Checking amps on 2400 volt motors

[zog]

I was, but I'm home sick, so, my coworkers are now. I called one of them and read him the posts I have received on this. He asked me to copy and e-mail it to him. He said he would print it out and give it to the boss in the morning. Of course I'll have to leave out some of my comments!

Dont forget to leave off the comment below your signature

 

[zog]

We discussed that and the big boss is saying the CT's may be the wrong size. He wants a "true " reading...... We have a company that we use for our high voltage stuff, they could do the tests, but the big boss doesn't want to spend the money.

Ok, your boss is an idiot. Have your HV guys do a TTR on the CT's to verify nameplate data, that will prove alot more than his "experiment" will. I know some good guys in Greenville if you need them, probally the same guys you use already (Starts with "I")

 

[hockeyoligist2]

(Starts with "I")

Yes Sir, You are correct!

 

[zog]

Yes Sir, You are correct!

Good guys, I consider the owner a good friend.

 

[LarryFine]

We discussed that and the big boss is saying the CT's may be the wrong size.

Other than not being able to meter the service at 100%, the 'wrong' CT shouldn't be an issue. I believe the CT's and the meter must be made/set for the same current ratio.

 

[don_resqcapt19]

Right but he wont be able to run the ground sheild back through the clamp on meter, this is how a CT is installed but not an option for this test.

I do need to correct my last post, it wont read zero, but the reading will not be accurate.

The only inaccuracy would be from the current on the shield, correct? In the installation where you run the complete cable including the shield through the CT and then bring the shield back through the CT, that will cause any current on the shield to be canceled out leaving you with a true reading of the actual conductor current.

 

[zog]

The only inaccuracy would be from the current on the shield, correct? In the installation where you run the complete cable including the shield through the CT and then bring the shield back through the CT, that will cause any current on the shield to be canceled out leaving you with a true reading of the actual conductor current.

Right, but that wouldnt be the case for the proposed clamp on reading.

 

[don_resqcapt19]

Right, but that wouldnt be the case for the proposed clamp on reading.

Just so I understand...the clamp on reading will read the current on the conductor, but the current on the shield will be added or subtracted from the conductor current if you put the clamp on around both.

 

[Cold Fusion]

Just so I understand...the clamp on reading will read the current on the conductor, but the current on the shield will be added or subtracted from the conductor current if you put the clamp on around both.

That's my understanding. My experience has been that the phase current readouts having the error doesn't matter much. For a zero-sequence CT it does matter.

cf

 

[Cold Fusion]

Other than not being able to meter the service at 100%, the 'wrong' CT shouldn't be an issue. I believe the CT's and the meter must be made/set for the same current ratio.

Generalization based on OP's discussion (which means I could be all wet):
For the type of equipment the OP is discussing, my experience has been that the important parts are:
The CT are all the same;
The ratio is within range.

The readouts\indicators\protective relay inputs, are generally programmable for the CT ratio.

However, if the meter is a mechanical movement, then you are dead on. The meter scale has the match the CT ratio.

cf

 

[quogueelectric]

I used to have an article from a fed lab where an emloyee did exacty what you are suggesting with a fluke multimeter on a 2400v motor starter and he is dead now. A slow painfull death fromthe arcflash. he thought it wuold read out of range well he was wrong and dead too. Do0nt do it. PM me and get my phone # I want to talk to your boss.

 

[LarryFine]

PM me and get my phone # I want to talk to your boss.

PLEASE record the call!

 

[Cold Fusion]

I used to have an article from a fed lab where an emloyee did exacty what you are suggesting with a fluke multimeter on a 2400v motor starter and he is dead now. A slow painfull death fromthe arcflash. he thought it wuold read out of range well he was wrong and dead too. Do0nt do it. PM me and get my phone # I want to talk to your boss.

This tragic death you quote, wasn't that caused by a multimeter test leads being directly connected to the MV, to measure voltage?

If so, that is not what the OP has outlined. The OP is discussing using a clamp-on ammeter to measure motor current. No direct electrical connection. As has been mentioned earlier, In certian cases, 600V CTs are used on MV cables.

Just to be clear: I am not advocating the OP do this job. In fact I'd say they shouldn't.

I'd do it, and likely use a 600V CT - just not at the motor connection box and probably not with a direct-read clamp-on. There are other more convenient, lower risk places.

And no, I would not call in a specialty team to do a wicked expensive TTR - when all I want to do is verify the installed CT markings reasonably match the measured turns ratio.

I am certainly not demeaning the tragic accident you quote. I am saying this job can be dome safely if one understands the equipment and it's limitations

cf

 

[zog]

And no, I would not call in a specialty team to do a wicked expensive TTR - when all I want to do is verify the installed CT markings reasonably match the measured turns ratio.


cf

We charge $100 for a CT test that includes a TTR. Hardly wicked expensive.

 

[Cold Fusion]

We charge $100 for a CT test that includes a TTR. Hardly wicked expensive.

You're right. That is an excellent price. I didn't have any idea it would be that inexpensive.

That sure isn't much for driving out, opening up the switchgear, (do you have to un-terminate the conductor and pull off the CT), record the CT data, setup and do the test, fold up, re-terminate, put the cabinet back on, drive back to the shop, write up the report, email it over - no hard copy

I would have figured the first one was $500 and the next two were $100 each. And I'd be waiting in line for the guy that could do it to get free for a half a day.

At $100 each I'd definitely be calling you.

cf

 

[quogueelectric]

This tragic death you quote, wasn't that caused by a multimeter test leads being directly connected to the MV, to measure voltage?

If so, that is not what the OP has outlined. The OP is discussing using a clamp-on ammeter to measure motor current. No direct electrical connection. As has been mentioned earlier, In certian cases, 600V CTs are used on MV cables.

Just to be clear: I am not advocating the OP do this job. In fact I'd say they shouldn't.

I'd do it, and likely use a 600V CT - just not at the motor connection box and probably not with a direct-read clamp-on. There are other more convenient, lower risk places.

And no, I would not call in a specialty team to do a wicked expensive TTR - when all I want to do is verify the installed CT markings reasonably match the measured turns ratio.

I am certainly not demeaning the tragic accident you quote. I am saying this job can be dome safely if one understands the equipment and it's limitations

cf

Ok I reread the op and what he is saying is to read motor start/run amps. I understand that you may do this as a daily routine but he did state that the equipment is only rated at 600 volts. The reasoning that you could turn it off and know enough to bypass any shielding and semiconductive material by measuring in the peckerhead is clever. Stand across the room in case it blows up is where common sence flies out the window. Either purchase equipment rated at the voltages it is being used at or do it yourself and only put yourself at risk. The specific accident involved voltage readings and he assumed it would read OL because it was rated at 1000v. The engineers calculated the arcflash at 30,000* farenheight if I remember correctly.

 

[Fulthrotl]

We discussed that and the big boss is saying the CT's may be the wrong size. He wants a "true " reading...... We have a company that we use for our high voltage stuff, they could do the tests, but the big boss doesn't want to spend the money.

then have the a$$whole hang the meter on himself.

 

[Fulthrotl]

I used to have an article from a fed lab where an emloyee did exacty what you are suggesting with a fluke multimeter on a 2400v motor starter and he is dead now. A slow painfull death fromthe arcflash. he thought it wuold read out of range well he was wrong and dead too. Do0nt do it. PM me and get my phone # I want to talk to your boss.

when you're done talking to him, post his picture, so i can just walk up
to him in the parking lot, and slap him silly. no explanation why, just a
sound beating. he's too stupid to comprehend an explanation.

just leave him with a clamp on, clamped on someplace sensitive and
personal....

 

[zog]

You're right. That is an excellent price. I didn't have any idea it would be that inexpensive.

That sure isn't much for driving out, opening up the switchgear, (do you have to un-terminate the conductor and pull off the CT), record the CT data, setup and do the test, fold up, re-terminate, put the cabinet back on, drive back to the shop, write up the report, email it over - no hard copy

I would have figured the first one was $500 and the next two were $100 each. And I'd be waiting in line for the guy that could do it to get free for a half a day.

At $100 each I'd definitely be calling you.

cf

I am talking shop test, on site with travel you are about right.

 

[mxslick]

You're right. That is an excellent price. I didn't have any idea it would be that inexpensive.

That sure isn't much for driving out, opening up the switchgear, (do you have to un-terminate the conductor and pull off the CT), record the CT data, setup and do the test, fold up, re-terminate, put the cabinet back on, drive back to the shop, write up the report, email it over - no hard copy

I would have figured the first one was $500 and the next two were $100 each. And I'd be waiting in line for the guy that could do it to get free for a half a day.

At $100 each I'd definitely be calling you.

cf

Even at $500 each it would be a bargain compared to paying out death benefits to the worker's next of kin.

As far as that OP's boss, I am amazed that everytime I think someone can't possibly be so stupid, along comes a bigger stupe.