# Switchgear 1.1



## Wmackay (Sep 22, 2010)

Any body Know 
1. what this is 
2. what is happening (root cause)


----------



## daveEM (Nov 18, 2012)

I see you figured out how to post a pic.

I don't know. Did you look up? Perhaps a body in the rafters. 

Someone smarter than me will be along.


----------



## Wmackay (Sep 22, 2010)

yes got the pic
lt is dripping from The "coil" around the neutral bus


----------



## Nick0danger (Aug 19, 2012)

Some weird harmonics, that are causeing the dielectric material to melt on the CT?


----------



## Wmackay (Sep 22, 2010)

why have a ct on the neutral


----------



## Nick0danger (Aug 19, 2012)

No idea but that is most likely what it is. Are there VFD,s being feed perhaps there monitoring the buss bars, to ensure the VFD;s work right. It might not be a CT but sure looks like it to me.


----------



## Wmackay (Sep 22, 2010)

I thought so to maybe part of NGR monitoring but why would it be resting on the bus bar
and is there a danger here


----------



## 8V71 (Dec 23, 2011)

Did anyone look around back to see if the rear mount broke off?


----------



## macmikeman (Jan 23, 2007)

The CT secondary circuit was opened while the primary was energized causing a meltdown of the CT coil windings insulation material.


----------



## Wmackay (Sep 22, 2010)

All I have is the pic sent to me but I will ask


----------



## Pharon (Jan 20, 2014)

Wmackay said:


> why have a ct on the neutral


Could be part of the residual ground fault sensing. No idea what would cause it to melt, though.


----------



## Wmackay (Sep 22, 2010)

Not sure I understand why the open would cause this 
but I will check your link
I have little experience with these switch boards

thanks for the response


----------



## Wmackay (Sep 22, 2010)

That was my opinion I can't think of any other reason the CT would be around a neutral bus


----------



## Big John (May 23, 2010)

Your neutral CT is used either for metering or ground-fault or zero-sequence protection schemes. My guess is that it got open-circuited and developed internal shorts that caused it to overheat and melt down.

Usually they literally burn up, but I've seen "melted" CTs before.


----------



## brian john (Mar 11, 2007)

Big John said:


> Your neutral CT is used either for metering or ground-fault or zero-sequence protection schemes. My guess is that it got open-circuited and developed internal shorts that caused it to overheat and melt down.
> 
> Usually they literally burn up, but I've seen "melted" CTs before.


Except if it is only on the neutral it is most likely a residual GFPE System

But on third look it appears to be rather long and most likely encompasses the neutral and phase conductors, Open secondary of the current sensor and this could be in the control wiring or a bad GFPE relay.

GE Switchboard?


----------



## Big John (May 23, 2010)

brian john said:


> ...But on third look it appears to be rather long and most likely encompasses the neutral and phase conductors...


 Yeah, that's why I threw the zero-sequence guess in there, because it looks a little to big for basic neutral current CT.


----------



## brian john (Mar 11, 2007)

Big John said:


> Yeah, that's why I threw the zero-sequence guess in there, because it looks a little to big for basic neutral current CT.


And not nit-picking but these general considered are Current Sensors and are not standard CT's.


----------



## Big John (May 23, 2010)

brian john said:


> And not nit-picking but these general considered are Current Sensors and are not standard CT's.


 What's the difference other than secondary values?


----------



## brian john (Mar 11, 2007)

Big John said:


> What's the difference other than secondary values?


As far as I know that is it. EMON tells me what we call their CT's are current sensors.

I believe the size of the "window CT's" utilized in GFPE Zero Sequence systems required a different design to retain accuracy and hence a sensor design was utilized (I was told this and have no proof this is true)

I had an extra long day and only skimmed this article/

http://www.abb.us/product/ap/db0003db004279/3D629C66613C0EBAC1257BDE00449919.aspx

http://www.altenergymag.com/emagazine/2012/06/how-to-choose-and-implement-current-sensors/1920


----------



## Wmackay (Sep 22, 2010)

I am not sure of the Switchgear mfg
if the secondary is open no current is flowing right?
why then would it over heat?
why would one coil circle neutral and phase conductors?
what would it pick up?
trying to learn something here and I appreciate your input


----------



## KDC (Oct 19, 2012)

A CT really, really doesn't like to be open circuited, in this they're very different than potential transformers. 

The exact nature of this eludes me, because nobody I've talked to can explain it in detail, other than "don't open circuit CTs, circulating currents, badness"

One coil around all phases and the neutral would be sensing any imbalance between them.


----------



## Pharon (Jan 20, 2014)

CT's should be installed with shorting blocks, so you can safely work on them without having to take down the power. The reason for this is because the way a CT works is that it's basically a step up transformer that gives you very high voltage and very low current. So if you try and lift the CT wire, you'll get an arc. To prevent this, a shorting block lets you tighten down a screw that shorts out the CT, which isn't that big of a deal because the current is so low. In a PT, you're generally transforming the voltage down to 120V, so lifting a fuse block isn't an issue from an arcing perspective.


----------



## Tsmil (Jul 17, 2011)

A CT coil is simply a transformer secondary winding. The conductor that it is over is the primary winding. When the CT coils circuit is closed, voltage is held low. If the CT circuit is open, the voltage generated by the coil would climb to its full potential based on winding ratios. Since the CT coil is not designed to operate in this open state, the insulation of the windings is not sufficient and insulation failure can occur; not to mention the voltage potential you can get from the leads. 

If your CT coil has 10 windings and you have it wrapped around a 120 volt line, the potential voltage generated could be as high as 1200 volts. 

I'm pretty sure this is how I remember the lecture.


----------



## Tsmil (Jul 17, 2011)

Wmackay said:


> why would one coil circle neutral and phase conductors? what would it pick up?


Ground fault current.


----------



## Wmackay (Sep 22, 2010)

Thanks for the inputs 
enlightening to say the least

I do have 2 points of question

1. I would think that current flow would cause heat. As you said Voltage is just potential how does it produce heat in an open circuit ?

2. I have seen GFPE sensors around the neutral near the NGR connection I have seen them, on paper, separately around each phase but I don't understand how a single coil around all phase and neutral conductors would read. If I could clamp an ampmeter around all 4 conductors I would get a reading?


----------



## Tsmil (Jul 17, 2011)

Wmackay said:


> Thanks for the inputs enlightening to say the least I do have 2 points of question 1. I would think that current flow would cause heat. As you said Voltage is just potential how does it produce heat in an open circuit ? 2. I have seen GFPE sensors around the neutral near the NGR connection I have seen them, on paper, separately around each phase but I don't understand how a single coil around all phase and neutral conductors would read. If I could clamp an ampmeter around all 4 conductors I would get a reading?



1. If the voltage becomes too high, it will break down the insulation on the windings causing arcing or short. Now you have current flow. 

2. In a circuit with no fault, the current between phases and neutral would be balanced and a zero reading would be read with a single coil around all the phases and neutral. In a circuit that has a ground fault, the current would no longer be balanced as some current is taking the path of ground back to source. Your clamp ammeter would give you a reading of the imbalance.


----------



## Wmackay (Sep 22, 2010)

Ok the coil works thanks for clearing that up 

still not clear on how the voltage is breaking down the insulation?


----------



## KDC (Oct 19, 2012)

Wmackay said:


> Thanks for the inputs
> enlightening to say the least
> 
> I do have 2 points of question
> ...


Can't really speak on #1, but #2 I can. 

In a normal circuit, the sum of what's going out and what's coming back should be 0. This applies to 3 phase as well, just the math gets more complicated. 

So putting your meter around all 3 phases and neutral, you should read 0.

(In fact, you should be able to clip all 3 phases and then the neutral separately and get the same number each time)

If there's a ground fault however, that means that some of the current won't be returning on that path, and you will read that "missing" current when you clip all phases and neutral together.


----------



## KDC (Oct 19, 2012)

High enough potential will overcome the dielectric value of the insulation. The insulation is only rated to withstand a certain voltage, exceeding that and there's a point where it the insulation just can't do it anymore. 

Back to the water analogy that gets used, enough pressure and water will start coming out the weakest points.


----------



## Wmackay (Sep 22, 2010)

thanks guys I am getting a lot here

I think I got the voltage thing now. 
The close insulated wires in the coil are acting as a capacitor and as the voltage is increased the charge jumps across the insulation "acting as a dielectric" and thus the failure .
Is that it ? am I close?


----------



## Wmackay (Sep 22, 2010)

would this be a coil failure or an outside device is at cause?


----------



## Zog (Apr 15, 2009)

Wmackay said:


> Any body Know
> 1. what this is
> 2. what is happening (root cause)


Guys already covered what that is, the cause is the filler ITE used in thier CT's back in the 70's, can't recall the specific materials (I should, I wrote a paper on this 10 years ago). 

Pretty common.


----------



## brian john (Mar 11, 2007)

KDC said:


> A CT really, really doesn't like to be open circuited, in this they're very different than potential transformers.
> 
> The exact nature of this eludes me, because nobody I've talked to can explain it in detail, other than "don't open circuit CTs, circulating currents, badness"
> 
> *One coil around all phases and the neutral would be sensing any imbalance between them*.


One Current Sensor around the phase and neutral bus and if there is a ground fault and the fault current exceeds the GFPE relay setting, this trips the switch or circuit breaker.


----------



## brian john (Mar 11, 2007)

Pharon said:


> *CT's should be installed with shorting blocks, so you can safely work on them without having to take down the power*. The reason for this is because the way a CT works is that it's basically a step up transformer that gives you very high voltage and very low current. So if you try and lift the CT wire, you'll get an arc. To prevent this, a shorting block lets you tighten down a screw that shorts out the CT, which isn't that big of a deal because the current is so low. In a PT, you're generally transforming the voltage down to 120V, so lifting a fuse block isn't an issue from an arcing perspective.


CT's for GFPE's for low voltage switchboards seldom to never come with shorting blocks.


----------



## brian john (Mar 11, 2007)

> Originally Posted by *Wmackay*
> _why would one coil circle neutral and phase conductors? what would it pick up?_


 In a Zero Sequence GFPE system all 3 phases and the neutral; pass through a "Window CT", the sum of the current read is ZERO "0" amps, if there is a ground fault downstream of this system and there are no accidental or intentional grounds on the neutral besides in the main switchboard at the neutral ground bond, then the CT sensing this ground current. If there is ground on the neutral downstream from the main neutral ground bond this can affect the pickup current of the GFPE.

Read this

http://www.electriciantalk.com/f2/addressing-ground-fault-issues-483/


----------



## Wmackay (Sep 22, 2010)

so the root cause of this "meltdown is insulation failure or open CT?


----------



## Pharon (Jan 20, 2014)

brian john said:


> CT's for GFPE's for low voltage switchboards seldom to never come with shorting blocks.


Don't I know it. But it sure does make life easier if taking the load down is a big deal.

Where it's the biggest headache for me is with metering devices. If they need to be replaced and happen to be in a critical automatic transfer switch, it's pretty important to make sure there is a shorting block. Why they're not more common, I have no idea. Seems like pretty short money to solve a very long term maintenance problem.


----------



## 8V71 (Dec 23, 2011)

Zog said:


> Guys already covered what that is, the cause is the filler ITE used in thier CT's back in the 70's, can't recall the specific materials (I should, I wrote a paper on this 10 years ago).
> 
> Pretty common.


It reminds me of Glyptal (GLPT) high voltage insulating varnish.


----------



## Zog (Apr 15, 2009)

Wmackay said:


> so the root cause of this "meltdown is insulation failure or open CT?


Possibly, more likely it is the design issue with those ITE Ct's.


----------



## brian john (Mar 11, 2007)

Zog

Can you explain the differences between a Current Transformer and a Current Sensor?


----------



## Zog (Apr 15, 2009)

brian john said:


> Zog
> 
> Can you explain the differences between a Current Transformer and a Current Sensor?


Symantics. Same thing. 

The failure the OP has on his hands is fairly common for these CT's/Sensors. I have seen this same failure maybe 5 or 6 times in the last year. It was a problem with the hardners used during manufacturing of ITE/ABB sensors in the 70's (?), high tempature and humidity accelerated the liquification of the epoxy fillers. ABB actually issued a part 21 notice (Huge deal in the nuclear world) on this exact problem.


----------



## Pharon (Jan 20, 2014)

Zog said:


> ABB actually issued a part 21 notice (Huge deal in the nuclear world) on this exact problem.


Is this it?

http://pbadupws.nrc.gov/docs/ML0224/ML022410017.pdf


----------



## Pharon (Jan 20, 2014)

Looks like it's only an issue if the CT is set at it's highest instantaneous value (12X), and only during a single phase to ground fault condition, which causes saturation and breakdown of the insulation. And ABB stopped making these CT's in 1991. They corrected the problem by adding an additional 10% turns on both primary and secondary windings.

It also doesn't appear to be an issue with ungrounded or high resistance grounded systems, or on systems with additional ground fault protection.


----------



## Zog (Apr 15, 2009)

Pharon said:


> Is this it?
> 
> http://pbadupws.nrc.gov/docs/ML0224/ML022410017.pdf


No, that's a different issue.


----------



## Pharon (Jan 20, 2014)

Zog said:


> No, that's a different issue.


There's one on this list dated April 17, 1989 entitled "Epoxy Anhydride Compound Found to be Softening or Liquefying in Low Voltage Current Transformers and Ground Sensors" -- that's probably it... but I can't seem to find a copy of the actual document anywhere.

http://www.nrc.gov/reading-rm/doc-collections/event-status/part21/part21rpts-1994-1977.pdf


----------



## Zog (Apr 15, 2009)

Pharon said:


> There's one on this list dated April 17, 1989 entitled "Epoxy Anhydride Compound Found to be Softening or Liquefying in Low Voltage Current Transformers and Ground Sensors" -- that's probably it... but I can't seem to find a copy of the actual document anywhere.
> 
> http://www.nrc.gov/reading-rm/doc-collections/event-status/part21/part21rpts-1994-1977.pdf


Thats it, you can't see it because it is archived. Too large of a file to post here.


----------



## Pharon (Jan 20, 2014)

Ah, I thought it wasn't accessible because it was older than 1995. That seems to be where they stop the online archive database.

Too bad -- I'm really curious what's in that document now. Maybe I'll call up my ABB rep and see if he can send me a pdf copy.


----------



## Big John (May 23, 2010)

Pharon said:


> There's one on this list dated April 17, 1989 entitled "Epoxy Anhydride Compound Found to be Softening or Liquefying in Low Voltage Current Transformers and Ground Sensors"


 So that happens independently of CT operation? It's just a chemical failure?


----------



## Pharon (Jan 20, 2014)

Who knows. Trying to track down the article now - stay tuned.


----------



## Zog (Apr 15, 2009)

Big John said:


> So that happens independently of CT operation? It's just a chemical failure?


Chemical failure caused by high humidity and tempature, we see this a lot doing field work in the Southeast, had several of these in Florida last year. 

What happens is the thermoset epoxy resin encapsulant material de-polymerizes and returns to a liquid state. This is due to some CT's that has incorrect mixing or formulating of the encapsulant material during manufacturing. <1% of ITE CT's in service are affected which seems small but given the 500,000+ CT's in service that makes it not so uncommon. The failures only seem to happen under high tempature and humidity conditions. I had a pile of them in my warehouse (Before we had a tempature controlled warehouse) melt a few years back, I will see if I can find the photo.


----------



## Zog (Apr 15, 2009)

Here are the photos I promised, you can clearly see which ones came from those improperly mixed encapsulant production runs and which ones were mixed correctly.


----------



## Big John (May 23, 2010)

Anyone else reminded of that scene from _Raiders of the Lost Arc? _


----------



## Zog (Apr 15, 2009)

Big John said:


> Anyone else reminded of that scene from _Raiders of the Lost Arc? _


Lost "Arc" :laughing: I see what you did there.....


----------

