Problems with Multilin M60's and Motor Service Factor of 1.0

[t3ch4276]

Hi,
I'm a bit of a lurker; have not been too active here before though. I'm an Electrical Engineering Student in hopefully my last year and have been working as a Field Technician for the last ten years or so.
I work in a refinery where there is a small variety of motor protection; usually some type of GE Multilin, the very occasional Macrotek, and even the electro-mechanical type as well.

I ran into the problem with the M60 while troubleshooting another intermittent problem that seemed to be surfacing on the protective side of a 4160V Motor-Starter. The style of relay is a M60-C00-VFH-F8A-H5C-M8A-P6B and the version is 3.44.

Upon simulation of start up and transferring to a running state at FLA, the relay would trip off within two to three seconds. At inrush to 95%FLA and 105%FLA, would run pretty much forever. But at 100%FLA, would pause, and trip. I tested another at this point and had the same phenomenon happen. Upon investigating the trip calculations, it seemed that the relay has a divide by zero problem when the motor Service Factor is set at 1.0. Rather than tripping in an infinitely long time, the relay buggers out and trips quickly on a Thermal trip.
I was looking for some outside information/experience as GE Multilin only stated that they don't suggest to set the SF at 1.0. My thoughts are that it shouldn't be available if it's going to nuisance trip at FLA if the motor is derated to 1.0 or happens to be rated at 1.0. Has anyone else came across this before and dealt with GE regarding it?

Thanks

 

[dpc]

they don't suggest to set the SF at 1.0

That's a fairly amazing recommendation for a premium motor relay.

The M60 is fairly new - it could be a program error/glitch of some type. So if the SF is set at 0.99 or 1.01 do you have the same issue?

Was the simulation done by actual current injection into the relay?





David Castor

http://www.cvoes.com

 

[t3ch4276]

I thought that was a bit of a mediocre response too.
Yes, the simulation was with secondary injection. The entire startup process was used: motor starter closed, secondary current roughly 5 times FLA was injected, reduced to FLA where the relays tripped. I ran the simulation on more than one relay when I began to suspect a problem internal to the relay.

These relays can adjust the SF from 1.0 to 1.25. But yes, at 1.01, the relay will operate as it would be expected to.

 

[electricpete]

That's funny (although I don't think someone whose motor tripped would think so). You’d think the software would be set up to prevent you from putting in 1.0.

=====================================
(2B)+(2B)' ?

 

[dpc]

Actually, I'd think a S.F. of 1.0 should be the default in a properly designed relay.

Seems like a programming problem in the firmware. As a workaround, using a setting of 1.01 should not cause any issues in the real world for a motor with a SF of 1.0.

Nice work in doing a proper simulation to figure out the issue.

I'd anticipate a firmware update fairly soon. Until then, SEL makes a nice motor relay.

Dave