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Thread: Triplen Harmonics, 5th Harmonic, Drive Isolation Xfmr, Generator

  1. #11
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    Ah so the PMG for the AVR isn't quite helping with the sensing its just providing a steady power source for the AVR. I thought the PMG was the Ace in the hole for situations like this. I guess the AVR needs a filter to be able to sense better.

    We always get PMG generators but I guess I over estimated their abilities.

    Quote Originally Posted by Jraef View Post
    In the 80s when solid state drives and soft starters started to really proliferate to where they ended up in places that were on generators, this problem was rampant. Caterpillar was notorious for it and there were a LOT of Cat gensets out there, especially in the fishing industry in Seattle where I was working at the time. So Cat came up with a retrofit kit for their AVR, basically just a filter for their sensing circuit. Worked great and I installed a bunch of them, then eventually they built it into all of their new gensets and the problem went away.

    Now what I think might be happening is that a lot of low cost generators are hitting the market that are knock-offs built in China from expired patent documents, so the designs they are knocking off are pre-fix. But at the same time, thyristor drives are now so rare that the issue doesn't show up enough for anyone to take notice. The reason I suspect this, is that the same thing happened with soft starters, but as I said, the problem disappeared in the 90s and 2000s because of the fix. But lately I've been seeing it show up again on new soft starter installations for sewage lift stations, and every time I go out to investigate, it's been a cheap Chinese genset that looks almost EXACTLY like the old Cats I used to see in the 80s, just not yellow. I checked with Cat to see if I could get their retrofit kit any more, nobody there had ever even heard of it, they were likely all too young... Drive isolation transformers do the trick too, but it's a much more expensive solution.

  2. #12
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    Quote Originally Posted by Besoeker View Post
    Odd.
    I've been involved with DC thyristor drives, thyristor front ends on inverters, and Kramer recovery bridges since the early seventies. Not a problem I have ever encountered.
    How many on Generators?

    Phil

  3. #13
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    Quote Originally Posted by Phil Corso View Post
    How many on Generators?

    Phil
    All of them.
    Si hoc legere scis nimium eruditionis habes.

  4. #14
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    2 - 30HP each or so motors on the drives. (that is 2 drives total, one 30HP motor on each)

    Quote Originally Posted by spraymax6 View Post
    Ah so the PMG for the AVR isn't quite helping with the sensing its just providing a steady power source for the AVR. I thought the PMG was the Ace in the hole for situations like this. I guess the AVR needs a filter to be able to sense better.

    We always get PMG generators but I guess I over estimated their abilities.

  5. #15
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    Quote Originally Posted by Besoeker View Post
    Odd.
    I've been involved with DC thyristor drives, thyristor front ends on inverters, and Kramer recovery bridges since the early seventies. Not a problem I have ever encountered.
    Interesting. Well if you had ever witnessed it, you wouldn't forget it. The generator engine would start acting funny, the soft starters or drives would then start going haywire and motors would stall, then if they didn't trip fast enough, the generator would. On a crab boat in the Gulf of Alaska, that was a major catastrophe...

    Maybe it was a peculiarity with the AVRs that Cat was using? It wasn't just Cat though, it's just that they were so ubiquitous. It might be that it was the AVR that was the issue, and other people here were using the same AVR that Cat was using.
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