Overload keeps tripping

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jwilsonjr said:
snip....
The overload trips even if the disconnect to the motor is shut off and the motor is disengaged from the conveyor system so there is no mechanical load on the motor
... snip
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You are stating two scenarios here.
1) the motor disconnect is opened
2) the motor mechanical load is disconnected

If it is still tripping with a motor disconnect opened downstream, it can ONLY be the conductors or a termination somewhere between the OLR and the disconnect.

If it is tripping when the motor disconnect is closed but the mechanical load is removed, it may be related to harmonics causing too much heating in the OL thermal sensors. You may have a number of issues there, I have seen it happen; i.e. inductive coupling from another load (or the other motor), capacitance in the cables causing the drive output to mis-fire, all kinds of things. It may be something that can be solved with load reactors if you don't have them. I always recommend load reactors on drives with multiple motors because I have seen a lot of screwy things like this. Often times it damages the VFD as well.

Describe the entire circuit in more detail if you have the time.

By the way, it couldn't have been ambient temperature because the SSOL was tripping too and they are all ambient insensitive.
 
Jraef said:
You are stating two scenarios here.
1) the motor disconnect is opened
2) the motor mechanical load is disconnected

If it is still tripping with a motor disconnect opened downstream, it can ONLY be the conductors or a termination somewhere between the OLR and the disconnect.

If it is tripping when the motor disconnect is closed but the mechanical load is removed, it may be related to harmonics causing too much heating in the OL thermal sensors. You may have a number of issues there, I have seen it happen; i.e. inductive coupling from another load (or the other motor), capacitance in the cables causing the drive output to mis-fire, all kinds of things. It may be something that can be solved with load reactors if you don't have them. I always recommend load reactors on drives with multiple motors because I have seen a lot of screwy things like this. Often times it damages the VFD as well.

Describe the entire circuit in more detail if you have the time.

By the way, it couldn't have been ambient temperature because the SSOL was tripping too and they are all ambient insensitive.
Click to expand...
how do you test for harmonic related problems?
 
I don't see how a standard overload could possible trip if there is no current flowing through it. They operate by generating a small amount of heat, and when they get too warm, they trip.

I have also heard SS overloads can be a little funky when used on VFDs, so I would not use them there, but standard overloads should be OK.

As for the suggestion of adding load reactors, I tend to concur, especially since you probably have some long runs out to the motors. However, since the OL trips w/o the motor even being connected, I suspect it is not the solution to this particular problem. AB does suggest the use of terminators on 1305 drives IIRC.

How long does it take to trip?

Is there any chance you managed to cross wire the overloads so one leg of the overload is actually wired to the wrong motor?
 
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electricalperson said:
how do you test for harmonic related problems?
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Difficult without some very expensive metering and recording equipment. In general, it's difficult to even measure the normal current on the output of a VFD because of harmonics, that's why SSOLS typically are not good at it (at least the cheap ones). Actually measuring the harmonics and then knowing what effect that might be having is very very expensive and difficult to do with any certainty. It's probably cheaper to add a reactor and see if it helps. If it doesn't, it was still a good idea for other reasons.

pertersonra said:
Is there any chance you managed to cross wire the overloads so one leg of the overload is actually wired to the wrong motor?
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Now THERE's a great idea to check on! That would explain a lot.

By the way, when I said that if the disconnect was open and it was still tripping, I meant that it would have to be a leak in the wires or termination somewhere; petersonra is correct, you HAVE to have current flowing.
 
tripping overload

tripping overload

petersonra said:
I don't see how a standard overload could possible trip if there is no current flowing through it. They operate by generating a small amount of heat, and when they get too warm, they trip.

I have also heard SS overloads can be a little funky when used on VFDs, so I would not use them there, but standard overloads should be OK.

As for the suggestion of adding load reactors, I tend to concur, especially since you probably have some long runs out to the motors. However, since the OL trips w/o the motor even being connected, I suspect it is not the solution to this particular problem. AB does suggest the use of terminators on 1305 drives IIRC.

How long does it take to trip?

Is there any chance you managed to cross wire the overloads so one leg of the overload is actually wired to the wrong motor?
Click to expand...
What are terminators? I had a contractor install line reactors. The VFD would get an overvolt fault when you applied power so the reactor was removed. The overloads are wired correctly to each motor.
 
tripping overloads

tripping overloads

zog said:
There is no such thing as infinite resistance. What was you test voltage and what readings did you get.
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The megger was set to 1000 volts. The scale reads from left to right begining with the infinity symbol. That is where the needles settles at during the reading. If I short the test leads together the needle swings to the right settling on zero ohms.
 
still tripping

still tripping

Jraef said:
You are stating two scenarios here.
1) the motor disconnect is opened
2) the motor mechanical load is disconnected

If it is still tripping with a motor disconnect opened downstream, it can ONLY be the conductors or a termination somewhere between the OLR and the disconnect.

If it is tripping when the motor disconnect is closed but the mechanical load is removed, it may be related to harmonics causing too much heating in the OL thermal sensors. You may have a number of issues there, I have seen it happen; i.e. inductive coupling from another load (or the other motor), capacitance in the cables causing the drive output to mis-fire, all kinds of things. It may be something that can be solved with load reactors if you don't have them. I always recommend load reactors on drives with multiple motors because I have seen a lot of screwy things like this. Often times it damages the VFD as well.

Describe the entire circuit in more detail if you have the time.

By the way, it couldn't have been ambient temperature because the SSOL was tripping too and they are all ambient insensitive.
Click to expand...
Motor B is still wired as motor A used to be. It still has the same old Solid State overload. This unit has never tripped. Would a harmonic problem trip both overloads? The wires going to the seperate motors are run in seperate conduits as well.
 
electricalperson said:
yea. do you need a power quality analyzer?
Click to expand...


Not exactly EP. You can test for the presence of harmonics just by comparing a readout from a non-RMS meter compared to a true RMS meter and go from there. You can see troubles, but nothing like a PQA where you can determine what levels you have and where. If you get a chance, look at Fluke's new 345. Boyyyyy, is she a beauty:grin:
 
jwilsonjr said:
The megger was set to 1000 volts. The scale reads from left to right begining with the infinity symbol. That is where the needles settles at during the reading. If I short the test leads together the needle swings to the right settling on zero ohms.
Click to expand...

If you look closley you will see the "Infinity" mark is to the right of the full scale deflection of the meter.

What is the highest reading on the scale before "Infinity"?
 
zog said:
If you look closley you will see the "Infinity" mark is to the right of the full scale deflection of the meter.

What is the highest reading on the scale before "Infinity"?
Click to expand...
I believe it is 1000 megohms. I do not have access to the megger at this time.
 
What brand is the manual overload relay? I know the SSOR was the original culprit, but just curious.

I think that your type od Variable drive has the possibiltiy of outputting data to a computer...not sure if that would help
 
jwilsonjr said:
Maybe someone can help me out there.
I am using a Allen Bradley 1305 VFD to control the speed of two 1.5 HP motors that move a conveyor chain in our plant. Recently the solid state overload relay began tripping on Motor A. I removed the motor from the conveyor system and checked the motor out with an ohm meter as well as incoming voltage and found the motor to be good as well as the 480v feed. After repeated tripping we installed a new motor which was tested prior to installation. More tripping. I replaced the solid state overload with a new relay. More Tripping. I installed a manual Motor starter protector to replace the solid state relay after being told that solid state relays don't like VFD's. More tripping. The overload trips even if the disconnect to the motor is shut off and the motor is disengaged from the conveyor system so there is no mechanical load on the motor.
I have used a megger to test all of the wiring and all rings out ok. Anybody got a clue. Any info would be welcome.
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tell us more about the two 1.5 HP motors. Are they identical? Is either motor dual speed?
 
OL Tripping, what's the load current?

OL Tripping, what's the load current?

Have you taken current readings, and got lucky to catch a trip? Load's vary due to many mechanical reasons. What are the number of starts per hour excessive starting will heat an overload. Normally starts on drives are not as big of an issue, but you have included O/L's, correctly, with multiple motors per drive. Went back and read the O/L trips under no load, and still after being replaced, and after the motor was replaced... This is new
 
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This doesnt make sense

This doesnt make sense

I would start by asking if there are 2 separate drives driving 2 separate motors. What is the nameplate fla on each motor?? What is the current draw on each leg at start and run?? What is the voltage reading at the motor phase to phase and Phase to ground A-B-C. What is the heater set at and or what is the number on the heater is it solid state bimetalic or eutectic solder?? If a ct heater section is used does the load wire pass through the donut only once ?? The most likely thing that I can think of is that one of the T-splices is wrong in the peckerhead. Sometimes a wrong splice can cause the motor to run no load yet trip under load. It is unclear from the op where the disconnect is. Is it at the motor or at the drive? Are the screws on the overloads tight? This ought to keep you busy for a little while. Dont forget to lockout tagout work safe.
 
This post cant end here

This post cant end here

Like Radio Shack youve got questions?? Weve got answers. Maybe Im too impatient. Wouldnt gear reduction have been cheaper??
 
jwilsonjr said:
What are terminators? I had a contractor install line reactors. The VFD would get an overvolt fault when you applied power so the reactor was removed. The overloads are wired correctly to each motor.
Click to expand...
AB sells terminators that install at the motor to deal with reflected wave issues from IGBTs. I think the 1305 drives are one of them that needs them after a certain distance.

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1204-in002_-en-p.pdf

Why would line reactors have any effect on the DC bus voltage?
 
jwilsonjr said:
I believe it is 1000 megohms. I do not have access to the megger at this time.
Click to expand...

Then all you know is it is greater than 1000M, which isnt much but high enough to not be causing your problem.
 
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