Troubleshooting quandry?

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e57

e57

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San Francisco, CA
Got a dough mixer with a 240 Delta (highlegged) feed. 238, 238, 247 running...

The main motor is a wye/delta constant torque and is over the Ohm capability of the meter I had with me today.... But when running there is one leg drawing MUCH less than the other two. 26, 26, 18....

Main machine over-loads trip after a while, and has that electrical genie fart smell. :D

Machine technichian was claiming POCO "Current inbalance" - "Happens all the time..." - Took a while to talk him past that and is thinking possible motor failure (My thinking) , or a bad contact now.

There was one moment when the voltage was reading 36, 236, 241 - but I think that was when the the unit was tripped and did not open all poles and read through the motor.... Haven't seen it since.... Intermitant phase loss?


So.....

Motor toast????? What say you?
 
Is this real delta high leg, from the poco, or manufactured 3-phase? Your numbers sound more like what you'd expect when the machine is served by a rotophase.
 
mdshunk said:
Is this real delta high leg, from the poco, or manufactured 3-phase? Your numbers sound more like what you'd expect when the machine is served by a rotophase.
Click to expand...

Open delta at the street - (turn a V counter-clockwise, and ground the mid of the bottom...)
 
e57 said:
(turn a V counter-clockwise, and ground the mid of the bottom...)
Click to expand...
Yeah, got a handle on that.

Seems like I remember a Square D bulletin about sizing the overloads specially if you have delta. Does that ring a bell?

In any event, it sounds like you were crippled by the test equipment you had available today, eh?
 
mdshunk said:
Yeah, got a handle on that.

Seems like I remember a Square D bulletin about sizing the overloads specially if you have delta. Does that ring a bell?
Click to expand...

Ooooooo...... (Not sure if you remember my "ratted someone out thread" This is that joint - where some hack swapped the high-leg on most everything. Long story full of irony there when I have time.) If say someone swapped the leads (Would have had to do it twice since rotation is fine) for an over-load with different settings leg to leg is your thinking?

Didn't check the settings.... But the amperage reading doesn't sound right to me, or the "I'm a motor about to blow" stink in evidence.
 
e57 said:
Ooooooo...... (Not sure if you remember my "ratted someone out thread" This is that joint - where some hack swapped the high-leg on most everything. Long story full of irony there when I have time.) If say someone swapped the leads (Would have had to do it twice since rotation is fine) for an over-load with different settings leg to leg is your thinking?
Click to expand...
No, I was just thinking that the overload could be sized differently on the one leg, but I might be wrong.

I'd rather think that hack single phased it for a period of time and got that motor most of the way to toast. The appliance tech, bless his heart, doesn't have a clue. "Current imbalance"... yeah, got it bubba. The reason is why, and he wants to blame that on you. It's a shame that you didn't have a chance to ohm out the windings or do a megger check.
 
mdshunk said:
No, I was just thinking that the overload could be sized differently on the one leg, but I might be wrong.

I'd rather think that hack single phased it for a period of time and got that motor most of the way to toast.
Click to expand...

Both are possible - I'll check them out again Monday.
 
Who's overload relay is it? Some, like the Square-D solid state OL, have phase current imbalance protection set at fairly low levels that cannot be defeated and is notorious for nuisance tripping.

But you have almost a 30% current imbalance there, that's the kind that will overheat your motor pretty quick even if the highest phase current is still below the FLA. that OL tripping may be what is preventing a fire!
 
More stuff to consider:

  • The heating effect of voltage imbalance is 2x the square of the imbalance percentage. So in your case, you have a 4.5% Vimb, so it is heating the motor 40.5% higher than if it were balanced.
  • NEMA requires derating a motor if the Vimb exceeds 1%, but no more than 5% total and the derate is the square of the Vimb. So at 4.5%, you would need to derate that motor to 80% of its full load rating. You didn't post the FLA.
  • For every 10 degrees C you increase the motor temperature, you cut the insulation life by 50%.
 
mdshunk said:
No, I was just thinking that the overload could be sized differently on the one leg, but I might be wrong.
Click to expand...

There is absolutely no reason that you would size the overloads different depending on the phase you are connected to.

It would really help if we knew more about what overloads and starter are installed. Melting alloy (eutectic solder), bimetallic, and solid-state all have different reactions to current imbalances.
 
Jraef said:
More stuff to consider:
  • The heating effect of voltage imbalance is 2x the square of the imbalance percentage. So in your case, you have a 4.5% Vimb, so it is heating the motor 40.5% higher than if it were balanced.
  • NEMA requires derating a motor if the Vimb exceeds 1%, but no more than 5% total and the derate is the square of the Vimb. So at 4.5%, you would need to derate that motor to 80% of its full load rating. You didn't post the FLA.
  • For every 10 degrees C you increase the motor temperature, you cut the insulation life by 50%.
Click to expand...
Did you use 238, 238, 247 volts? I get a 2.5% imbalance or a 12.4% temperature increase.
 
e57 said:
Got a dough mixer with a 240 Delta (highlegged) feed. 238, 238, 247 running...

The main motor is a wye/delta constant torque and is over the Ohm capability of the meter I had with me today.... But when running there is one leg drawing MUCH less than the other two. 26, 26, 18....

Main machine over-loads trip after a while, and has that electrical genie fart smell. :D

Machine technichian was claiming POCO "Current inbalance" - "Happens all the time..." - Took a while to talk him past that and is thinking possible motor failure (My thinking) , or a bad contact now.

There was one moment when the voltage was reading 36, 236, 241 - but I think that was when the the unit was tripped and did not open all poles and read through the motor.... Haven't seen it since.... Intermitant phase loss?


So.....

Motor toast????? What say you?
Click to expand...
What do you mean wye/delta? Can it be wired either wye OR delta or is it a wye start delta run? Does it come with wiring diagram on motor somewhere?
 
Jraef said:
  • You didn't post the FLA.
Click to expand...

Would have required riggers - if not at least two more people. Motor is installed from under a very large cast iron base, (Silly Germans) and the name plate is on the back against the wall. (Typical....) The machines technician has all the normal data and readings for the motors and machine et al in some manual he'll be dragging over Monday...

The over-load that's tripping is the main one for the machine (two motors and a control circuit) - the two motors have individual protection as well (After the one in question) - but so far have not tripped???? And those I know do not have any individual settings to have been switched.

For every 10 degrees C you increase the motor temperature, you cut the insulation life by 50%.
Click to expand...
Not doubting anything else you said - but this one might be a bit of an over-statement... ~20F increase would not cut insulation life that much.... :rolleyes:

While I don't consider the voltage imbalance that extreme - for it to do any significant damage IMO they would have had to throw a larger than normal log of dough, or a brick or two in it to actually do the damage. Which they have assured me the haven't done. (Small batches for some time now...) And it also would not explain the significant (>30%) current differance observed with those voltages at present.

I'm thinking more and more that Marc may have it - it may have been single phased for a bit.... Not sure how or why???? That dope may have even grounded a phase - he had no clue...
 
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quogueelectric said:
What do you mean wye/delta? Can it be wired either wye OR delta or is it a wye start delta run? Does it come with wiring diagram on motor somewhere?
Click to expand...
Wye start delta run - machine has a full schematic and the relays marked as such.
 
quogueelectric said:
Is this a new installation or has this machine been running here for some time.?
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15 years - started this after the hack job that hi-legged a cash register, 2 reffers @ $3K ea., and reduced the life of a couple HPS ballasts out front. As this item doesn't have a neutral - I find it hard to pin it on him but would not be suprised...
 
e57 said:
Would have required riggers - if not at least two more people. Motor is installed from under a very large cast iron base, (Silly Germans) and the name plate is on the back against the wall. (Typical....) The machines technician has all the normal data and readings for the motors and machine et al in some manual he'll be dragging over Monday...
Click to expand...
Sounds like the perfect job for the see-snake......
 
It doesnt seem to have a problem with startwindings amperage just run windings amperage?? What brand and type of overloads are installed in the starter?? Bimetalic, eutectic solder, solid state? Wouldnt be telemechanique not sure of the spelling I think it is a french company but they are used in some square d mccs they have a built in very tight voltage imbalance tolerance and in some fringe areas of power distribution the voltage difference is enough to trip this relay.
 
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