People, Have any one of you experi 1

[HiSet]

People,
Have any one of you experienced problems with Multilin make SR760 relay regarding it's immunity (or rather lack of) against transients.This relay often under goes software reset while carring fault current.

 

[jnims]

That's one I haven't heard, but I am aware several other probelms this relay has had over the years:

(1) Temperature problems
(2) Unintentional trip contact closure when a circuit element in the relay failed.
(3) Failure to enter reclosing cycle under certain conditions.

 

[jbartos]

Suggestion: It would be more appropriate to pursue this matter with the manufacturer tech support since it may need a special remedy, e.g. computer modeling.

 

[dpc]

I have not heard of this problem before. Is there any chance the control power supply to the relay dipped during the fault? Did the relay generate any events in the event log?

I would be surprised if high level of CT input current, by itself, could cause the relay to reboot. The CT inputs go through another secondary CT inside the relay that provides some additional isolation and buffering.

Funny things happen during faults....

 

[kevd]

Problems like this are not necessarily with the relay unit. There are lots of cables coming into relays that can carry common mode and differential mode pick-up. Inadequate installation earthing is generally the most likely suspect. GE are a big organisation that do extensive EMC testing of equipment, so it would be suprising if they had a generic problem (but not impossible!).

Under fault conditions, earth fault currents raise the local earths potentials and cause high voltages to appear all over the system, the switching action of breakers chopping high currents cause even bigger transient voltage oscillations at kHz, MHz and even GHz frequencies. This really does expose either inappropriate signal earthing systems (or indeed dud equipment).

I bet the first thing tech support ask is confirmation that the earthing is to their installation recommendations. If you can confirm this to their tech support then you have may have a point for them to investigate further.

Saying all that not enough equipment manufacturers make their software EMC tolerant. There is an enormous amount that can be done in software to aid in EMC immunity and prevent "software resets" or "lock-ups" during faults.

The IEE in the UK have published a really good EMC paper which also covers software. You can hunt it down here

http://www.iee.org/

Good luck in your investigations

KevD

 

[HiSet]

Thanks People in general and Kevd in perticular. I am also thinking on these lines.In our case we are using plenty of I/O's for logging alarms, status and trip coil supervision etc. Is there a chance that transient spikes may be riding through these wires ? I trust GE to provide some sort of filter across their I/O to block or shunt spikes.What possible tests could confirm this theory? What's the issue with autoreclose ?

 

[busbar]

Long Shots — May provide some insight…

http://pm.geindustrial.com/FAQ/Documents/General/GER-3061.pdf

http://pm.geindustrial.com/FAQ/Documents/General/GER-3204.pdf

http://pm.geindustrial.com/FAQ/Documents/General/GER-3205.pdf

 

[jbartos]

Suggestion: Additionally, the relay functioning can be verified by an oscilloscope measuring the fault current and monitoring the fault current waveform. Any discrepancy could then be found presentable to the relay manufacturer.

 

[kevd]

Proving the "theory" of this failure mode will not be easy. EMC issues are never black and white.
The articles suggested by Busbar are excellent papers - what is interesting is that this type of problem has been known about for 40 years or more, but manufacturers and system integrators still make installations that suffer from interference from well known phenomenon!

1) Earthing
Start with the earthing arrangement in the switchgear. How is the earth run to the switchgear earth bar. The earth should be a short as possible and be a suitable CSA.

How is the switchgear earthed to the site earth?

Is the site earth OK?

By the way is this an existing switchboard that has been upgraded or a new switchboard?

2) Cable Segregation
The next is to check how all the cables into the relay are run in relation to high current carrying cables or busbars.

Something that upsets the microprocessor could very well be related to the incoming power supplies. Make sure these cables are well segregated from everything else and are made off as short as possible.

Signal cables run next to earthed bodies exhibit very low inductance and reduced pick-up characteristics.

Any screen cables should have their screens terminated with 360 degree terminators. NOT PIGTAILS!

3) Tests
jbartos suggestion is a good one and helps Tech-support get to the bottom of the issue.
Another test would be a high speed scope on measuring the voltage on the earth going into the relay and power supplies that may catch the offending spike. However, the spike period can be micro-seconds so triggering needs to be just right. Good scope leads are a must if you are to eliminate any other types of interference.

Happy hunting!

kevd