Load Sharing

Hint: if two identical pumps are running in parallel in a piping circuit, one doesn't get twice the flow as when one pump is running.

Hint: if four identical pumps are running in parallel in a piping circuit, one doesn't get four times the flow, and one doesn't get twice as much flow as when two pumps were running.

Why? What happens when the system (i.e. the load in this particular case) characteristics are considered?

More input is required.

1) The governor response is not the same in all the sets.One has to study the behaviour pattern of each set and adjust the setting.

2) Do you get this problem when the load is steady and balanced.

3) Do you get this problem cropped up suddenly or at the time of synchronisation

4)When is the load applied to sets, Is it while synchronising or after bringing all the sets to parellel.

This problem has to be studied in detail for proper solution, for which detailed input is required.

thanks ramvinod.

anothe findings , that the frequency / speed in Gen sets control panel (GCP) can be adjusted thru manual speed adjuster button, eventhough all genset run in auto mode.

the manual speed adjuster button in each genset found not same , and I think it will affect to distribution of load in each gen sets

What do you think ramvinod?

The GCP controllers of woodward are automatic, this means that the voltage bias and speed bias signals sent by these GCPs to the DG sets automatically depending on the configuration set on these GCPs.

Manual provision is just to increase/decrease the speed/voltage manually.Auto mode will override the manual setting.

Hi Adrian, Are the synchronization lights out when the generator is connected, and are the voltages the same? A small voltage difference can cause one generator to hog the load...Clintb32

Hi adrian,

Are all the gen sets started and paralleled automatically.

As electrical load increases or decreases is adjustment carried out automatically i.e. do gen sets start up, parallel, and shut down as per load requirements or do gen sets start automatically and paralleling carried out manually.

Hi Mobi,

All starting process in control automatically.

Each Genset will start or stop based on the total load Should 7 gen sets , but the GCP monitor that the load can be hold by 5 genset , 2 two genset will be commanded to trip),

Another findings, that there are manual speed adjuster in each Genset control panel , which still in series connectin with GCP (although it is in auto mode), and the setting is different in each genset.

Increase /decrease speed can be done thru this knob.which is not pure automatically any more.

Suspect the different setting in this knob as the cause of unbalance load in a sets gen sets.

What do you think Mobi?

Adrian, this could be your problem, as you suggested.

I am not sure how your system operates, but can the speeds/voltages be set with all controls in manual and increasing loads from 1 gen set through to seven i.e. from no load through to full load, ensuring when each gen set comes on load it does grab the required % of load.

If not the particular gen set (sets) can then be sped up or slowed down manually, whatever is required. After it is all set go back onto automatic control.

adrian,

This actually this should have been one of the very first things you looked at. On each gen you should start and run offline and adjust the freq (speed) and voltage dead nuts on. Use a good meter, don't rely on the panel meter unless you know you have good meters out to .00. Same with volts. Get them all as close to the same as possible.

If you have the system capability to parallel up gens but NOT take load do so. Adjust your gens offline and then put them on the bus with no load so you can verify that you have no current runnig between the units.

Then apply load and determine and /or set load share.

Adrian:

1. By process of elimination try to determine which gensets do NOT have load sharing problems. Then concentrate your troubleshooting efforts on the generators that do not properly respond to adding or dropping significant loads, when attempting to synchronize or run them in parallel, with the units that share loads normally.

2. Are all the prime movers identical or of the same manufacture and/or type? Example: It would be dificult to parallel and keep in syncronization a reciprocating and turbine engine, even if their respective generators were the same KW, because they respond differently to load changes.

3. Verify that your current system load is not exceeding the combined KW of the gensets that you are attempting to synchronize or run in parallel.

Mariner

As stated already a bit more info is needed for anyone to be helpful.

Are you in startup? If so...then certainly, with 9 gen sets you should have a rep there, either from the switchgear maker or Woodward.

Which model of GCP? Are you using LS breaker modules? It initially sounds like your load share lines are not talking but without better info it's hard to say.

Check all the obvious...

Go for Computer Based Optizers for Load sharing.Avilable from Volvo and likes.

Is this Woodward GCP computer based?

This is a classic case of one generator trying to hog the load, and will happen if that generator is running at higher speed than others.

1. Check whether all generators are in isochronous mode.

If they are in droop mode, all gennies should have same droop setting.

To avoid the droop tuning keep all of them in isochronous and test.

2. Are the load sharing lines connected? if yes are they in right polarity?

You did not mention whether you are in the process of commissioning or this problem has cropped up after the gennies have been running well for some time?

This is a very important input and the troubleshooting will differ in each case.

Good luck.

Do let us know the status of the problem..

i have the same problem.i have two gen set caterpillar 3412 and 3508.the latter are more bigger kw.when parallel the 3412 take the bigger load 350kw the 3508 take only 50kw.when i open the breaker of the 3508 the 3412 will not carry the load and will going to shut down.the 3412 has a capacity of 600kw while the 3508 has 650 kw.i got 480 volts 60 hz .and what makes the power factor not the same the other lag and lead the other one.i check all the ct's and pt's..i am using 2301a woodward load sharing module..can u guys help me on this one...thanks Roland of saipan