Capacitor loading on transformers

[cranky108]

Does anyone know where to find a good reference on capacitor loading of power transformers?

We are interested in the limits and issues with how much capactinance we can put under extreem conditions (stability limits).

 

[7anoter4]

The capacitance in series with transformer reactance will reduce the reactance and will expose both Capacitor and Transformer in a fault
case to a increased short-circuit current. The limit will be maximum permitted current up to protection acting time.

 

[magoo2]

I'm afraid I don't agree with 7anoter4.

Most capacitance, whether it be in lines, cables or capacitor banks is shunt capacitance. As such, it will not reduce the reactance and won't result in higher fault currents.

There are series capacitors, but these are used much less than shunt banks.

As far as transformer loading, you can load a transformer up to its MVA rating in Mvar provided you don't have any MW to go with it. There is no stability issue in my opinion.

 

[waross]

Drawing inductive VARs causes quadrature voltage drops.
Supplying capacitive VARs causes quadrature voltage rises.
Back in the days before power factor controllers were readily available or affordable it was common to correct the power factor of a plant by permanently connecting a bank of capacitors. Issues would arise in plants with a poor power factor during operating hours. Quite a lot of capacitance may be added to correct the power factor. Then in the night when the plant was not operating and the main load was lighting, the capacitors would drive the voltage up to the point of burning out lamps.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[7anoter4]

Thank you, magoo2.Of course I agree with you if the fault would be downstream of the capacitor connection point, but what if the fault will be
in the Capacitor itself some where let's say in the middle?

 

[7anoter4]

Practically you are right nothing could happened as anyway the battery reactance is far from resonance.
I encountered once a problem with a serially coupled battery used to reduce the transformer reactance in order to facilitate a rapid
reactive power injection .The receiver was a flatting mill supplied directly from a high voltage grid.
The huge battery was in resonance with the high voltage /medium voltage transformer connected with a 60 MVAr synchronous condenser.
In this case the short-circuit power of about 5000 MVA was brought down to medium voltage bus rated of 500 MVA only.

 

[cranky108]

After asking many questions, the concern is apperently the LTC of the transformer. It was reported, and I can't ask the guy because he has retired, that there is an increased burning of the LTC contacts on leading power factor.

Because of this concern, our dispatchers are not using the distribution substation banks. They instead use the transmission banks.

 

[jghrist]

One thing to be concerned with is resonance at or near a harmonic order if there are nonlinear loads. See IEEE Std 519, IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems