Maybe somebody could help me with SR4B generator? 2

[g4rce]

I have realy big problem with SR4B generator.. The problem is that CDVR can't work properly well. It shows an alarm "Field overcurrent". Has anyone experience??? I was trying to find help at local distributor, but it was nothing..

 

[waross]

Posibilities;
Shorted revolving diodes.
Shorted exciter windings.
Shorted wiring from the voltage regulator to the exciter.
Shorted field winding.
Bad voltage regulator.
Have you checked the field current?
If the field current is not actually high, then you have a voltage regulator problem.
If the field current is high, check the rotating diodes and surge suppressors first.
yours

 

[itsmoked]

Was it working and just failed or sitting and now doesn't work?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[g4rce]

Yeah, waross, I've allready 3 times have checked all the things you are talking about... They were correct by the manuals of Caterpillar.. Itsmoked: it was working for 1 year untill this problem has began.

 

[waross]

What is the field current? Is it high?


Next step;
With the engine stopped, disconnect the field and apply a variable AC voltage to the field. This should induce a current in the rotor circuit without having to run the set. Now you can check the current/and or voltage at the rotating diodes.
If the current is high you have a problem in the main field. If the current is low,you have a problem in the exciter.
Note, shorted turns in the exciter field usually shows up as heating in the exciter field with AC applied.
What does CDVR stand for?
respectfully

 

[alehman]

How do you know the CDVR is good? Did you replace it?
Is this a PMG exciter?

I recently experienced a shorted exciter stator on a Cat unit, so don't overlook anything there.

waross: Caterpillar Digital Voltage Regulator

 

[g4rce]

Thanx, waross, I'll try to do it..

alehman, I've replaced 3 CDVRs, but at the ending it was the same result. Yeah it's a PMG exciter.. Metering with megohmmeter I have found that any insulation in main field and in exiter field was correct. Metering with multimeter I the test of main field, diodes, exiter was correct too..

One more question.This genset has very big vibration.. Can't it be a problem with main rotor???

 

[edison123]

The field overcurrent and high vibration indicate your main rotor winding has inter-turn shorts.

If you can access the main rotor winding, then do an ac volt drop test and see if the poles drop almost equal voltages (within 10%).

 

[g4rce]

thanx edison, but i can't get so easy near the rotor poles..

 

[mkees]

If I recall, you may be able to check the main rotor at the rotating rectifiers. Disconnect the output side of the rectifiers and I think that is the input to the main rotor windings. There is also a proceedure to check the the rotating rectifier assembly, did you perform that proceedure? Do you have the CDVR software, or CAT ET to set-up the CDVR?

 

[edison123]

I am sure you must be able to isolate the main rotor winding from the rotating rectifier. Then, you can do a RSO test / AC impedance measurement (to compare with original value) to confirm turn shorts.

*When you are in darkness, no point praying to God. Instead, Pay the Utility Bill*

 

[pmanole]

check settings for overcurrent protection.should be 12A

 

[JIMGEN]

If the exciter fields, exciter rotor and main stator and fields are within specs, and the exciter bridge is ok, then disconnect the vr and apply 12 DC voltage to the field wires, and run the unit. You should get voltage out of the unit and the voltage should be the same for all three phases. For Example on a 500kw set you will probably get a voltage in exess of 250volts.
This would be a good indication that the set is ok. Did you measure the exciter current and voltage with the unit running with no load?
Yes if you have vibration then one or more of the rotor poles could be partially shorted. Also if you run the unit with the vr you will quite often have trouble producing full voltage rating of the set. If so the vr may be over powered but also the exciter fields may be over heated. You can field ck the rotor as follows:
Again apply DC to the fields with the unit shut down and use a hacksaw blade to ck the magnetic field on each of the rotor poles. If one of the poles is starting to short you will notice the difference in the magnetic field.
I think you have a failing rotor which is not uncommon in the SR4 alternators.