Synchronized Generator Current

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Thread Starter

Barbican

Hi guys

I got two generators that are synchronized. When the breakers for the both gensets closes while the outgoing feeder is open, the ammeters shows current around 90 amps on each phase. What is causing this ?

The gensets are 500KVA

Thanks
 
barbican,

We presume by "feeder breaker" (sometimes called the "tie" breaker) you are referring to a breaker downstream of the two genset generator breakers that connects the output of one or both of the gensets to a grid or large load. And, further, we presume there is no transformer on the output of either genset--either before the generator breakers or after the generator breakers--providing some impedance between the two generators before the feeder breaker.

What happens when only one generator is operating at rated speed and the feeder breaker is open? Is there current showing on the phase ammeters? If so, what's the magnitude of the current?

Are you certain that when the gensets are synchronized to each other with the feeder breaker open they are not supplying a small load (lights; pumps; fans; etc.)?

It's not uncommon for small gensets when being operated independently of a grid or larger load to provide power to local, smaller loads (sometimes called "Auxiliary" or "House" loads) consisting of lights, pumps (fuel and/or cooling water), and fans (compartment ventilation fans; cooling water hear exchanger fans; etc.).

The other thing that happens when two gensets are synchronized to each other and the governors are <i>not</i> properly tuned or something has changed to cause the previous governor tuning(s) to need to be changed is that one generator can be supplying current (positive current) to the other generator--which has actually become a motor and drives the prime mover (a reciprocating engine or hydro turbine or small steam (or "expander") turbine). This is also called "reverse power" for the genset which is being "driven" or receiving power from the other genset--and is generally not good for the genset (there are, or should be, reverse power relays to protect against this phenomenon).

Hope this helps! If you can provide more information, we might be able to offer more insight.
 
Barbican... what you are "seeing" is a high circulating-current between alternators.

It is the result of their internal EMF's (technically Air-gap voltage magnitudes, Egp1 and Egp2) being unequal.

What are their terminal voltages, Vt1 and Vt2, before the synchronizing breaker is closed?

Regards,
Phil Corso
 
I apologize for the late reply and i appreciate your guys support.

In details, The two gensets are rated for 500KVA and are connected to a synch panel which has two Motorized circuit breakers one for each genset, and a main outgoing (feeder) breaker, there is no load connected behind the feeder CB. The problem is that when the outgoing feeder is ether closed or open, we are having reverse current between the generators, some times it shows up as +KW on one genset and -KW on the other (in the range of 80 KW's, some times vice versa. As soon as the gensets are synchronized to each other with both breakers closed, the current starts to rise up to 190 Amps on each phase in matter of seconds. as i understand it is that one of the generators is motorizing the other, some times genset 1 motorizes genset 2 and some times the opposite happens. I have checked and tested all the control, Speed and Voltage to make sure the synch panel has control over them, nether does the synchroscope show any frequency slip, so your guys help would be very appreciated, any ideas on what i should test or if there is something i have missed ?.

PS

The open circuit voltage on the both sets are identical, 460VAC on both of them with a frequency of 60HZ stable.
 
Barbican... just prior to closing the breaker used for synchronizing:

1) What is the difference between the two voltage magnitudes?

2) Which one has the higher voltage?

3) What is the speed-differential between the two?

4) Which one is the faster?

Phil Corso
 
Phil

I have commented on your questions below,

> 1) What is the difference between the two voltage magnitudes?

The voltage difference between the two voltages, is plus minus delta 3 volts.

> 2) Which one has the higher voltage?

Both has equal voltages

> 3) What is the speed-differential between the two?

plus minus delta 3 RPM's (Rated engine speed 1800 RPM)

> 4) Which one is the faster?

Both are the same.

I am using Comap Inteligen to synch the sets together. I got 7 other setups like this one working perfect with no problems.

Thanks again.
 
Barbican... The voltages and speed should not, repeat, should not be the same.

I believe you need to review your Synchronizing Procedure! I suggest you Search Control.com's archives for "Sync" or "Synchronize"

Phil
 
B
This happens because of your fuel governor insensitivity/control loop. Contact the diesel engine vendor for fuel governor control loop check and adjust accordingly. governor droop settings to be fine controlled.
This phenomenon can be reduced by putting series reactor or transformer in between the common voltage bus and individual generators.
 
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