Reactive power regulation on the island power plants 6

[slavag]

Dear All.
Do you use Capacitor banks on the generation buses in case of island power plants?
On the one bus up to 4-6 generators and outgoing feeders.
Thanks in advance.
Best Regards.
Slava

 

[mgtrp]

We do not, as the generators provide the required reactive power for any connected loads. We've never had the situation where the reactive power requirement was so great that it might make sense.

 

[slavag]

mgtrp, thnaks for the answer.
Im agree with you.
But, I think about possible situation, that a generators will operated with cosPhi=1

 

[rasevskii]

The CosPhi of the operating generators on an island system will be the same as the CosPhi of the load, assuming that the AVRs are properly set up and cross current compensation circuits are working correctly. Unlikely that you will have loads with a CosPhi of 1, or purely resistive. There are always some motors and transformers around that will require some VARS.

You cannot use any kind of Power Factor (CosPhi) controller on the generators, that must be disabled on an island system. Exception: One small generator (say a heat recovery turbine) paralleled with other much larger units, could use a PF controller if the VAR output of that unit was small compared to the other units.

Note that PF control is usually a slow-acting function that shifts the AVR voltage setting of the concerned generator.

rasevskii

 

[waross]

I have two answers:
1> PF at 80% or better. The generator will run a little hotter because of the extra current but not above design temperature. In this instance it may be better to add some capacitors at the load to reduce the line current and the line losses.
2> PF below 80%. If the PF drops below the generator rating, the allowable kW will be reduced from rated kW due to thermal issues. The addition of capacitors will allow the generator to operate at 80% PF or better and full kW will be available.
Remember that the capacitors are supplying the VAR demand of the load and if a part of the load that is drawing energy at a low power factor is lost, the generator may become over-excited.
I prefer to add the capacitors as close to the load as possible, and connected in such a way that if the load is lost, the capacitors go with the load.

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

 

[catserveng]

I have done two island mode plants, 6 2MW units and 4 2.5MW units where we had to add capacitor banks for correction.

Both site were large construction sites, first a dam project in SoCal with VERY strict emissions requirements. The contractor liked to oversize motors, we had an N+2 plant, we could add more capacity to deal with the poor power factor, except our emissions controls on the engines did not work as well as needed (both DPF's and SCR's were required). We installed an automated 12kV cap bank with 4 MVAR capacity in 500kVAR steps, cap bank automation was done by PLC managaing load demand start/stop for plant. Plant was in operation for 2.5 years.

Second plant was the 4 2.5MW 480 units at a large excavation for a government project that lasted 3 years, also had very strict emissions requirements and same problems, used same type solution but got by with a smaller cap bank on that job.

In both cases the centrally controlled cap banks solved our operational problems and allowed for best possible engine efficiency and lowest emissions.

On the second site the intial attempt was to use local cap banks at certain poor power factor loads. On that job we were not responsible for the primary distribution, only know they had problems and the contractor asked us to apply the system cap banks after about 2 months of their mitigation attempts.

I can provide further details if needed on the dam project, on the second project I'm bound by an NDA.

Hope that helps, Mike L.

 

[slavag]

Dear friends, thanks a lot for your answers.
Special to Mike.
Im not need on this moment some technical details, answer: use or not use, is enough for me.
Have a nice week end.
Best Regards.
Slava

 

[Yuma]

Hi Slava,

We don't have capacitors in our islands.
All of our generators are cos phi=0,8, and are not run in cos phi control mode, but in voltage control mode.

Hope it helps.

 

[rmw]

Slavag,

I think this thread is mature enough and the subject well covered enought that I can now say it is nice to see you post. I haven't seen (and that may just be me) you on site very much lately and always enjoyed and appreciated your input to this site.

rmw

 

[slavag]

Dear rmw.
Thanks a lot for your words.

Always nice, meet a old friends again .

Best Regards.
Slava