Parallel Generators Power Factor Distribution

It is the characteristics of the load that determine the power factor.

Since the 2 are in parallel, therefore the load is the same for both, One generator is delivering almost all the reactive power required by the load while the other is delivering only (almost) active power. Therefore, I am afraid, your answer does not help here.

I am assuming the load is being distributed unequally, one generator is feeding more than the other.

Are there ammeters on the output of the individual generators?

IIUC, when generators are run in parallel, typically one is set up as the lead (I forget the right name) and one is set up to follow (again, I can't recall the name), which, I would guess, naturally leads to one generator taking up more of the load than the other.

If you wanted to experiment, you might be able to (manually) (slightly, slowly, and carefully) speed up the generator with the lower power factor. I think you would see it pick up more load and go to a higher power factor.

Note: I am not an expert in this field, and have little knowledge of the dangers of attempting to speed up a generator manually as described--maybe you want to wait for other advice. ;-)

Your experiment: You need to increase the voltage and not the speed. The speed will remain the same if you increaseit manually since they are in sync.

Increasing the voltage knob slightly will achieve what you aimed at. But it does not help on the long run.

The problem is in the setting of the Load sharing device that must be present in such a system: The 2 prime movers + Alternators have, each, a load sharing governor etc...

You will need to provide more information about your system to get an answer that will start you in the right direction.

Are you running in parallel with the utility or isolated from it? In island mode, isolated from the utility, vars are determined by the load and also affected by the balance of the voltage regulators. Do the math on what you are supplying to the load and you may find it does not equal what the gens are doing. For example if you are supplying 1000amp to the load and your generators are equaling 1400amp then an imbalance between the gens may be creating a circulating current between them.

Usually a system designed to run parallel with the utility will have var/power factor control and this may need to be balanced. Different systems are designed differently. I've seen individual var/pf controllers at each gen control a single control in the utility parallel control. Either way you still need to verify your regulators are balanced closely.

IF YOU ARE RUNNING TWO GENERATORS IN PARALLEL-

1.ARE THEY DIRECTLY SYNCHRONISED

2.OR SYNCHRONIZED THROUGH INDIVIDUAL GENERATOR TRANSFORMER SECONDARY SIDE.

3.IF THEY ARE SUPPOSE DIRECTLY SYNCHRONISED THEN THERE SHOULD BE SOME STEPS TAKEN

A EXCITATION CKTS OF TWO SHOULD BE CHECKED FOR AVR AND DROOP COMPATIBILITY-AND THE EXCITATION SHOULD BE CONNECTED THROUGH A CROSS DIFFERENTIAL CURRENT COMPENSATION SYSTEM.

IF THEY ARE SYNCHRONISED THROUGH A GENERATOR TRAFO EACH THEN ADJUST THE DROOP OF EACH UNIT FOR PROPER SHARING OF REACTIVE KVAR.

REMEMBER WHETHER THEY ARE IN SOLO OR PARALLEL WITH GRID THE PF SHARING SHOULD BE SAME FOR PROPER EFFICIENT OPERATION.

As per my practical knowledge, If active power shearing is same then look on reactive shearing. For that Increase voltage of low power factor OR decrease voltage of high power factor OR do both simultaneously to achive same power factor ie. 0.8 lag.

When two generators are running in Synch and both are loaded with almost equal kW, p.f. is affected by AVR setting. Check AVR setting

1. Mode of operation - voltage control / Field control? - Both should be in voltage control. AVR is kept in Field control for large machines during maintenance.

2. MVAr limit of both AVR

3. Voltage setting in both AVR - set both voltage setting to 1.0 p.u.

For further suggestion, give details of your system.

Mind that, it is not advisable to run generators at 0.6 p.f. and take corrective action.

Please check whether the AVR is in automode or mAnual mode. If in auto mode , change to manual mode and adjust the excitation suitably to achieve the var sharing acording to the load condition

The power factor of a generator running in parallel with other generators is nothing but the reactive load shared by that particular generator. The reactive load shared by a generator can be increased or decreased by increasing or decreasing the excitation current of the generator.The generator which shares more reactive load ( assuming all generators are of equal capacity) will show lower power factor. The total reactive load on the system is decided by the load power factor but the power factor of the individual generators is decided by their excitation ( rotor DC current).As the total reactive load is a load characteristic, if you try to increase the power factor of one generator, the power factor of other parallel running genearators will automaticall go down. This happens automatically because of the automatic voltage requlator of each generator.

PRIYADARSHAN

To better address the concern of Guest, here are some questions I would like to know:

1. Are the 2 Gas Engine Generators identical?

2. Are they running with a synchroscope?

Please provide me the needed information.

It is difficult to reply without knowledge of your system - is it manual? - or is there an automatic load sharing system?

1. The simplest system is when engine speed and voltage regulator have a standard fall of output speed and voltage from no-load to full-load. If the sets are adjusted to have the same no-load values, they will share in proportion to rating. In practice, there is "drift" of governor speed and AVR voltage with temperature and time, but with hand adjustment of governors and AVRs, the system frequency and voltage can be kept at suitable values and sharing can be achieved.
2. Typical values for 1. are that on each set working alone, frequency/speed fall 4% from no-load to full-load and voltage falls 3% from unity power factor to rated kVA zero power factor lagging.
3. The basic fact to remember is that governor frequency adjustments will affect active [kW] load sharing and AVR voltage adjustments will affect reactive [kVAr] load sharing. Interaction between kW and kVAr is characterised by kVar adjustments having small effect on kW sharing - but kW sharing adjustment will affect kVAr sharing.
   
4. If there is an automatic system, there are a wide variety of systems possible. A tight control of system frequency/voltage is possible, with the disadvantage that high control loop gains increase stability problems.

My applause to all contributors especially to 67Model for his very informative contribution. Job well done.

May I add something which will support 67Model.

1. I would like to reiterate that the control of kW load can be done by adjusting the governor. In effect, we are adjusting the speed/frequency of the generator, the result of which is the control in kW load sharing.
2. Control of kVAR load can be achieved by adjusting the AVR. In effect, we are adjusting the the voltage/excitation, the result of which is the control in kVAR load sharing.

Now going back to my query:

1. Are the generators identical?
   
2. Are they connected to a synchronizing panel?

These are very important in analyzing your system especially in the distribution of loads. Assuming these 2 machines are identical i.e. same Name Plate Rating, speed, they are in-phase upon synchronization, same polarity etc.

The question is, why one generator has 0.6 to 0.7 pf while the other 0.8 to 0.95? How is their load sharing?

If the 2 are running at the same speed their kW loads are the same or almost the same. The problem lies on their kVAR and kVA load sharing. The 0.6-0.7 pf generator delivers greater current, consequently, greater in kVAR load, hence, giving more kVA than the other generator. To lessen the burden in this generator, the higher pf machine should be adjusted by increasing its excitation (increasing its kVAR) to a level where both machines power factors are near with each other (load dictates pf of the machines). In this case, kVA delivers by each machines are almost the same.

Hope this will help us...

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"Iron sharpens iron"