Blown Transformer Cutout

[mivey]

How well do insulated buckets protect you if a glove fails during hot line work?

Better than 100% rated. You could bare hand the line out of the bucket. However, the bucket won't insulate the rest of you, like your shoulder brushing up against something else around you.

Redundancy is a good thing.

 

[mivey]

Basically close to the substation. I know of POCOs who use companion IIs on all pole pigs.

Why are you more likely to test larger units?

Yes, closer to the station. All is probably overkill but I'd rather see that than none, which is what a lot of POCOs do.

 

[mivey]

Cost. You have to weigh the cost of the unit vs time to test.
EVERY XF above a 1500 including station transformers, are tested with TTR and inspected should a station breaker or fuse blow.

 

[mbrooke]

Yes, closer to the station. All is probably overkill but I'd rather see that than none, which is what a lot of POCOs do.

Some linemen take out k-mates. Any idea why?

 

[mbrooke]

Better than 100% rated. You could bare hand the line out of the bucket. However, the bucket won't insulate the rest of you, like your shoulder brushing up against something else around you.

Redundancy is a good thing.

But my understanding is that without a metal suit its extremly painful even for 7.2/12.47Y.

 

[mbrooke]

You don't. There are no absolutes. It is risk management.

So do linemen not get injured when a unit blows?

 

[Hv&Lv]

But my understanding is that without a metal suit its extremly painful even for 7.2/12.47Y.

Nope.

Line to line or line to neutral?

line to neutral. 24,940 LL.
But you NEVER want to risk working with one hand on the phase and the other hand at any different potential.

 

[mbrooke]

Nope.

What is the typical body current?


l

ine to neutral. 24,940 LL.
But you NEVER want to risk working with one hand on the phase and the other hand at any different potential.

Makes sense, this I can agree with.

 

[GoldDigger]

But my understanding is that without a metal suit its extremly painful even for 7.2/12.47Y.

Transmission line voltages like 100,000kV, are a different matter. You do see the helicopter linemen wearing a mesh suit and using a corona discharge stick to equalize voltage as they approach. Birds may still be able to be comfortable since their smaller bodies have a lower capacitance to the environment and span a shorter distance in the potential gradient around the wire.

 

[mivey]

But my understanding is that without a metal suit its extremly painful even for 7.2/12.47Y.

not at all.

 

[mivey]

Some linemen take out k-mates. Any idea why?

if they do it without reason then it is ignorance.

 

[mivey]

So do linemen not get injured when a unit blows?

if they are close. most linemen are smarter than that and are trained to prepare for the worst.

do you turn your head when you cut a breaker on in a panel? I do. I have seen what can happen when things go wrong. You might get burned but if you turn your head at least you will still have eyes to find an escape route.

the little things can make a big difference. linemen should be trained to use every little trick to stay alive and minimize injury. still, some get hurt and killed. tired, carless, fate, etc. it is a dangerous job.

 

[mivey]

What is the typical body current?

zero, or close enough to zero not to matter.

 

[paulengr]

Alright. But how do you know that a 15-50kva transfomer will not blow its lid with scalding hot oil going all over the place when the fuse is thrown in?

It’s been my experience that electrical equipment rarely just randomly fails for no reason. You’ve got level, pressure, and a temperature gauge. There is a primary and secondary fuse. Lots of things that you can check. If nothing else you can see it swelling up or seeping oil ahead of time. Transformer failures are very rarely surprises.

 

[Hv&Lv]

Alright. But how do you know that a 15-50kva transfomer will not blow its lid with scalding hot oil going all over the place when the fuse is thrown in?

I have seen quite a few blow the lid and never catch on fire. Usually a lightning storm does that.

transformers that have the lid blown off with the oil on fire are rare, as stated earlier. And it’s true, you never know when it’s going to happen. Overloads that have time to heat the oil are the most common culprit here. Fusing a transformer that is too small for the load with too big a fuse can heat the oil to temperatures that will take very little to ignite the oil.

Any overloaded transformers that are aged, especially those that have blown a fuse or two only to have the lineman place a bigger fuse to keep from changing it out, are especially dangerous.

I watched a local volunteer fireman on a de energized transformer fire spray water up to the transformer. Water went into the can. The resulting blast of hot oil and the fire ball was a good lesson learned. Spray the bottom of the can, cool the oil. Don’t put water on an oil fire.

 

[mbrooke]

not at all.

Alright- but remember I'm talking about no gloves- just a bucket.

 

[mbrooke]

if they are close. most linemen are smarter than that and are trained to prepare for the worst.

do you turn your head when you cut a breaker on in a panel? I do. I have seen what can happen when things go wrong. You might get burned but if you turn your head at least you will still have eyes to find an escape route.

the little things can make a big difference. linemen should be trained to use every little trick to stay alive and minimize injury. still, some get hurt and killed. tired, carless, fate, etc. it is a dangerous job.

Sounds like that danger comes from closing in cutouts.

FWIW I read where one guy lost his life when a hydraulic recloser exploded in front of him.

 

[mbrooke]

zero, or close enough to zero not to matter.

Micro amps are far from zero.

 

[mbrooke]

I have seen quite a few blow the lid and never catch on fire. Usually a lightning storm does that.

Don't lightning arrestors prevent that?

t

ransformers that have the lid blown off with the oil on fire are rare, as stated earlier. And it’s true, you never know when it’s going to happen. Overloads that have time to heat the oil are the most common culprit here. Fusing a transformer that is too small for the load with too big a fuse can heat the oil to temperatures that will take very little to ignite the oil.

Alright. But remember all resi transformers work on overloads and have over sized fuses.

Any overloaded transformers that are aged, especially those that have blown a fuse or two only to have the lineman place a bigger fuse to keep from changing it out, are especially dangerous.

I watched a local volunteer fireman on a de energized transformer fire spray water up to the transformer. Water went into the can. The resulting blast of hot oil and the fire ball was a good lesson learned. Spray the bottom of the can, cool the oil. Don’t put water on an oil fire.

This is good advice- thanks

 

[mivey]

Alright- but remember I'm talking about no gloves- just a bucket.

I know. I've bare-handed lines many times from a bucket.