Tap Changer on Transformer

Yes & NO

And what does it mean?

It means that from the dribble of information provided, a torrent of questions will be needed to ascertain a viable answer.

Are you frightened of using words or something?

If they already exist, why would you bother to take the tap changers out? Even if unneeded, they won't hurt anything.

@ Tornado

Actually, I'm going to install 18 units of 2500 kVA transformer. If I order them without tap changer, the price will go down more than USD 14.000. That's the reason I want to take it out.

Get an engineer (or doctor) to look at your problem. Before you make a very expensive mistake.

I think the doctor is the better option because it will be cheaper to fix your imagination.

Stop giving worthless comments!

You're OP

Suppose I have 6 units of generators that feed a busbar. From the busbar the voltage will be stepped up via 4 units of transformers.

Can I take out all of the tap changers from the transformers? As the voltage regulation will be done by the generators?

Post #5

Actually, I'm going to install 18 units of 2500 kVA transformer. If I order them without tap changer, the price will go down more than USD 14.000. That's the reason I want to take it out.

If you can't make your mind up how do you expect any one to take you seriously?

Would it make any difference between 4 and 18 transformers?

Quote "Actually, I'm going to install 18 units of 2500 kVA transformer. If I order them without tap changer, the price will go down more than USD 14.000. That's the reason I want to take it out."

Are you referring to a tap changer or transformers with taps? Big difference.

@ wareagle
It's transformer with the usual +/- 2 x 2.5% tap

There are just too many unknowns in the stated system to be able to say it is safe to take out the transformer tap changers and rely on the generator regulation.

A proper study and assessment of the customer's system and requirements is necessary (and worthwhile) before the order is placed with the transformer supplier.

Don't forget to get approval from the client (especially if the client originally specified or expects tap changers), after all you cannot put them in later after the transformers are built.

The SLD looks like this:

The distance between all of the generators and 11 kV bus is around 30 m.

I'm sure the generator can maintain the 415 V at the output, and therefore 11 kV at the main busbar. That's the reason I want to take out the off load tap on all of the 2500 kVA transformer.

I will supply you all 18 transformers with tap changing without the additional cost of USD 14,000.

Given the information provided I am a little concerned that tap changers may be only one of your problems. What you are describing resembles powering an 11kV power grid of a small town, city or large industrial park using generators in an island mode (complete isolation from the power grid) in the event of loss of (or rarer - lack of) grid supply.

I have only done one of these before and that was only 1-4 generators at 2500kVA total for a small town, and even then it was complex enough with all the CT's, VT's, circuit breaker, protection relay, load sharing and synchronization, etc required. Your project is much, much more complicated.

And yes my 2500KVA transformer was ordered with a tap changer and it was used for fine-tuning the output voltage.

I am only aware of a few sites in the world that currently use a system this large. Are you able to provide more information on this rather large application?

Is this an Australian mining site application where the generators are being used for black-start island-mode emergency supply?

Yes! It's an island mode of the main supply for Australian mining. The generators aren't used for black-start only, because they didn't connect it to other power supply.

When you say 'fine-tuning', it means for all of the transformers? Then you have to shut down the supply for "small town"? Why can't the generator do the voltage regulation?

I think the reasoning behind it was that the voltage regulation was still handled by the generators but the fine tuning (up to +/-5% output voltage step changes) was handled by the transformer tap changer. I think the main reasons for having it were to increase the output voltage to compensate for voltage drop. I think we did need to change the tap to increase the voltage during commissioning.

I don't know much about the generator output voltage regulation, it may be that the generator output voltage cannot be adjusted that much. The generator literature may offer some insight.

Yes! It's an island mode of the main supply for Australian mining. The generators aren't used for black-start only, because they didn't connect it to other power supply.

I thought so <cringe>. The fuel storage facilities and monthly bill must be enormous. Did the customer not look at other (cheaper and greener) alternatives such as a small natural gas power station?

It mainly depends upon the grid to which you are connecting. If the nearest recieving station has frequent load (reactive) changes due to more distribution lines feeding end level customers and the load flows are not controlled ,the voltage get more fluctuations. Indirectly it can be determined by voltage used for transmision. Generator transformer used at 400kv level wont use OLTC due to cost reduction and stability of grid voltage.

It mainly depends upon the grid to which you are connecting. If the nearest recieving station has frequent load (reactive) changes due to more distribution lines feeding end level customers and the load flows are not controlled ,the voltage get more fluctuations. Indirectly it can be determined by voltage used for transmision. Generator transformer used at 400kv level wont use OLTC due to cost reduction and stability of grid voltage.

Voltage controll by AVR of generator is possible upto certain limits only. After connecting it with a grid. The grid voltage cannot be controlled by your generator avr, it depends on VAR demand in the grid because voltage & VAR is related. Since you actually controlls the VAR output of your generator which cannot meet the system demand, so there is possibility of Under voltage trip. this can be controlled upto some level by using Tap changers.