Hi to all..

I have to synchronize 4 6.14MW generator and connect it with the local utility. My problem is, what is the right type of potential transformer or voltage transformer to be used. Regardless of the voltage,, im afraid the PT i will use might affect the phase angle and other factors to be considered in synchronising. Of corse when doing synchro, our sensing is connected in the low voltage side of the instrument transformer. Can anyone help me with these??

Thanks

 

Responding to Blackstoneboy's 04-Feb-09 (03:33 query...

What is intervining (utility) transformer's primary and secondary winding connecton arrangement?

Regards, Phil Corso ([email protected])

 

The system voltage of the generators is 13.8kv, while the utility is 34.5kv.. The power transformer to be used is YN-yn connected.

What about the Vts?? What connection will i use??
Does Vts also have phase shifts just like power transformer??

Thanks

 

Blackstoneboy... because the HV and LV winding connections of the power xfmr are both wye-connected then the phase-shift "seen" by the corresponding VT secondaries, is "essentially" small!

I said "essentially" because there is some phase-shift. Its magnitude and angle are influenced by:

1) The utility transformer's primary and secondary winding impedances.

2) The effect of taps (they change ratio and impedance) in the HV winding of the utility xfmer

3) Yes, the VT effects are similar to those of the power xformer.

4) The VT burdens will also influence phase shift.

Regards, Phil Corso ([email protected])

 

If it does have phase shifts, how can we guarantee the accuracy our system using these instrument transformers? As we know that synchronizing is very sensitive when it comes to phase angle and frequency.

Thanks for your kindness in replying to my inquiries phil. I really appreciate it.

Thanks...

 

Blackstoneboy,
It's not a question of accuracy.

First, I know of no syncronizing specification so sensitive that it can't meet a manufacturer's recommendations for voltage magnitude, phase deviation, and speed of closure.

However, my point was to make you aware there are several areas, that if ingored, could cause problems.

In my experience, the greatest potential (excuse the pun) for error occurs when xfmer taps are involved.

Regards, Phil Corso ([email protected])