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#3 Engine Generator


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In the test position #3 generator shows good freq's good volts in all three phases. When switch is placed to On generator falls off line and out light comes on no freq's no volts. We have changed the generator, the line contactor, the GCU and replaced the Contactor C/B and replaced the diodes and it stills does the same thing. Help Please we have troubleshot this for 2 days and still nothing.

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I have fought this same type of problem before, and it can be very tough to isolate. Do you get an error code on your GCU when this happens?

When you say you replaced the line contactor, shall I guess you mean the generator-to-bus contactor K53C? While that one does connect that generator to the switching system, it is not always the one that is causing the problem.

Without a contactor tester, it is a tedious and time-consuming thing to test the individual switches in the contactors. Then again, if you are lucky, you might try running the engine and watch the generator light while someone "taps" on the other contactors to see when the generator comes back on line.

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Watch each phase of the #3 Gen as you place it "online" to see if the voltage drops off. You will have to reset the Gen each time if this is not the issue... (Voltage may drop off on a single phase only)

Have you started #1,2or 4 first and see what happens?

Try to start #2, if the generator stays on line your issue is on the primary side of the # 3 bus contactor.

With #2 Gen online the K2 and K6 relays are energized. Power flows through the #3 contactor K7 (deenergized state) or Aux contacts.

If the Gen stays on line there is not a "Load" issue originating at the Main AC BUS or the Main TR's converting AC to DC to feed the Main DC bus.

Please post the results here so I can follow your Tshooting...

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Not specialist but trying to help on the bases of GCP if system is similar.

Loosing/tripping voltage and frequency once generator is connected to the bus means that “the generator is automatically disabledâ€. Disabling the generator is a function of GCP/GCU once receiving abnormal feedback signals such as:

1- Overvoltage condition sensed by overvoltage circuit within the GCP (if the case is actual it can be seen on the indicator as a voltage overshooting at the moment of switching ON.

Possible causes:

a- Generator malfunction.

b- Voltage regulator malfunction.

c- GCP malfunction.

2- Ground Fault condition (30 amps deferential) sensed by Ground Fault Transformers, there function is to monitor Gen Contactor wires (If Gen Output is low) they will feed back to the GCP to take the generator off the line in addition to removing the excitation field.

Possible causes:

a- Ground Fault Transformers malfunction.

b- Contactor wires malfunction.... Gen. Output circuit…. (Beyond my level to spot how and where to check)

Just one Q;

Was the malfunction accord once the generator takes the load of particular Bus or any Bus?

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Thanks everybody for the help the Ground Fault Transformer in the Engine fixed the problem. I Ohmed it and from pin A to Pin D on the tranformer it jumped in ohms from 1.0 all the way to 80. We ahd just changed the engine so I checked the old one and it read 1.0 ohms so I changed it and it worked like a champ.

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For about ten minutes it worked, then the GCU tripped it off again and right back to square one. After some careful trouble shooting we found that pins A and B on the current transformer cannon plug, right next to the Generator were wired wrong in backshop. We switched the wires back around and it fixed the problem. After seeing this I wouldnt doubt that the CT was bad from backshop too.

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Mike Bischoff & I lost two days of our lives that we'll never get back troubleshooting an ATM generator, after I asked about 5 people if they were sure everything was hooked up right, after an ISO cann. "Oh yea, everything is on right."

Turns out the T5 and T6 leads were swapped on the ATM generator. Worse thing was, they were marked with tape. Even worse thing was T6 had an old piece of tape on it that showed it as T5. I only blame myself though, should have started from ground zero. If I've told this story before, I apologize.

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