GE Multilin 369 Motor Protection Relay Power Source

[jucesanc]

I'm replacing two motor protection relays with new GE Multilin 369's. The current motor protection relays get their power from the same source as the motor, via a control power transformer that drops the voltage from 4160V to 120V. I'm just confused about a line in the GE Multilin 369 installation manual. It reads: "For applications where the control power for the 369 is available from the same AC source as that of the motor, it is recommended an uninterrupted power supply be used to power up the relay, or alternatively, use a separate DC source to power up." I guess I just don't understand the wording. Is this recommending to use a UPS for the multilin 369 power source. I was planning to use the control power transformer with the same power source of the motor.

 

[petersonra]

I think they want to make sure the relay remains powered up even if the power source is off.

 

[zog]

You want the relay to still operate on a loss of power to the motor. Likely trip the breaker on UV

 

[dkidd]

They are not talking about a UPS.

From the manual:

The Test Output Relay feature provides a method of performing checks on all relay contact outputs. The feature can also
be used for control purposes while the motor is running. The forced state overrides the normal operation of the relay output.


The forced state, if enabled (energized or de-energized), forces the selected relay into the programmed state for as long as
the programmed duration. After the programmed duration expires, the forced state will return to disabled and relay operation
will return to normal. If the duration is programmed as Static, the forced state will remain in effect until changed or disabled.
If control power to the 369 is interrupted, any forced relay condition will be removed.

 

[jucesanc]

Likely trip the breaker on UV

I'm still a bit new to all this. What is UV?

 

[petersonra]

I'm still a bit new to all this. What is UV?

undervoltage

 

[Ingenieur]

we tap power off before the vcb
you need the relay to remain energized if the vcb trips

 

[Ingenieur]

You want the relay to still operate on a loss of power to the motor. Likely trip the breaker on UV

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

 

[jucesanc]

we tap power off before the vcb
you need the relay to remain energized if the vcb trips

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?

 

[Ingenieur]

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?

so you can reset faults that latch
possibly time and restart
see trip messages/diagnostics

suppose you cycle power to the relay and it attempts to restart?

 

[zog]

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.

 

[Ingenieur]

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

 

[Jraef]

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.

 

[MRKN]

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).

 

[jim dungar]

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.