Transformer

I am S.Karthick was born on 1991 at Neyveli, situated in Tamilnadu,
India. I had completed my Diploma in Electrical and Electronics
Engineering in 2010 and Bachelor’s degree in Electrical and
Electronics Engineering in 2013 at IFET College of Engineering,
Villupuram, Tamil Nadu, India. Now I am currently working in kuwait
at kharafi National as Electrical Engineer. I have published two
national journal. My areas of interests are power electronics, Power
system issues, computer networks and electrical machines.
Karthi.myeee@gmail.com

 Core
 Winding
Tank
 Conservator
 On load tap changer (OLTC)
 Buchholz Relay
 Pressure Relief Device
 Bushing
 Breather
 Oil & Winding Temperature Indicator
 Cooling Fan With Motors

 The core consists of three column, parallel, laminated
cold-rolled non-aging silicon-steel having high
permeability and low hysteresis loss.
 The steel sheet is thoroughly coated on both sides of
each sheet with insulating properties to reduce eddy
current losses to minimum.
 Structural rigidity is given to the core by the use of
steel plates at the bottom of the core.
 So that distortion due to short circuit stresses or
transport handling is prevented.

 The OLTC provides uninterrupted voltage regulation of
transformers under load. The voltage is regulated by
changing the voltage ratio(16steps, rated
voltage10%). This is done in steps.
 The transformer is equipped with a tap winding whose
tapping's are connected with the tap selector of the
OLTC.

This is the reason that the OLTC is designed
for immersed installation in the transformer
tank to keep the distances from the tap
winding terminals to the tap selector short.
The OLTC is activated by a motor drive. Drive
shafts and bevel gear units mechanically
connect the motor drive to OLTC head.

 Most of faults in the transformer are accompanied
by the generation of gases due to decomposition of
oil and insulating material.
 However, if such a fault is limited within a
small scale, gases are generated slowly and collected
at the ceiling of the tank cover while rising in the oil in
the form of bubbles.
 If a serious fault happens, gases are generated
abruptly to increase the hydraulic pressure in the tank,
causing the oil flow toward the conservator or pressure
relief vent.

 The Buchholz relay is mounted halfway in the course of
the pipe connecting the conservator and transformer
tank to each other.
 It operates the alarm contact against slowly generating
gas or the trip contact against abruptly generating gas.
 The Buchholz relay be consisted with housing, two(2)
float, alarm & trip contact.

 The pressure relief device is attached on the cover
of transformers. When the internal pressure in
transformers rises over the standard value, the
diaphragm is operated to prevent the explosion of
the tank.
 When a flow is occurred in the transformer oil, which
leads the radical increase in pressure, this increased
pressure make the tank burst. However it does not
have the strong bursting power as much as
hydrogen, acetylene and air.

 The Dehydrating Breather is connected with
conservator or gas oil sealed tank with pipe
which was located to see the stand point and
protect the dust and moisture come into the
conservator or gas oil sealed tank by the
transformer breathing.
 The dehydrating breather is separated from
main body for shipment and reassembled on
the site.

 Oil & winding temperature indicator
measures the top-oil temperature and
winding
temperature.
 It is a standard instrument for cooling, control
and protection for transformer.
 temperature indicator is consisted with
casing, sensing system, capillary tubing and
switches.

• In our plant we are using two types of transformers.
 Power transformers.
 Generator Transformer (15.75 KV/275 KV )
 Unit Transformer (15.75 KV/11.5 KV )
 Station Transformer (132 KV/11.5 KV )
 Coupling Transformer (275 KV/132 KV )
 Dry type Transformer
 LCI Transformer (11 KV/2080 V )
 Exciter Transformer (11 KV/860 V )
 Auxiliary transformer (11 KV / 415 V )
 Instrument transformer.

 An outdoor, oil-filled generator transformer is
provided to transform the generator voltage up to the
electric utility’s 275 switchgear voltage level
 The following accessories and feature are provided
 On load tap changer with AVR on HV winding
(± 8 x 1.25%, 17 steps)
 Sudden pressure relay with alarm and trip
contacts
 Pressure relief device with indicator and trip
contact
 Liquid level gauge with alarm contact
 Buchholz relay alarm trip.

 Thermometer with alarm and trip contacts
 Current transformers
 Lv terminations suitable for isolated phases bus
duct
 Hv terminations suitable for 300kv oil filled
cable connection.
Major components:
 Conservators
 On-load tap changer
 Transformer hv bushing chamber
 Buchholz relay

 Pressure Relief device
 Bushings
 Breather
 Neutral sf6 circuit breaker
 Oil and winding temperature indicator
Conservator:
 In rubber cell conservator, the oil surface is
completely isolated from the atmosphere by
installing an oil-resistant rubber cell in interior of
the conservator, so that atmospheric pressure is
always maintained without the necessity of
employing intervening mediums.

 The outside of the rubber cell attached on the inside
of the conservator is filled with insulating oil.

ITEM NO DESCRIPTION PARTICULARS
1 Rated power 218/290 MVA
2 Design ambient temperature
3 Rated voltage HV 275KV wye connected
4 Rated voltage LV 15.5KV delta
connected
5 Vector group reference YND1
6 Type of cooling ONANA/ONAF

 An outdoor, oil-filled generator transformer is provided
to transform the generator voltage up to the electric
utility’s 275 switchgear voltage level
 On load tap changer with AVR on HV winding (± 8
x 1.25%, 17 steps)
 Sudden pressure relay with alarm and trip contacts
contact

 An oil immersed, on load tap changing transformers
suitable for outdoor installation under the service
conditions.
 The transformers shall be able to operate for 30 seconds
with voltage of 1:3 times rated voltage.
 The mechanical and electrical design of the transformer
and their accessories will strictly follow the IEC standard
60076,137,214.
 The following accessories and feature are provided
(± 8 x 1.25%, 17 steps)
contacts

contact
 Thermometer with alarm and trip contacts
 Lv terminations suitable for power cable
connection.
 Hv terminations suitable for power cable
connection.

3 Rated voltage HV 275 KV wye
connected
4 Rated voltage LV 132 KV wye
connected
5 Rated voltage TV 13.2 KV delta
connected
6 Vector group reference YNyn011
7 Type of cooling ONAN/ONAF

 Unit transformer is a oil-immersed and two winding
transformer .
(± 8 x 1.25%, 17 steps)
contacts
contact

Thermometer with alarm and trip contacts
Lv terminations suitable for power cable
connection.
 Hv terminations suitable for I.P.B connection.

3 Rated voltage HV 15.75 KV
4 Rated voltage LV 11.5 KV
5 Vector group reference Dyn11
6 Type of cooling ONAN / ONAF

 Station transformer is outdoor, oil-immersed and
three winding, HV winding 275kv wye connected ,
LV winding 11.5kv wye connected, TV winding
6.25kv delta connected.
(± 8 x 1.25%, 17 steps)
contacts
contact

Thermometer with alarm and trip contacts
 Lv terminations suitable for power cable
connection.
 Hv terminations suitable for power cable
connection.

2 Design ambient temperature 55° c
3 Rated voltage HV 275 KV wye connected
4 Rated voltage LV 11.5 KV wye connected
5 Rated Voltage TV 6.25 KV delta connected
6 Vector group reference YNYn0(D11)
7 Type of cooling ONAN/ONAF

 Auxiliary transformer are outdoor, oil-immersed and
two winding transformer, Hv winding 11kv delta
connected, LV winding 0.433kv wye connected.
 This transformer is provided with radiators for
cooling the oil.
 Winding temperature indicators with alarm and trip
contacts
 It is equipped with off circuit tapping switch for
voltage variation of ±5% in steps of 2.5%

MAJOR COMPONENTS:
 Oil temperature indicator
 Winding temperature indicator
 Dehydrating breather
 Pressure relife device
 Magnetic oil level gauge
 Buchholz relay

1 Rated power 2500 & 2000KVA
2 Design ambient temperature 55° c
3 Rated voltage HV 11KV delta connected
4 Rated voltage LV 0.433KV, wye
connected
5 Vector group reference Dyn11
6 Type of cooling ONAN

 Only the Core is similar to power
transformers.
 End Frames are Electro Galvanized and
bought on finish basis.
 The windings are made of Bare and Fiber
Glass & Enamel Insulated Copper
Conductors.
 Windings are made on special steel molds
with Fiber Glass Mat and Epoxy Resin
Insulation.

 FG End Blocks and Cylinders are required
prior to Core-coil assembly.
 Enclosure is required at least 30 days before
testing.
 Core-Coil assembly is put in the enclosure
and complete assembled transformer is
tested.
 The Dry Type Transformer is dispatched in
complete assembled condition after testing.

Two special-purpose transformers are
uses to take measurements.
potential transformers
current transformers.

Transformer

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