuse wires after the circuit connections by the staff-in-charge. are checked PROCEDURE: 1. The circuit connections are made as per the circuit diagram. 2. Keeping the motor field rheostat in which minimum position, generator field rheostats in maximum position and the starter in its off position, the main supply is switched ON to the circuit. 3. The motor is started using the 3-point starter by slowly and carefully moving the starter handle from its OFF to ON position. 4. The motor is brought to its rated speed by adjusting its field rheostat and checked with the help of the tachometer. 5. With the DPST switch open, the potential divider is slowly varying until generator voltage is equal to its rated value (220V). The terminal voltage and the field current are noted in the tabular column. 6. The DPST switch on the load side is now closed and the load on the generator is gradually increased in steps. At each step the speed of the generator is checked and maintained constant at its rated value by adjusting the field rheostat of the motor. After satisfying this condition of each of loading, the terminal voltage(VL), field current(IF) and the load current (IL) are noted down in the tabular column. 7. This procedure is continued until the generator is loaded to 120%of its rated value. 33
  30. 30. 8. Once the experiment is completed the load on the generator is gradually decreased, the various rheostats are brought back to their original position in sequence and the main supply is switched OFF. PROCEDURE FOR MEASUREMENT OF ARMATURE RESISTANCE: 1. The circuit connections are made as per the circuit diagram. 2. Keeping the lamp load at the OFF position the main supply is switched ON. 3. The load is increased such that the current in the circuit is approximately adjusted to 25%,50% and 75% of rated current of the generator and at these load conditions the armature voltage (V) and current(I) are noted in the tabular column. CALCULATION: 1. Determinations of armature resistance(Ra); The armature winding resistance is calculated using ohms law Ra=Va/Ia for each set of readings and the average of them is calculated. The effective resistance of the armature winding after taking into account the effect of temperature rise and skin effect is 1.2 times the average resistance Ra i.e. Ra(effective)=1.2 Ra(average). 2. To plot the internal characteristics, the armature current and the induced EMF are calculated using the expression, Ia=IL+IF and Eg=VL+IaRa(eff) 3. The plots of VL Vs IL and Eg Vs Ia are drawn to scale in the same graph sheet. RESULT: The direct load test on the given self-excited DC generator has been conducted and the internal & external characteristics are plotted. VIVA QUESTIONS: 1. What is the difference between a separately excited dc generator and shunt generator? 2. If a DC shunt generator fails to build up voltage, what may be the probable reasons? 3. What is SPST? What is its use in this experiment? 4. What is the reason the presence of residual magnetism in the field poles? 5. Why does the terminal voltage decrease as the load current increases?
  31. 31. Lab Manual Electro-Mechanical Systems SZABIST OPEN CIRCUIT CHARACTERISITICS AND LOAD TEST ON DC SHUNT GENERATOR TABULAR COLUMNS OPEN CIRCUIT CHARACTERISTICS: SL.NO. Field If Amps Current Generated Eg Volts Voltage 1 2 3 4 5 6 7 8 9 35
  32. 32. OPEN CIRCUIT CHARACTERISITICS AND LOAD TEST ON DC SHUNT GENERATOR TABULAR COLUMNS To find Armature Resistance Ra: SL.NO. Armature Current Armature Voltage Armature Resistance Ia (Amps) Va (Volts) Ra = Va/Ia (Ohms) 1 2 3 4 Average Ra LOAD CHARACTERISTICS:
  33. 33. Lab Manual Electro-Mechanical Systems Load SL.NO. Voltage VL Volts Load Current IL Amps Field Current If Amps Armature Current Ia Ra Ia = IL+If Amps Volts SZABIST Generated Voltage Eg = VL + Ia Ra Volts 1 2 3 4 5 6 MODEL CALCULATION: Ia = IL+ IF Eg=VL + IaRa(eff) EXPERIMENT NO 6 DATE: LOAD TEST ON D.C. SERIES GENERATOR AIM:To conduct the load test on the D.C. Series Generator and hence to plot the load characteristics APPARATUS REQUIRED:SL.NO. 1. 2. 3. 4. 5. DESCRIPTION Voltmeter Ammeter Loading Rheostat Tachometer Connecting wires RANGE 0 – 300 V 0 – 10/20 A 5 KW ----- TYPE MC MC -Digital --- QTY 1 1 1 1 As reqd. THEORY: 37
  34. 34. In a D.C. series generator the field winding is connected in series with the armature winding. In this case the armature current flows through the field winding as well as the load. Since the armature winding and the field winding are in series the armature current is the same as the field current. The field winding has less number of turns of thick wire and hence its resistance is low. Ia = Ise = IL The load characteristics of a D.C. series generator are plotted with the load current (I L) on the X-axis and the Voltage (V) on the Y-axis. As in the case of the D.C. shunt generator there are two types of load characteristics: 1. Internal characteristics – Induced emf E vs Load current IL. Here the drop is due to armature reaction. 2. External characteristics – Terminal Voltage V vs Load current IL. Here the drop is due to armature and series field resistance. The Voltage equation of a D.C. series generator is given by V = E – Ia(Ra + Rse) The load characteristics are shown in the model graph. It will be noticed that a series generator has rising voltage characteristic i.e. with increase in load, its voltage is also increased, but it is seen that at high loads, the voltage starts decreasing due to excessive demagnetizing effects of armature reaction. In fact, terminal voltage starts decreasing as load current is increased as shown by the dotted curve and for a particular high value of load current the terminal voltage is reduced to zero. PRECAUTIONS: 1. The Starter handle should be kept in OFF position at the time of switching ON the supply to the DC motor. 2. The field rheostat of the DC shunt motor (prime mover) should be kept in the minimum resistance position. PROCEDURE: 1. Connections are given as shown in the circuit diagram. 2. The DC supply is switched ON and the DC shunt motor (prime mover) is started using the 3point starter. 3. The motor is brought to its rated speed by adjusting its field rheostat and the same is checked with the help of a tachometer. 4. The load DPST is now closed and the loading rheostat is switched on in steps and at each step the motor speed is maintained constant by adjusting the motor field rheostat and then the terminal voltage (VL) and the load current (IL) are noted down. 5. The procedure is continued until the load current is equal to 120% of the rated current of the generator.
  35. 35. Lab Manual Electro-Mechanical Systems SZABIST 6. After the experiment is completed the load on the generator is gradually decreased to minimum and then the main supply is switched OFF. 7. The resistances of the armature and the series field winding of the generator are found by giving low voltage supply and connecting a voltmeter and ammeter. 8. The external and internal characteristics of the given DC series generator are plotted. GRAPHS: (i) External characteristics: Terminal Voltage (VL) VS Load Current (IL) (ii) Internal characteristics: Generated EMF (Eg) VS Load current (IL) RESULT: The load test on the DC series generator has been conducted and the load characteristics have been plotted. VIVA QUESTIONS: 1. What is a DC series generator? 2. What are the factors on which the generated emf in a DC series generator depends? 3. Why is value of the series field resistance low? 4. Comment on the shapes of the load characteristics of DC series generator. 5. How does armature reaction affect the terminal voltage of a DC series generator at high load current? 39
  36. 36. Lab Manual Electro-Mechanical Systems SZABIST LOAD TEST ON DC SERIES GENERATOR TABULAR COLUMNS To find Armature Resistance Ra SL.NO. Armature Current Armature Voltage Armature Resistance Ia (Amps) Va (Volts) Ra = Va/Ia (Ohms) 1 2 3 4 Average Ra To find Series Field Resistance Rse SL.NO. Current Ise Voltage (Amps) (Volts) 1 2 3 4 Vse Series Field Resistance Rse = Vse/Ise (Ohms) Averag e Rse LOAD TEST : Load SL.NO. Current IL Amps 1 Load Voltage VL Volts Load Current Ia (Ra+Rse) Generated Voltage IL = Ia =Ise Eg = VL + Ia (Ra+Rse) Amps Volts Volts 2 3 4 5 6 41
  37. 37. Lab Manual Electro-Mechanical Systems EXPERIMENT NO 7 SZABIST DATE: LOAD TEST ON SINGLE PHASE TRANSFORMER AIM: To conduct load test on single phase transformer and to obtain percentage efficiency & regulation. APPARATUS REQUIRRED: Sl.No Apparatus 1. Voltmeter 2.` Ammeter 3. Lamp load 4. 1ф Transformer 5. Wattmeter 6. Auto Transformer Type MI MI UPF Range (0-300)V (0-5)A 3KW/230 V 1 KVA, 230/230V 0-300/5A 230V/0-270 V Quantity 2 2 1 1 2 1 NAME PLATE DETAILS Single Phase Transformer Primary Voltage : 230 V Secondary Voltage : 115 V Capacity : 1 KVA Frequency : 50 Hz Fuse Rating: 125% of rated current 125*4.34 /100 ≈ 5 A THEORY: When the secondary is loaded the secondary current I2 is setup. The magnitude and phase of I2 with respect to V2 is determined by the characteristics of the load. The secondary current sets up its own mmf and hence its own flux ф2 which is in opposition to main primary flux ф which is due to I0 the secondary ampere turns N2*I2 are known as demagnetizing ampere turns .The opposing secondary flux I2 weakens the primary flux ф momentary. Hence primary back Emf E1 tends to be reduced. For a moment V1 gain the upper handover E1 and hence causes more current to flow in primary. Let the additional primary current be I2 1 .It is known as load component of primary current. This current is antiphase with I21 the additional primary mmf N1*I2 sets up its own flux ф2 1 which is in opposite to ф2 and is equal to its magnitude. Hence the two cancel each other out. So the magnetic effects of secondary current I2 are immediately neutralized by the additional primary current I2 1.Hence whatever the load conditions be, the net flux passing through core is approximately the same as no-load. 43
  38. 38. PRECAUTIONS: 1.The autotransformer should be kept at minimum voltage position. 2.Before switching off the supply the variac should be brought back to0 minimum voltage position. PROCEDURE: 1.Connect as per the circuit diagram 2.Close the DPST switch 3. .Adjust the Auto transformer till the rated voltage is reached 5. Note down the readings of primary voltmeter, ammeter and wattmeter& secondary voltmeter, ammeter and wattmeter 6.Apply load in steps and note down the corresponding reading till the rated current is reached. GRAPHS: 1.Output power Vs efficiency 2. Output power Vs % regulation RESULT: Thus the load test on single phase transformer was performed and the respective graphs were plotted. VIVA QUESTIONS: 1. What is the principle of a transformer? 2. What are the types of transformer? 3. What are the applications of transformer? 4. Why is the capacity of a transformer specified as KVA and not as KW? 5. What is the condition for maximum efficiency of a transformer and at which load does it occur? 6. Why is the efficiency of a transformer higher than that of motors?
  39. 39. Lab Manual Electro-Mechanical Systems SZABIST LOAD TEST ON SINGLE PHASE TRANSFORMER TABULAR COLUMN mf1 = SL.NO Primary . Voltage V1 1 Primary Current I1 W1 mf2 = Sec. Voltage V2 Sec. Current I2 W2 Input Power W1 x mf1 Output Power W2 x mf2 Efficiency η% Regulation % 2 3 4 5 6 MODEL CALCULATION: Output power % Efficiency η = X 100 Input power E0 – V % Regulation = X 100 V 45
  40. 40. Lab Manual Electro-Mechanical Systems SZABIST 47
  41. 41. EXPERIMENT NO 8 DATE: OPEN CIRCUIT AND SHORT CIRCUIT TESTS ON SINGLE PHASE TRANSFORMER AIM: To conduct OC and SC tests on single phase transformer and to draw the equivalent circuit and obtain percentage efficiency & regulation at UPF &0.8 PF(lag&lead). APPARATUS REQUIRED: Sl.No 1. 2. 2.` 2.` 5. 4. Apparatus Voltmeter Voltmeter Ammeter Ammeter Wattmeter 1ф Transformer Type MI MI MI MI LPF 5. 6. Wattmeter Auto Transformer UPF Range (0-300)V (0-150)V (0-5)A (0-2)A 0-300/2.5A 1 KVA, 230/230 -115V 0-150/5A 230 V/0-270 V Quantity 1 1 1 1 1 1 1 1 Fuse Rating: 125% of rated current 125*4/100=4.34 ≈5 A THEORY: The purpose this test is to determine no load loss or core loss and no load current I0 which is helpful in finding X0 and R0. One winding of the transformer whichever is convenient but usually HV winding is kept open and the other is connected to its supply of normal voltage and frequency. A wattmeter W, voltmeter and ammeter A are connected in the present case. With normal voltage applied to the primary normal flux will be set up in the cores hence normal iron losses will occur which are recorded by the wattmeter. As the primary no load current Io is small. Cu loss is negligibly small in primary. Hence the wattmeter reading represents the core loss under no load conditions. It should be noted that since I0 is very small, the pressure coils of wattmeter and the voltmeter are connected such that the current in these do not pass through the current coil of wattmeter.
  42. 42. Lab Manual Electro-Mechanical Systems SZABIST 49
  43. 43. PRECAUTIONS: 1. The autotransformer should be kept at minimum voltage position. 2. Before switching off the supply the variac should be brought back to minimum voltage position. PROCEDURE: OC TEST: 1.Connect as per the circuit diagram 2.Close the DPST switch 3. .Adjust the Auto transformer till the rated voltage is reached 5. Note down the readings of primary voltmeter, ammeter and wattmeter. 6. Adjust the Auto transformer till the ZERO voltage is reached 7. Open the DPST switch SC TEST: 1.Connect as per the circuit diagram 2.Close the DPST switch 3. .Adjust the Auto transformer till the rated CURRENT is reached 5. Note down the readings of primary voltmeter, ammeter and wattmeter. 6. Adjust the Auto transformer till the ZERO voltage is reached 7. Open the DPST switch FORMULAE: R0 =V1/IW X0 = V1 /Iμ IW = I0 COS ф0 Iμ = I0 Sinф0 Z01 = VSC/ISC RO1=WSC/ISC2 _________ XO1 = √ Z012-R012 ISC(RO1COSф0 -XO1 Sin ф0 ) % Regulation at lead = ___________________________ X V1 100
  44. 44. Lab Manual Electro-Mechanical Systems ISC(RO1COSф0 + XO1 Sin ф0 ) % Regulation at lag = ___________________________ X V1 CU Losses = WSC * X2 SZABIST 100 Where X = Load Output power = KVA*1000*X *PF watts Input power = Output power + Losses Output power Efficiency = ____________ Input power X 100 GRAPHS: 1. % Regulation Vs power factor 2. Output power Vs efficiency RESULT: Thus the OC & SC tests on single phase transformer was performed and the respective graphs were drawn. VIVA QUESTIONS: 1. What is the purpose of OC and SC tests? 2 Why the core is laminated? 3. What is meant by regulation? 4. Define the term transformation ratio? 5. What are the components of no load current? 51
  45. 45. OPEN CIRCUIT AND SHORT CIRCUIT TESTS ON SINGLE PHASE TRANSFORMER TABULAR COLUMNS OPEN CIRCUIT TEST: VO Volts IO Amps Wattmeter Reading (mf = ) Observed Actual WO WO x mf Watts SHORT CIRCUIT TEST: VSC Volts ISC Amps Wattmeter Reading (mf = ) Observed Actual WSC WSC x mf Watts
  46. 46. Lab Manual Electro-Mechanical Systems SZABIST PREDETERMINATION OF EFFICIENCY AT DIFFERENT LOADS: (i) At Unity Power Factor Load % of Input WC= Current full load Losses X2 WSC I X Wi = x mf Amps (as WOx mf Watts decimal Watts fraction) Total Output Input Losses Power Power Wi+WC Watts Watts Watts Efficiency η % ¼ (0.25) ½ (0.5) ¾ (0.75) 1(full load) (ii) At Load % of Current full load I X Amps (as decimal fraction) 0.8 Power Factor (lag) Input WC= Total Output Input 2 Losses X WSC Losses Power Power Wi = x mf Wi+WC WOx mf Watts Watts Watts Watts Watts Efficiency η % ¼ (0.25) ½ (0.5) ¾ (0.75) 1(full load) 53
  47. 47. Lab Manual Electro-Mechanical Systems EXPERIMENT NO 9 SZABIST DATE: SWINBURNE’S TEST AIM: To predetermine the efficiency of a DC shunt machine by conducting the Swinburne’s Test 1. as a motor 2. as a generator NAME PLATE DETAILS: DC SHUNT MOTOR 5 HP Rated Voltage : 230 V Rated Current: 17 A Rated Speed : 1500 RPM Excitation Voltage: 230 V DC APPARATUS REQUIRED: SL.NO. 1 2. 3. 4 4. 5. 6. APPARATUS Ammeter Ammeter Voltmeter Voltmeter Rheostat Rheostat Tachometer RANGE 0 – 10 A 0 – 1/2 A 0 – 300 V 0–5V 250 Ω, 1.5 A 1200 Ω, 0.8 A TYPE MC MC MC MC MC MC Digital QUANTITY 1 No. 1 No. 1 No. 1 No. 1 No. 1 No. 1 No. FUSE RATING: Fuse rating = 40 % of rated current = 40/100 * 17 = 6.8 A ≈ 10 A THEORY: In this method the losses are measured separately and from their knowledge efficiency at any desired load can be predetermined. Hence the only running test needed is the no load test. This test is applicable to the machine in which flux is practically constant i.e shunt wound and compound wound machines. The machine is to run as a motor at its rated voltage. The speed is adjusted to rated speed with help of shunt field regulator. The no load current and field current are measured using ammeters. This test is convenient and economical because power required to test a large machine is small i.e. only input power is required. The efficiency can be predetermined at any load because constant losses are known. In this test we are not taking into account the change in iron loss from no load to full load. In this test it is impossible to know that whether commutation would be satisfactory at full load and whether temperature rise would be within specified limits. 55
  48. 48. Lab Manual Electro-Mechanical Systems SZABIST PRECAUTIONS: 1. The field rheostat must be kept in minimum resistance position. 2. The starter handle must be kept in OFF position before switching ON the supply. 3. The motor must be started at no load condition. PROCEDURE: 1. Connections are made as per the circuit diagram. 2. The supply is switched ON by closing the DPST switch. 3. The field rheostat is adjusted till the motor attains its rated speed. 4. The readings of the ammeters and voltmeter are noted under no load conditions. 5. The rheostat is brought back to the minimum position and the supply is switched OFF. 6. The DC resistance of the armature is determined using a voltmeter and an ammeter. FORMULA: Constant Losses Wc = VIo – (Io – Ish)2 Ra Watts As a Motor: Input power = VLIL Watts Ia =IL – If Amps Armature Cu loss = Ia2 Ra Watts Total Loss = Wc + Cu loss Watts Output power = Input – Total loss Watts % Efficiency = Output/Input * 100 As a Generator: Ia =IL + If Amps Armature Cu loss = Ia2 Ra Watts Total Loss = Wc + Cu loss Watts Output power = VLIL Watts Input power = Output + Total loss Watts % Efficiency = Output/Input * 100 GRAPHS: 1. Output power Vs efficiency ( as a motor) 2. Output power Vs efficiency ( as a generator) RESULT: Thus the Swinburne’s test ( no load test) was conducted and the following efficiency were predetermined at different loads: 1. Efficiency as motor 2. Efficiency as generator. 57
  49. 49. VIVA QUESTIONS: 1. What is the purpose of Swinburne’s test? 2. What are the constant losses in a DC machine? 3. What are the assumptions made in Swinburne’s test? 4. Why is the indirect method preferred to the direct loading test? 5. The efficiency of DC machine is generally higher when it works as a generator than when it works as a motor. Is this statement true or false? Justify your answer with proper reasons.
  50. 50. Lab Manual Electro-Mechanical Systems SZABIST SWINBURNE’S TEST TABULAR COLUMNS (i) VO Volts (i) SL.NO Motor on No Load IO Amps If Amps Ia = IO – If Amps Speed (N) RPM 1500 To find Armature Resistance (Ra) Armature Voltage Armature Current V I Volts Amps Armature Resistance Ra Ohms 1 2 3 4 Average Ra 59
  51. 51. PREDETERMINATION OF LOSSES AND EFFICEINCY AT DIFFERENT LOADS: (i) As a Motor: SL. NO Load Voltage VL Volts Load Current IL Amps Armature Current Ia Amps Copper losses Ia2 Ra Watts Total losses Wi + Wc Watts Input Power VL IL Watts Output Power I/P losses Watts Efficie ncy η % 1 2 3 4 (ii) SL. NO 1 2 3 4 As a Generator: Load Voltage VL Volts Load Current IL Amps Armature Current Ia Amps Copper losses Ia2 Ra Watts Total losses Wi Wc Watts Output Power + VL IL Watts Input Power Effici ency O/p+losses η Watts %
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  53. 53. EXPERIMENT NO 10 DATE: SEPARATION OF IRON LOSSES IN DC MACHINE AIM: To separate the no load losses in a DC Machine as iron losses and mechanical losses. APPARATUS REQUIRED: SL.NO 1. 2 3. 4. 5. APPARATUS Voltmeter Ammeter Ammeter Voltmeter Rheostat 6. Rheostat 7. Tachometer RANGE 0 – 300 V 0 – 5/10 A 0 – 1/2 A 0–5V 1200 Ohms, 0.8 A 250 Ohms, 1.5 A -- TYPE MC MC MC MC -- QTY 1 1 1 1 1 -- 1 Digital 1 Fuse Rating Calculation: Fuse rating = 40% of rated current (since No Load) = 40/100 x 19 ≈ 10 A THEORY: In a DC motor, the no load input power supplies for the following losses: 1. Constant loss consisting of the iron losses or core loss and the mechanical loss due to friction and windage. 2. Armature copper loss and field copper loss (usually negligible). In this experiment, the no load test is conducted on a DC motor in order to obtain the constant losses. The mechanical loss is separated from the constant losses and hence the iron losses are determined. The constant losses are calculated as follows:i.e. Constant losses = No load input – Armature Cu loss (Ia2Ra) Wc = VaIa – Ia2 Ra The mechanical loss Wm is found from the graph Hence the core losses or iron losses Wi = Wc – Wm PRECAUTIONS: Before switching ON the supply it is ensured that: 1. The field rheostat is kept in minimum resistance position. 2. The armature rheostat is be kept in maximum resistance position.
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  55. 55. PROCEDURE:1. Connections are made as per the circuit diagram. 2. The DC supply is switched ON and the motor is started using 3-point starter. 3. The armature rheostat is adjusted from maximum position to obtain the rated voltage. 4. The field rheostat is adjusted to obtain the rated speed. 5. The readings of the voltmeter and ammeter are noted. 6. By varying the armature rheostat the voltage is gradually reduced till the current becomes almost constant. The readings of the voltmeter and the ammeter are noted in the tabular column. 7. The armature resistance (Ra) is determined by voltmeter – ammeter method by giving low voltage DC supply. 8. The armature copper loss is calculated and hence the constant losses are obtained. 9. A graph is drawn with constant losses along Y-axis and no load voltage along the X- axis. 10. The mechanical loss is found from the graph hence the iron losses are determined. FORMULAE USED: No load input power Wo = VoIo Watts Armature current Ia = Io – If Amps Armature Copper loss = Ia2Ra Watts Constant losses Wc = VaIa – Ia2Ra Watts Mechanical loss = Wm (from graph) Watts (friction and windage) Core losses or Iron losses Wi = Wc – Wm Watts GRAPH : Constant losses VS No load voltage RESULT: Thus the total no load losses in a DC machine have been separated as iron losses and mechanical loss. VIVA QUESTIONS: 1. What are the losses in a DC machine? 2. Why is the field copper loss negligible at no load? 3. Why does the armature resistance increase when the motor is running? 4. How can the mechanical losses be reduced? 5. How can the core losses be minimized?
  56. 56. Lab Manual Electro-Mechanical Systems SEPARATION OF IRON LOSSES IN DC MACHINE SZABIST TABULAR COLUMNS To find Armature Resistance Ra SL.NO. Armature Current Armature Voltage Armature Resistance Ia (Amps) Va (Volts) Ra = Va/Ia (Ohms) 1 2 3 4 Average Ra SEPARATION OF IRON LOSSES: Mechanical Loss Wm = ______Watts (From the graph) S.No. No Load No Voltage load (Vo) current (Io) Volts Amps No load Input Power Wo = VoIo Watts Field Current If Amps Armature Armature Constant Current Cu Loss loss Ia Ia2Ra Wc = Wo – Amps Watts Ia2Ra Watts Iron loss Wi = Wc – Wm Watts 1 2 3 4 5 6 7 8 65
  57. 57. Lab Manual Electro-Mechanical Systems SZABIST EXPERIMENT NO 11 DATE: HOPKINSON’S TEST AIM: To conduct the Hopkinson’s test on the given pair of DC machines and to obtain the performance curve. NAME PLATE DETAILS: Generator: Power : 3 KW Voltage : 220 V Speed : 1500 RPM Current : 11 A Motor: Power : 5 HP Voltage : 220 V Speed : 1500 RPM Current : 17 A APPARATUS REQUUIRED: SL.NO 1 2 3 4 5 6 APPARATUS Voltmeter Voltmeter Ammeter Ammeter Tachometer SPST knife switch RANGE 0 – 600 V 0 – 300 V 0 – 20 A 0–2A TYPE MC MC MC MC Digital QTY 1 2 2 2 1 1 Fuse Rating: Fuse Rating = 125% of rated current = 125/100 * 17 ≈ 20 A THEORY: In this method full load test can be carried out on two shunt machines without wasting their outputs. The two machines are mechanically coupled and adjusted so that one of them runs as a motor and the other runs as a generator. The mechanical output of the motor drives the generator and the electrical output of the generator drives the motor. Due to losses the generator output is not sufficient to drive the motor and vice 67
  58. 58. versa. The motor is started with no load. Then the field of one is weakened and the other is strengthened so that the former runs as motor and the latter as generator. Initially the SPST switch is kept open. The field is adjusted so that the motor runs at rated speed. The voltage is adjusted by the field regulator until the voltmeter reads zero indicating that the voltage is same in polarity and magnitude as that of main supply. Then the switch is closed to parallel the machines. By adjusting the respective field regulators any load can be thrown on the machine. Generator current I 1 can be adjusted to any desired value by increasing the excitation of generator or by reducing the excitation of motor. The power required for this test is very small when compared to the full load power of two machines. As machines are tested under full load conditions the temperature rise and commutation quantities are observed. PRECAUTIONS: 1. The starter handle must be kept in OFF position at the time of switching on supply 2. The field rheostat of the motor must be kept in minimum resistance position. 3. The SPST switch is closed only when the voltmeter connected across the motor and generator shows zero reading. PROCEDURE: 1. Connections are made as per the circuit diagram. 2. The supply is switched ON by closing the DPST switch. 3. The motor is started using three point starter. 4. The direction of rotation of the motor is checked if it is proper otherwise the field terminals of the motor are interchanged. 5. The field rheostat of the motor is adjusted till the motor attains its rated speed. 6. The field rheostat of the generator of the generator till the voltmeter connected across the SPST switch reads zero. 7. The SPST switch is closed. 8. The readings of the ammeter and voltmeter are noted and tabulated.
  59. 59. Lab Manual Electro-Mechanical Systems SZABIST FORMULAE: 1. Armature Cu loss of generator = (Ifg + Ig)2 Ra Watts 2. Armature Cu loss of motor = (Ig + Im – Ifm)2 Ra Watts 3. Shunt Cu loss of generator = Vg Ifg Watts 4. Shunt Cu loss of motor = Vm Ifm Watts 5. Power drawn from supply = Vm Im Watts 6. Stray loss Wc = VmIm – {(Ifg + Ig)2 Ra + (Ig + Im – Ifm)2 Ra + VgIfg + VmIfm} Watts 7. Stray loss of single machine = Wc/2 8. Total loss in generator = Wc/2 + (Ifg + Ig)2 Ra + Vg Ifg Watts 9. Total loss in motor = Vm Ifm + (Ig + Im – Ifm)2 Ra + Wc/2 Watts 10. Output of generator = Vg Ig Watts 11. Input of generator = Output + losses 12. Efficiency of generator = output power/input power * 100 % 13. Input to the motor = Vm (Ig + Im) Wattts 14. Output power of motor = Input – losses Watts 15. Efficiency of motor = Output power/Input power *100% GRAPHS : 1.Output VS Efficiency (of generator) 2. Output VS Efficiency (of motor) RESULT: Thus the Hopkinson’s test was conducted and the performance curve drawn. VIVA QUESTIONS: 1. What is the purpose of Hopkinson’s test? 2. What are the advantages of Hopkinson’s test? 3. What are the conditions for conducting the test? 4. Why the adjustments are done in the field rheostat of generator and motor? 5. If the voltmeter across the SPST switch reads zero what does it indicate? 69
  60. 60. HOPKINSON’S TEST TABULAR COLUMNS Motor Vm Volts Generator Im Amps Ifm Amps Vg Volts Ig Amps Ifg Amps Armature Cu Loss of Generator (Ig+ Ifg)2 Ra Watts Armature Cu Loss of Motor (Ig+ImIfg)2 Ra Watts Shunt Cu loss of generator VgIfg Watts
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  62. 62. EXPERIMENT NO 12 DATE: SUMPNERS TEST AIM: To predetermine the efficiency of the transformer at any desired load and power factor by conducting the Sumpners test. APPARATUS REQUIRED: SL.NO. 1. APPARATUS Ammeter 2. Voltmeter 3. Wattmeter 4 Transformer 5. 6. Autotransformer SPST knife switch TYPE MI MI MI MI MI LPF UPF Single phase RANGE 0–1A 0–5A 0 – 300 V 0 – 600 V 0 – 150 V 300 V/2.5A 150 V/5A 1 KVA 230/230 – 115 V Single phase 230 V/0 – 270 V QUANTITY 1 1 1 1 1 1 1 2 2 1 FUSE RATING: Fuse rating = KVA* 1000/Rated Voltage = 1000/230 = 4.34 A ≈ 5 A THEORY: This test provide data for finding the regulation, efficiency and heating under load condition and is employed only when two similar transformers are available. One transformer is loaded on the other and both are connected to the supply. The power taken from the supply is that necessary for supplying the losses of both transformers. Primaries of the two transformers are connected in parallel across the same AC supply, with switch S open and the wattmeter W1 reads the core losses for the two transformers. The secondary are connected that their potentials are in opposition to each other. This would be VAB = VCD and A is joined to C with B is joined to D in this case there would be no secondary current flowing around the loop formed by the two secondaries. PRECAUTIONS: 1. The variac of the auto transformer should be kept at minimum voltage position. 2. Before switching off the supply the variac of the auto transformer should be brought back to minimum voltage position.
  63. 63. Lab Manual Electro-Mechanical Systems SZABIST PROCEDURE: 1. 2. 3. 4. 5. Connect as per the circuit diagram. Close the DPST switch. Adjust the variac of the auto transformer connected to transformer 1 to get the rated voltage. Note down the reading of ammeter, voltmeter & wattmeter of transformer1. Close the SPST switch if the voltmeter connected across the SPST switch reads zero. It not the interchange the terminals of second transformer secondary to get zero reading at SPST switch. 6. Adjust the variac of the auto transformer connected to transformer 2 to get the rated current. 7. Note down the reading of ammeter, voltmeter & wattmeter of transformer2 8. Bring the auto transformer variac to zero position & switch off the supply. FORMULAE: Core losses Wi=W1/2 Watts Copper losses, Wc=W2/2*X2(Watts) Where, X=percentage of Load Total losses=Wc+Wi Watts Output power=KVA*100*X*p.f Watts Input power=Output power+losses Watts Efficiency=Output/Input*100 GRAPH: Output power Vs Efficiency at UPF and 0.8 power factor. RESULT: Thus the Sumpner’s test was performed and the efficiency was predetermined and the respective graphs were drawn. VIVA QUESTIONS:1. What is the purpose of conducting the Sumpner’s test? 2. What are the losses in a transformer? 3. Why LPF wattmeter is used in OC test? 4. Why UPF wattmeter is used in SC test? 5. What is meant by predetermination of efficiency? 73
  64. 64. SUMPNER’S TEST TABULAR COLUMNS TFR.1 Current I1 A TFR.2 Current I2 A TFR.1 Voltage V1 V TFR.2 Voltage V2 V TFR.1 W1 TFR.2 W2 Watts Watts PREDETERMINATION OF EFFICIENCY AT DIFFERENT LOADS (i) At Unity Power Factor Load % of full Core Copper Total Output Input Efficiency Current load Losses losses Losses Power Power η I X Wi = WC= Wi+WC % Amps (as W1/2 W2 /2 * Watts Watts Watts 2 decimal Watts X fraction) Watts ¼ (0.25) ½ (0.5) ¾ (0.75) 1(full load) Load Current I Amps (ii) At 0.8 Power Factor (Lag) % of Core Copper Total Output full load Losses losses Losses Power X Wi = WC= Wi+WC (as W1/2 W2 /2 * Watts Watts 2 decimal Watts X fraction Watts ) ¼ (0.25) ½ (0.5) ¾ (0.75) 1(full load) Input Power Watts Efficiency η %
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  66. 66. Lab Manual Electro-Mechanical Systems SZABIST EXPERIMENT NO 13 DATE: STUDY OF THREE PHASE TRANSFORMER CONNECTIONS AIM: To conduct the three phase transformer in various modes and to obtain the voltage current relations. APPARATUS REQUIRED: APPARATUS Voltmeter RANGE (0-600)V (0-300)V Ammeter (0-10)A (0-5)A 3 Phase transformer 415/470V 3 Phase auto transformer415/(0-470)V 3 Phase load 5.1KW TYPE MI MI MI MI QUANTITY 2 2 2 2 1 1 1 THEORY: MODES OF CONNECTIONS: 1. Yyo-Normal star (HV)/Normal star (LV) 2. Yyo-Normal star (HV)/Reverse star (LV) 3. Yvl-Normal star (HV)/Normal delta (LV) 4. Ydll-Normal star (HV)/Reverse delta (LV) 5. Ddo-Normal delta (HV)/Reverse delta (LV) 6. D6-Normal delta (HV)/Reverse delta (LV) 7. Dy11-Normal delta (HV)/Normal star (LV) 8. Dy1-Reverse delta (LV)/Normal star (LV). STAR/STAR (OR) Y/Y CONNECTION: This connection is for high voltage transformer. The phase voltage 1/√3 of line voltage. The ratio of line voltage is 1/3 1 ◦ &2◦ signs is the same as the transformer ratio of each transformer. The phase shift of 30 b/w the phase voltage and line voltage both on primary and secondary side, This connection works only if the load is balanced with the unbalanced load. The neutral point shift thereby voltage is unequal. The effect of unbalanced load can be illustrated by placing single load between phase of neutral on the secondary side. Another 77
  67. 67. advantage of stabilizing the primary neutral by connecting it to the neutral of the generator is that it eliminates distortion in the secondary phase voltage.
  68. 68. Lab Manual Electro-Mechanical Systems SZABIST DELTA/DELTA CONNECTION: This connection is for low voltage transformer. The ratio of transformation between primary and secondary line voltage is exactly as same as that of each transformer. There is an angular displacement between primary and secondary voltages. Moreover, there is no internal phase shift between phase and line voltage on the other side. Wye/DELTA (or)Y/A CONNECTIONS: This connections is at the substation of the transmission line where the voltage is to be stepped down. The primary winding is Y-connected and ground neutral. The relation between secondary and primary line voltage is 1/√3 times transformer ratio of each transformer. There is 30◦ shift between primary and secondary line voltage which means that Y-Delta transformer bank cannot be parallel with either a Y-Y as Delta-Delta bank. Also third harmonic current flows through the delta to provide a sinusoidal flux. DELTA/Wye (or)DELTA/Y CONNECTIONS: This connection is generally employed when it is necessary to step up the voltage. The neutral of the secondary is grounded for providing three phase 4 wire service. This connection can be used to serve both the 3 phase power equipment and single phase lighting circuit. This connections is not open to the floating neutral and voltage distortion because of the existence of delta connection, allows the path for the third harmonic current. It would be observed that the primary and secondary line voltage and line current are out of phase with the each other by 30◦ . Because of this 30◦ shift it is impossible to parallel such a bank with a delta-delta or Y-Y bank of transformer even though the voltage ratios are correctly adjusted. The ratio of secondary of primary voltage is √3 times the transformer ratio of each transformer. PRECAUTIONS: 1. The DPST switch is closed only if the circuit connections are correct. 2. The variac should be kept in minimum voltage position before switching ON the supply. 3. Before switching OFF the supply, the variac should be brought back to its minimum voltage position. 79
  69. 69. Lab Manual Electro-Mechanical Systems SZABIST PROCEDURE: 1. 2. 3. 4. Connections are given as per the circuit diagram. The connection was delta-delta connection. 415V was supplied to the primary side. One load was supplied to the primary side, readings of ammeter, voltmeter are noted down. 5. Readings are tabulated. RESULT: Thus the three phase transformer was connected in delta-delta and the voltage current relation were obtained. VIVA QUESTIONS: 1. What are the various types of three phase transformer connections? 2. What is meant by vector grouping? 3. State the relationship line voltage and phase voltage in star connection. 4. What are the different types of three phase transformers? 5. What are the applications of the different types of three phase transformers? 81

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