86 relay current draw? 5

[eeprom]

Hello,
I'm troubleshooting a failed trip circuit for an 86 lockout relay. This is a GEI-28712E, similar to an Electroswitch. The 86 coil is tripped by one of several relays. The contacts for one of the relays has been welded closed, and I'm trying to figure out how that could have happened.

There was a standing trip on one of the relays, and the operator didn't know, and he kept trying to reset the 86. He held the 86 in the reset position long enough that it started to smoke. An observer told me he held the switch for at least 5 seconds, trying to get it to reset. I'm pretty sure this is what caused the welded relay contacts.

The current rating of the welded contacts is 30A for 0.2 second, and a continuous rating of 7A (at 125VDC). The trip voltage is 125VDC. The GE manual for the 86 says that at 125VDC, the resistance of the 86 trip coil is 24.3 ohms at 25 degrees C, and that the seal in time is 0.2 seconds. But this doesn't add up with a welded contact that can handle 30A. According to the manual, I could hold the handle to reset as long as I want and I'd never pass 5A.

I'm trying to figure out what the steady state current through that coil would be. If it's just a coil, then after the transient, it's a short circuit. But the manual says 24.3 ohms? Is there a resistor in series with the coil, or is that the impedance of the transient measured at 0.2 seconds?

Thanks for your help
EEPROM

 

[cranky108]

Another thing is, the older GE lockouts had a problem with becoming sticky, if not torqued to the proper adjustment from time to time. That can cause a welded contact, as the lockout operates too slow.

If you have this type of lockout that requires torqueing, you need a program to check them from time to time.

 

[LionelHutz]

Huh, how could figuring out why the contact in the protection relay failed not be about the 86 relay? You asked why the contacts in your protection relay failed. You also posted that it happened after the operator held the 86 until its trip coil started to smoke. The smoking hot temperature of the trip coil could have easily caused the coils of varnished wire to melt together causing a short in the coil, either partial or complete. Those shorted coils could then easily cause a MUCH higher current in the circuit. But hey, why would anyone need to investigate the ACTUAL IN CIRCUIT 86 relay as a possible cause?

 

[waross]

This post has nothing to do with the lockout relay, other than trying to determine the steady state current flow.

You may be labouring under a misconception.
May I suggest that determining the normal current may not be as important as determining what the abnormal current may have been?

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[eeprom]

Well, I'll say you guys are persistent....

Here's some measurements from the field. I would love to see someone apply ohm's law to this. Because this makes no sense to me. And the guy doing the measuring is very good. These are accurate measurements.

Measurements on lockout relay....................
Resistance of coil, 2 measurements: 23 ohms, 23.4 ohms. GE manual says coil it should be 24.3
Current through coil during reset, 3 measurements: 14.5A, 10.2A, 7.9A (done in order about 30 seconds apart)
Standing voltage: 132V.
Voltage during resets: 129V.

For a fairly stable voltage, and coil resistance, I got 3 wildly different current measurements.

From the point of view of the failed contact in the exciter, this is not enough current to damage it. So that problem remains unsolved. All I know is that the contact will not change state. I assume it's welded shut.

For the lockout relay, I believe this is what's happening. The insulation is damaged, but it's intact enough that it doesn't show up on a resistance test. When you push current through it, the insulation breaks down enough to allow the current to take multiple paths through the windings; this would explain the higher than expected current. The current causes heating in the coil, raising the resistance of the wire. This could explain why the current measurements go down over time.

The lockout relay need to be replaced, so no need to discuss that. But I would like an opinion on the different current measurements.

 

[RedSnake]

Since I am not a gentleman, I guess I am excluded and will give it another try.

This is a manual I found it seem to be old maybe there are newer.

https://npeinc.com/manuals/LV breaker manuals/GENERAL ELECTRIC/GEI-28712E - HEA Relay.pdf

But from my understanding the coil is to realize the latch when tripping and the reset is mechanical?

So the coil should not be energized at all at a reset.

What makes a contact burn together isn't the amps over it when it is fully closed which are the values you provided max 30 A and continues 7 A.
But the arc that burns between them when opening and closing them and for how long that arc is lit.
And that time gets longer if it closes or opens to slow or if it does not open enough which will happen after a time if a build up from earlier arcs are left unattended or if the power consumer is a coil with a magnet and there is no arc protection over the coil or it is broken like a capacitor, diod, free wheeling diods, or such.

BR A



“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[LionelHutz]

Nothing you posted explains the high current of the first test. Coil heating could explain the current going down during the subsequent tests.

That is showing that datasheet theory doesn't beat actual testing. If the tripping current is really 14.5A on a good 86 relay then that could explain the contact welding, even when the contact is supposed to be rated for switching that level of current.

 

[RedSnake]

Meaning that if the function of the coil is to realize the latch it will be energized as MKFPG sad with 125x125/24 = 651 watts for 0.2 sek 200ms but if you pull it for 5 sekunds it's not made to withstand that, so smoke there will be...

I have had the same problem with a bipolar relay it burns after power outages because there is no compressed air avalibul so the takeover function can not be completed and do not come.

/A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[bacon4life]

When did the relay contact last attempt to open? I was a bit confused whether the relay contact never changed state because it was welded, or whether the relay never attempted to open the relay contact. The interruption rating of relay contacts is often less than 0.5A @ 125 VDC. If the 86 was already damaged, the relay could have been damaged during a previous operation.

 

[RedSnake]

Totally beside the point..
With 125x125/24 = 651 watts I could heat my car motor in the winter I think the engine preheater is between 550 -750 W even that will not help when it is -30 C at times.

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[stevenal]

Star for Bacon. It is unlikely the protective relay contact is rated to interrupt 86 coil current. With the series contacts held closed, protective relay contacts will weld.

We smoked an 86 one day when commissioning. The panel drilling was off a bit, and the shaft rubbed against the hole. The hole was enlarged when the replacement went in, and commissioning proceded.

 

[davidbeach]

This thread and another recent about tripping contacts points out the absolute need to understand the expected operation of very common T&D P&C designs where external clearing contacts allow operating contacts to function flawlessly apparently way outside their ratings. One medium sized utility can have thousands of them. The perform yoeman duty year after year. But abuse them, even a little, and all bets are off.

Do it right and the ratings really don’t matter. Do it wrong and there are no ratings that can make it work. Well established practice.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Palletjack]

I’ve had these trip coils burn out before. It’s why we have a couple of extra trip coils.
I didn’t read every comment, but was the fault cleared when the guy held the handle to reset for so long?
I really don’t understand why he was holding it so long anyway. If it doesn’t reset either the coil is drawing the latching mechanism or the latching mechanism is broke.

Change the coil, test the 86T, and see what caused it to trip. Forget about trying to figure out how many amps it pulls.
I seriously doubt that’s the issue.

 

[mvcjr]

Hi!

It could be possible that the trip contact of your protection relay is set to latched operation which you might have misconstrued as welded. A simple reset of the protection relay may release the latched trip contact.

Regards.

 

[lvardeman]

>> "I got 3 wildly different current measurements"
Redsnake's excerpt from the manual mentions a capacitor. Decreasing current could be a function of the capacitor charging.

 

[RedSnake]

I was thinking that too, but since no more information or electrical drawings was provided (I am not familiar with this kind of equipment) I didn't point it out.

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein