Distribution Transformers

Transformer is an electrical device which, by the principles of electromagnec inducon, transfers electrical energy from one electric circuit to another, without changing the frequency. The energy transfer usually takes place with a change in voltage and current. Transformer either increases or decreases AC voltage.

Trans Power Soluons is manufacturing wide range of oil cooled distribu]on and medium power transformers and is o ering a complete electrical soluon to customers. TPS is focused to cater the requirements of private & industrial customers and o ers best & opmal soluon to the situaon.

Distribu]on Transformers are designed & manufactured in accordance to IS 1180 Part 1 ( 2014). Due consideraon is given to understand the requirement, and thereaer our markeng team o er appropriate soluon to the situation. Our team is experienced enough to suggest soluon for HT Protecon, LT distribu]on network & panels.

TPS is manufacturing all its products under stringent quality control & standard and is catering the requirements of industrial customers. The team of engineers having rich experience in design, producon & markeng are involved to manufacture the transformer and thereaer test the transformer for all roune test as per standard for validaon of design and to ensure fulfillment of customer requirement.


The magnec core of the transformer is built up of cold rolled grain oriented silicon steel laminaons. Hi – B Grade & Laser scribed laminaon is used to reduce the No load losses and noise level of transformer. CRGO Laminaon are cut at an angle of 45 deg and core leg & core yoke laminaons are interleaved in mitre joints in order to facilitate the passage of maximum magnec flux within core construcon. This reduces No load losses, No load current & Noise level.



The Windings are designed to opmize dynamic, thermal, mechanical & electrical stress depending upon the current & voltage requirements. Depending upon current requirement & design criteria, di erent types of windings such as Spiral cross over, connuous Disc, Helical windings or paral interleaved winding are used. The winding machines are equipped with hydraulic break system which ensures the proper tension is maintained during the formaon of winding. Dovetailed key spacers are employed to give the extra strength to the winding. Axial & Radial cooling ducts in and between secons of the windings allow the free flow of oil around the conductors.


The magnetic core with the windings and some accessories fi.ed together forms the acve part of the transformer also called core & coil assembly. The windings are slipped over the core legs & laminations of the upper yoke are interleaved.

All connections between windings and bushings & tappings to tap changer are made. The Tap changer allows the increase or decrease of a certain no of turns in the high voltage winding in order to compensate for a voltage drop or to adopt the transformer to an unstable supply so that the rated low voltage can be maintained. Subsequently, the top cover, on which the bushing for high voltage and low voltage are already fixed, is field.



A Transformer should contain no traces of humidity, otherwise, there will be danger of flash over within the windings. The acve part of transformer is completely dried before transformer is filled with oil under vacuum. The tank with acve part in it, is connected to an oil supply and placed inside a vacuum chamber. A vacuum is applied & when the required vacuum is reached, the oil is admitted into the tank. The rising oil drives out any remaining air & acve part is completely submerged.



Tank fabricaon drawings are prepared in Auto Cad. The system determines the opmum size and the number and locaon of required tank supports. Occasionally the corners of the tank will be rounded o  to further reduce the transformer weight without sacrificing quality and reliability.


The objective is to reduce the tank size and weight as much as possible, which facilitates easier handling, transportation and installation on site. All tanks are designed to withstand full vacuum as specified in CBIP Manual and are manufactured from high-quality steel sheets.All MS parts are grit blast cleaned to remove weld spaer, mill scale and oxides, providing an excellent surface for the adherence of the primer and paint. The inside of the tank is painted with a white color oil resistant paint to create good visibility during internal inspection.Tanks are tested for welding leaks through die penetration test ( Magna Flux ) there are the complete tank is tested for oil tightness via penetration and pressure test at the tank manufacturer place. Further, the complete assembled Transformer is again tested for 24 hrs leakage test aer complete tesng through a oil pressure head to ensure that no Seepage is possible in any case.


We use sasfactory protecon against corrosion & rusng. All surfaces of steel parts are shot blasted cleaned to remove weld spaer, mill scale and oxides, in compliance with Swedish standard SIS 055900 to SA 2.5 quality prior to painng. This provides an excellent surface for the adherence of the primer Thereaer tanks and steel are painted with one primer and two final coats with minimum thickness of 160 microns.



All transformers are subject to all roune tests in our in-house tesng laboratory confirming to latest naonal and internaonal standards. Tests are intended for evaluang the basic validaon of design, performance parameter, safety & reliability of the transformers. TPS is equipped with adequate digital precision meters such as power analyser WT- 300 of Yokogawa (Japan). WT – 300 is used for measuring the load losses, Impedance voltage, No Load Losses & no Load currents. All tesng & measurement equipment being used are duly calibrated from NABL labs & records are being maintained for customer’s verificaon.

All Transformers are  subject to all roune tests. This includes the following tests which is in house facility.


  1. Insulaon Resistance Test ( Megger Test)
  1. Resistance measurement of winding.
  1. Turns Rao Test.
  1. Polarity & Phase sequence test.
  1. No Load losses & No Load current measurement at rated voltage & frequency
  1. Load losses & impedance voltage measurement at rated current.
  1. Break down voltage test for insulang oil.
  1. Dielectric test
  1. Leakage test of complete transformer.


Type tests are special tests which are oponal and are carried out at addional applicable fees, to be born by the customer. These tests are organized at independent test labs such as CPRI & ERDA. They include 1. Lightening Impulse test. 2 . Short Circuit test 3. Temperature rise test.


Standard Distribution Transformer Specifications

Standard Distribution Transformer Specifications
Installation Indoor or Outdoor as per customer requirement.
No of Phase 3 Phase.
Frequency 50 Hz
Voltage Ratio 11/0.415 kV
22/0.415 kV
33/0.415 kV
Insulation Class Class ‘A’ / Class ‘B’
Vector Group Dyn11 or as desired by customer
Winding Material Copper
Tappings (Off Load Type) Generally +5% to -10% in steps of 2.5% on HT winding.
However, it can be offered  as per customer requirement.
Termination As per customer requirement.
Cooling ONAN ( Oil Natural Air Natural).
Cooling arrangement Corrugated tank or with Pressed steel Radiators as per customer
Colour As a standard, we offer paint shade as Seimens Grey (RAL 7032),
however  colour paint shade can be changed as per requirement
of customer.


Following Standard, fi.ngs are provided in general as standard for all rangs, however in case if the client insist for any extra oponal fi.ngs, The same can be provided at adadditionalost.


  • Rang & Diagram Plate .
  • Drain cum boom filter valve.
  • Earthing Terminals.
  • Cooling radiators.
  • Liing Lugs.
  • Uni / Bi – direconal rollers.
  • Thermometer pocket .
  • Explosion vent with diaphragm.
  • Oil level indicator.
  • Oil conservator with drain plug.
  • Air release hole with plug.
  • Top filter valve.


  • Bucholz relay with alarm & trip contact.
  • Marshaling box.
  • Oil Temperature indicator with alarm & trip contact.
  • On Load Tap Changer OLTC.
  • Winding temperature indicator with alarm & trip contact.
  • RTCC ( Remote Tap Changer control ) Cubicle.
  • Magnec oil level gauge with alarm & trip contact.
  • AVR ( Automac Voltage regulator).
  • Pressure release valve with alarm & trip contact.

Cable box on HT & LT Side.



  1. Transformers are manufactured in accordance to IS : 1180 : 2014 / IS : 2026 for temperature rise, dielectric test & insulaon levels. Transformers for exports /overseas requirements are designed & manufactured in accordance to IEC 60076.
  1. The overload withstand capacity of transformer is as per IEC 354.
  1. Tolerance applicable for no Load losses, Load losses, Total Losses, Impedance voltage & Voltage rao are in accordance to IS 1180.
  2. Tapping rao for standard transformers is +5% to –10% for high voltage winding variaon.
  1. Distribu]on Transformers are with oil natural air natural cooling and generally with Copper conductor for both primary & secondary winding.
  1. The transformers are supplied both with pressed steel radiators and with corrugated tanks.

Maximum Total Losses (Was) for 11 kV DT as per IS 1180 ( Part 1)

  1. For Transformers with Voltage class above 22 kV and up to and including 33 kV, The permissible total loss value shall not exceed by 7.5% of the maximum total loss as per above table.
  2. For Transformers with Voltage class above 11 kV and up to and including 22 kV, The permissible total loss value shall not exceed by 5% of the maximum total loss as per above table.

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