GE/Multilin 369 Relay Repeat-Start Inhibit Configuration 1

[Bilegan]

Last week during tuning adjustments of our DCS system, the GE/Multilin 369 relay reported trip instead of start inhibit. Note that there was no overload during the trip. Our operations personnel doubted the repeat-start inhibit was activated during a second re-start attempt during DCS “tuning”.

They insist the repeat-start inhibit of GE/Multilin 369 relay should not be reported same as a trip to the DCS.

Does anyone encountered such case before? What are the modifications required, I need your expert advice!




Regards,
Bilegan

Murphy's Law - If anything can go wrong..it will.

 

[jraef]

Without looking at the manual, I'm pretty sure you can set up any condition to be something like Trip, Alarm, Indicate or Ignore in a 369. So if it is set for Trip, you will get a trip. As to "should"? It's your call, that's why they make it selectable. The manual will tell you what the factory default setting it.

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[jraef]

I took a look at the manual and I was wrong, but one of the beauties of having a good relay like this is having a historical record of what made it trip!

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[rockman7892]

Bilegan

I'm not sure I understand the conditions that you are questioning when the relay indicated a trip. What the motor running or stopped? What was happening at the time.

As Jraef mentioned the relay will indicate a tripped condition anytime one of the paramaters set to activate the trip functions exceed their setpoints. For example current unbalance, RTD High Temperatures, and Ground Fault currents are all examples of paramaters that can be set to activate the trip output on the relay when these paramaters exceed their setpoints.

The start inhibit function looks at the thermal model of the motor in the relay and compares the current thermal capacity used in the motor to the learned amount ot thermal capcity needed to start the motor stored in its memory. It the learned starting capacity in the relays memory exceeds the amount of avaliable capacity currently avaliable in motor then the relay will inhibit this motor from starting until the current thermal capacity of the motor reduces to an amount that will allow the motor to start sucessfully based on its learned information. The time that must elapse before this start inhibit is removed is a function of the presnet thermal capacity, the learned starting capacity, and the stopped cooling rate all present in the relay. The start inhibit function is selected in the relay and can be set to enable or disable. I believe if the function is disabled the relay defaults to a 15% capacity value that the relay must reduce to before another start is allowed.

It is also possible that the start inhibt function is assigned to the trip relay since the trip relay is part of the control circuit. In this case the start inhibit function when active would activate the trip relay to prevent the control system from trying to start the motor. I've seen this lead to confusion when looking at these relays.

 

[Bilegan]

Is a modification to the auxiliary contacts of GE/Multilin 369 relay in the motor control circuit of 4.16kV MCC can help to solve the problem of repeat-start inhibit should not be reported as a trip signal to the DCS?

The 778HP, 4kV blower motor was running, operations personnel were fine tuning the DCS when GE/Mutlilin 369 reported trip to the DCS instead of start inhibit. Maybe repeat-start inhibit was activated during a second restart attempt during DCS “tuning”; data shows motor current at 74A which increased to about 83A before declining and then increasing – perhaps during first restart.


Regards,
Bilegan

Murphy's Law - If anything can go wrong..it will.