MEP-804B paralleling issues.

[uscgmatt]

Good evening everyone,
We picked up an MJQ-48B power plant for work through GSA excess. They have a build date of 12/2010, but they are both like new. Everything works great except for the paralleling. I've followed the -10 manual and all I get on the synchronizing lights is a steady dim light, not the pulsating lights. The manual says this is caused by bad phase sequence. But both sets power a 3 phase motor in the correct rotation, so I dont think that's the reason. Has anybody encountered this before? Oh, this happens no matter which set is set to number 1 and 2. Thanks.

 

[DieselAddict]

Have you checked to make sure phase 1 of each generator match each other as well as phases 2 and 3?

 

[uscgmatt]

That's what I thought. Each gen has l1 l2 and l3 to their respective terminals. Plus I have a 3 phase motor hooked up to the distribution box and it spins the same way when each gen powers it. If the phases are mismatched the motor will change direction. Atleast that's what normally happens, this is my first dealings with these sets.

 

[DieselAddict]

Sorry to ask but you have checked on the generator end and the switchbox end?

You can have the generators out of phase with each other but the motor will still spin in the same direction.

As an example if generator 1 was wired to the motor as (gen-motor) 1-1, 2-2, and 3-3 you would get the same rotation as if it was wired 1-2, 3-1, 2-3. BUT.. You can see that the two generators would not be in phase with each other (2 and 3 are flipped on the generator side).

I'm not saying this is your problem but this is the easy error to detect since its just wiring.

Once you've ruled out a wiring error the troubleshooting moves to instruments and measurements.

 

[uscgmatt]

I see where you are coming from. As for the wire labeling its correct, but we know how that goes. I will trace them out from the gen head (T1-T10) to the switch box. Hopefully that will fix it. Thanks for the help.

 

[Guyfang]

Often, when I saw this sort of thing, it was a problem in the junction/switch box on the master set. Normally it was the power cable ends, or on the CB's in the box.

 

[uscgmatt]

That would have been to easy. Time to get deep into the manual.

 

[Guyfang]

Do you have the TM's and schematics for the PP set?

 

[uscgmatt]

I do. I just found one of the 2 paralleling/switch box cables had a short to ground, fixed that now to check the other.

 

[Guyfang]

Was it the control wires? The 4 small wires that are "safty" circuits to keep the CB's from closing when both sides of the cable are not connected?

 

[uscgmatt]

Problem solved. In the -10 it says not to close the ac circuit interrupt switch on either generator nor close the load contractors until directed to do so. I did not close the contactors in the in the distro box because of this. Come to find out, thank you schematics. You need to to feed the output board in the offline generator to complete the syncro light circuit. Now I can parallel, now I just need to bring my drash unit back for the 14kw load to see how it acts when paralleled. I wasnt very happy paralleling with 0 load. But I was taught to never parallel generators with no load, another point I dont like in the manual.

 

[DieselAddict]

Nice. Glad to hear you got it figured out.

 

[Guyfang]

Glad your fixed. I agree, the procedure is not clear. Back in the day, say 1973 or so, it was a much simpler procedure.