CAT XQ400-3456 w/SR4B & VR6
CAT XQ400-3456 w/SR4B & VR6
(OP)
Experienced equipment failure within a load connected to a distribution system powered by the subject M/G.Point of L-L/L-G fault was transformer isolated from M/G 480 VAC output.During the failure, the M/G output went to O volts but did not trip off-line (output CB remain closed). After the fault was cleared/isolated, the M/G set was shutdown and restarted. M/G output came up normally. Is this an indication of regulator over-excitation shutdown? If so what would be potential causes? M/G is SE PMG.
Thanks





RE: CAT XQ400-3456 w/SR4B & VR6
As I remember the OEL is fixed at 90 VDC for 10 seconds, so if you go full field and the PMG has enough power to keep up, the OEL will stop excitation.
What kind of electrical protections are you using? Relying on the CAT control panel? What panel? If you had an event that required enough field to trip the OEL function in the AVR, the AVR stopped exciting and the breaker still didn't open, sounds like you have an improperly protected system.
Hope that helps,
Mike L.
RE: CAT XQ400-3456 w/SR4B & VR6
Thanks
Phil
RE: CAT XQ400-3456 w/SR4B & VR6
The standard CAT protection packages tend to have some holes in them, the EMCP3 is better than the EMCP II, but not easy to properly setup, and frankly, not as good as an off the shelf protective relay like a Basler GPS100. Since most packages this size go into standby systems, minimum protection is usually a good thing, that may not be the case in your situation.
The OEL as far as I know needs to see a full field condition for the time period before it shuts off, if the field output drops below the threshold and then goes back again, I don't think it is cumlative. I had a jaw crusher a couple of years ago the operators were overfilling and the motor would nearly lock, had a data logger on it and saw the field go full, voltage start to fall off, then the rock would break and the field would drop back down, this went on for about a week until they popped a couple diodes.
I never seen this AVR have OEL related problems on high harmonic loads, usually if the load is distorted enough you'll have issues with maintaining rated voltage, the AVR will either drive low or high depending on how it interpets the waveform and voltage value. Most common mode of failure where I've seen the OEL on these do it's job is on paralleled units and the rotating rectifier lost a diode or two (or three or more), and the field went full, then went out altogether, resulting in a loss of excitation or reverse VAR trip. Did have a rental project a few years back with 10 units feeding a large single step up transformer, first unit on line on Monday usually couldn't heat it up, and it would hit the OEL on really bad days.
Hope that helps,
RE: CAT XQ400-3456 w/SR4B & VR6
Phil.
RE: CAT XQ400-3456 w/SR4B & VR6
On your last post you mentioned reverse VAR trip. Is this a function that the regulator acts on alone or takes an input from an auxiliary sensor (option)? Would this condition set a fault code and shunt trip the M/G output circuit breaker?
Thanks
Phil
RE: CAT XQ400-3456 w/SR4B & VR6
I worked in the CAT system for a lot of years, I never was a fan of the CAT electrical protections, EMCPII was lousy, EMCP3.X is supposed to be better but problematic, hard to program and impossible to properly (in my opinion) test and verify. In most applications I tried to install a generator protective relay, used Basler GPR's, which are pretty basic but at least better than the package protections, and everything else up to an SEL300G. IF your system is important, protect it. The generator is supplied with enough stuff to barely protect itself in a stand alone condition, and not always even that. After looking at hundreds of broken, burnt, toasted and abused generator ends over the years, I like to see at least a simple generator protective relay in addition to whatever the manufacturer supplies, not just CAT, but even some of supposed better products, like Cummins Power Command, I have found lacking at times.
I like to see at least over and under voltage and frequency, over current and over load, even on standby packages (surprises me to this day how I still run into overloaded standby generators even with all the sizing softwares and supposed better engineering practises). If a generator is supporting a large UPS or drive system I also like to add a reverse VAR protection, since so many use PF correction caps and leave them connected when operating on the generator.
my 2.5 cents worth