Transformer presentation by Walid Karim

1. PRESENTATION ON GHPP
TRANSFORMER.
O&M TEAM GULPUR HYDRO POWER PROJECT KOTLI.
O&M TEAM GHPP 1
Presentation on GHPP transformer

2. WHAT IS TRANSFORMER .
• A transformer is a static device.
• The word ‘transformer’ comes form the word ‘transform’.
• Transformer is not an energy conversion device, but it is device that changes
AC electrical power at one voltage level into AC electrical power at another
voltage level through the action of magnetic field but with a proportional
increase or decrease in the current ratings., without a change in frequency.
• It can be either to step-up or step down.
O&M TEAM GHPP 2

3. STRUCTURE OF TRANSFORMER.
• The transformer consist of two inductive coils ,these are electrical separated but linked through a
common magnetic current circuit.
• These two coils have a high mutual induction.
• One of the two coils is connected of alternating voltage ,the coil in which electrical energy is fed with
the help of source called primary winding (P) shown in fig.
• The other winding is connected to a load the electrical energy is transformed to this winding drawn out
to the load this winding is called secondary winding(S) shown in fig.
O&M TEAM GHPP 3

4. • The function of the core is to transfer the changing magnetic
flux from the primary coil to the secondary coil.
• The primary has N1 no of turns and the secondary has N2 no of
turns.
• The of turns plays major role in the function of transformer.
O&M TEAM GHPP 4

5. WORKING PRINCIPLE
• The transformer works in the principle of “Faraday Law of
mutual induction”.
• “The principle of mutual induction states that when the two
coils are inductively coupled and if the current in coil change
uniformly then the e.m.f. induced in the other coils. This e.m.f
can drive a current when a closed path is provided to it.”
Faraday Law of mutual induction
O&M TEAM GHPP 5

6. HOW IT WORKS.
• When the alternating current flows in the primary coils, a changing magnetic
flux is generated around the primary coil.
• The changing magnetic flux is transferred to the secondary coil through the
iron core.
• The changing magnetic flux is cut by the secondary coil, hence induces an
e.m.f in the secondary coil.
O&M TEAM GHPP 6

7. • Lets have e brief look on how it works.
O&M TEAM GHPP
7

8. BASIC PARTS OF TRANSFORMER
These are the basic components of a transformer.
1.Laminated core
2.Windings
3.Insulating materials
4.Transformer oil
5.Tap changer
6.Oil Conservator
7.Breather
8.Cooling system
9.Buchholz Relay
O&M TEAM GHPP
8

9. • Core
• Core is made up of thick laminated sheets of
metal.
• It provides a low reluctance path to the flow of
magnetic flux.
• The core acts as support to the winding in the
transformer.
• It is made of laminated soft iron core in order to
reduce eddy current loss and Hysteresis loss.
• The composition of a transformer core depends on
such as factors voltage, current, and frequency.
Eddy currents are loops of
electrical current induced within
conductors by a changing
magnetic field in the conductor
due to Faraday's law of
induction.Hysteresis loss. Hysteresis
loss is caused by the
magnetization and
demagnetization of the core
as current flows in the forward
and reverse directions.
O&M TEAM GHPP 9

10. • Winding.
• Two sets of winding are made over the transformer
core.
• These are insulated from each other with some
insulating material.
• Winding consists of several turns of copper conductors
bundled together, and connected in series.
• Classification of winding.
Primary
Winding
Secondary
winding
O&M TEAM GHPP 10
The conductive
material used in
the manufacturing
of GHPP
windings is the
electrolytic copper
99,9% pure, under
bars shape,
normally insulated
with Kraft paper

11. • Insulating Materials
• Insulating paper and cardboard are used in transformers to
isolate primary and secondary winding from each other and
from the transformer core.
• Transformer oil is another insulating material. Transformer oil
performs two important functions:
• The transformer's core and winding must be completely
immersed in the oil. Normally, hydrocarbon mineral oils are
used as transformer oil.
1.insulating function 2.It can also cool the core and coil assembly.
Oil contamination is a serious
problem because contamination robs
the oil of its dielectric properties and
renders it useless as an insulating
medium
GHPP transformer has
OFWF , cooling
technique
O&M TEAM GHPP 11
DB45#

12. • Conservator
• The conservator conserves the
transformer oil.
• It is an airtight, metallic, cylindrical
drum that is fitted above the
transformer. The conservator tank is
vented to the atmosphere at the top,
and the normal oil level is
approximately in the middle of the
conservator to allow the oil to expand
and contract as the temperature varies.
• The conservator is connected to the
main tank inside the transformer,
which is completely filled with
transformer oil through a pipeline.
O&M TEAM GHPP 12

13. • Breather
• The breather controls the moisture level in the transformer.
Moisture can arise when temperature variations cause
expansion and contraction of the insulating oil, which then
causes the pressure to change inside the conservator.
• If the insulating oil encounters moisture, it can affect the
paper insulation or may even lead to internal faults. Therefore,
it is necessary that the air entering the tank is moisture-free.
The transformer's breather is a cylindrical container
that is filled with silica gel. When the atmospheric air
passes through the silica gel of the breather, the air's
moisture is absorbed by the silica crystals. The breather
acts like an air filter for the transformer and controls
the moisture level inside a transformer. It is connected
to the end of breather pipe
O&M TEAM GHPP
13

14. • Tap Changer:
• The output voltage of transformers vary
according to its input voltage and the load.
• In order to balance the voltage variations, tap
changers are used. Tap changers can be either
on-load tap changers or off-load tap changers.
In an on-load tap changer, the tapping can be
changed without isolating the transformer from
the supply.
O&M TEAM GHPP 14
GHPP TAP CHANGER
 Tap changer type:
OLTC
 Taping range:132+/-
8x1.25%
 Nu of taps: 17
 OLTC should be filled
of oil up to the
appropriate level, by
the sampling valve.

15. • Cooling system.
• TYPES OF COOLING.
Oil natural (ON) cooling
Oil natural air forced (ONAF)cooling
Oil natural water forced (ONWF) Cooling
Oil forced air natural (OFAN) cooling
Oil forced air forced (OFAF) Cooling
Oil forced water forced (OFWF) Cooling
The medium of cooling
Air Oil
15
Water
GHPP POWER TRANSFORMER has
OFWF cooling system.

16. • Buchholz Relay
• The Buchholz Relay is a protective device container housed over the
connecting pipe from the main tank to the conservator tank.
• It is used to sense the faults occurring inside the transformer.
• It is a simple relay that is operated by the gases emitted during the
decomposition of transformer oil during internal faults. It helps in sensing and
protecting the transformer from internal faults.
O&M TEAM GHPP 16

17. • Lets see how Buchholz relay operate.
• It helps in sensing and protecting the
transformer from internal faults.
O&M TEAM GHPP 17

18. • Specification of GHPP Transformer.
• Quantity 2 Sets
• Type 3 phase
• Applicable IEC Standard IEC60076
• MVA rating 67 MVA
• Cooling OFWF
• Frequency 50 Hz
• Rated voltage 132 kV
• Rating of Low Voltage Winding 11 kV
• Maximum operating voltages on HV. 145.2 kV
• Minimum operating voltages on HV. 118.8 kv
• Connection of windings Yndll
• Max winding temperature rise 65°C
• Max oil temperature rise 40°C
Yndll: it indicates phase
displacement and discrimination
of HV and LV side.
Y connection on HV side.
d means delta connection on
LV side.
O&M TEAM GHPP 18
Total
Weight=74000kg
Weight without
oil=54000kg

19. OPERATION OF GHPP TRANSFORMER.

Before energizing the transformer, the following verifications
must be done.
At Radiator
disk valve
open 
At Transformer
conservator, insulating
valve
Blind flange
valve
closed
open 
1. Valves
O&M TEAM GHPP 19

20. OPERATION OF GHPP TRANSFORMER.
2. Following Oil characteristics should be checked
before energizing
Measure the oil dielectric strength.
Dielectric strength.
It is defined as the
maximum voltage
required to
produce a dielectric
breakdown through
the material and is
expressed in terms
of Volts per unit
thickness.
According to IEC60422 standard the min break
down voltage of same rating T/F should be
These standard should also be
verified.
50 KV Min
item Oil standard
Water content (mg/L) ≤15
Dielectric loss factor（90℃） ≤0.010
Breakdown voltage，(kV) ≥50
O&M TEAM GHPP
20

21. OPERATION OF GHPP TRANSFORMER.
• 3-PROTECTION SWITCHGEAR
O&M TEAM GHPP 21
Check the Buchholz relay assembly.
 Purge the relay
 Test the alarm
 Check sample from Gas bleed
 Test the tripping circuit isolating from main
system

22. 3-PROTECTION SWITCHGEAR
O&M TEAM GHPP 22
Open the disconnectors.
Putt ON the protection circuit.
Test the alarm and trip circuit.
At end, purge the relay.
Check the corresponding signal at control room.
Check the circuit breakers actuation.
Check all external protections, such as the maximum current relays, differential relays.
Purge the bushings.
Check the thermostats indicators and their regulations.
Check if there is enough clearance between the alive parts and the ground.
Check if the bushing connections are in phase

23. OPERATION OF GHPP TRANSFORMER.
AIR BREATHER
Check all breathers, namely the silica gel condition, if it
turned pink or dark brown replace it.
TAP CHANGER:
• Purge the tap changer and check the position correspondence
between the tap changer and the motor drive unit.
• Test the stop-ends and the crank lock should be fully
operational.
• To energies the transformer for the first time, the on-load tap
changer shall be placed in the maximum voltage ratio position
and for next on requirements.
MOTORFANS AND MOTORPUMPS
- Check the motors supply voltage and their sense of rotation.
- Test the run and stop signaling.
- Check if the circulation indicators are assembled and working
properly.
--Check and regulate, for the expected temperatures, the motor fans
and/or motor pumps thermostats
O&M TEAM GHPP 23
Inspection before energizing.

24. OPERATION OF GHPP TRANSFORMER.
OFF-CIRCUIT TRANSFORMER CONNECTION.(LAST INSPECTION)
• All safety ground connections shall be removed.
• All personnel shall be kept away from the transformer. The working area shall be marked.
• Check the tank ground connection and the fire protection system.
• Energize the transformer.
• At the energizing moment, check if the external protection relays have an adequate reaction.
• Then, check if there are any abnormal noises on the transformer.
• Perform some maneuvers with the on-load tap changer.
O&M TEAM GHPP 24

25. MAINTENANCE
• During the transformer working life, the following maintenance and vigilance cares must be taken, in order to
avoid damages and work interruptions.
 The silica gel color must be inspected each 2 months.
 The silica gel must be replaced as soon as 2/3 of its volume change to
pink colour.
OIL CONDITION
 The oil dielectric strength shall be measured each 2 years.
 Each 3 years must be checked its acidity and the interfacial tension tests.
THERMOMETERS AND RELATED DEVICES
 If there are suspicions of malfunction, the thermometers shall be calibrated, making
comparisons with laboratorial values.
 Thermometers shall be replaced, if any damage is found.
BUSHINGS INSPECTION.
 The bushing porcelains must be cleaned each 2 months.
 After cleaning, the porcelains shall be inspected and, if there is any
fracture or fissure, they must be replaced, in order not to imperil the
transformer work.
 Check the connector contact tightness.
O&M TEAM GHPP
25

26. SUMMARY OF PERIODIC MAINTENANCE.
Short verification
Air breather Pressure Each 2
months
Relief valve Each 2
months
Bushings Each 2
months
Thermometers Each 2
months
Oil levels and
leakages
Each 2
months
Cooling Each 2
months
Command boxes Each 2
months
Complete verification
Oil condition
- Dielectric
strength
- - Acidity
- Interfacial
tension
Each 2 years
Each 2 years
Each 3 years
Each 3 years
Painting Each 12 months
Protections relays Each 2 years
O&M TEAM GHPP
26

27. GENERAL PROBLEMS AND TROUBLESHOOTING
Problem Possible causes Measures / actions
 Winding and/or oil
 Temperature indicator
 Alarm
 Increase on winding temperature
 Cooling circuit breakdown
 Long-lasting overcharge
 Note down temperature(in limits)
other wise shut off.
 Check overcharge.
 Check cooling circuit.
 Buchholz relay
Alarm
 1-Lack of oil on the conservator
(leakages)
 2-Gas forming, caused by
internal breakdown
 Disconnect transformer.
 Analyze gas, if any.
 Connect transformer
again if causes are (1) or(2).
If not, contact manufacturer
 Buchholz relay
Trip
 Lack of oil
 Internal breakdown
 Do not connect transformer
again without analyzing causes and
contact manufacturer.
 Pressure relief valve
Trip
 Obturation of breather (check
silica gel)
 Increase of internal pressure.
 Check effective operation
of the valve (see optical indicator).
 Check operation of the
Buchholz
 Cooling system fail  Electrical circuit breakdown
 Oil or water pump(s) breakdown
 Motor-fan(s) breakdown
 Check streams
 Check cooling
 Replace motor
O&M TEAM GHPP 27

28. GENERAL PROBLEMS AND TROUBLESHOOTING
Problem Probable cause Action
 Control fail  Relay breakdown
 Lack of control voltage
 Check relay
 Replace feeding
 AC supply fail  Relay breakdown
 Lack of AC supply voltage
 Check relay
 Replace feeding
 Water high pressure  Water stream misadjusting  Check streams
 Oil level (Alarm maximum)  Level indicator malfunction
 Oil over-temperature
 Excess of oil
 Check relay
 Replace feeding
 Oil level (Alarm min)  Level indicator malfunction
 Leak of oil
 Check level indicator
 Eliminate leak
 Replace oil
O&M TEAM GHPP 28

29. O&M TEAM GHPP 29