Capacitor Bank failure mode?

[steve66]

Now I see the "Class T" label just to the right. They are fast acting fuses. From Coopers Site:

The space-savers. Counterpart of the KTN-R/KTS-R LIMITRON fuses, but only one-third the size; thus, particularly suited for critically restricted space. A single-element fuse; extremely fast-acting. Provides a high degree of current limitation on shortcircuits for excellent component protection. Must be oversized in circuits with inrush currents common to motors, transformers, and other inductive components (will give only short-circuit protection). Commonly applied in electric heat circuits, load centers, disconnect switches, meters, stacks, etc.​

I'm thinking if the breaker tripped, and the fuse didn't, then the fault must have been prior to the fuses.

Unless someone just turned off the breaker, or someone has replaced the fuses.

 

[ohmhead]

Well dont know why not there , But i can say Eaton or cutlerhammer is junk and if you have polyproylene film type caps and your pf correction is not adjustable by load swings with motors your going to blow them everyday . there cheap junk !! also its who installed or picked that var for that load ? just a opinion not say iam correct but id say there blown out.
fluke has a capacitor meter mfd / ufd thats how you check a cap safely with power off . take care iwire tell us what you find ?

 

[mivey]

Read the nameplate: no fluids!:smile:

Don't clutter up my post with the facts.

 

[iwire]

Did you check the resistance of the internal discharge resistors?

No, I would not have thought to and would not know how.

How about discharge time?

No, I would not have thought to and would not know how.

Did you measure the capacitance of all terminal combonations?

No, I would not have thought to and would not know how.

Well that was easy

Did you have a bonding wire between the panel and the cap enclosure?

Yes, a 1/0 copper.

I think you want to megger at 1000V.

I have no doubt your right, I am a newbie with megameter, trying first to 'do no harm'.

Sounds like an arcing fault due to switching surge or harmonic ringing.

Is there a reasonably priced cure?

What a heck does it supposed to accomplish in this service anyway?

This is a moderate sized super market in a chain of about 20, they have capacitors at many of their locations. They feel it is worth it.

Figure 15 to 25 compressors, all of them going on and off all the time but almost always some are running 24/7.

 

[iwire]

Could it be that a cap was internally shorted to its case? Look for arcing to the enclosure beneath each cap's case.

I was all over that thing, I removed it and flipped it over, even got some paper towels and some cleaner and cleaned up the exterior looking for any signs of arcing........... found nothing.

Are you sure the arcings are from a one-time event and not over time? I know they look like it, but you never know.

There is a 1/0 copper EGC between the cap enclosure and the service gear, it has to be a pretty serious ground fault to still blast the locknut which was fairly tight.

There may have been a short to the raceway outside of the cap enclosure, so check all of each conductor for nicks.

I pulled them out, three 22' lengths of 500 copper, they look OK.

 

[iwire]

are those fuses at the top? if so, i assume you checked them.

You would think so, but not really.

I put a meter across them and it showed continuity but I am not sure that I am not reading the indicators and I did not get around to unbolting the fuses.

Do you have anything that can actually measure the capacitance?

I don't think so, my Fluke 87 can but I assume these are many times the size my meter could do anything with. I really have not worked with caps so I just don't know.

it looks like it might have blown fuse indicators on it.

Sure does.:smile:

 

[jim dungar]

It appears that there are no arcing marks on the inside of the capacitor enclosure. It looks like the burned locknuts are only in the wireway.

 

[iwire]

First off, Steve's right, it has blown fuse indicators, follow the red wires to the front panel.

Well yeah :grin:

Second, Bob look very closely at the capacitor on the top right: Those marks on top of the case make me wary. I'll bet if you looked at the sides or under that unit you'll find a blowout.

I bet I had those two on the right out and in my hand, they look good other then that stuff on top.

Also, are any of the cap's tops bulging? Even a slight bulge means an internal fault has happened.

Nope

My suggestion would be to install a PQM with recording function for a week, and if the PF stays within desired limits, abandon the cap bank. If the PF needs correction, find out the correct value needed and replace the cap bank.

The customer has decided they want the caps.

Edited to add: Based on the look of the top of the cap bank can, it could also have been a one-time fault caused by liquid entry.

NEMA 3R enclosure, I would say that was a drink spilled on the unit, it was quite sticky and disgusting.

I'd still do the PQM to see if the caps are even needed before reconnecting.

I see no reason to, is there one?

 

[iwire]

Bob, are those loads continuous? Or do several motors cycle on and off at random? If they cycle on and off a lot, I'd agree with Laszlo when he said this:

Several motors going on and off but very rarely do they all go off, almost never and it will only be for a short time till pressure drops and they come back on line.

Any idea how long the bank was online and in use before it failed or was disconnected?

Nope

My electrical "bible", the "Standard Handbook For Electrical Engineers" (McGraw-Hill, Fink and Beatty authors) discourages the use of single-point power factor caps in multi-motor applications, preferring correction at each motor or group of motors (MCC perhaps?)

That is all well and good but that is not going to happen. :smile:

 

[iwire]

Will they let you bring in a testing company?

It strikes me that the small size and simplicity of this unit would not justfy the cost of that.

But I could be wrong.:smile:

Lets say one or two of the caps are shorted...what would happen if Bob reengerized the capacitors?

My guess is I would darken the entire store due to the mains GFP.

My fear is I would be burned.

 

[Pierre C Belarge]

It strikes me that the small size and simplicity of this unit would not justfy the cost of that.

But I could be wrong.:smile:





My guess is I would darken the entire store due to the mains GFP.

My fear is I would be burned.

Two things I really dislike when it happens to me.


A good lesson here.
As much as we have seen in our time in the industry, there is always some things we just do not know about. I am curious about the outcome of this situation.
Keep us posted, please.

 

[hurk27]

Just a little food for though

Has anyone considered a lightning strike?:wink:

 

[electricalperson]

theres a couple ways to test capacitors with a multimeter. you can ohm out the capacitor with an ohm meter and if it starts at a low reading then increse to OL (open) the cap is fine a capacitor is just 2 conductors seperated by insulation or 3 in the case of a 3 phase cap

 

[hurk27]

It wont go all the way to open because of the drain resistors

 

[electricalperson]

It wont go all the way to open because of the drain resistors

well it should read to the value of the resistors if its below then its shorted

 

[steve066]

If I'm reading this table right (37.0-3 and 37.0-4) 200 KVAR wouldn't be recommended until you get to about 800 HP of motor loads.

http://www.eaton.com/ecm/idcplg?Idc...eased&Rendition=Primary&&dDocName=TB02608001E



Steve

 

[wireguru]

any signs of arcing at the lug in the cap bank where the egc was landed?

 

[izak]

Bob, do you feel like this thread is going nowhere, and you just need to replace the Cap bank, and give the customer what they want, even if it IS overkill?

hehee

sounds like thats where you are at now....

 

[iwire]

Bob, do you feel like this thread is going nowhere,

No, I am learning. I know very little on this subject and I have never been afraid to ask question about what I don't know ...... I could never make it as a lawyer.

and you just need to replace the Cap bank, and give the customer what they want,

Well that was my opinion going into this thread.

even if it IS overkill?

Now I am not so sure I want to do that, the paper steve066 has me thinking about recommending a different sized unit.

 

[iwire]

It appears that there are no arcing marks on the inside of the capacitor enclosure. It looks like the burned locknuts are only in the wireway.

You are correct but I can find no reason for those marks in the wireway at all, the conductors tested fine and look OK.

If it was easy I would not have had to ask. :smile: