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  1. #1
    Join Date
    Feb 2009
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    West Fla. since 2002, Central Va. before that
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    27

    York YS Chiller Ground Fault

    I have a 265hp York YS with a solid state starter.

    About 3 weeks ago it tripped the 500amp Seimens GFI breaker back at the MDP but not the 400amp breaker on the front of the machine.
    I disconnected the motor leads and it megged grounded.
    We removed it and our local motor shop found it not needing a rewind but instead needing just cleaning, dipping, baking, etc.
    They ran the motor at their shop with no load.
    BTW: While the motor was off we replaced the compressor shaft seal.

    We reinstalled the motor and restarted the machine but the GFI tripped again.
    Thinking that the GFI may be faulty we called in Seimens who tested the breaker and found only one issue: the instantaneous interupting rating was set lower than they recommend at about 2000amps so they raised it to something more like 3500amps.

    It tripped again.
    Just a slight "click" or "bump" is heard and the breaker tripps.

    Today I am thinking about disconnecting the coupling and trying the motor with no load. If that tripps the GFI then I thought I might try the motor "across line" (with out the starter). If it still trips then it's back to the drawing board for the motor shop I guess.

    I'm wondering:
    1). how long the chiller will even let me run the motor with the coupling disconnected before it shuts down on oil failure, etc.?
    2). if the motor runs across line and indicates a problem in the starter, how on earth will I ever narrow that down?

    Any advice would be greatly appreciated.

  2. #2
    Join Date
    Feb 2009
    Location
    good old Europe
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    160
    It will have almost no affect on the starting amps with or without compressor coupled, because the starting current is mainly caused by the breakaway torque on the rotor itself. The problem could be one of the thyristors in your SSS. You should check them and the triggerboard for loose connections or broken parts (e.g. varistors, resistors, capacitors).
    "Quality exists, when the price is long forgotten."

    Henry Royce

  3. #3
    Join Date
    Feb 2009
    Location
    West Fla. since 2002, Central Va. before that
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    27
    No loose parts or broken parts in the sss.
    No burns or smokey places either.

    I did attempt to start it with out the coupling.
    It made it's signature "buzz" for like 1/4 of a second and tripped the GFI.
    No fire, no smoke, no thing but a tripped GFI.
    It must be tripping on ground fault rather than over current because 500+ amps would put on more of a show.
    Jumping the motor across line looks like it would be a rediculous exercise at this point.

    That brings me to the starter itself.
    Does anybody have any directions on troubleshooting the individual SCR's, etc or should I just get on the phone to Baltimore Parts and get a new starter?

  4. #4
    Join Date
    Feb 2009
    Location
    good old Europe
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    160
    Quote Originally Posted by curlydogmaster View Post
    That brings me to the starter itself.
    Does anybody have any directions on troubleshooting the individual SCR's, etc or should I just get on the phone to Baltimore Parts and get a new starter?
    I suspect that they are quite expensive, even the single SCR`s! It isn´t easy to test them, because you can´t test them under load. If you have access to a FLUKE 434 power analyzer you could probably measure the voltage and current drawn by each phase just before the switch trips to see which of the SCR´s makes the problems. Does the Siemens breaker has a communication port? If yes, perhaps the guys from Siemens can see which phase is the one!
    And yes, there is a trouble shooting guide for the SSS. Which style starter you have liquid cooled, style A or B?
    "Quality exists, when the price is long forgotten."

    Henry Royce

  5. #5
    Join Date
    Feb 2009
    Location
    West Fla. since 2002, Central Va. before that
    Posts
    27
    Water cooled.
    m/n: SSS14L-46A
    s/n: EHR-14B
    p/n: 371-01210D007

    I does have a communications port.
    I'll talk to Seimens about identifying which phase but they couldn't even tell me it it was over current or ground fault.

    Thanks again!

  6. #6
    Join Date
    Sep 2007
    Location
    Somewhere in the world.
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    1,602
    If it was me I would disconnect cuppling and spin it , if it spins then it ain't the compressor , next your going to need a book to troubleshoot that style A LCSS starter to figure out what is going on obviously it ain't the motor.
    Arguing with your Boss is like wrestling with a pig in
    mud.
    After a while you realize that while you are getting
    dirty, the pig is actually enjoying it.

    It is not exactly cheating, I prefer to consider it
    creative problem solving.

    25 years ago we had Bob Hope , Steve Jobs , and Johnny Cash today we have no Hope no Jobs and no Cash !
    I can fix broke but i can't fix stupid !

  7. #7
    Join Date
    Jul 2008
    Location
    Washington, DC
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    1,582
    I was thinking maybe this is caused by a bad line reactor, so after some googling I found this. As you know a GFI is looking for current leakage, so if the components test out ok, I think you need to look at how the motor is grounded or something along these lines.


    PWM Drives — Measurement 5
    Leakage currents (common mode noise)

    Leakage currents
    Leakage currents (common mode noise) capacitively coupled between the stator winding and frame ground will increase with PWM drives as the capacitive reactance of the winding insulation is reduced with the high frequency output of the drive. Another leakage current path may exist in the capacitance created when the motor cables are placed in a grounded metal conduit. Therefore, faster rise times and higher switching frequencies will only make the problem worse.

    It should also be noted the potential increase in leakage currents should warrant close attention to established and safe grounding practices for the motor frame. The increase in leakage currents can also cause nuisance tripping of ground fault protection relays, override 4 to 20 mA control signals, and interfere with PLC communications lines.

    Measure common mode noise by placing the current clamp around all three motor conductors. The resultant signal will be the leakage current.

    A common mode choke can be used to reduce leakage currents (see Figure 5A). Also, special EMI suppression cables can be used between the drive output and the motor terminals. The copper conductors of the cable are covered with ferrite granules, which absorb the RF energy and convert it to heat. Isolation transformers on the ac inputs will also reduce common mode noise.

    http://www.davis.com/techinfo/techin...rement-ASD.htm

  8. #8
    Join Date
    Dec 2008
    Location
    Dixiana, AL
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    2,609
    Disconnect the "T" leads off of the SCR's and give the thing a start signal. That'll tell you if it's the starter or the motor. If the starter, you still have to narrow it down to which component (you may come out cheaper with junksons prices to buy the whole starter and replace it than individual components), but at least you'll know for sure you're lookin' in the right place. ATL hookup probably wouldn't be a good idea.

  9. #9
    Join Date
    Feb 2009
    Location
    West Fla. since 2002, Central Va. before that
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    27
    I'm not gonna try ATL...the building would brobably shake apart from the 3000 amp in-rush.
    I did disconnect the motor leads and I've got 480v line-to-line and 277v line-to-ground on the output of all three output terminals before I even apply a start signal.
    Is that normal?
    Thanks again for any additional advice!

  10. #10
    Join Date
    Feb 2009
    Location
    West Fla. since 2002, Central Va. before that
    Posts
    27
    The motor megged at 2M @ 1000v so I can't blame the motor.
    I spent some time checking the starter for grounds, shorts, etc until I called the tech from Seimens as I was driving.
    He informed me that the GFI breaker isn't necessarily seeing ground fault current.
    Because this is a 3-wire circuit and there isn't a neutral, the breaker really just looks at the three individual phase currents and if it sees an inballance in excess of a setting on the front of the breaker, it tripps. In my case it is set for 40%. Well, that changes everything!
    I have been looking for grounds but it is more likely an SCR that's not firing correctly which could easilly cause that sort of a current inbalance. My plan is to crank up that inbalance setpoint and hopefully the motor will start. From there I can hopefully determine on which phase the problem exists.

    Now, anybody have any ideas for testing the solid state starter??? Anybody???

  11. #11
    Join Date
    Feb 2009
    Location
    good old Europe
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    160
    What about to fit a much smaller 3 phase motor (e.g. 3hp) to the output of the SSS instead of the compressor motor? Then starting and take measurements until the chiller trips on something else (low motor current, oil pressure, etc.).
    "Quality exists, when the price is long forgotten."

    Henry Royce

  12. #12
    Join Date
    Feb 2009
    Location
    West Fla. since 2002, Central Va. before that
    Posts
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    Yea, thought about that.
    No motor attached gets me nothing.
    Hopefully something will show its self tomorrow but I wish I had a more clearcut proceedure for testing the SCR's and the trigger circuit.
    I hate stabbing in the dark...

  13. #13
    Join Date
    Dec 2008
    Location
    Dixiana, AL
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    2,609
    Quote Originally Posted by curlydogmaster View Post
    Yea, thought about that.
    No motor attached gets me nothing.
    Hopefully something will show its self tomorrow but I wish I had a more clearcut proceedure for testing the SCR's and the trigger circuit.
    I hate stabbing in the dark...
    You're not stabbin' in the dark - check your e-mail. Let me know if I can help.
    (look under troubleshooting 1/2 phase fault)

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