Hi!

I had a problem recently regarding the balancing of load of the paralled generator. Can you give me some details on how to perform some adjustment for speed droop so that the load is equally distributed? Why is it that sometimes the kw reading is same for two generators but the amperes are different? Thank you and waiting for your reply.

Our system uses electric governor.

 

Hello Luigi,

Well, first of all few tips.

Let us say 2 gens are running in parallel, then then it is advisable to keep the gens in isochronous mode and use 1% droop in AVR.

Also check the Kvars sharing of the two gens they should be saame (Max tolerance 2.5%)

If you reduce the voltage of Gen 1 then its PF will increase but its KVAR will reduce.

Everything is related to speed and voltage...

Good luck!!

 

I believe the gensets shall remains in DROOP to allow voltage and frequency (thus Q and P) to equlize and get the load shared

 

Hi Sir,
Thanks for your help. I really appreciate your effort. The other problems is that I don't have any experience checking kvars sharing setting & even adjusment. How can i check kvars in % I'm only sure the voltage adjustment using voltage trimmer. Can you send me proper way of balancing of two parallel en set.

Thanks for your help.
Luigi

 

Hi Sir,
thanks also for your help and input. I don't still understand on how the droop is being check, what are the paramenters need to check & adjust to get the laod shared.

Thanks again Sir. I really aprreciate your inputs.
Luigi

 

Re your question on how to set the generators, I would recommend the following:

1. Try to determine the droop characteristic of your generator controllers. This is done by varying the speed of the generator (put mor load or less load) and see the speed difference. Keep in mind that droop is defined as the speed change (in %) required to achieve full load from full speed no load condition. From the load increase and the speed change you get from your test you can determine the droop characteristics of your gensets.

2. The same test can be repeated (or use the same test to determine this) to determine the droop characteristic of your gensets' voltage regulators. To help you here you must have a kVAr meter. Again determine the kVAr load increase and the voltage drop. From it determine voltage regulator droop. This test may be tricky as voltage regulator will also compensate for the kW increase on the generator.

3. Finally from the genset documentation, find out which control settings (trimmers, or other forms of settings) you can adjust setpoint and droop of speed and voltage.

Ideally the genesets should have the same speed setpoints and droop settings and the same voltage setpoints and droop characteristics for propoer load sharing. In practice you may have to compromise on your settings to get the required load sharing you desire.

To help you, you can start the tests with the generators running at full speed but without any load, and running seperately. This will give you the nominal setpoints for speed and voltage for each generator. Then do the load tests described above, and from the two tests you can plot the response curves for the gensets. From then you can determine the sharing you expect to have when they run in parallel.

One other important note, ensure that the prime movers are running at nominal temperature when you do the above tests. A cold engine will have a different response to loading than a hot engine, for the same settings.

 

Thanks. I have another qustion. I'm noy vey well versed in electrical power engineering so I could not understand some of the terms. Like how to keep the gen set in isochronous mode and this using 1% droop from the avr(how?) How to check the kvar sharing of two gen. pls explain in a simple way. I appreciate sir your info.

Many thanks,
luigi

 

First of all you need to make a distinction between speed control and voltage control. Isochronous control refers to speed control, and this control mode makes the control system maintain exactly the nominal frequency of your generator (i.e. 50Hz, or 60Hz as applicable). Normally such control mode is intended for stand alone generators. Operating a generator in such a mode with other generators in parallel will either cause the generator in isochronous mode to take all the load variations, or else cause a power oscillation between the generators.

On the other hand the 1% droop referred to in the AVR, is the parallelling capability of the AVR with respect to, mainly, reactive power sharing. In this respect to measure the reactive power you either need a reactive power meter, or else a power factor meter fitted as part of the genset instrumentation. To check the sharing simply read the reactive power from the above-mentioned meters (from the MVAr meter it is direct, from the PF meter you need kVAr=VIsin(pf)). To set the kVAr sharing, you need to follow my procedure mentioned in my earlier posting.

 

dear Jojo,
first of all thank you for your info. I'm in industry for quite long time but never do any adjustment like this. My friend told me also that adjustment can be done using voltage adjuster in the panel refer as vad, during parallel operation tune the voltage knob adjuster of each genset until desire sharing (amp) is attain. Is that right too.

Luigi

 

Before proceeding, please take a class or do research. Done improperly dangerous currents and torque can damage equipment.

Important points to know is the voltage regulator is NOT the power adjustment. In a parallel system, it is the reactive power adjustment and to a point it has some voltage control. Do a search online for finite grid and infinite grid for more on this subject. The current diffrences you are seeing between gensets could simply be one is taking the reactive power. Balancing the AVRs between sets should balance the reactive current load.

The prime mover throttle is the only power adjustmet. Your wattmeters should give an acurate indication of the power delivered by each genset. Adjust the governers so the gensets pick up part of the load and properly share it.

If the gensets are providing the same power to the load, but the amperages vary by quite a bit, the answer is in the adjustment of the voltage regulators. Before messing with them, please do some research or training. Done improperly, it can lead to excessive current, core saturation, overheating of windings and core, leading to destruction of the genset.

Done properly the regulator can provide stable regulation and balanced currents from the gensets.

If your load is reactive either leading or lagging, you want the gensets to share the reactive load equaly. This is adjusted with the voltage regulator adjustments. Many gensets have a current transformer which feeds the avr to help control PF in parallel operation.