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Discussion Starter · #1 ·
Here is the situation. We have a plant with several large motors. 125hp, 50hp, and 40 hp ect.. the 125 hp has burned up. they are all connected to a 480v corner grounded delta service. the service is fed by 3 x 100kva overhead transformers. The utility company has had to come out and change a blown tranny fuse, I am told. Could the loss of a leg cause this motor to single phase and blow? Why wouldn't the electronic soft start on it, not prevent this? None of the other motors seem to be damaged. I believe the motor, burned while one of the utilities leg was down, from what I am told. Any ideas, or explanations would be greatly appreciated. Thanks
 

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Huntxtrm said:
Here is the situation. We have a plant with several large motors. 125hp, 50hp, and 40 hp ect.. the 125 hp has burned up. they are all connected to a 480v corner grounded delta service. the service is fed by 3 x 100kva overhead transformers. The utility company has had to come out and change a blown tranny fuse, I am told. Could the loss of a leg cause this motor to single phase and blow? Why wouldn't the electronic soft start on it, not prevent this? None of the other motors seem to be damaged. I believe the motor, burned while one of the utilities leg was down, from what I am told. Any ideas, or explanations would be greatly appreciated. Thanks
First off, 125 HP is not large. Even if the motor was running on 2 phases, you should have overload protection. So I can't see blaming the PoCo. Does your soft start have phase loss detection? Maybe the motor failed and took out the fuse.
 

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First off, 125 HP is not large. Even if the motor was running on 2 phases, you should have overload protection. So I can't see blaming the PoCo. Does your soft start have phase loss detection? Maybe the motor failed and took out the fuse.
from. this explanation your overload might have been set too high. please check And see if this is so

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Discussion Starter · #4 ·
That is what I was thinking, but I was told overload had nothing to do with it. It has electronic soft starts, that are set up by the equipment company. I have no idea, what they where set at. I'm not experienced with the electronic soft starts
 

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Discussion Starter · #5 ·
If it where standard electronic overloads, and they where set properly, they would have tripped, in my mind.
 

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what do these motors do? do you measure the motors insulation condition?. can you take any pics?
 

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Discussion Starter · #7 ·
what do these motors do? do you measure the motors insulation condition?. can you take any pics?
I'm not on site, I'm just going by what I am told. It is a 125hp compressor. For conveying granulated materials.
 

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Huntxtrm said:
That is what I was thinking, but I was told overload had nothing to do with it.
Of course the O/L had nothing to do with it, the jumper looked fine afterwards.
 

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That is what I was thinking, but I was told overload had nothing to do with it. It has electronic soft starts, that are set up by the equipment company. I have no idea, what they where set at. I'm not experienced with the electronic soft starts
The overload has EVERYTHING to do with it. Whatever fuse or breaker feeds the soft start was probably only sized to provide overcurrent protection, not overload protection.

In such a scenario the only thing saving you from smoking a motor when single phasing is the overload device. Which, we assume, in this case, is the soft start. In most cases a single phasing motor won't draw enough current to trip the overcurrent protection.
 

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What model soft-start? An "electronic" soft-start that size very likely had protection built in that should've caught either the single-phase or overload condition. It definitely sounds like there was a setup issue.
 

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I've had a 1,000 hp vfd single phase and keep going.. The 480 voltages were out to lunch and some of the smaller motors had tripped.. They AC Fail relay was still "happy" when I got there.. When I checked, one the lines on the utility had came unhooked to the fuse..

Overloads would play a huge part in it.. If the motor wasn't close to loaded, the overloads may not have tripped with a single phase.. If they weren't set up properly, they wouldn't have tripped.. Not sure if the soft start settings may need to be adjusted..
 

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KennyW said:
The overload has EVERYTHING to do with it. Whatever fuse or breaker feeds the soft start was probably only sized to provide overcurrent protection, not overload protection. In such a scenario the only thing saving you from smoking a motor when single phasing is the overload device. Which, we assume, in this case, is the soft start. In most cases a single phasing motor won't draw enough current to trip the overcurrent protection.
There is a drive that I installed a few years ago. It had a bypass feature in it, but you had to disable the o/l function to get it to run. You did have single phase protection as a consolation prize.
It was a factory rep that did the start up and showed it to me in "his" manual. It wasn't in the customers install data.
I can't remember the drive brand, but it was a smaller drive 5/7 hp or so..
I posted about it 2 years or so ago here.

Man I'm getting old and can't remember anything.
 

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There is a drive that I installed a few years ago. It had a bypass feature in it, but you had to disable the o/l function to get it to run. You did have single phase protection as a consolation prize.
It was a factory rep that did the start up and showed it to me in "his" manual. It wasn't in the customers install data.
I can't remember the drive brand, but it was a smaller drive 5/7 hp or so..
I posted about it 2 years or so ago here.

Man I'm getting old and can't remember anything.
Yeah i could see that- I would think they expect you to use external overload protection in that case, so having to disable the internal protection is a "reminder". They mention it in the technicians manual because he's supposed to be clever enough to realize that you don't just bypass it and run, but that there's another step involved (installing separate OL protection that is on the line side of both the bypass and drive). :)
 

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KennyW said:
Yeah i could see that- I would think they expect you to use external overload protection in that case, so having to disable the internal protection is a "reminder". They mention it in the technicians manual because he's supposed to be clever enough to realize that you don't just bypass it and run, but that there's another step involved (installing separate OL protection that is on the line side of both the bypass and drive). :)
The factory rep said it was a PoS idea, but you only had the choice of one or the other..
 

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Discussion Starter · #16 ·
You are all confirming what I am thinking on the overloads. This starter is a factory installed starter. I think the tech from the equipment company, that started the machine and commissioned it, might not have checked the ol settings in it. I figure the more expensive the starter, the better it should protect the motor. If set up properly. On these jobs we(the electricians) just size the wire and the ocpd. They come out and start, and test the machine.
 

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[QUOTE On these jobs we(the electricians) just size the wire and the ocpd. They come out and start, and test the machine.[/QUOTE]

pretty much the same thing happens where I work. bt the moment they hand over the machine and.finish all the paper work am usually the first one to get the schematic and confirm everything is ok and in the process learn the machine not because its a duty bt out of self will(john valdes motivated me on this)

I dnt know how big is the plant where you work, bt I do work in a big plant. and mostly work night shifts. take a scenario a machine like that fails, you didn't install it the guys did their work and left.you haven't bothered to check what. they did.

now you are the only electrician/technician.in the plant. all the operators are looking at you to solve that problem.mostly they come stand where you are

to avoid this embarrassment,I make sure I learn the machine before hand


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Discussion Starter · #18 ·
[QUOTE On these jobs we(the electricians) just size the wire and the ocpd. They come out and start, and test the machine.
pretty much the same thing happens where I work. bt the moment they hand over the machine and.finish all the paper work am usually the first one to get the schematic and confirm everything is ok and in the process learn the machine not because its a duty bt out of self will(john valdes motivated me on this)

I dnt know how big is the plant where you work, bt I do work in a big plant. and mostly work night shifts. take a scenario a machine like that fails, you didn't install it the guys did their work and left.you haven't bothered to check what. they did.

now you are the only electrician/technician.in the plant. all the operators are looking at you to solve that problem.mostly they come stand where you are

to avoid this embarrassment,I make sure I learn the machine before hand


Sent from my HUAWEI Y210-0100 using Tapatalk 2[/QUOTE]

If I where the facility electrician, I would be able to do that. I am just part of the installation team. I am setting myself to learn more on these starters, never less. The equipment company supplies many different configurations of these machines, that's why thier tech commissions them. The plants do not have an onsite electrician, and they are scattered across the country. But, when something like this happens, I get pulled into the mix. So, I am going to spend more time with the equipment people, from now on. Even though it's not part of my scope. Just to save time and equipment in the future. And to provide a better service.
 

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THE "BIG RED MACHINE"
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let us know when you come to a conclusion what happened to the motor. sounds like there might need to be more detailed commissioning process, a systematic orientation to the customer that's the equipment is setup correctly.
 

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If I recall correctly you can lose a phase on a delta system and still have 3 phase, UT Woolf only be at 58% capacity though
 
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