Multilin 735

[pocketchange]

I have had three Multilin 735 relays have violent failures with what seems to be the power supplies. I have talked to my local rep. and he says that there are no known problems. They all were installed in 2000 and I'm wondering if 7 to 8 years is the total life for this particular relay? I have around 20 of these protecting my primary feeders to different substations. Right now I don't know if I need to be concerned or not.

 

[slavag]

Hello.
Problem of all types of protection relays from all mnf it's electrolit capacitors are installed in the power supply.
What is influence:
1. Ambient temp. ( for example, 40deg is recommended for about life cycle 20years, with 50deg life cycle will about 10years). please take in account, amb. temp not in relay rooms, near to relay or in cubicle.
2. Ripples of DC.
3. Hummidity.
Check all of those points.
Regards.
Slava

 

[Zogzog]

What exactly is a "violent failure"?

 

[RRaghunath]

Steady Overvoltage in input power supplies also could be one of the points, as these power supply modules of year 2000 are not likely to be SMPS based that will have wide voltage tolerances.

 

[pocketchange]

slavag
1. Switchgear room is climate controlled. Approx. 70F,
I wouldn't believe that inside the relay case there
would that great of a deviance in temp other than the
heat generated by the relay in its case.
2. The relay is on a latching 4160v contactor, which means
that the relay recieves its control power from the cpt
on the contactor.

Zogzog

By violent failure I mean that the relay was emitting enough
smoke that it was detected by the fire alarm system.

raghun

the range of the power supply is from 90 to 265 vac. It will also operate from 90 to 300 vdc.

I appreciate everyone's reponses...Still waiting on GE to
see if there are any known problems, ie batch failures, recalls, etc.

Thanks

 

[andross]

Hi,

I have come across a number of multilin 469, which have been reported as not working correctly. In each case the problem has been with the capacitors in the power supply. When replaced, relay operation is okay.

Andross.

 

[dpc]

There's a known issue with the electrolytic capacitors in these relays when they are stored for a long period of time in de-energized condition.

Other than that, I'd agree that persistent overvoltage on the control power input is one possibility. I believe these relays have two different power supplies, depending on the voltage range, or maybe there is a jumper.

I assume you are not talking failures in the output relays, which is a fairly common problem with all digital relays.

It would help if you could tell us more about the failure mode.

 

[pocketchange]

The relays protect the primary contactors that feed 2500 kva transformers which feed double-end subs.ie Main tie Main systems. In one instance the relay tripped and while trying to investigate why the relay operated it began smoking. The relay was still energized but with no load. In another instance the relay itself began clicking and all the led indicators illuminated. I have put a recorder on the system to monitor the voltage, current, harmonics, etc. and in the last 48 hrs. there has been no disturbances.
My problem is that I have a whole line up with these relays protecting my feeders and if they are prone to failure after an undetermined amount of time I would like to be proactive in the replacement of the units or look at replacing with different protection.

 

[slavag]

Hi Pocketchange.
First of all, if you want sleep and good weak-end, replace those relay ASAP. Protective relays are smoking, it's not games and I think you don't have time for some monitoring..
Second, sorry, I'm not understand exctly, what is a power supply of those relays. What do you mean "cpt on contactor"?
Regards.
Slava

 

[slavag]

BTW, I think, DPC know, what he say:
see manual: 125Vdc, 250Vdc nominal voltages, but range of
HI is from 88-300V dc. not clear for me.
Regards.
Slava

 

[slavag]

And last note.
Possible also some other problem.
As I see from manual it's "plug unit" relay.
Disconnect unit and check visually, probably it's not PS, this PS must have internal fuse and overvolatge protection.
Regards.
Slava

 

[dpc]

Sorry pocketchange, I missed your info on the power supply.

I'd take one apart to see what you can see. But I'd definitely be leaning toward replacement, since I don't count on GE for a lot of help in these situations.

The SEL-501 is a nice, inexpensive OC relay if you don't need anything fancy. If it ever fails, you can send it back to Schweitzer and they'll send you a new one.

 

[pocketchange]

Thanks everyone for your support on my problem..

 

[rbulsara]

Interesting thread!

I would think relying on unpredictable source voltage (even through CPT) as "control power" source is not a good idea. Using a separate conditioned and stable power source, preferably DC, would be a better choice for control power to protective relays.

Since control power stay on continuously, I would also suspect the sustained overvoltage or even frequent voltage spikes as the cause.

 

[RRaghunath]

pocketchange,

you haven't clarified as to the observation on the failed relay, i.e. whether it is the failure of the output relay or the failure of power supply module (capacitor etc.). I see you said there was a lot of smoke, is it from the electrolytic capacitor in the power supply module?

Further, the relay auxiliary power supplies are derived from the control power transformer of the MV contcator control scheme. If I guess right the control power for these contactors is 240V AC.
Now, if you consider the switchgear busbar voltage could be a bit above the normal rated voltage and there is a possibility that the control power transformer will have taps, putting things together, I see a possibility of the relay receiving more than 265V AC (if not, atleast working near its upper limit). Could you measure the voltage at the relay input terminals to check on this?

If you have to go ahead and replace all the relays, I see it is a big task and hence it is worthwhile to investigate little more so as to identify the cause and prevent further failres, if possible. Hope you would agree.

 

[slavag]

Hello.
CPT, CPT..... Now, I understand what is it. ( O.K. we use other term).
Rbulsra was very correct. I say, is very bad idea use CPT as source for the digital relays. I'm strongly recommend use
DC source, as Rbulsara saied, or some UPS ( not so good, but much better then CPT).
In additional to my 3 points and Rughun point: Voltages dip's and transients are "kill" those capacitors.

DPC, about contacts, possible open other discussion.
Regards.
Slava

 

[Lencho]

Hello,

The Multilin 735s have been in the market since 1993. They are good O/C protection relays. The root causing of Electronic component or product can only be performed by qualified and certified personnel. You should contact the factory to get the products returned, serviced and return to you with the service report. You may obtain the support information from product label, manual or company website.

Thanks

 

[dinocu]

Hey pocketchange,

I just came back from site where they had a 735 fail and it triggered the fire supression system before blowing the control fuses in the panel. This relay is also being fed off a set of bus PT's. I talked to GE and they said nothing like this has ever happened before... yeah right!

 

[rbulsara]

dinocu:

Was the cause of the failure investigated. The morale of this thread is that do not use bus PTs to feed relays! That is a bad implementation.