Cat 3306 - VR3 Troubleshooting 1

[Mztr45]

I have a new problem with my power plant on the boat. Had some maintenance done, including insulation tests. Went to put a generator on the bus and it wasn't producing voltage. Suspected fuses on the VR3, and sure enough they were blown. Put new ones in, switched it into auto mode and saw it start to ramp up voltage on the voltmeter and then dropped down to 0 again, fuses blown again. Figured the AVR is dead, wrangled up some "new" VR3's and have tried two different ones, not blowing fuses now, but not producing voltage either. Tried setting it over to manual (it's a 7C2700 controller on my swbd), still no voltage. Took some readings off the F1 & F2 and getting essentially 0 coming out (like 230millivolts). The L1 exciter stator is reading 4.2ohms so that appears to be good and resistance to ground on it shows OL so that's good too.

I've got a sneaking suspicion i've got a bad diode on the RFA but just want to exhaust all my options before I have to pull a bunch of stuff apart to get access to them.

And yes, I know the VR3's are obsolete, but it's what i've got and upgrading to VR6's at this time is last resort since it would be like a 150+ man hour job with the necessary cable runs and interferences. It's going to happen, just...not now.

Any other tests to do to nail this down further, or time to bite the bullet and get into the RFA and start testing diodes?

 

[waross]

And yes, I know the VR3's are obsolete, but it's what i've got and upgrading to VR6's at this time is last resort since it would be like a 150+ man hour job with the necessary cable runs and interferences. It's going to happen, just...not now.

And upgrading to a VR6 still won't cure bad diodes.
Did someone megger the field without disconnecting or shorting the rotating diodes?
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Mztr45]

Did someone megger the field without disconnecting or shorting the rotating diodes?

My question as well. No way to ever know for sure since I wasn't standing there when it was done. They did meg the field (F1 & F2) to ground, and the instructions include making sure those connections are lifted from the AVR prior to doing so. And these are guys I trust and they do it for multiple other boats with the same set up (except they have the VR6 upgrade done), so it's not like they're running around blowing up AVR's left and right. Accidents happen and i'm not mad, just trying to get this gen up and going again so we can get underway and work these buoys on the lakes.

 

[TugboatEng]

Found AVR's are usually dead AVR's. They don't get removed from service in working condition.

Diode Failure Scenarios Modes of Failure, Causes and Effects - MER Equipment

https://merequipment.com/wp-content/uploads/Diode-Failure-Scenarios.pdf

If you expect diode failure, inspect them before running the unit again as diode failure can cascade into exciter and rotor failure.

Are you getting a partial voltage form generator when it is completely unloaded? Residual magnetism should produce some voltage. If you are seeing none then the stator is shorter.

 

[Mztr45]

In general I agree, with found parts generally being unreliable. In this case, I know some of the ones I received were uninstalled to do a conversion to new digital voltage regulators.

Got into the gen today, pulled all the diodes, tested them, all were good. Since I had the end bell off, went ahead and gave the exciter stator windings a gentle wipe down. Tried flashing the field as per the manual with a 6 volt lantern battery. Moved on to next step as per the manual which was to hook up a big 12v battery to the F1 & F2 connections for the field winding and then ran the gen at half rated speed (900rpm), which it did start putting out voltage on the sensing lines, saw 139vac across 20 to 22, for reference my working gen reads 240vac across 20-22 and about 120ish on each individual sensing line. when it's at rated and in auto voltage mode. Moved on to next step, took the voltage droop rehostat out of the loop, remote voltage adjust knob out, put the jumper in from 4 to 7, took the voltage controller at the swbd out of the loop so the only thing hooked up to the avr was the voltage sensing lines and the exciter. And nothing. I'll see like 8 or 9 volts on the sensing lines and like millivolts dc on the F1 & F2 when running at rated speed (1800rpm). So i'm at the point where it says to fabricate a tester for the AVR using a 240vac source, a 100w bulb and a switch. Probably going to have a tougher time finding a 100w incandescent than getting those AVR's since everything is LED nowadays.

When you say partial voltage from the generator unloaded, do you mean partial voltage on the sensing lines with the engine stopped, or engine running? Or do you mean partial voltage on the exciter stator winding?

 

[waross]

I'll see like 8 or 9 volts on the sensing lines and like millivolts dc on the F1 & F2 when running at rated speed

Found AVR's are usually dead AVR's. They don't get removed from service in working condition.

There may be a connection here.

When you say partial voltage from the generator unloaded, do you mean partial voltage on the sensing lines with the engine stopped, or engine running?

Engine running at rated speed.
This is based on the assumption that the sensing lines are still properly connected to the generator windings.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!