Problems with failing relay coils?

First thoughts:

1: Manufacturer: Buying cheap imports, perhaps? 2: Vibration: Failure internal to coil or connecting conductors? 3: Storage: Relays contaminated by, say, solvents at some time?

Yeah, me too! I cant see theP/F affecting relay coils particularly in that number and also the DC failures. I would suggest trying a few of some other manufacturers relays.

Second thoughts:

Disassemble a few of them and find where the open circuit is, in each case.

Then look at the end of the broken wires and the area of the break under a microscope. Even a single magnifying lens will possibly do.

If the wire ends show the sharp edges of fatigue failure - then I would suggest looking again at vibration as being a possible cause. Even a relatively low amplitude vibration at the resonant frequency of the connecting wires can cause premature failure. The frequency will be quite high and might not be immediately evident.

If the area of the break shows evidence of tracking and insulation failure - then I would look again for the possibility of contamination, eg smoke particles.

If the wire ends have the rounded profile of melting but the unit doesn't show the signs of long term overheating, then that would tend to indicate rupturing under a short-term, very high voltage (and hence current) overload. That would be worrying...

I would still hope that vibration was the cause. That is probably the easiest to fix.

For 8 relay coils to die in one panel, in one week must be a voltage related problem.

Power factor would have very little, if any measurable effects on relay coils.

You say PFC is the only common factor, but what about the supply... that's common too.

sQuick..

Did this installation EVER work or are these failures in the first week of operation???

"These relays have been in operation for six years, no vibration in panels, they are Omron relays."

What are the date codes on the failed relays? How does that compare with the ones that don't fail? Are all the failures from the same panel? You need to do a fault tree analysis.

Al

Did the OP supply this info off line?

If in fact the setup has been working for six years then something quite serious has happened in the week in question.

Careful reading says "The 240 VAC is from 1 phase of the same 415 V system and neutral"

The relays are said to be 110 volts (and 24).

Am I confused or is the OP?

What are the voltages AT the relay coil terminals?

What country is all this in.

There is no 110volts in a normal UK system. Is there a second transformer to supply 110 volts for the relays?

Wot's Your Real Problem?

110 Volt relays - the supply is from a 415V/110V transformer. 24 VDC relays - 240V into a DC Power Supply, 24 VDC out. The 110 V relays are failing in different MCC cubicles, the 24 VDC relays are failing in the PLC panel.

The measure voltages at the coils are 110VAC and 23.9 VDC. Had the PF panel switched off for two days now, don't want to tempt fate but no failures yet!

couple of thoughts: Is the 24VDC supply regulated? Could be the pf caps are resonating with some harmonics in the system. This could cause higher peaks of the sine waves. If these are just rectified in the power supply, you could have higher voltage on the output. Also, the AC coils would see this as well.

Have you put a recorder on the ac and dc. Even a Fluke 87 has Min/Max capability. There could be higher voltages under some conditions.

Yes it's a regulated DC supply, I will be putting a recorder on the system week after next, on hol next week.

Cheers Jim