To Fuse or not to fuse...That is the question

[Dark Knight]

SOS...

We are having a discussion about if the secondary at a CCVT should be fused or not. The company I work for now does not fuse the secondary on the CCVTs. The company I worked for before coming here did not do it.

I was explained about the reason to not fuse it but I totally forgot. During a quick research I did found that manufacturers provide a table IF(sic) fuses are required.

Flyer, Wolverine, Benbo and the gang...What is your opinion on this? What does your company do?

Thanks in advance... :bio:

 

[Wolverine]

Brief answer:

A CCVT is just a capacitor, right? So a failure (short) on the secondary side is just shorting out a capacitor. No appreciable current flows. Better to slug-it than to have to send a man out at 3AM on Xmas morning to replace a $2 blown fuse.

CT's not so - a failure on the secondary will burn until it clears.

(For the uninitiated, a CCVT is a Capacitor Coupled Voltage Transformer, a large device used to sense the voltage on a high V power line. It consists of a series of capacitors that step down the voltage to something that won't fry your face off. If you don't know what a capacitor is, can't help you)

Thanks for letting me flex my Mad Engineering Skillz.

 

[NCcarguy]

hummmmm... I can't even think about answering that question,

but I sure would like to know why when I set my tester to the 600v and stuck the black wire to one prong, and the red wire to the other prong on a 220v breaker the damn tester exploded in my hand! It was about the closest I've ever come to a heart attack I think!

If you tag one prong and a ground you would see 120+/- (115v), either red or black....but if you tagged them both I should have just read 230+/- (220v)....but the damn thing just exploded!

sorry for thread hijacking, it's kinda my thing.....

 

[Flyer_PE]

I'm with Wolverine on this one. For the CCVT , the consequences of having the fuse blow are worse than having the thing short out.

I've never seen a fuse on the secondary side of a CT. That seems like a sure fire way to violate the first canon of electrical engineering. Thou shalt not make fire!

 

[FLBuff PE]

For you EE guys/gals:

 

[Freon]

I concur with Flyer and Wolverine. Fire + high voltage = angry firemen.

 

[Wolverine]

I've never seen a fuse on the secondary side of a CT. That seems like a sure fire way to violate the first canon of electrical engineering. Thou shalt not make fire!

D'oh! Yes, of course you're right - you don't fuse CT's. I was so busy flexing my Mad Engineering Skillz, I went and said something silly. They will burn if you open them up though. Not that I've ever seen anything like that. bzzzzzzttt ! ! !

 

[Dark Knight]

I went and said something silly. They will burn if you open them up though. Not that I've ever seen anything like that. bzzzzzzttt ! ! !

I understood what you meant. I know that anyone that worked on relays knows that CT SHALL NOT be fused. I did see an open CT circuit, or at least what was left of it. The voltage on those open terminals rise like the cost of living in Florida in zero time. When the voltage become to high it jumps to wherever it can. Expensive fireworks, if you ask me and extremely dangerous. One of my former co-workers almost lost his hand when he inserted a GE test plug without shorting links in a live CT circuit. I was not with him but he showed me the scars that event left.

Thanks for your input Wolve, and to you as well Flyer.

 

[Flyer_PE]

Right after I got out of school, I had a relay engineer training me how to "stab out" relays for testing. On day one, he gave me the big speech about not opening the secondary of the CT. On day two, we were setting up to calibrate a relay. He starts to insert the insulating stab and I see he's off by one pole on the test switch. I get the following out of my mouth : "Hey, are you su zzzzzzzzzzzzzzzzzzzzt". Nobody hurt, but it scared the crap out of both of us.

 

[Dark Knight]

Right after I got out of school, I had a relay engineer training me how to "stab out" relays for testing. On day one, he gave me the big speech about not opening the secondary of the CT. On day two, we were setting up to calibrate a relay. He starts to insert the insulating stab and I see he's off by one pole on the test switch. I get the following out of my mouth : "Hey, are you su zzzzzzzzzzzzzzzzzzzzt". Nobody hurt, but it scared the crap out of both of us.

Do not blame you for being scared. It is scary.

When I was a Relay Engineer(Oh happy times) always was very careful with the CT circuits. I even worked on energized distribution breakers that had e-mech relays and did my testing without incidents. Even tested live diff e-mechs. Was just a matter of having and following a plan. The image of of my co-worker's burned hand was always on my mind. That gives you extra motivation to pay attention to details.

I remember that my boss had me calculating the voltage for an open BCT on a transformer. I came with the value and he told me that was going to be the voltage I was going to have in my hands if I forgot to place the shorting links and open a CT circuit. Not to be taken lightly.

 

[Wolverine]

I hated those @#%$@ GE test paddles, as does everyone I think. With Westinghouse, you can give it a little test pressure but abort if you hear the bzzt. With GE, you are committed. Line it up, take a deep breath, start to press, stop, check your wiring again, line it up again and take another deep breath, then press. Sigh of relief if you don't hear bzzt or ker-chunk-chunk.

 

[Flyer_PE]

Worst one I ever did myself was during a functional test at the nuclear plant. I heard a relay chatter in the panel when I installed a jumper. No harm to the plant since it was just an alarm relay. The control room operator was pretty pissed at me though because I saturated the old dot-matrix printer with about 30 minutes worth of printing "alarm-clear-alarm-clear....."