generator parallel operation

Why don't you just add some capacitors and correct your power factor rather than trying to find a way of distributing it evenly.

This problem is related to the difference in the voltage of both the generators. Setting of both the AVR may not be same. Diesel generator might have higher voltage as compare to the turbo generator. You may check and adjust the AVR setting of both the generators.

The diesel generator is producing more voltage and hence is hogging the reactive power.

a) Check no-load voltages of both generators,

b) Check droop of both generators in AVR. It is normally kept at 2%.

c) Check the voltage at say 70% load on each generator individually. ( They should be same)

Let us know the results.

Cheers

As suggested by other members, AVRs to be properly tuned and matched for droop.

Members have given very good suggestions.But can u throw some more light by giving the rating of the geneartors ,their out put voltage and excitation values .This may throw up some more good ideas.

Under the desired load, via the VAR (Voltage adjust rheostat) adjust both AVRs (Automatic voltage regulator) to where the amps are as low as they can go on each system, while maintaining acceptable bus voltage.

To have the amps and VARs track proportionately with load, you need to set up the AVR's droop capability. Depending on the model, there can be a droop resister with a sliding tap that is used for this function.

For 30 years now, we use cross current compensation CTs to 'talk' to each AVR if so equipped, for VAR sharing For the past 10-12 years, we use sophisticated controllers that are combination units that load share the watts and VARS automatically in the same controller (WW GGP30 series and the new EasyGen), or via a PLC. Check and see if the older unit can be fitted with a proportional actuator to match the other unit.

Call Woodward governor, or Basler Electric and tell them your set up and ask for a solution.

The generator suffers (not the engine) with high VARs in the form of rotor heat (excitation levels high to the rotor to drive the VARs) and stater winding temps higher (due purely to more amps coming off), so if the extra VARs don't harm anything, including the rotor or stater temperatures of the generators, maybe you do not need to adjust anything. I have loads that are 0.3 PF, and I don't worry, but I designed my generator (the alternator) to take it. The engine does not see VARs, only watts.

Take care of harmonics on line if there are sensitive pieces of equipment on the bus (PLCs). High harmonics may knock out a PLC or UPS computer that is controlling something critical. Then you will need some reactors on line as previously discussed.

I think this is a problem of excitation. However, find below my comment to the thread Recirculating current posted on 10/11/2007. I hope that it will help.

"It is expedient to have all parallel-running generators carry their proportionate share of total reactive load. To do this, they must each have the same generated e.m.f. - which is a function of field excitation.

However, where two generators are running under unequal excitation , the generated e.m.f.s would not be the same. This difference in voltage, E₁- E₂, sets up a circulating (or cross) current, I_c which is equal to this voltage difference divided by the total impedance of the two machines,

i.e.

I_c = (E₁ - E₂)/2Z

The main effect of the circulating current is the increase in kVAr output of the generator with higher excitation and reduction in that of the other. The additional loading, and the subsequent heating effects, limit the active power output of the former. There is also the lowering of the busbar voltage.

Adjustment of the machines' excitation will however correct this."

As pointed by others its purely excitation problem, which is due to performance of AVR and its setting. Pl check your AVR.

so adjust no load voltage ,same on the both alternators,same Hz,with set voltage pot.

each alternator with nominal load of 50% adjust droop pot ,to drop voltage about 2%.

later in parallel you can make fine adjustment ,but only on droop pot,carefully it is tricky.

about load sharing ,depend of governor ,diesel will respond quick because of electronic governor.

If both alts same and 2/3 pitch (ie Leroy, Newage etc) set droop same so on load and offload voltages match. They will naturally share

If mismatched or say Cat alts 5/8 pitch go with active var control, Woodward offer some controllers based on their own (EGCP) and Leonard Riglerbau they bought out (Easy Gen etc)

"Better" makes are

Suggest Deep Sea Electronics for operator simplicity on straight forward DG sets.

Comap for engineer solution say on Gas powered sets

Or Deif for wind power.

Cat Powerwizard, Cummins Power Command.... run... run away very fast ;)

JB

hello

DG with electronic governer has a voltage and speed regulation compared to the TG with mechanical governor. also for any sudden change in the reactive power requirement ( due to starting of large induction motor), the DG AVR shall respond much faster then the TG. The emf induced by the alternator shall be result of rate of change of flux density of rotor with respect stator and rate of change depends upon the speed and flux density depends upon the excitation current of the rotor. the resultant response to the sudden reactive power demand by the system will be met by the generator with better voltage regulation

The soltuion to your problem shall be setting the droop of the electronic governor to its maximum and reduce the respose time so that sufficent time is given to TG to take the load

Hope this wil solve your problem