NALCO is a government-owned integrated aluminum company based in Odisha, India with bauxite mines and alumina refinery located in Damanjodi. The refinery requires 85MW of electricity to operate, with 64% generated on-site by a steam-based coal fired power plant known as the Steam & Power Plant. Power requirements are divided into critical and non-critical loads, with non-critical loads able to be reduced during shortages to maintain continuity of operations. NALCO also receives power from the state grid and its own large thermal power plant located in Angul, Odisha.

1. NATIONAL ALUMINIUM COMPANY LIMITED
(A Government of India Enterprise)
Mines & Refinery Complex
Damanjodi, Koraput
TRAINING REPORT
ON
CENTRAL DISTRIBUTION OF POWER
&
DETAILS OF ELECTRICAL EQUIPMENT
AT NALCO, DAMANJODI
INTERNSHIP PERIOD- 10 January 2022 to 09 Feb
TRAINING PERIOD
10th January 2022 to 09th February 2022
SUBMITTED BY-
RACHANA SHARMA
REF NO- TRG/01/26/564
REGD NO- 2021110072
BRANCH- ELECTRICAL ENGINEERING
GOVERNMENT COLLEGE OF ENGINEERING KALAHANDI

3. I have taken efforts during this internship training. However, it would not
have been possible without the kind support and help of many individuals
present in the organization. I would like to extend my sincere thanks to all
of them.
I also feel proud to say that due to the keen knowledge of working members
present at NALCO, Damanjodi it is very easy for me to earn a lot of
knowledge about different areas present in NALCO.
I am highly indebted to the Training guide SAI MADHULATA
RUDRARAJU, Asst - Manager (Electrical) for his guidance and for
providing me with the constant necessary information regarding the
training & also for his support in completing the training report. I gratefully
acknowledge for his inspiration, valuable guidance, and support
throughout my training.
I wish to express my grateful thanks to the Head of the Department Mr.
R.N. Swain, DGM (Electrical) for allotting me in different areas and also
for providing all the assistance extended during the training period for
successful completion of my training.
Finally, I would like to thank all the employees of the different shops
allotted to me at NALCO, Damanjodi, who have helped me and cooperated
with me during my training and report work.

4. TABLE OF CONTENTS
INTRODUCTION 1 -2
ABOUT NALCO DAMANJODI 2 - 4
POWER REQUIREMENT OF NALCO DAMANJODI 5
POWER GENERATION UNIT OF NALCO DAMANJODI 6 – 7
SPECIFICATION OF EQUIPMENT AT STEAM & POWER PLANT 8 – 9
ABOUT ELECTRICAL SUBSTATION 9 – 10
TYPES OF SUBSTATION 11 – 15
CLASSIFICATION OF SUBSTATION 16
ELEMENTS USED AT ELECTRICAL SUBSTATION 17 – 23
POWER DISTRIBUTION SYSTEM OF NALCO, DAMANJODI 23 – 25
PANELS AT CENTRAL DISTRIBUTION SUBSTATION 25 – 26
LOOP & UNIT SUBSTATIONS OF NALCO, DAMANJODI 27
PROTECTION SYSTEM USED AT CDS NALCO, DAMANJODI 28 – 34
ELECTRICAL HT/LT MOTOR PROTECTION 35 – 39
ADDITIONAL INFORMATION 40 - 41

5. [1]
NATIONAL ALUMINIUM COMPANY LIMITED (NALCO) which comes under Ministry of
Mines, Govt. of India was established on 7th January, 1981 is a schedule 'A' Navratna
Central Public Sector Enterprise (CPSE) having its registered- office at Bhubaneshwar.
NALCO is one of the largest integrated Bauxite-Alumina-Aluminium- Power Complex in
Asia. In the financial year 2020-2021, NALCO has a net sales turnover of Rs. 8,869.29
crore and net profit of Rs. 1,299.56 crore. Presently, Government of India holds 51.28%
equity of NALCO.
The Bauxite Mine & Alumina Refinery of NALCO is located at Damanjodi in the Koraput
district of Odisha holding a normative capacity of 68.25 lakh TPA & 21.00 lakh TPA
respectively. The company's Aluminium smelter holding 4.60 TPA and Captive Power
Plant having generation capacity of 1200MW is located at Angul, Odisha.
NALCO has its regional sales offices in Delhi, Kolkata, Mumbai, Chennai, and 8
operating stockyards at various locations in the Country to facilitate domestic
consumers. NALCO utilizes Kolkata and Paradeep ports as its bulk-shipment facility for
the export of Alumina/Aluminum.
NALCO produces Aluminum and Alumina as its principal products like Standard Ingots,
T-Ingots, Sow Ingots, Billets, Wire Rods, Rolled Products & Chequered Sheets, Calcined
Alumina, Alumina Hydrate, Specialty Alumina & Hydrates, etc.
NALCO has diversified into wind power with the commissioning of a 50.4 MW Wind
Power Plant at Gandikota, Andhra Pradesh in 2012. The second Wind Power Plant of
47.6MW at Jaisalmer, Rajasthan was commissioned in 2014. Growing further in
enhancing its renewable energy portfolio, a 50 MW Wind Power Plant in Jaisalmer,
Rajasthan & 50.4 MW Wind Power Plant at Sangli, and Maharashtra was commissioned
in FY 2016-17. The total Wind Power Plant in operation is 198 MW and a further 25 MW
wind power plants are in pipeline. The Company has also utilized the available rooftop
space in the Corporate Office, Township, Research Centre, Training Centre at
Bhubaneswar for setting up of 800 KWp Solar Power Plants at its premises to join hands
for carbon neutrality.

6. [2]
With its consistent track record in capacity utilization, technology absorption, quality
assurance, export performance, and posting profits, NALCO is a bright example of
India’s industrial capability.
Damanjodi is a town located on the foothills of Panchpatmali mountain range in the
Koraput district of Odisha. The town was founded as a residential area for employees
of the National Aluminum Company Ltd (NALCO), a company that was established to
harness the bauxite-rich deposits of the Panchpatmali range.
BAUXITE MINES
The Company has its bauxite mines situated on a plateau in Damanjodi, Koraput, in
the State of Odisha. This bauxite deposit is mined by a fully mechanised system having
a capacity of 6.8 MT per year. Panchpatmali plateau stands at an elevation of 1154 m
to 1366 m above mean sea level. Bauxite occurs over the full length of the
Panchpatmali plateau, which spans over 18 km

7. [3]
The Salient Features:
 Area of deposit – 16 sq. KM.
 Resource – 310 million tonnes.
 Ore quality – Alumina 45%, Silica 3%.
 Mineralogy – Over 90% gibbsitic.
 Overburden – 3 meters (Average).
 Ore thickness – 14 meters (Average).
 Transport – 14.6 KM long, single flight, multi-curve cable belt conveyor of 1800
TPH capacity.
ALUMINA REFINERY
The alumina refinery is located at Damanjodi, Odisha, approximately 14 km from the
bauxite mine at Panchpatmali. The mined-out bauxite is transported from captive mine
to refinery by a 14.6-km-long single-light multi-curve 1800 tonnes-per-hour (TPH)-
capacity cable belt conveyor. The alumina produced is transported to aluminium
smelter at Angul (Odisha) and to Vizag (Andhra Pradesh) port by rail.
The present capacity of Alumina Refinery is 22.75 lakhs TPA. Alumina produced is used
to meet the Company’s requirements for the production of primary aluminium at the
smelter. The surplus alumina is sold to third parties in the export markets.
The Salient Features:
 4 Nos of production streams.
 The atmospheric pressure digestion process at 107°C.
 Pre-desilication and inter-stage cooling for higher productivity.
 Energy-efficient fluidised bed calciners at 1400tph.
 Co-generation of 5 × 18.5MW power by use of backpressure turbine in steam
generation plant.

8. [4]
ALUMINIUM SMELTER
The 4,60000 TPA capacity Aluminium Smelter, located at Angul in Odisha,
is based on advanced technology of smelting and pollution control. The plant
manufactures Ingots, Sows, Billets, Wire Rods, Strips and Rolled Products,
besides T.lngot and Chequered Sheets.
CAPTIVE POWER PLANT
Close to the Aluminium Smelter at Angul, a Captive Power Plant of 1200
MW Capacity has been established for firm supply of power to the Smelter. The
coal demand of the Plant is met from a nearby mine of Mahanadi Coalfields
Limited. The plant is also connected with the State Grid for sale of surplus power.

9. [5]
The Mines & Refinery complex of NALCO, Damanjodi requires an overall 85MW of
electricity. For generation of electricity, NALCO has its own power generation plant
which generates nearly about 64% of the total power for running the plant smoothly.
NALCO also generates 1200 MW of power at its own Captive thermal power generation
plant which is located at Angul district of Odisha.
So, the rest 36% of the total required power for NALCO Mines and Refinery Complex,
Damanjodi
is being fulfilled by this Captive thermal power generation plant which is present at
NALCO,
Angul. In order to utilise this power, NALCO uses the grid of state government i.e.,
Odisha Power
Transmission Corporation Limited (OPTCL) which is located at Lakshmipur of Odisha
and pay’s accordingly as per the Power Purchase Agreement (PPA).
AN AVERAGE POWER FIGURES OF PLANT:
GRIDCO Generated Total Frequency 220KV 11KV
OPTCL GENERATED TOTAL FREQUENCY 220KV 11KV
MAX 30.60 MW 54.40 MW 85.00 MW 50.09 Hz 236.10 KV 11.15 KV
MIN 8.90 MW 48.60 MW 57.50 MW 49.83 Hz 219.30 KV 10.75 KV
Generated Power Factor = 0.88
Import Power Factor = 0.87
Capacitor Bank = 451 MVARH
Plant Load Excluding Mines & Township = 72.38 MW
The Total Alumina Refinery load excluding Mines & Township is 72.38 MW.
There are several load units present in the Alumina Refinery of NALCO, Damanjodi.
Some of
those are Boilers, Capacitor Bank (451 MVARH), Calcinators, Ball Mills, Battery Unit.
So, as per
the requirement of power, the various load units are divided into two parts i.e., Critical
Unit &
Non – Critical Unit. Critical units are those units that required an uninterrupted
power supply
whereas Non – Critical units are those units whose power requirement can be ignored
in case
power is insufficient for the entire requirement. When there occurs power shortage
then some
power is adjusted in the non–critical unit to maintain continuity by minimising the
production.

10. [6]
A separate power generation plant is situated at "Mines & Refinery complex of NALCO,
Damanjodi. This power generation plant fulfils 64% of the total power required for
running the plant.
The Power Plant present at NALCO, Damanjodi uses steam & coal as its main resource
for the generation of electricity. Therefore, the power plant is said as "Steam based
Coal Fired Power Plant”, which is named as “Steam & Power Plant (SPP)”.
For the production of Alumina from Bauxite, some amount of steam is required. Hence,
a separate steam production unit is located inside the Mines & Refinery complex of
Damanjodi. The steam produced in the steam production unit not only fulfils the
requirement for the production of Alumina from Bauxite but it is also used in the Steam
& Power Plant for the production of electric power. For fulfilling the coal requirement,
NALCO purchases coal from “Mahanadi Coalfields Limited (MCL)” and transports the
coal from the coal mines of MCL to Mines & Refinery Complex, Damanjodi by Railway
in wagons.
At first, Coal is transported from the coal mine of MCL to the Steam production unit by
railway in wagons. An underground conveyor belt is situated near the wagons, the coal
is directly unloaded from the wagons to the underground conveyor belt. The coal
transported from the coal mines is of non–uniform size. So, in the next step, the coal is
pulverized i.e., the raw coal is brought to fine powdered form. Pulverization makes the
coal more efficient for burning. The raw coal from the conveyor belt is transferred to the
coal bunker. The coal bunker is supplied to the coal mills or pulverizer by a raw coal
feeder. Then the raw coal is pulverized into 200 mesh size in the coal mill or pulverizer.
After that, the powdered coal is carried from the coal mill or pulverizer to the boiler
through coal pipes by high-pressure hot air. Then the pulverized coal–hot air mixture is

11. [7]
burnt in a boiler at 1300 °C in the combustion zone. After the combustion of the coal,
the ash is collected to the ash handling plant. Then the ash is finally collected to the
ash storage yard. There is a water tube boiler hanging at the top of the combustion zone.
After heating, the water is converted to steam in the boiler. The steam is separated from
water in the boiler drum. Then saturated steam from the boiler drum is taken to the
Low-Temperature Superheater, Platen Superheater and Final Superheater respectively
for superheating. The superheated steam from the final super heater is taken to the
High-Pressure Steam Turbine (HPT). In the HPT the steam pressure is utilized to rotate
the turbine and the resultant is rotational energy. From the HPT the out coming steam
is taken to the Re heater in the boiler to increase its temperature as the steam becomes
wet at the HPT outlet. After reheating this steam, it is taken to the Intermediate Pressure
Turbine (IPT) and then to the Low-Pressure Turbine (LPT). The outlet of the LPT is sent
to the condenser for condensing back to water by a cooling water system. This
condensed water is collected in the hot well and is again sent to the boiler in a closed
cycle. The rotational energy imparted to the turbine by high pressure steam is converted
to electrical energy in the Generator.
LAYOUT OF COAL FIRED POWER

12. [8]
BOILERS:
A Boiler is also known as a steam generator. It is a container in which preheated water
is directly supplied from the economizer and steam will be taken out at desired
pressure, temperature and flow.
SPECIFICATIONS OF BOILERS
MAKE M/S BHARAT HEAVY ELECTRICALS LIMITED
CAPACITY 4 Boilers of 200 Tonnes Per Hour
1 Boiler of 250 Tonnes Per Hour
TYPE VU40
Bi–drum
Natural Circulation
Oil/pulverized coal–fired (p. f. fired)
Fixed tangential corner fired
TURBOGENERATOR:
A turbogenerator is an electric generator connected to the shaft of a steam turbine or
gas turbine for the generation of electric power.
SPECIFICATIONS OF TURBOGENERATORS
MAKE M/S BHARAT HEAVY ELECTRICALS LIMITED
CAPACITY TG-1 = 18.5MW
TG-2 = 18.5MW
TG-3 = 18.5MW
TG-4 = 19.1MW
TG-5 = 19.5MW
TYPE Extraction type Back Pressure Turbine Generator
TG-1 TG-2 TG-3 TG-4 TG-5
POWER 18500KW 18500KW 18500KW 19100KW 18500KW
POWER FACTOR 0.8 0.8 0.8 0.8 0.8
APPARENT POWER 23125KVA 23125KVA 23125KVA 23875KVA 23125KVA
VOLTAGE 11000V 11000V 11000V 11000V 11000V
STATOR VOLTAGE 1100V 1100V 1100V 11000V 11000V
STATOR CURRENT 1214 Amp 1214 Amp 1214 Amp 1214 Amp 1214 Amp
ROTOR VOLTAGE 415V 415V 415V 415V 415V
ROTOR CURRENT 536 Amp 536 Amp 536 Amp 536 Amp 536 Amp
SPEED 3000RPM 3000RPM 3000RPM 1500RPM 1500RPM
FREQUENCY 50Hz 50Hz 50Hz 50Hz 50Hz
CONNECTION STAR-STAR STAR-STAR STAR-STAR STAR-STAR STAR-STAR
COOLANT AIR AIR AIR AIR AIR

13. [9]
BRUSHLESS EXCITER:
Brushless exciters are widely used in power stations to furnish the excitation current
for the main alternators.
SPECIFICATIONS OF BRUSHLESS EXCITER
MAKE M/S BHARAT HEAVY ELECTRICALS LIMITED
CLASS F
CONTINUOUS POWER 130KW
CONTINUOUS VOLTAGE 210V
CONTINUOUS CURRENT 620Amp
EXCITATION POWER 338W
EXCITATION VOLTAGE 30.51V
EXCITATION CURRENT 11.08Amp
SPEED 1500RPM
VOLTAGE 220V
CURRENT 6.56A
FREQUENCY 75Hz
PHASE 3-phase
A substation is the intermediate means between high voltage transmission or distribution
and end-user including connecting generators, transmission or distribution lines, and
loads to each other, and generally stepping higher voltages down to lower voltages to meet
specific customer requirements. For example, we cannot use electricity directly from the
11 KV power line or 33 KV power line. In order to use energy from these lines, we would
have to get power through substations from these lines. Therefore, it is required to install
a substation there. Also, if we want to transmit electrical energy over a long distance,
then it is also required to install a substation to get high voltage for transmission. Also,
a substation is required for the control of energy i.e. changing frequency, converting from
ac into dc or inverting from dc into ac, for switching of different feeders and transmission
lines etc. The substation can be as simple as one pole-mounted transformer near our
homes and villages or factory and as complex as several power transformers, auxiliary
transformers, CTs, PTs, circuit breakers, isolators, bus-bars, LPS, LT panel, HT panel,
PFI plant, AVS, IVS, ATS, HT cable, LT cable, MDB board, SDB board, IPS, & others small
& heavy electrical equipment’s all in one yard. Yet both you can call substations.

14. [10]
To conclude, a substation is an integral part of a power system. The continuity of the
electric energy supply system is solely depending on the substation. So, enough care
should be taken when designing and setting up a sub-station in a suitable place.
Some points are as follows
 The substation must have the chance of easy operation and maintenance.
 The place must be proper for setup a substation. It must be setup near the centre of load.
 The substation must have enough safety apparatus or safety setup. There must be enough
chance for running the maintenance and clearing process. Also, there should be setup for
fire protection.
 The system must be reliable. When designing protected gears and other instruments must
be included. The construction process also maintained properly for reliable operation.
 The capital cost must be as low as possible.
A Primary power line side
B Secondary power line side
1 Primary power lines
2 Ground wire
3 Overhead lines
4 Transformer for measurement of electric voltage
5 Disconnect switch
6 Circuit breaker
7 Current transformer
8 Lightning arrester
9 Main transformer
10 Control building
11 Security fence
12 Secondary power lines
SUBSTATION LAYOUT

15. [11]
Transmission Substation- The three-phase power leaves the generator and enters a
transmission substation at the power plant. This substation uses large transformers to
convert or step up the generator's voltage to extremely high voltages for long-distance
transmission on the transmission grid. Typical voltages for long-distance transmission
are in the range of 110KV to 765KV. The higher the voltage, the less energy is lost due
to resistance.
A typical maximum transmission distance is about 483 kilometres. High-voltage
transmission lines are quite obvious when you see them. They are huge steel towers
strung out in a line that stretches toward the horizon.
All high-voltage towers have three wires for the three phases. Many towers also have
extra wires running along the tops of the towers. These are ground wires and are there
primarily in an attempt to attract lightning.
Distribution Substation- A distribution substation transfers power from the
transmission system to the distribution system of an area. The input for a distribution
substation is typically at least two transmission or sub transmission lines. Input voltage
may be, for example, 115 kV, or whatever is common in the area. The output is a number
of feeders. Distribution substation typically operates at medium voltage levels, between
2.4 kV-33 kV. The feeders run along streets overhead (or underground, in some cases)
and power the distribution transformers at or near the customer premises. In addition
to transforming voltage, distribution substations also isolate faults in either the
transmission or distribution systems. Distribution substations are typically the points
of voltage regulation, although on long distribution circuits (of several miles/kilometers),
voltage regulation equipment may also be installed along the line. The downtown areas
of large cities feature complicated distribution substations, with high-voltage switching,
and switching and backup systems on the low-voltage side. A distribution substation is
a combination of switching, controlling, and voltage step-down equipment arranged to
reduce sub-transmission voltage to primary distribution voltage for residential, farm,
commercial, and industrial loads.

16. [12]
Distribution substation is generally comprised of the following major components:
 Supply Line
 Transformers
 Busbar
 Switchgear
 Outcoming feeders
 Switching Apparatus
 Switches
 Fuses
 Surge Voltage Protection
 Circuit Breaker
 Grounding

17. [13]
Converter Substation- Converter substations may be associated with HVDC converter plants,
traction current, or interconnected non-synchronous networks. These stations contain power
electronic devices to change the frequency of current, or else convert from alternating to direct
current or the reverse. Formerly rotary converters changed frequency to interconnect two
systems; nowadays such substations are rare.
Different types of converter station used for DC end.
 HVDC Converter station
 Traction substation
 Rotary converter or synchronous converter
 Static converter i.e., Thyristor, Rectifier, Inverter station etc.

18. [14]
Collector Substation- In distributed generation projects such as a wind farm or photovoltaic
power station, a collector substation may be required. It resembles a distribution substation
although power flow is in the opposite direction, from many wind turbines or inverters up into
the transmission grid. Usually for economy of construction the collector system operates around
35 kV, although some collector systems are 12 kV, and the collector substation steps up voltage
to a transmission voltage for the grid. The collector substation can also provide power factor
correction if it is needed, metering, and control of the wind farm. In some special cases a collector
substation can also contain an HVDC converter station. Collector substations also exist where
multiple thermal or hydroelectric power plants of comparable output power are in proximity.

19. [15]
Switching Station (Switchyard)- A switching station may also be known as a
switchyard, and these are commonly located directly adjacent to or nearby a power
station. In this case the generators from the power station supply their power into the
yard onto the generator bus on one side of the yard, and the transmission lines take
their power from a Feeder Bus on the other side of the yard.
An important function performed by a substation is switching, which is the connecting
and disconnecting of transmission lines or other components to and from the system.
Switching events may be planned or unplanned. A transmission line or other component
may need to be de-energized for maintenance or for new construction, for example,
adding or removing a transmission line or a transformer. To maintain reliability of
supply, companies aim at keeping the system up and running while performing
maintenance. All work to be performed, from routine testing to adding entirely new
substations, should be done while keeping the whole system running.
A switchyard will also exist when high voltage lines need to be converted to lower voltage
for distribution to consumers. The function of electrical switch yard is to deliver the
generated power from power plant at desired voltage level to the nearest grid or in
another way we can say simply switching the received power supply from various
generating stations to various locations with respect to their requirement. Therefore, a
switchyard will contain current carrying conductors, grounding wires and switches,
transformers, disconnects, isolators, remotely controlled arc snuffing breakers,
metering devices, etc.

20. [16]
The substations can be classified in several ways including the following:
1. Classification based on voltage levels
A.C. Substation: HV (between 33 KV and 66 kV),
EHV (132 kV and 400 kV),
UHV (above 400 kV),
MV/ distribution substation/public substation (2kV to 33kV),
LV/private substation (220V and 440V),
HVDC Substation.
2. Classification based on configuration
AIS- Conventional Air insulated outdoor substation (up to 800 kV)
GIS- SF6 Gas Insulated Substation (GIS)
Composite- These types of substations having combination of the above two
3. Classification based on construction features
Outdoor substation-It is under open sky (rated voltage beyond 66kV).
Indoor substation- This is inside a building (rated voltage beyond 11kV).
Mining substation- Needs special design consideration because of extra precaution
for safety needed in the operation of electric supply.
Mobile substation-Temporary requirement.
Pole substation- This is an outdoor substation with equipment installed overhead
on H- pole or 4-pole structure.
4. Classification based on construction features
Step Up Station- Associated with generating station as the generating voltage is
low.
Primary Grid Substation- Created at suitable load centre along primary
transmission lines. (Step down 66kV from 220 kV)
Secondary Substation- Along secondary transmission line (step down to 11 kV).
Distribution Substation-Created where the transmission line voltage is
step down to supply voltage. Bulk supply and industrial substation is similar to
distribution sub-station but created separately for each consumer. 11kV delivered
to distribution substation.
5.Classification based on services
Power-factor Substation-They improve the power-factor of the system by using
synchronous condensers.
Frequency Substation- Those substations which change supply frequency
Industrial Substation- Those substations which supply power to industries

21. [17]
BUS BAR:
Electrical busbar is simply a type of conductor that collects the power supply from
the incoming feeder and distributes it to the output feeder as required. In other
words, it is a kind of electrical power junction in which all the currents coming and
going together meet.
Thus, the electric bus bar collects electric power in one place. Electrical busbars
use isolators and circuit breakers that operate at fault times and protect the
equipment in the substation.
Types of Bus Bar Arrangement
 Single Bus – Bar arrangement
 Single Bus-Bar Arrangement with Bus Sectionalized
 Main and Transfer Bus Arrangement
 Double Bus Double Breaker Arrangement
 One and a Half Breaker Arrangement
 Ring Main Arrangement
 Mesh Arrangement
 Sectionalized Double Bus Bar Arrangement

22. [18]
POWER TRANSFORMER
The Power transformer is a one kind of transformer, that is used to transfer electrical
energy in any part of the electrical or electronic circuit between the generator and the
distribution primary circuits. These transformers are used in distribution systems to
interface step-up and step-down voltages.
The transformers used in generating substation for stepping up the voltage for
effective transmission i.e. less line loss is called as Step up transformer whereas the
transformer used in distribution substation for stepping down the voltage for
commercial and residential use.
Transformers have two windings, being the primary winding and the secondary
winding. The primary winding is the coil that draws power from the source. The
secondary winding is the coil that delivers the energy at the transformed or changed
voltage to the load.
A 3 winding transformer is a form of single-phase setup that requires primary,
secondary, and tertiary winding. Unlike the more common transformers with only the
primary and secondary winding, the former has a tertiary winding for low-voltage
output.
We also use a special type of transformer called autotransformer which has single
winding. In power station we use autotransformer when ratio of primary voltage and
secondary voltage is less than 2 otherwise we use two winding transformers.

23. [19]
POTENTIAL TRANSFORMER
A potential transformer (P.T.) is an instrument transformer which is used for the
protection and measurement purposes in the power systems. A potential
transformer is mainly used to measure high alternating voltage in a power system.
CURRENT TRANSFORMER
A current transformer (CT) is a type of transformer that is used to reduce or
multiply an alternating current (AC). It produces a current in its secondary which
is proportional to the current in its primary. Current transformers, along with
voltage or potential transformers, are instrument transformers.

24. [20]
CIRCUIT BREAKER
A circuit breaker is an electrical safety device designed to protect an electrical
circuit from damage caused by an overcurrent or short circuit. Its basic function is
to interrupt current flow to protect equipment and to prevent the risk of fire.
Unlike a fuse, which operates once and then must be replaced, a circuit breaker
can be reset (either manually or automatically) to resume normal operation.
INSULATOR
An insulator gives support to the overhead line conductors on the poles to prevent
the current flow toward earth. In the transmission lines, it plays an essential role
in its operation. The designing of an insulator can be done using different
materials like rubber, wood, plastic, mica, etc. The special materials used in the
electrical system are glass, ceramic, PVC, steatite, polymer, etc. But the most
common material used in the insulator is porcelain and also special composition,
steatite, glass materials are also used.
Types of Insulators
 Pin Insulator
 Suspension Insulator
 Strain Insulator
 Shackle Insulator
 Post-Insulator
 Stay Insulator
 Disc Insulator

25. [21]
ISOLATOR
Isolator is a mechanical switch which isolates a part of circuit from system as when required.
Electrical isolators separate a part of the system from rest for safe maintenance works.
Types of Isolator
Single break Isolator- In this type of isolator, arm contact is separated into two
elements. The first arm contact holds male contact, as well as second arm contact,
holds female contact. The arm contact shifts because of the post insulator rotation
upon which the arm contacts are fixed. The post insulators rotation stacks in
reverse to each other which makes to shut the isolator by shutting the arm
contact. Post insulators counter-rotation stacks to open the arm contact, as well
as an isolator, rotate into an off condition. Generally, the motor-operated isolator is
used however an emergency manual operated isolator is also offered.
Double break Isolator- This type of isolator consists of three loads of post
insulators. The middle insulator holds a flat male or tubular contact that can be
turned straightly by a spin of the middle post insulator. The rotation of the middle
post insulator can be done by a lever method at the bottom of the post insulator,
as well as it is related to manual operation (operating handle) or motorized
operation motor (using motor) of the isolator via a mechanical knot rod.
EARTH SWITCH
The Earth Switch is a manually operated device with safety interlocking keys,
designed to ground electrical circuit on both side of AC Vacuum Circuit Breaker
when the AC Vacuum Circuit Breaker is open. This ensures the safety of the
maintenance personnel during maintenance and routine checking.
Earthing switches are mounted on the base of mainly line side isolator. Earthing
switches are normally aligned vertically at on condition so these are called
vertically aligned switches. Earthing arms (contact arm of earthing switch) are
normally aligned horizontally at off condition.
LIGHTNING ARRESTER
A lightning arrester (also called lightning Isolator) is a device used on electric
power transmission and telecommunication systems to protect the insulation and
conductors of the system from the damaging effects of lightning. The typical
lightning arrester has a high-voltage terminal and a ground terminal. When a
lightning surge (or switching surge, which is very similar) travels along the power
line to the arrester, the current from the surge is diverted through the arrester, in
most cases to earth.

26. [22]
WAVE TRAP
Wave trap is a device which prevents the high-frequency carrier signals (40KHz to
1000KHz) to enter the substation side. It is also known as line trap. It is connected
in series with the transmission line. It is designed to carry the rated power
frequency (50Hz or 60Hz) current, as well as to withstand the substation fault
currents.
CAPACITOR BANK
Capacitor banks reduce the phase difference between the voltage and current. On
the addition of power bank, the current leads the voltage, hence the power factor
angle is reduced.
Capacitor bank is used for reactive power compensation and power factor
correction in the electrical substation.
CAPACITOR VOLTAGE TRANSFORMER
The capacitive voltage transformer step-down the high voltage input signals and
provide the low voltage signals which can easily measure through the measuring
instrument. The Capacitive voltage transformer (CVT) is also called capacitive
potential transformer.
The capacitive potential divider, inductive element and the auxiliary transformer
are the three main parts of the capacitive potential transformer.
BUS COUPLER
A bus coupler is a device which is used to couple one bus to the other without any
interruption in power supply and without creating hazardous arcs. Bus coupler is
a breaker used to couple two busbars in order to perform maintenance on other
circuit breakers associated with that busbar. It is achieved with the help of a
circuit breaker and isolators.
CORONA RING
In high voltage systems due to ionization of fluid such as air surrounding a
conductor that is electrically charged, an electrical discharge occurs. This
discharge is known as Corona Discharge (also known as the corona effect).
Corona discharge can cause an audible hissing or cracking noise as it ionizes the
air around the conductors. This is common in high voltage electric power
transmission lines. The corona effect can also produce a violet glow, production of
ozone gas around the conductor, radio interference, and electrical power loss.

27. [23]
To reduce this effect Corona ring is used. The purpose of the corona ring is to
distribute the electric field gradient and lower its maximum values below the
corona threshold, preventing corona discharge. Corona rings are used on very high
voltage power transmission insulators and switchgear, and on scientific research
apparatus that generates high voltages.
The distribution of electrical power at NATIONAL ALUMINIUM COMPANY LIMITED
(NALCO), Damanjodi is checked & maintained by a number of small electrical
substations located inside the plant premises. Among all the small electrical
substations there is a central substation located inside the plant which acts as a
master of all the small electrical substations. The central substation located inside
the Refinery complex of NALCO, Damanjodi is named as “CENTRAL
DISTRIBUTION SUBSTATION” commonly called as CDS.
An overall 85MW of electrical power is required for the mines & refinery complex of
NALCO, Damanjodi. So, the main objective of CDS is to receive electrical power
from the state grid that is located at Laxmipur of Odisha and also from the
Turbogenerators located at the Steam & Power plant of refinery complex NALCO,
Damanjodi. And then distribute all the received power efficiently throughout the
Mines & Refinery Complex of NALCO, Damanjodi for the smooth running of the
Plant.
A 220/33KV grid of Odisha Power Transmission Corporation Limited (OPTCL) is
located at Laxmipur of Odisha. From this 220/33KV grid, a 37.008 Kms long
220KV DC transmission line is supplied to the termination switchyard at
Damanjodi, which has been transferred to M/s. Odisha Power Transmission Co.
Ltd. (OPTCL) for operation and maintenance. From the termination switchyard,
NALCO receives two separate 220KV incomers at the 220KV Switchyard which is
located at the Central distribution substation of NALCO, Damanjodi.
The Central distribution substation of NALCO, Damanjodi also receives power from
the state grid at 132KV level through two separate 132KV incomers to the 132KV
switchyard.
 Jayanagar – Sunabeda – Damanjodi, Incomer – 1 [Machhkund Source / BTH Source].
 Jayanagar – Damanjodi, Incomer – 2 [BTH Source].
If we study the present scenario of the mines & refinery complex of NALCO,
Damanjodi. The remaining power i.e. the power required to run the plant excluding
the power from SPP is drawn from the two 220KV incomer which is coming from
the Laxmipur of Odisha under normal circumstances. The other two i.e. Incomer –
1 and Incomer – 2 is kept on standby for emergency situations.

28. [24]
The Balimela – Talcher – Hirakud Power generating stations are commonly called
as BTH. The 220/33KV grid of Laxmipur is the most reliable source and NALCO,
Damanjodi draws around 30MW of power from it under normal operating
conditions. However, in case of emergency situations when power from the
Laxmipur grid is not available or the power quality is very poor, power is drawn
from the BTH source and Machhkund Source. BTH is also Odisha’s most reliable
power generating source. As Odisha shares 50% of the total generating power from
the Machhkund source, NALCO is allowed to draw around 15MW only in
emergency condition.
The received 220KV power from the Laxmipur grid is stepped down to 132KV using
two separate 90/120MVA Auto Transformers and then it is supplied to 132KV
Switchyard located at the Central distribution substation of NALCO, Damanjodi.
Then the received 132KV power is again stepped down to 33KV and 11KV level at
132KV switchyard, through five nos of power transformers located at the 132KV
switchyard of Central Distribution Substation of NALCO, Damanjodi.
The Central Distribution Substation of NALCO, Damanjodi contains 5 nos. of
Power Transformer, 1 nos. of Distribution Transformer.
To Mines- The LV side that is 33KV side of TR – 1103 & TR – 2103 feed power to
the Mines located at Panchpatmali hills of Damanjodi, Odisha through 33KV
Switchboard and two nos of 33KV Overhead power lines.
Also, there is an alternate source to Mines through one 5 MVA, 11/33KV
transformer at MRS feeding the old 33KV Overhead power line.
To Alumina Refinery- The LV side that is 11KV side of TR – 1101, TR – 1102, TR –
1104 & TR – 1105 is connected to the 11KV Switchboard located at CDS through
Bus duct.
Also, the power generated from the Turbogenerators at the Steam & Power Plant
present at NALCO, Damanjodi is of 11KV level and is connected to the 11KV
Switchboard located at CDS through Bus duct.
POWER TRANSFORMERS WITH THEIR RATINGS AND THEIR SUPPLY AREAS
SL. NO. TRANSFORMER PRIMARY / SECONDARY
VOLTAGE
RATING LOAD
1 TR – 1101 132/11KV 26.5MVA To Alumina Plant
2 TR – 1102 132/11KV 26.5MVA To Alumina Plant
3 TR – 1103 132/33KV 10.0MVA To Mines
4 TR – 1104 132/33/11KV 37.5MVA To Alumina Plant
5 TR – 1105 132/11KV 37.5MVA To Alumina Plant
DISTRIBUTION TRANSFORMERS WITH THEIR RATINGS AND THEIR SUPPLY AREAS
SL. NO. TRANSFORMER PRIMARY / SECONDARY
VOLTAGE
RATING LOAD
1 TR – 2103M 11/33KV 7.5MVA To Mines

29. [25]
So, in all the 11KV Switchboard receives power through 4 nos. of Power
transformers and 5 nos. of Turbogenerators.
Finally, from here the power is distributed to 11KV substations located at different
process areas/load centres, by 11KV Cross linked polyethylene cable (XLPE)
through loop and radial feeders.
DUPLEX PANEL
Duplex panel houses 2 rows of panels. The front houses remote control and
meeting circuit for 2 nos. 132KV incomers & one bus coupler, 2 nos. 220KV
incomers & one bus coupler, 4 nos. Power transformer, 2 nos. Auto transformer.
Whereas the rear panel houses the relay and protection circuit. Also, front panel
houses communication windows for all switchyard equipments including the
compressors.
SIMPLEX PANEL
Simplex panel houses the remote control and meeting circuit for 11KV incomers
and outgoing feeders at CDS. Also, it houses the remote annunciation for all 11KV
panels.
OLTC PANEL
The 5 Nos OLTC (on load tap changer) at CDS are used to change tap position of
11KV and 33KV power transformer online whenever there is need to change the
voltage at 11KV and 33KV bus.
METERING PANEL
Metering Panel is the instrument that display an input signal in an analog or
digital form. Many metering panels also include alarm options as well as the ability
to transfer data to a computer. Panel meters take a sample of the voltage or
current to create a visual representation of the measured value.
ELECTRICAL CONTROL SYSTEM (ECS)
The Electrical Control System (ECS) is used to effect load shedding to save plant
from different contingencies during TGs islanding. ECS is also used for data
acquisition, alarm generation, historian and report generation.

30. [26]
BATTERY BANKS & BATTERY CHARGERS
Battery banks and battery chargers are installed in all the 11KV substations to
generate 110V DC source for protection & control of 132KV and 11KV equipments.
Also, this supply is extended to all the unit substations and control rooms for
6.6KV motor control, 6.6KV and 415V switchboard control and for emergency DC
lighting.
CARRIER COMMUNICATION
There are three nos of Power Line Carrier Communication (PLCC) panels at CDS
control room and essential carrier communication equipments at 132KV
switchyard & 220KV switchyard to communicate with grid substations at
Jayanagar, Sunabeda & Laxmipur.
Transmission Line 132KV 02 Grid Owned
220KV 02 Grid Owned
Switchyard 132KV 08 Bays
220KV 04 Bays
Power Transformer 132/33/11KV 05 Outdoor
Auto Transformer 220/132KV 02 Outdoor
Capacitor Bank 11KV 04 25MVA
Loop Substation 11KV 21 Metal Enclosed
Unit Substation 6.6/0.433KV 45 Indoor
Load Centre 6.6/0.433KV 152 Metal Enclosed
Transformers 11/6.6 or 0.4KV 446
Motors 11KV 08 Direct on line (DOL)
Motors 6.6/0.4KV >4000 Direct on line (DOL)
Variable Frequency Drive (VFD) 0.65KV >200

31. [27]
LOOP SUBSTATIONS (11KV) WITH LOAD CENTRES
LS – 01 / LS – 01E
SETTLER & WASHERS
LS – 02 / LS – 02E
HYDRATE FILTRATION & PRECIPITATIONS
LS – 03 / LS – 03E
CALCINATION PLANT & ALUMINA HANDLING
LS – 04 / LS – 04E
EVAPORATION BATTERIES, LIME HANDLING
LS – 05 BALL MILLS, DIGESTION, DESILICATION
US – 03E BALL MILL – 701, CR – 701 (3RD PHASE), 3RD
STREAM PREDESILICATION, DIGESTION
US – 03EX BALL MILL – 1001/1002, CR – 1001 (4TH PHASE)
GTS / E COMPRESSORS, COOLING TOWERS, TOWNSHIP, WI
US – 01 SECONDARY CRUSHER, BAUXITE HANDLING
1HA BOILER #1
2HA BOILER #2
3HA BOILER #3
4HA BOILER #4
5HA BOILER #5
US – 22 WATER INTAKE
UNIT SUBSTATIONS (11KV) WITH LOAD CENTRES
STREAM: 1 & 2 (19 NOS) STREAM: 3 & 4 (10 NOS)
US 19 BAUXITE HANDLING US 02E BAUXITE HANDLING & CRUSHER
US 01 SECONDARY CRUSHER US 02EXBAUXITE HANDLING & PD
US 03 DIGESTION & DESILICATION US 03E DIGESTION & PD
US 05 1ST PHASE SETTLER & WASHER US 04E SETTLER & WASHER
US 06 2ND PHASE SETTLER & WASHER US 05E SECURITY FILTRATION
US 07 CAUSTICIZATION US
06E
3RD HYDRATE FILTRATION & PPT
US 08 SECURITY FILTRATION US 06EX4TH HYDRATE FILTRATION & PPT
US 09 HYDRATE FILTRATION & PPT US 07E 3RD & 4TH CALCINATION
US 10 EVAPORATION & COOLING TOWER US 08E 3RD EVAPORATION
US 11 CALCINATION US 08EX4TH EVAPORATION
US 13 COMPRESSOR & COOLING TOWER
US 14 WORKSHOP
US 15 FUEL & OIL HANDLING
US 16 ALUMINA HANDLING
US 17 ADMIN BUILDING & TC
US 18 WASTE WATER TREATMENT
US 20 LIME HANDLING
US 21 WATER TREATMENT
US 22 WATER INTAKE

32. [28]
RELAYS
A relay is automatic device which senses an abnormal condition of electrical circuit
and closes its contacts. These contacts in turns close and complete the circuit
breaker trip coil circuit hence make the circuit breaker tripped for disconnecting
the faulty portion of the electrical circuit from rest of the healthy circuit.
 Measures / Receives Data
 Currents, Voltages, etc.
 Determines whether the condition is abnormal or not
 Overcurrent, undervoltage
 Sends command to isolating device
 Isolating device maybe a circuit breaker or contactor
TYPES OF RELAYS
Protection relays are mainly based on their characteristic, logic, on actuating
parameter and operation mechanism.
 Based on operation mechanism
 Electromechanical relays
 Static relays
 Digital relays
 Numerical relays
 Based on Characteristic
 Definite time relays
 Inverse time relays with definite minimum time(IDMT)
 Instantaneous relays.
 IDMT with inst.
 Stepped characteristic.
 Programmed switches.
 Voltage restraint over current relay.
 Based on logic
 Differential.
 Unbalance.
 Neutral displacement.
 Directional.
 Restricted earth fault.
 Over fluxing.
 Distance schemes.
 Bus bar protection.
 Reverse power relays.
 Loss of excitation.
 Negative phase sequence relays etc.

33. [29]
 Based on actuating parameter
 Current relays.
 Voltage relays.
 Frequency relays.
 Power relays etc.
 Based on application
 Primary relay
 Backup relay
Actually, a relay is nothing but a combination of one or more open or closed
contacts. These all or some specific contacts the relay change their state when
actuating parameters are applied to the relay. That means open contacts become
closed and closed contacts become open.
RELAYS FOR TRANSFORMER PROTECTION
SL. NO. VOLTAGE RATIO &
CAPACITY OF
TRANSFORMER
RELAYS ON
HV SIDE
RELAYS ON
LV SIDE
COMMON RELAYS
1 11/132KV Generator
Transformer
3nos Non-
Directional
O/L Relay
----
Differential Relay or
Overall differential Relay
Overflux Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT
Trip Relay
WT Trip Relay
1 no Non-
Directional
E/L Relay
and/or
standby E/F +
REF Relay
----
2 13.8/220 KV
15.75/220 KV
18/400 KV
21/400 KV
Generator Transformer
3nos Non-
Directional
O/L Relay
----
Differential Relay or
Overall differential Relay
Overflux Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT
Trip Relay
WT Trip Relay
1 no Non-
Directional
E/L Relay
and/or
standby E/F +
REF Relay
----
3 220 /6.6KV
Station Transformer
3nos Non-
Directional
O/L Relay
3 nos Non-
Directional
O/L Relay
Differential Relay
Overflux Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT Trip Relay
WT Trip Relay
1 no Non-
Directional
E/L Relay
and/or
standby E/F +
REF Relay
4 Gen-volt/6.6KV UAT 3nos Non-
Directional
O/L Relay
3nos Non-
Directional
O/L Relay
Differential Relay
Overflux Relay
Buchholz Relay

34. [30]
OLTC Buchholz Relay
PRV Relay
OT Trip Relay
WT Trip Relay
5 132/33/11KV upto 8 MVA 3 nos O/L
Relay
1 no E/L Relay
3 nos O/L
Relay
1 no E/L Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT Trip Relay
WT Trip Relay
6 132/33/11KV above 8 MVA &
below 31.5 MVA
3 nos O/L
Relay
1 no
Directional
E/L Relay
3 nos O/L
Relay
1 no E/L Relay
Differential Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT Trip Relay
WT Trip Relay
7 132/33KV, 31.5 MVA & above3 nos O/L
Relay
1 no
Directional
E/L Relay
3 nos O/L
Relay
1 no E/L Relay
Differential Relay
Overflux Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT Trip Relay
WT Trip Relay
8 220/33 KV, 31.5MVA &
50MVA 220/132KV, 100 MVA
3 nos O/L
Relay
1 no
Directional
E/L Relay
3 nos O/L
Relay
1 no E/L Relay
Differential Relay
Overflux Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT Trip Relay
WT Trip Relay
9 400/220KV 315MVA 3 nos
Directional
O/L Relay
(with
dir.highset)
1 no
Directional
E/L relay.
Restricted
E/F relay
3 nos
Directional
O/L Relay for
action
3 nos
Directional
O/L Relay
(with
dir.highset)
1 no
Directional
E/L relay.
Restricted
E/F relay
Differential Relay
Overflux Relay
Buchholz Relay
OLTC Buchholz Relay
PRV Relay
OT Trip Relay
WT Trip Relay
Over Load (Alarm) Relay

35. [31]
PROTECTION PROVIDED FOR 132KV & 220KV INCOMERS
SL.NO. PROTECTION USED REMARK Nomenclature
1 DISTANCE PROTECTION Distance Protection is a Non-unit
System of Protection, which measures
the Impedance between the Relay
Location and the point where the fault
is incident and compares it with the
Set Value. Since it protects a certain
Length of Transmission Line, it is
called a Distance Relay.
30G
30H
30J
2 BUS BAR DIFFERENTIAL
PROTECTION ZONE – A/B &
CHECK ZONE
Check zone is a safety precaution to
avoid tripping of bus bars due to
defective CT Switching relays.
87A
87B
87C
3 DIRECTIONAL OVER CURRENT
(O/C) PROTECTION
Due to its ability to detect the
direction of a short-circuit
current, directional overcurrent
protection helps to protect an
installation against short-circuit
currents that could circulate in both
directions through the circuit breaker.
67A
67C
4 DIRECTIONAL EARTH FAULT
(E/F) PROTECTION
It is used to differentiate between
different fault types to ensure
that co-ordination between
protection devices such as
distribution circuit breakers and
reclosers is maintained.
67N
5 NON – DIRECTIONAL OVER
CURRENT (O/C) PROTECTION
This Induction Type Overcurrent
Relay works on the induction
principle and initiates corrective
measures when current in the circuit
exceeds the predetermined value.
51A
51C
6 NON – DIRECTIONAL EARTH
FAULT (E/F) PROTECTION
It is a secondary relay which is
connected to the voltage and
current transformers of the object
to be protected.
67N
7 REVERSE POWER PROTECTION
WITH UNDER FREQUENCY
If the sum of connected loads and
losses in the system exceeds the
amount of mechanical power
provided by the generators, rotors
will slow down and therefore the
frequency drops. Conversely if the
generated energy is more than
demand the rotors will speed up
and the frequency will rise.
32
81

36. [32]
PROTECTION PROVIDED FOR 132KV POWER & 220KV AUTO TRANSFORMER
SL.NO. PROTECTION USED REMARK Nomenclature
1 DIFFERENTIAL PROTECTION protective relay that functions on a
percentage, phase angle, or other
quantitative difference between two
currents or some other electrical
quantities.
87
2 BUS BAR DIFFERENTIAL
PROTECTION ZONE – A/B &
CHECK ZONE
Check zone is a safety precaution to
avoid tripping of bus bars due to
defective CT Switching relays.
87A
87B
87C
3 NON – DIRECTIONAL OVER
CURRENT (O/C) PROTECTION
AT HV SIDE
Non-directional overcurrent is a
protection scheme developed to
protect power system equipment
from overcurrent and short-circuit
currents regardless of the direction of
current flow.
50HV
51HV
4 NON – DIRECTIONAL EARTH
FAULT (E/F) PROTECTION
AT HV SIDE
It is a secondary relay which is
connected to the voltage and
current transformers of the object
to be protected.
51NHV
5 RESTRICTED EARTH FAULT
(E/F) PROTECTION
Restricted earth fault protection is
provided in electrical power
transformer for sensing internal earth
fault of the transformer.
64R LV
64R MV
6 STANDBY EARTH FAULT
(E/F) PROTECTION
Standby Earth Fault Protection is a
course protection used predominantly
as a back up to other protection.
The protection consists of a CT and
basic relay, the CT is placed as
close as possible on the earth path
return to the star point of a transformer.
51N LV
7 NON – DIRECTIONAL OVER
CURRENT (O/C) PROTECTION
AT LV SIDE
Non-directional overcurrent is a
protection scheme developed to
protect power system equipment
from overcurrent and short-circuit
currents regardless of the direction of
current flow.
50LV
51LV
8 NON – DIRECTIONAL EARTH
FAULT (E/F) PROTECTION
AT LV SIDE
It is a secondary relay which is
connected to the voltage and
current transformers of the object
to be protected.
51N LV
9 DEFINITE TIME OVER CURRENT
(O/C) PROTECTION
A definite time over-current (DTOC)
relay is a relay that operates after a
definite period of time once the
current exceeds the pickup value.
Hence, this relay has current setting
range as well as time setting range.
51 O/L
10 BUCHHOLZ TRIP A Buchholz relay is a safety device
mounted on some oil-filled

37. [33]
power transformers and reactors,
equipped with an external
overhead oil reservoir called a
"conservator". The Buchholz relay is
used as a protective device sensitive
to the effects of dielectric failure
inside the equipment. A generic
designation for this type of device
is "gas detector relay".
11 WINDING TEMPERATURE
INDICATOR (WTI) TRIP
The WTI means winding temperature
Indicator which indicates the
winding temperature of the
transformer and operates the alarm,
trip, and cooler control contacts.
This instrument operates on the
principle of thermal imaging and it is
not an actual measurement.
12 OIL TEMPERATURE
INDICATOR (OTI) TRIP
The OTI means Oil Temperature
Indicator which indicates oil
temperature of the transformer and
operates the alarm, trip, and cooler
control contacts. This instrument
operates on the principle of thermal
imaging and it is not an actual
measurement.
13 PRESSURE RELIEF VALVE
(PRV) TRIP
If pressure arises inside a
transformer and exceeds a pre-set
pressure limit, the pressure safety
valve opens its valve clap, which is
held by a spring and releases the
internal pressure until it declines.
14 ON LOAD TAP CHANGER
(OLTC) BUCHHOLTZ TRIP
On-load tap changer (OLTC), also
known as On-circuit tap changer
(OCTC), is a tap changer in
applications where a supply
interruption during a tap
change is unacceptable, the
transformer is often fitted with a
more expensive and complex on
load tap changing mechanism.
PROTECTION PROVIDED FOR 11KV CDS & LS OUTGOING FEEDERS
SL.NO. PROTECTION USED REMARK Nomenclature
1 OVER CURRENT (O/C)
PROTECTION
Overcurrent protection is protection
against excessive currents or current
beyond the acceptable current rating
of equipment. It generally operates
instantly.
2 EARTH FAULT (E/F)
PROTECTION
It is a safety device used in
electrical installations with high

38. [34]
earth impedance. It detects small
stray voltages on the metal
enclosures of electrical equipment.
The result is to interrupt the
circuit if a dangerous voltage is
detected.
PROTECTION PROVIDED FOR 11KV TRANSFORMER OUTGOING FEEDERS
SL.NO. PROTECTION USED REMARK Nomenclature
1 INSTANTANEOUS OVER
CURRENT (O/C) PROTECTION
This relay is referred as definite
(instantaneous) overcurrent relay.
The relay operates as soon as the
current gets higher than a preset value.
There is no intentional time delay set.
There is always an inherent time delay
of the order of a few milliseconds.
2 INSTANTANEOUS EARTH
FAULT (E/F) PROTECTION
The relay employs the well-known
high impedance principle and is
used for restricted earth fault
protection of machines,
transformers and reactors.
It can also be used for capacitor
bank unbalance protection when the
bank is connected in star-star
formation with a CT in the neutral link.
3 OVER CURRENT (O/C)
PROTECTION
Overcurrent protection is protection
against excessive currents or current
beyond the acceptable current rating
of equipment. It generally operates
instantly.
4 EARTH FAULT (E/F)
PROTECTION
It is a safety device used in
electrical installations with high
earth impedance. It detects small
stray voltages on the metal
enclosures of electrical equipment.
The result is to interrupt the
circuit if a dangerous voltage is
detected.

39. [35]
Conventional Motor Protections:
i. Thermal
ii. Short Circuit [I₂(inst)]]
iii. Stalling [I1(t)]
iv. Negative Sequence [I₂]
v. Earth fault [Io]
 Most of the winding failures can be directly or indirectly attributed to
Overloading (prolonged/cyclic)
Unbalanced supply voltage
Single Phasing
 In general, insulation life is halved for 10° C rise in temperature above the
rated value.
 Motor thermal protection is provided by "Thermal replica" modeling which
considers motor as a homogenous body, creating and dissipating heat at a
rate proportional to temperature rise.
 This instantaneous protection Is used to protect upstream equipments in
case of a dead S/C in motor windings or terminal flashovers.
 In some cases, where fault level is more than the contactor current breaking
capacity, S/C protection by the relay is disabled (CTMM401) and fuse is
allowed to provide S/C protection (e.g. US13 & US09).
 S/C protection is invariably provided in motors fed through CBs.
 If a motor stalls during running due to jamming or excessive loading it
draws high current which may reach upto starting current. This high
current is detrimental to the health of the motor.
 So, a definite time delay O/C stall protection is provided with a time delay of
value greater than starting time but less than locked rotor withstand time.

40. [36]
This is caused by too much load on a motor. Systems are protected by overload
protection relays. While overloads are allowed for a short time (usually minutes),
prolonged overloads will use thermal action to cause a protective device to trip.
 NPS is generated from unbalanced voltage condition i.e. unbalanced loading,
loss of phase, single phase faults.
 For same voltage, NPS current drawn by motor is 6 times the PPS current
drawn. So, a voltage unbalance of 17% will result in an NPS current more than
the rated current of the motor.
 Moreover, in rotor the frequency of NPS current is 2 fs. Due to skin effect rotor
heats up rapidly due to NPS current.
 Most motor protection relays measure NPS component of current and provide
IDMT/DT NPS protection
 In power system low voltage condition occur due to more demand of load, or
it may happen due to other abnormal conditions. But motor supplied voltage
should not go beyond its limit (As mention in name plate of motor) otherwise
it can damage motor.
 Whenever moor supplied in low voltage condition, at that time suddenly
torque on motor get reduce about 20%, now if motor carries light load it
might not get affected by it but if motor is on loading condition, then it will
try to maintain torque, so motor will take higher current from its source, due
to which winding will heat up and it can damage insulation and winding due
to which motors life goes reduce.
 This is what reason that motor should be protected from under voltage
condition.
 Over voltage in motor occurs whenever it is supplied beyond its rated
voltage.
 This condition must need to identify immediately as overvoltage creates
stress on insulation, which affects on motor's life.
 Due to over voltage magnetizing current in motor increases and this will
increase iron loss of motor, due to which winding will heat up. However, load
current will be reduce as voltage increases also sleep will decrease, and
motor efficiency will also increase slightly. Overvoltage in motor is protected
through numerical relay.

41. [37]
 One of the most common faults to occur on a motor is a stator winding fault.
Whatever the initial form of the fault (phase, etc.) or the cause (cyclic
overheating, etc.), the presence of the surrounding metallic frame and casing
will ensure that it rapidly develops into a fault involving earth.
 Therefore, provision of earth fault protection is very important. The type and
sensitivity of protection provided depends largely on the system earthing, so
the various types will be dealt with in turn.
 It is common, however, to provide both instantaneous and time-delayed
relay elements to cater for major and slowly developing faults.

42. [38]
1. PURPOSE: REWINDING OFLT AND HT MOTORS
2. SCOPE : IMSPIELEC/4
3 RESPONSIBILITY: HOD (EIEC)
4. ACTIVITIES: Clean the
- Clean the motor body with air / water as suitable.
- Dismantle the motor.
- Inspect the stator and rotor for any abnormality.
- Check IR value.
- Cut the windings at one end and strip-off the windings from the other end.
- Clean the stator slots with air and cleaning agents.
- Dry in the oven.
- Make the coils to the shape.
- Cut the insulation materials to the size.
- Insert the insulation material and coils in the slots and then the wedges.
- Complete the winding with polarity checking.
- Preheat the stator.
- Varnish the stator.
- Bake in the oven at deg (approx) temperature.
- Conduct high voltage test in case of HT motors.
- Assemble the motor.
- Take IR & PI value in case of HT Motor.
- Take No-load trial run and note current.
- Greasing of rotor shaft extension to prevent corrosion.
- Paint Motor Body.
- Paint the date of RM and work order No.
5. Safety Precautions:
1. Use proper / tested sling while handling the motor.
2. Use proper size bearing puller.

43. [39]
1. PURPOSE
The purpose of this procedure is to indicate the method adopted for carrying
out overhauling of LT and HT Motors.
2. SCOPE : IMSP/ELEC/4
3 RESPONSIBILITY: HOD (ELEC) / I/C ERS
4. ACTIVITIES:
- Clean the motor body completely by air / water as suitable.
- Take IR value.
- Take out coupling / pulley if applicable.
- Mark DE /NDE end shield.
- Dismantle the motor.
- Clean and check the bearings.
- Check the stator and rotor for any abnormalities.
- Clean the stator windings and the rotor with compressed air and then cleaning
agent if required.
- Dry the stator and rotor if required in an oven.
- Apply varnish / gelcoat if required and redry.
- Grease the bearings with Servogem 2 / Lithon 2 or equivalent grease.
- Assemble the motor.
- Record IR value and PI value in case of HT Miter.
- Take no-load trial run and note the no-load currents and check for any
abnormalities.
- Greasing of rotor shaft extension to prevent corrosion
- Paint motor body if required.
- Paint the date of overhaul and work order no Tool & Tackles:
Bearing puller, Ox-acetylene gas set, Insulation Tester Safety Precautions:
- Use proper / tested sling while handling the motor.
- Use proper size bearing puller.
- Use nose mask while cleaning the motor winding.

44. [40]
Highest rated motor of 3050KW is used at the BALL MILL OF NATIONAL
AUMINIUM COMPANY LIMITED (NALCO), DAMANJODI
HYPER STEEL GRINDING MEDIA BALLS
Size- 75mm/90mm/100mm
Annual requirement - 450 MT
Approximate Unit Price: Rs. 52,000.00
Specification:
Hyper Steel Grinding Media Ball
as per IS: 6079/1989 Grade 2.
Chemical Composition
Carbon 1.60 % - 1.90%
Silicon 1.0 %Max.
Manganese 1.20% - 1.50%
Chromium 1.50% - 2.00%
Sulphur 0.06% Max
Phosphorus 0.06% Max
Hardness (Tested in accordance with IS 1500:1983) = 375 BHN (Minimum)

45. [41]
HIGH CHROME GRINDING MEDIA BALLS
High Chrome Grinding media 50 mm dia, 90 mm dia
Chemical composition:
Element Min(%) Max(%)
Carbon- 1.8 3.5
Manganese- 0.5 1.5
Chromium 11 18
Nickel 2
Molybedenum 2.5
Copper 2
Silicon 1
Sulphur 0.1
Phosphorous 0.1
Hardness- 57 HRC minimum
Retained austinite 15% maximum
Annual requirement - 150 MT
Approximate Unit Price: Rs. 66,000.00

46. It was a wonderful and learning experience for me while working on this
project. This project took me through the various phases of project
development and gave me a real insight to the world of Electrical
Engineering. The joy of working and the thrill involved while tackling with
various problems & challenges gave me keen knowledge of practical
approach.
Through this project I gained a lot of knowledge on electrical power
generation & distribution.
Hence at last I thank all those who directly or indirectly involved in the
completion of my project work.

47.  Plant Observation
 Manuals Provided
 Google Search Engine
 Web Resources of Nalco
 Area In Charges at Plant Premises