rise up in the grid voltage cause of cos phi inductive

[mottt]

spanish regulations, make me produce inductive power (over excited generator) when the grid is weak, and I got a low voltage group 1350 kw, and i start to control power factor, changing depending on the hour to satisfy the requirements of the grid ( in order to get more money from them)...and the grid voltage rise up from 400 to 430 or 435 v (the base voltage is 400) and the protection of overvoltage trips cause is adjusted on 105 % that means it trips when the voltage rises to 120 V... my question is:
could i rise the overvoltaje adjustement...in example to 10 %? cause i was thinking on modify the taps of the step on transformer but if i do it... i´ll got the same problem with the capacitive side (that voltage will drop) .... please any help will be great..... thanks a lot

 

[QBplanner]

I would not suggest you modify the Trx tap settings if they are the generator step-up Trx.

I am a little bite confused about 400V and 120V which voltage level are you using?
PF control may trigger the voltage flucutation problems depends on the system voltage.
THat is why most of the system generators control terminal voltage instead of PF control.

 

[mottt]

the voltage level is 400 V, and the spanish regulations order to support the grid injecting reactive current or taking reactive current from grid depending on the hour of the day (that is the consume at that hour).... THIS way the price of the kw per hour rise...and we get more money...
what i see about modify step up transformer is that the problem will move to the low voltage protection, cause the volts will go down when i´ll be on capacitive...
what do you think about changing the maximun voltage protection from 105 to 110 %??

 

[davidbeach]

You're on a rather soft system if your generators can push the voltage around that much. What is the 400V system voltage when you are at full power from the generators but at unity power factor (or as close to unity as you ever run)? If you are having overvoltage problems at/near unity you are probably fighting an LTC or voltage regulator that isn't expecting reverse power and is working against you. Your utility will likely need to fix that, though you may have to pay for the fix. If full power unity is near 400V and your voltage rise happens as you raise the excitation to produce more VArs, you may just find that your maximum VAr limit is lower than where you are trying to get. You might also be able to drive the voltage down through an LTC on your step-up transformer.

 

[QBplanner]

LTC transformer can not regulate voltage itself. In a strong system, LTC can regulate secondary side voltage in a certain range by using system Vars or local shunt compensation.
In a weak system, I assume your system is pretty weak and the POI fault level/generation capacity is less than 10. If that is the case, LTC won't buy you much.
Since I am not familiar with your system. if it is weak better use voltage control instead of PF control. Q & V you can only control one of them. in your case, better V.
I am not sure which type of O/V protection you are talking about. If it is your generator O/V protection, you may want to contact Manu.. If not, then probably you can modify from 105% to 110% I don't see any problems.

again, I am not a P&C guy but a system guy. Can't offer you further helps . Sorry!

 

[davidbeach]

Equipment doesn't generally much care for more than 110% sustained voltage. System needs to be brought under control. Running voltage control is another form of saying that your VAr capability is less than your scheduled VAr production.

 

[Hoxton]

Caution: generators are generally rated to + / - 5% voltage range (hence the trip at + 5% voltage).

Is your set connected to a 400V distribution system, in a factory say, then to the grid therough a 400 / 10kV transformer? If so, then you are in danger of putting all the factory equipment overvoltage.