Lowered Power FACTOR when Synchronised

[gulfgate]

Does synchronising, Diesel Gensets (1MW) ten in Number to a BUS bar system, Already having Power, Reduce the POWER FACTOR of the entire SYSTEM in synchronisation?

The Power Factor Drops from 0.8 to .65 only when the NEWLy INSTALLED 1MW Diesel Gensets are synchronised to the system. Are there any Suggestions as to what might be creating this problem?

 

[mdshunk]

My knee-jerk reaction is to guess that maybe they aren't synced as good as you think they area.

 

[CAPS]

I don't know anything about your generator controls, but an under-excited generator will have a lagging power factor and a over-excited one will have a leading one. This is one method of power factor control.

Apparently I like the word "one" today, but I think you know what I mean.

 

[coulter]

Does synchronising, Diesel Gensets (1MW) ten in Number to a BUS bar system, Already having Power, Reduce the POWER FACTOR of the entire SYSTEM in synchronisation? ...

The way you asked your question, it is hard to answer. I'll try and answer what I think your are asking.

Adding the new gens will not change the kw or kva of your loads. That means the pf of your loads don't change.

So why does your pf indication change? That depends on where you are measuring it.

Again the way you asked your question, my assumptions are:
1. you have an external power source coming into the site. Possibly a centeral generation, or perhaps already on-site large generation. This is where you are measuring the pf.

2. You added 10 meg capacity and now the pf reading (as measured above) is different

So what happened?

Well as CAPS said, if the new generators were under-excited, then they would appear as a heavy inductive load, drawing vars. The only place for these vars to come from, is your other generation. The pf meter on the other generation would then indicate a lower pf.

The answer to your question that you didn't ask, is fix the var sharing controls, or increase the base excitation to the new gens.

carl

 

[nawao]

Well as CAPS said, if the new generators were under-excited, then they would appear as a heavy inductive load, drawing vars. The only place for these vars to come from, is your other generation. The pf meter on the other generation would then indicate a lower pf.

The answer to your question that you didn't ask, is fix the var sharing controls, or increase the base excitation to the new gens.

carl

To solve this problem you should reduce the droop control from the AVR in order to increase the base excitation to the new gens.

 

[chaterpilar]

A low powerfactor indicates that the voltage of the incoming generator is higher than the bus voltage, try using fine trim to reduce the voltage, and you will see the increase in power factor.

Secondly check whether droop setting of the new incoming generaor is same as the rest of them. (typical value is 2%)

Cheers.

 

[gulfgate]

UPDATES from GULFGATE

UPDATES from GULFGATE

Thankyou all for the Very possible answers to the problem. But since the Question requires more DETAIL here are some.

BUS BAR VOLTAGES: 6.6kV (Main Transformer Secondary)
INcoming VOltages: 33kV(Main Transformer Primary)
Secondary Side Power Factor Reading(Excellent=0.8
BUT Problem occurs at the PRIMARY SIDE Power FACTOR(DROPS to 0.65)

Primary SIDE SOURCE=NATIONAL GRID.

Reconfirmed exact TIME for POWER Factor DROP:
When ALL BACK UP power is Switched ON (which are 2,30MW GT's,the 10 new Diesel GEnsets all synchronised), in the event of trying to reduce load on the GRID, The Problem OCCURs at the GRID SIde.
This causes Extensive VAR Losses to the GRID, That cannot be accounted for (Revenue) and hence Power Company requires us to REDUCE load, even though our system RUns at 0.8 pf at the Transformer Secondary and we use only about 5% of Total LOAD. Remaining are supplied by OUR Backup gensets.


I just want to make sure that there are no INTERNAL reasons, for this Bizzare phenomenon. I will check to adjust Individual GENSET Excitation Controls, which are usually auto compensated.

 

[mivey]

Sounds like your generators are providing the kW for the load and National Grid is providing the kVAR. Do you have your generators set to provide VAR for the loads? If the pre-gen load has an 80% pf, you should provide the same kVAR (or the minimum you can get away with, assuming National Grid might provide some with no penalty).

 

[gulfgate]

HI mivey,
If Pf is 0.8, Correct me if I am wrong, from the power triangle for the generator, THE KW and KVA would Coincide, and KVAR supplied by the internal GENSET side would be LOW as it is required to Supply only a LOW AMOUNT OF Kvar.ALso there are parallel Capacitor banks,that improve power factor,reducing KVARS/

Since Transformers are Always rated in KVA, would it be impossible to KNOW if the STEP DOWN TRFR in this takes up KVAR? Would a CAPACITOR BANK at the PRIMARY SIDE OF this improve the COndition.But do companies do that?

And if the GRID, PF is LOW, 0.65, then Why is this VOLTAGE CURRENT, PHASE Difference PRESENT only on this side?

 

[wirenut1980]

If the meter measuring this power factor is at the Grid service point, then in my experience, you will get screwy power factor readings due to the small amount of load going through the service point (5% loaded). For example, whenever I am measuring power factor at an industrial plant, my monitor will show an "expected" power factor during normal loading, but when the plant shuts down and loading through the CT is very low, and power factor readings are always very strange.

Another thought is can the meter measuring the .65 power factor differentiate between leading and lagging power factor? The reason I ask is that maybe your capacitors are fixed banks and the .65 pf is actually leading.

A transformer will have a certain amount of lagging (inductive) VARS depending on the amount of current flowing through it (the other variables are basically fixed). If it is only 5% loaded during the periods of poor power factor it is likely contributing very few inductive VARS.

 

[mivey]

...due to the small amount of load going through the service point...

Good point. I was just assuming they were only picking up a portion of the load.

 

[mivey]

HI mivey,
If Pf is 0.8, Correct me if I am wrong, from the power triangle for the generator, THE KW and KVA would Coincide, and KVAR supplied by the internal GENSET side would be LOW as it is required to Supply only a LOW AMOUNT OF Kvar.ALso there are parallel Capacitor banks,that improve power factor,reducing KVARS/

Since Transformers are Always rated in KVA, would it be impossible to KNOW if the STEP DOWN TRFR in this takes up KVAR? Would a CAPACITOR BANK at the PRIMARY SIDE OF this improve the COndition.But do companies do that?

And if the GRID, PF is LOW, 0.65, then Why is this VOLTAGE CURRENT, PHASE Difference PRESENT only on this side?

I'm not sure what you mean by the kW and kVA would coincide. The genset should provide the VAR needed by the load. For example (just guessing at some load numbers):
Before the 10 MW diesels: 60 MW, 75 MVA, 45 MVAR, 0.8 pf
Bring diesels on line to provide 10 MW and 0 MVAR: 50 MW, 45 MVAR, 67 MVA, 0.74 pf

Are the capacitor banks only brought on when the generators run?

Not sure exactly what you are asking about the transformer but, transformers are rated in kVA which is made up of both kW and kVAR so the transformer sees both.

Capacitors are normally on the load side. At the transmission level (above 69 kV), you will normally use a generator to provide the VAR needed. At 33 kV, there very well could be a capacitor bank installed.

I would doubt the National Grid pf is low.