Three-phase Transformer Basic Guidelines 2022 | Daelim Belefic

Electric power is the engine of our economy, and power transformer is highly important for the power industry. There are two types of power transformer: single phase transformer, and three phase power transformer. They are both very common in our daily life. 

So what are the types of three phase transformer? Where are three phase transformers used? You may have many questions about three phase transformers. Check out today’s article to find out the answers. 

What are the types of three phase transformer?
Where are three phase transformers used?
How to test three phase transformer?

three phase power transformer

1.What are the types of three phase transformer? 

For power transformers, we can distinguish by different attributes. 

1). By cooling system: There are oil immersed transformer and dry type transformer. 

Oil immersed transformer is filled in with mineral oil or vegetable oil as cooling liquid. And some oil immersed transformers need cooling fans on the radiator, to improve the heat dissipation. 

Now let’s take a look at the cooling system. Transformer with mineral oil immersed call “ONAN” cooling, which means “oil nature air nature”; if with cooling fans, it will be called as “ONAF”, which means “oil nature air forced”. If the transformer is filled with vegetable oil, the cooling system will be called as “KNAN”, if with cooling fans, it will be a “KNAF” transformer. 

Dry type transformer is produced with cast resin, without any cooling oil, but the cooling fans can be added as optional accessories. So dry type transformer without cooling fans, the cooling system is called “AN”, which means “air nature”; dry type transformer with cooling fans, the cooling system is “AF”, which means “air forced”. 

2). By installation: There are pole mounted transformer, pad mounted transformer, and substation type transformer

Pole mounted transformer usually has smaller rated capacity, so they can be installed on the telephone pole. The installation of pole mounted transformer are as follows: 

a). The transformer platform on the column adopts a double-pole equal-height arrangement. The commonly used poles are 12-meter and 15-meter non-prestressed concrete poles. The installation method of the transformer is side-mounted, and the high-voltage lead is drawn from the side of the overhead insulated wire.

b). The position of the center line of the transformer and the integrated distribution box should be consistent with the center line of the channel steel.

c). The horizontal inclination of the transformer and the integrated distribution box shall not be greater than 1/100 of the root opening of the platform.

* Process specification of pole mounted transformer:

First of all, the transformer must meet the design requirements, and all accessories and spare parts of the transformer must be readily available.

Secondly, the appearance of the transformer body and accessories must be carefully inspected, and the requirements of no damage and deformation must be met, and the paint is in good condition.

Finally, the oil tank of the transformer must be kept in good sealing, there is no oil leakage or oil leakage, and the oil level at the oil mark is normal.

three phase pad mounted transformer

Pad mounted transformer has many advantages such as small footprint, convenient operation, high application benefits, flexible combination methods, and high operational safety. electric equipment.

Installation of pad mounted transformers

The pad mounted transformer is relatively firm, saves materials, has a low cost and is easy to maintain. Generally, it is built on the ground with bricks or stones and concrete. The terminal of the high-voltage line can double as the starting rod of the low-voltage line.

The height and top area of the platform depend on the size of the transformer. Usually, the height of the platform should be 1.5-2.0m. When the height is less than 1.5m, a fixed barrier with a height of not less than 1.7m should be installed around it. Keep a distance of 1.5m between the barrier and the live part. Each side of the top of the platform should exceed the transformer shell by 0.3m. Generally, the length is 1.5-2.5m and the width is 1.0-1.5m.

Substation type transformer has bigger capacity than the other two types, the installation work is harder and need a professional engineer team and worker team to support. 

Substation type transformers have a solid foundation. The foundation is generally made of bricks and stones, and the surface is plastered with 1:2 cement mortar. In order to ensure safety and prevent people and animals from approaching the live parts, a fence or fence with a height of not less than 1.7m should be set around the transformer. m, the gate of the fence or fence should open outwards. The grid spacing of the fence and the net distance between the lower horizontal fence and the ground shall not be greater than 200mm.

2.Where are three phase transformers used?

The application of three phase transformer is also different based on the type of three phase transformer. 

Three phase pole mounted transformers are a very important part of the power transmission system, they are mainly used in telephone pole. You can find pole mounted transformers around street, farms, and near power substation. 

Three phase pad mounted transformers are including in the power distribution system, they has advantages such as easy installation. Three phase pad mounted transformers are mainly used in crypto mining farms, data centers, solar energy farms, etc... In our daily life, you can also find three phase pad mounted transformers near school, office building, hospital, park, even in your front yard. Pad mounted transformer filed with vegetable oil can be installed indoor, with mineral oil can only be installed outdoor. 

Three phase substation type transformer is the core of a power substation, core of the electric power system. They transfer the high voltage from the power plant, to the middle voltage in the substation, to the low voltage for the end users (factory, hospital, mining farm, public utilities, etc...). You can see the three phase substation type transformers in power substation, near power plant, factory, etc... Also there are some end users will need substation type transformer to transfer the middle voltage to low voltage, such as crypto mining farms, data cengers, etc... 

three phase transformer

3.How to test three phase transformer?

Three phase transformer testing items are also different based on the type of transformer and the standard of transformer. 

Basically, three phase transformer need to do the factory tests as below: 

 Resistance tests of all windings
 Ratio tests on the rated voltage and all tap connections
 Polarity and phase relation tests at rated voltage
 No load loss at rated voltage
 Exciting current at rated voltage
 Impedance and load losses
 Applied voltage test
 Induced voltage test
 Full wave impulse test

three phase power transformer test

Some customers might have special requirements on the testing items, such as lightning impulse test, temperature rise test. Those special tests are not including in the standard factory testing items, will need extra testing fee. Customer should inform the manufacturer that if they have special testing requirements, if so, what testing they need to do, so the manufacturer can add the testing cost in their transformer quote. 

For customers in USA and Canada, they might need UL or CSA certification & listed for their transformer. UL listed is for USA market, but also we have CUL which can be used in the Canadian market. 

The difference between UL and CSA is that if the manufacturer passed the UL listing inspection, their UL listed can be used everytime for the suitable transformer, no need to do UL testing everytime. But CSA listed need to do everytime when the customer needs, even it’s the same transformer, CSA will do one more inspection and testing to give the CSA listed. And for CSA listed, the voltage limit is 46kV, they are not able to do listing for bigger transformers with higher voltage. 

For UL listed, Daelim already applied and can produce up to 4000kVA, 34.5kV with UL certification. For CSA listed, customer should inform us that if they need it, if CSA listed is needed, we will contact CSA group in China and add CSA testing cost in our quotation, also put CSA inspection time into our production time, which usually take 2 weeks. 

For testing reports and certifications, Daelim has SGS test reports of three phase pad mounted transformers, from 500kVA to 3000kVA; CSA test report for 5MVA 44kV three phase substation transformers; CESI test report of single phase pole mounted transformers; and IEC type test report of main power transformers. 

transformer nameplate with UL

Daelim has over 15 years of experience in the designing, manufacturing, testing and shipping of three phase transformer. Our production range includs three phase oil immersed transformer, pole mounted transformer, pad mounted transformer, substation transformer, and main power transformer. 

If you have any projects needs three phase transformer, no matter it’s public tender, replacement, or direct purchase for your company own use, welcome to contact Daelim team for a suitable solution and fast delivery. 

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