Comments on: Parallel transformers benefits

By: Mathieu Guillot

Mathieu Guillot — Tue, 11 May 2010 12:08:47 +0000

The main parameter regarding circulating current is the transformers voltage ratio. They shall be equal as far as possible. For transformer with off load tap changer it’s important to check that the two transformers taps are in the same position.

By: Laurent

Laurent — Tue, 11 May 2010 09:02:48 +0000

thanks for your contributions and wish you the best for your surgery
Laurent M, moderator

By: Bhavani Prasad

Bhavani Prasad — Wed, 05 May 2010 15:02:47 +0000

In addition to the three points mentioned, there are two more obvious points – (1) same phase sequence and (2) same vector group.

By: Bhavani Prasad

Bhavani Prasad — Wed, 05 May 2010 15:00:53 +0000

This is a very important consideration which affects the installation cost. It does not affect the MVA rating of the incoming breaker from the transformer; But the outgoing breakers from the bus with more than one transformer feeding it will have to have a MVA rating corresponding to the feed from all transformers in parallel. If outgoing are many, it will blow up the cost. Designers prefer to put normal operation scheme without paralleling and provide buscouplers to have flexibility and transfer of load without break and also to obtainin or realize most of the advantages of two transformers in paralled

By: Bhavani Prasad

Bhavani Prasad — Wed, 05 May 2010 14:53:28 +0000

Operating identical (or nearly identical or equivalent) transformers does not pose problems. That is the transformers should have the same (1)voltage ratio, (2)same percentage impedance, so that load sharing is even at different loads, (3) protection to avoid flow of current from one to the other either as a fault current or a circulating current due to mismatch of internal voltage (terminal voltage will have to be the same as they are connected). Protection scheme will have to have reverse power relay.

Generally designers prefer to avoid parallel operation as operating personnel and maintenance personnel can create problems itf not adequately equiped. If parallel operation is provided to realize some of the advantages, then specific operating & maintenance instructions should also be dispalyed.

Transformer losses partly come down with parallel operation (Iron loss is not affected; But copper loss in comes down as it is proportional to the square of the current.)

By: Bhavani Prasad

Bhavani Prasad — Wed, 05 May 2010 14:41:28 +0000

…if one tr went down, the other would be switched in.” —– This is not transformers in parallel operation. This is a case of a standby being brought on line following a failure.

By: Huen Yeong Kong

Huen Yeong Kong — Tue, 04 May 2010 08:58:26 +0000

I am ending my participation on this blog. This is because
I shall be shortly going for major surgery in a local hospital.
Not being an expert, my remarks are basically armaturish.
Best regards to all of you. Please do not contact me by
email. Thanks.

By: Murugan

Murugan — Mon, 03 May 2010 12:45:26 +0000

sir,
i am an electrical engineer , work for saudi electricity company, i read your comment against parallel transformer benifits, it was very usefull to me , let me know the scematic diagram of the parallel connection of the transformer, then what is fs switchgear, i will be thankfull to you if you will reply to me

By: Murugan

Murugan — Mon, 03 May 2010 12:35:20 +0000

hi,
this is murugan , iam an elctrical enginner , i have been working as a project enginneer in transmission and distribution field , you gave some good needs, i want to know the parallel conection of transformer with single circuit line . i will be thankfull to you if you will give information about the above.

By: S.Khalid.Ali

S.Khalid.Ali — Tue, 27 Apr 2010 15:50:28 +0000

I work for Caterpillar Co; we usually connect our all generators in parallel those they output LV and then the Genset LV out put as each generator has its own MV transformer rating 13.8KV, then all transformers are connected to one buss-bar (we call it grid) through fs switch gear, mean each circuit has its own protection that is connected to grid. Furthermore, the advantage of raising the voltage is great as that decrease the diameter of supply conductor plus reduction of LV switch gears, as an example, we supply 10M Watts power at the distance of 200 meters through 4 500 mm2 cable that is almost 75% less copper conductor is used. Nevertheless, all that configuration required perfect design by professionals. As an engineer, that is one part of my activity as well. CAT trained their engineer and they have proper tool to train. I shall welcome any question if some body wants to explore it.