Know more about 25 kv oil immersed transformer - DAELIM

25 kv oil immersed transformer

This article is about the 25 kv oil immersed electrical power transformer. DAELIM transformer have rich experience in every voltage class power transformers.
We can provide you 25 kv transformer with the best quality and best service, our engineers team and sales teams are very professional, we will give you our best solution to meet your project requirement

Pad-mounted Transformer

We can provide you single phase and three phase pad mounted transformer

Dry-type Transformer

Type:Cast resin; Rated Capacity: Up to 25MVA; Rated Voltage: Up to 36KV;

Pole Transformer

TypeCSP type Frequency: 50/60Hz; Rated Power: 5~167kva

Oil immersed transformer

Frequency: 50/60Hz Rated voltage:10kv, 20kv,30kv Rated Power: 400~2500kva

Click below for quick review of 3 phase transformer

Basic tech spec requirement of the 25kv oil immersed transformer

Transformer shall comply with the requirement of BS 171: 1970, IEC60076, and any other related international specification. Any deviations from the specifications shall be mentioned as a specific item in your offer & be highlighted in the technical schedule.

The transformer shall be of Oil Natural Air Natural (ONAN) or ONAF oil filled type. Any other type if proposed by the Contractor shall be approved by the Buyer. The high voltage windings shall be provided with tapping from +7.5% to -7.5% in steps of 2.5% steps with constant flux variations. The preferred winding connection of the Step up Generator Transformer shall be YNyn0d11 to conform to the vector group of other existing power transformers

a) The transformer must be fully protected against any internal fault or overheating. The transformer HV side shall be connected from 11kV cables from the Wind Farm indoor Substation to the 25kV side of the grid through a 25kV Circuit Breaker.

b) The transformer shall be equipped excessive oil temperature protection (alarm 1st stage, trip 2nd stage) system. Equally the transformer shall be provided with pressure relief device. The oil temperature and pressure relief devices shall be provided with auxiliary contacts for alarm and trip purposes.

BUSHINGS, CURRENT TRANSFORMERS AND TERMINATIONS of the 25kv oil immersed transformer

1 The transformer LV and HV windings shall be brought out separately through bushings.

2 The Transformer phases shall be clearly marked and labeled using the nomenclature R, Y, B, N for High Voltage and r, y, b for low voltage winding.
Marking shall be of stainless steel plate and clearly visible from ground level.

3 High Voltage Bushings:

3.1 The HV bushings and terminals and LV terminals shall be similar to existing ones to facilitate integration to the existing system

3.2 The air clearances shall be so coordinated that the probability of a flash over from the terminal of one winding to the terminal of another winding is negligible. This shall be as per IEC 60076.

3.3 The creepage distance of bushings must not be less than 25mm /kV based on the highest operating phase-to-phase voltage.

3.4 The matching terminal clamps to connect the existing 75mm2 copper conductor shall form part of the delivery. This will be appreciated during the mandatory site visit

3.5 The neutral bushing insulation shall be rated for full voltage since the system may at times be operated with the neutral ungrounded

3.6 All bushings shall be of the outdoor type mounted on the transformer top cover

3.7 The bushings shall be provided with suitable test point for testing bushing capacitance and Tan-Delta.

3.8 Insulation rating shall be 28 KV for temporary over voltages for a period of one minute and BIL rating of 95KV

3.9 The air clearances shall be so coordinated that the probability of a Flash over from the terminal of one winding to the terminal of another winding is negligible as per IEC 60076.

3.10 the creepage distance of bushings must not be less than 25mm /kV based on the highest operating phase-to-phase voltage.

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The TANK AND its TANK COVER of the 25 kv electric power transformer

1. It should be made of carbon steel or stainless steel, and should be equipped with lifting lugs for lifting and moving with a jack during transportation and transfer.

2. The base of the tank shall be so designed that it shall be possible to move the complete transformer unit in any direction without injury when using rollers, plates or rails.

3 All joints other than those which may have to be broken shall be welded.

4 The main tank body shall be pressure tested so as to ascertain the soundness of all welded joints.

5 The top should be bolted and fully painted to prevent rusting from getting wet when it rains

6 Tank top cover shall be separated from the active part of the core i.e. it can be removed without disturbing the winding core assembly which is completely separated from the top cover.

7 Inspection openings shall be provided as necessary to give easy access to bushing terminations, tap-change switch, core earthing links, internal current transformers and any other components required to be accessed during the process of repair, maintenance and tests.

8 Tank cover and inspection covers shall be provided with suitable jacking and lifting arrangements. Inspection covers shall not weigh more than 25 kg each transformer.

9 The tank cover shall be fitted with oil filled pockets for installation of the bulbs of the various temperature indicators. The pockets should be of such design so that the installation / removal of the bulb fittings should in no way interfere with the transformer’s main tank oil. Protection shall be provided where necessary for each capillary tube. The pocket shall be fitted with a captive screwed cap to prevent ingress of water.

10 The pocket shall be located in a position of maximum oil temperature at maximum continuous loading, and it shall be such as to permit removal of the instrument bulbs without lowering the oil in the tank.

The bushings of the 25 kv oil immersed transformer

LV Transformer connections:

2.1 The LV terminals shall be of the clamp-type suitably sized for the rated current and the design short-time rating of the transformer in accordance with expected maximum fault level

2.2 Non-metallic phase identification plates colored Red, Yellow and Blue and labelled r, y, b shall be done at suitable location on top of the Transformer bushes or transformer body, so as to be visible from the ground level.

2.3 HV transformer connections

3.1 The 25kV conductors shall be brought out through suitably rated HV bushings. The HV terminals suitably sized for the rated current and the short-time rating shall be consistent with the expected maximum fault level at site.

3.2 Non-metallic phase identification plates colored Red, Yellow. Blue and Black and labeled R,Y B and N shall be provided at suitable location on top of the transformer bushes, so as to be visible from the ground level.

3.4 The HV bushing shall be supplied with clamps to adopt to the existing HT connections.

Read my article on Know More About Tips of single phase transformer

Tank and Accessories of the 25 kv oil immersed transformer

The exteriors shall be thoroughly cleaned by shot blasting or other approved methods and given a priming coat and two under-coats of durable weather-resisting paint. The final coat shall be Epoxy base with pu paint. Shade light grey 631 of IS: 5.

The interior of the transformer tank and other oil-filled chambers shall be cleaned of all scale and rust by shot blasting or other approved methods, and shall be given the required coatings of oil resistant paint.

Customized 25kV Transformer

As a professional transformer supplier, Daelim can customize various types of 25kv transformers according to your technical parameters and requirements, such as: single phase transformer ,single phase pad mounted transformer ,substation transformer,distribution transformer and 3-phase pad mounted transformer.

Not only can meet ANSI, IEEE, CSA, AS, IEC, but also meet the US DOE efficiency value.

So, if you are looking for 25kv transformer supplier, please contact Daelim.

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About Bin Dong

Hello, I am Bin, General manager of Daelim which is a leading transformer manufacturer. If you have problems when you are looking for the equipment, what you need to do is tell us.

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