Generators in Parallel Operation With Unequal Draw

A difference in voltages at the generator terminals and the difference in conductor sizes and lengths between each generator and the common point where the load is attached.

What type of load sharing are you using?

Is it synchronous, asynchronous or lead/lag?

I am curious to your answer, what are these load sharing types and under what factors do you apply them ?

Assuming that the engine governor droops are set the same then the engines will share the load according to the fuel supplied to each engine.

Synchronous load sharing - total kW generated is shared equally across all generators irrespective of their size.

Asynchronous load sharing - generator kW output is proportional to their size i.e. if one generator is twice the size of the others it will take twice the load.

Lead/lag - the lead engine will take most of the load until fully loaded, actually about 90%. As the load increases the next selected engine is loaded up and so on. Using this method you should cycle the lead/lag engines to ensure even running hours.

If your engines are synchronised monitor the fuel usage for disparity.

What is the load on the other one?

Was it noticed before?

If it was noticed before apply the same cure.

This may seem to be a stupid question...but are the generators' outputs synchronized? I assume you are trying to get additive current from two generators - each one putting out 200 amps. If they are not phase locked, the readings could just be showing you the sum and difference currents - not the actual current draw.

Once the two gennies are synchronised...watdefak,

the one running at higher speed will tend to take away the load and conversely the one producing more voltage will take away the kvars.

Try reducing the speed of the Gennie which is drawing higher current, and it will start taking lesser load.

Good luck

How are the two gennies' speeds to be different while maintaining synchronisation?

The oncoming generator has to have a slightly higher speed than the running generator, so that it takes load and does not trip on reverse current.

The phasing in a manual operation is also important that at the moment of connection, both are phased the same, if not, severe damage to both generators and anybody standing near them, could result!!

These type of operation should only be attempted by a fully trained person....

My understanding today is that the complete operation can be full automated and such knowledge is unnecessary....

Speed will only affect the frequency and KW, if the voltage is balanced on the two parallel generators and they are both in SYNC mode then try looking at your load sharing circuitry.

Only one factor in this case is considered, The Droop of Each Governor must be readjusted to be the same. The droop of a Governor of a generator (whatever its prime-mover is) is responsible, off course in parallel operation, for load sharing between any number of parallel generator.

Finally, you can even operate two non-identical generators in parallel (say 100Kva and 1000kva) by proper adjustment for the droop of each. Such that the load will be divided in a ratio of 1:10 respectively between these two generator.

Good Luck... Samak

Now how would I determine how much droop to apply ? Does it depend on the type of load or the running condition of each Generator ?

Is there some form of calculation or is done as neccessary as the load is applied ?

For adjusting the droop, there are controllers available like woodward.If you want to set the droop manualy, run each set and load the first set for 10% to 100% in stages of 10%, take the speed and frequency readings.similarly run the second set and load the set as said above take the readings of speed and frequency.both readings should match then only droop of both the sets are equal and then only the sets will share the active power proportional to the rating.

Each Governor has a droop setting tool starting from hydraulic type to computer based advanced one. generally, the droop setting is scaled numerically (may be per unit or per cent or ... etc.). Just set both to the same value.

Good Luck... Samak

You can balance the load by the exciters.

For sets to share the load proportional to the rating, there two elements, one is actual power and reactive power, actual power sharing depends on speed droop of the Engine and the reactive power sharing depends on output voltage and excitation of the alternator.

Both speed and voltage are to be controlled for proper load sharing .Nowadays good relaible controllers are available for controlling the speed and the vltage.

Load sharing really has to be accomplished by the generator governors which regulate the amount of fuel, steam or water flow depending on the prime mover used.

Adjusting load by varying the field voltage will have the potentially undesireable side effect of changing the VAR loading of the generators also.

This is analogous to running two centrifugal pumps in parallel piping. One doesn't get twice the flow.

Did anyone check the switches/contactors/breakers on the shiftless generator?

Hello,

The most probable cause is : not the same speed setpoint for both;

SOLUTION:

You have to reduce the speed of the one showing 400 A and at the same time, increase the speed of the one showing 0 amps.

Go very very slowly and watch the result

You are too vague. Are the units generators making DC current or are they alternators making AC.

Do you Know anything about the load sharing unit?

Load sharing units are manufactured by many Vendors like Siemens,GAC,Woodward ...

I have fair knowledge on these devices.

Ramvinod, you can share your knowledg please.

watdefac, you are in fact a bit vague for a question like this. Some of the answers above are correct and close but without the right info from you a good answer can't be given.

a. Are you running your gens connected to or isolated from the utility?

b. What kind of synch control, gov and load share control? I.E. Woodward 2301A with an LSM. Have you verified metering...that in fact 1 gen is pulling all the load?

c. Isochronous or droop. Unless you have really aged stuff it's uncommon to see droop sets these days, at least in these parts of the world.

Also, does your switchgear have VAR meters? Paralleled eng/gen speed differences affects KW...Volts affects vars.

Run each engine by itself unloaded. Check your freq which is directly related to gen speed. If you have a droop system the speed will be higher unloaded than loaded. You may not have this but you need to verify. Assuming you have an isoch control... run each gen not paralleled and unloaded. Verify and/or set each gen speed dead nuts to your system. i.e. 60.00hz. and use a good meter like an 87 not your panel meters. Don't set one gen faster...your sync controller will handle this with it's gain and damping. Only reason to have one unit faster is if you have passive paralleling.

Verify and set each gen voltage to be exactly the same.

Parallel the gens and run no load. Verify that you show no current, kw, or vars. If you have current flow with no load you have a cross current issue of circulating current between the gens that needs to be solved. If you see this get your gen service tech in to correct it.

Load up you gens (paralleled) and determine if they are sharing equal. If not determine if you have a Load Share Module or control. Verify the adjustment or have it verified by someone qualified to test. If you don't have an LSM VERY gently increase the eng speed on the unit with less KW until you are comfortable with the balance.

Take the gens off line and check freq on the adjusted unit to see how far apart they are. Parallel in several times to see that that is not affected.