Power factor correction - over compensation 4

[safy2004]

Hello,
A poor power factor can be improved by adding power factor correction capacitors to the plant’s distribution system. Correction capacitors provide needed reactive power (kVAr) to the load.
If some thing happened by an Inadvertent mistake, and the compensated reactive (capacitive) power is more than the inductive power, then the load is going to be capacitive, so what are the effects of this (capacitive) load on the MV and LV distribution network?
Is there any dangerous on the switchgears,circuit breakers, transformer, cable, and all other items of the distribution system?
Thanks.

 

[waross]

Too much capacitance will raise the voltage. Back in the day when bulk correction was common, The voltage could be driven high enough to cause very early failure of the lighting in a plant on the weekends when the lighting was almost the only load.

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

 

[crshears]

The overvoltages Bill mentioned are the worst problem with this situation, although not the only one...

Re: the question "If some thing happened by an Inadvertent mistake, and the compensated reactive (capacitive) power is more than the inductive power, then the load is going to be capacitive, so what are the effects of this (capacitive) load on the MV and LV distribution network?" the answer is that it depends on what the mistake is...

If by inadvertent mistake too many capacitors are placed in service on the distribution system during heavy load periods, not only will the distribution voltage rise to an intolerable level, but the total apparent power flow through the transformer could exceed its [their] rating, as the excess [lagging] reactive power supplied by the capacitors but not drawn by the load will flow out of the transformer to the supply side.

If by mistake the load is shed but the capacitors remain in service, the main problem to deal with will be high distribution system voltage, which can indeed rise to dangerous levels depending on the circumstances.

Transformers with underload tapchangers and automatic ditribution voltage regulating schemes may well go to bottom tap in an attempt to buck the voltage down into the normal range , and if while at bottom tap load is lost the voltage may rise unacceptably. Provided the facilities to do so exist, operators will routinely and pre-emptively remove capacitors from service in this situation.

The power engineer may arrange to have primary off-load tapchangers moved to a different tap in order to provide the operating staff with enough 'tap room' to address such situations, although this may not always be possible since such changes may well reflect back into the MV system, altering its characteristics; addressing such things can thus become something of a balancing act.

Unfortunately, short-sighted owners / financiers often demand miserly system design, engineers reluctantly provide it, and power system operators roundly and repeatedly curse it for years...

CR

 

[unclebob]

Capacitors will burn out from overvoltage stress.

 

[bacon4life]

Depending how the network operator charges for reactive power, the plant might be subject to unexpected power factor charges.

Highly capacitive loads are harder to interrupt than resistive loads. It might be possible switching device may not operate as expected. For example, a lineman might take a current reading at a 15 kV fused cutout before deciding whether to it is safe to use a loadbuster tool. Since the ammeter does not indicate power factor, he might not realize that the plant load was highly capacitive. One particular model of loadbuster can interrupt 900A of normal load, but only 120 amps to a capacitor bank.