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Thread: GE Multilin 369 Motor Protection Relay Power Source

  1. #11
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    Quote Originally Posted by Ingenieur View Post
    the uv coil is normally energized
    if you remove power it drops out

    the shunt coil needs power to trip, usually from a capacitive discharge ckt
    a C dumping to an L, very fast and positive
    If the breaker has a UV device yes but I am referring to the UV trip from the 369 relay, no coil, all microprocessor and sends a trip signal to the shunt trip coil.

  2. #12
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    Quote Originally Posted by zog View Post
    If the breaker has a UV device yes but I am referring to the UV trip from the 369 relay, no coil, all microprocessor and sends a trip signal to the shunt trip coil.
    yes
    the uv will drop out upon relay power loss
    the relay can be programmed no or nc
    we also power the relay and uv from the same source

    no
    the the shunt may not

    we set ours up to trip if the relay faults/losses power
    but we design to maintain power upon trip
    The difference between genius and stupidity is that genius has its limits.

  3. #13
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    Quote Originally Posted by jucesanc View Post
    If the power to the motor is lost, why would we still need relay to be energized? What would the relay be protecting at that point?
    It's not protecting anything any longer, but it does allow someone to READ what happened via the history in the relay without having to re-energize the motor controller. Also if they are using any kind of network communications, it allows the network to read the fault codes and history for annunciation elsewhere, like in a SCADA or DCS system. typically an MV motor is used on some very important part of a process and having it go down means serious economic consequences, so people who's head is on the block want to be able to explain it to the suits.
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  4. #14
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    Quote Originally Posted by Jraef View Post
    It's not protecting anything any longer, but it does allow someone to READ what happened via the history in the relay without having to re-energize the motor controller. Also if they are using any kind of network communications, it allows the network to read the fault codes and history for annunciation elsewhere, like in a SCADA or DCS system. typically an MV motor is used on some very important part of a process and having it go down means serious economic consequences, so people who's head is on the block want to be able to explain it to the suits.

    Also during brownout the thermal model in the relay may allow current to run rampant for a bit while motor terminal voltage rapidly decreases with constant torque requirements. In this case the increased current draw is like a positive feedback on bus voltage which hampers the ability to survive the brownout. So better to just trip. Also to protect windings in the motor (although overloads should catch this).

  5. #15
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    Don't forget the relay has a boot-up time. If it was powered from the same circuit as the motor, it could be possible the motor would start before protection is available.
    Just because you can, doesn't mean you should.

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