Protective relay behaving badly

[JBD]

Can any one help with a GE IFC53 relay that trips for no apparent reason.

The system is a 4160V air break circuit breaker with (3) IFC53 relays for 50/51 phase protection. The settings for the IFC53 are 400:5 CTs, Tap setting = 4(320A), Time dial = 4.0, and Instantaneous = 70(5600). This breaker feeds a 4160V motor starter that has 3R fuses for short circuit protection and a Multilin 269+ (pickup of 45A)for overload protection. The motor is started across the line with a FLA=32A and an inrush of 6.2x.

Occasionally, on start up, one of the IFC53 relays will trip on instantaneous. The relays have been tested multiple times and always pass. The Multilin 269+ and the 3R fuse have never tripped and both of their curves are far to the left of the IFC relay. The 50G relay has also never tripped.

 

[ANGIBEW25]

Hi JBD:
You may have a CT wiring issue or a CT Burden issue for the (3) CT's that are wired to the IFC relays.
I would check all of the CT secondary connections in this circuit. I would also test the CT's for ratio, polarity and saturation. Perhaps one of the CT's is breaking down.
Verify that the (3) CT's have the same characteristics and have the correct Class rating for the Burden of the secondary circuit. You may have to include Ammeters, Watthour Meters, Selector Switches, Wire Size and Length into your investigation.
If you prefer you can take some voltage and current measurements on start-up at the Relay CT input terminals and then do a little Ohm's Law.

Good Luck.
Ang

 

[JBD]

CT's are scheduled to be evaluated at the next system shutdown.

The only other device in the circuit is an ammeter and switch. Total lead length is just under 10 ft. Only one of the three relays trips. The problem follows the same relay even as it is moved from Phase A to B to C.

I was hoping for some additional ideas. Maybe it is something inherent in the IFC53 device when it is used on such a small load in relation to its settings.

 

[ANGIBEW25]

Hi JBD:
In your earlier post you did not state that the problem was following the relay. The relay settings appear to be proper for the load, possibly a little higher than necessary.
I suspect you have a faulty relay,and not a CT issue. Can you provide some additional information?
1. What is the TOC tap range for this unit?
.5-4.0 or 1.0-12.0 (It should be 1.0-12.0)
2. What is the range of the Instantaneous unit?
2-50 or 6-150 (It should be 6-150)
3. What position is the Instantaneous link in?
L or H (It should be H)
4. Have you physically inspected this relay?
5. Is there any non-factory replacement parts or hardware installed in this relay?
6. Is the relay frame or fingers damaged?
7. Who is testing this relay?
8. Has the testing been witnessed?

Some or all of these items you may have already covered, but I mention them only for the purpose of clarity.
Sometimes troubleshooting intermittent problems can be like chasing a balloon.
I would suggest replacing the relay at your earliest convenience.
Good Luck.
Ang

 

[burnt2x]

Is there a typo here? 32A FLA motor with 51 protection set at tap 4 (320A) - 1000%?

 

[dpc]

These instantaneous units are subject to nuisance tripping due to vibration, radio interference, and sundry other sources. I, personally, have tripped one by keying a 5 watt transmitter near one, as well as banging on the door where the relays were mounted. You may have one that is particularly sensitive to vibration. Kind of like setting a mouse trap.

I'd suggest just replacing the IT element and see if that solves the problem.

 

[JBD]

Burnt2x - the motor is being protected by a Multilin 269+ relay. The IFC relay 51 function is for cable feeder protection only.