power flex 4 fault 042

[bornwild]

hey guys,

I need urgent help. We have one power flex 4 and it is showing fault 042. checked the manual. it says check for short b etween u w phase. I cheked everythin ok. Check motor resistance. all ok. WHen i disconnect the motor the drive is increasin its frequency. Wht could be problem .Please help

[OkiePC]

I would recommend that you power down the drive and wait for the DC bus to bleed down. Then disconnect the motor leads from the drive and test the motor circuit for shorts to ground with a megger (megohmmeter) set for 1000V. You need at least a few megohms to ground in order for that drive to be "happy". I like to see a couple hundred megohms to ground, but in some wet environments, this is unrealistic.

Next, using a good quality ohmmeter, check the leg to leg resistance of the entire motor circuit. All three ohm readings should be the same within a couple %.

It is best to perform these tests without disturbing any other connections between the drive and motor. Don't open any local disconnects or do anything else that might affect the test.

If you pass all these tests, replace the drive.

Since you said the drive will run (without faulting?) and ramp up to command speed with the motor disconnected, I am pretty sure there is something wrong with the motor circuit, which includes all the wiring and the motor...

[bornwild]

thanks. i disconnected and checked resistance . all seem ok. but when i connect the drive it is faulted

[bornwild]

the manual says replace the drive if fault cannot be cleared

[sthompson]

Have you tried it without the Motor connected? If so, do you still get the Fault?

Stu.....

[bornwild]

Originally Posted by sthompson

Have you tried it without the Motor connected? If so, do you still get the Fault?

Stu.....

yes, I disconnected the wires form the drive goin to motor. The drive seems to run fine. The display shows it is increasin the frequency. I , still dont get what could be problem. I check resistance betweem UVW and ground all seem ok. I dont think it is drive problem .My electrician says it is motor which is causing this but all seems ok to me.

[sthompson]

Originally Posted by bornwild

yes, I disconnected the wires form the drive goin to motor. The drive seems to run fine. The display shows it is increasin the frequency. I , still dont get what could be problem. I check resistance betweem UVW and ground all seem ok. I dont think it is drive problem .My electrician says it is motor which is causing this but all seems ok to me.

What is the operating voltage of the VFD/Motor? How are you checking resistance to ground? An Ohmmeter isn't good enough, you need a Megger that puts a high enough voltage on the windings.

Stu....

[leitmotif]

I would disconnect motor leads from VFD and
1.. Megger phase to ground
2. Read phase to phase resistance with ohmeter. YOu can also put 6 or 12 VDC on motor leads read current and then calc resitance. Would want no more than 3 to 5% variation in resistance.
3. IF one and two OK then would give some thought to disconnect motor and megger line both phase to phase and phase to ground.
4. Hook motor to independent power supply and check line currents and line volt to ground at terminal box.

CURIOSITY
Could he hook resistors across VFD output correctly sized to compare to motor current? Waste of time since VFD runs OK unloaded or is it?

Dan Bentler

[DickDV]

How far in wire feet is the motor from the drive? Since this is a PF4, it's probably low hp which can be very susseptible to lead capacitance currents causing faulting.

And, follow OkiePC's advice on this exactly. Anything less than a 1000V megger is not going to help you. And use it to check phase-to-phase, not just phase-to-ground.

[fitzyD]

Try disconnecting the cable from the motor and cap the ends to make sure there are no problems with the cable itself.

[bornwild]

Originally Posted by leitmotif

I would disconnect motor leads from VFD and
1.. Megger phase to ground
2. Read phase to phase resistance with ohmeter. YOu can also put 6 or 12 VDC on motor leads read current and then calc resitance. Would want no more than 3 to 5% variation in resistance.
3. IF one and two OK then would give some thought to disconnect motor and megger line both phase to phase and phase to ground.
4. Hook motor to independent power supply and check line currents and line volt to ground at terminal box.

CURIOSITY
Could he hook resistors across VFD output correctly sized to compare to motor current? Waste of time since VFD runs OK unloaded or is it?

Dan Bentler

> Thanks all. I used a megger @1000v and tested with phase to ground . It was short. Damn motor. When i check with multimeter it is showing OL(open load). Can some one explain how applying high voltage gives more accurate results

[sthompson]

Originally Posted by bornwild

> Thanks all. I used a megger @1000v and tested with phase to ground . It was short. Damn motor. When i check with multimeter it is showing OL(open load). Can some one explain how applying high voltage gives more accurate results

Thanks for letting us know how it worked out.

Most MultiMeters only have a 9VDC Battery in them, which is no where near enough voltage to get the Motor Winding Insulation to break down. The higher voltage of the Megger is enough to cause the Insulation to break down if there is a weak spot. It is usually to ground, but it can also be from winding to winding. Sometimes even in the conductors from the VFD to the motor. Thus DickDV's and OkiepC's advice. A good quality Megger is indispensable when troubleshooting motor problems.

Stu....

[DickDV]

bornwild, insulation is similar to the wall of a pipe. Within a range of pressures, the wall functions properly but above that range it fails and the contents of the pipe escape.

Insulation also has a maximum voltage (pressure) rating that can change as it ages. Moisture and dust also can degrade it.

So, when checking the quality of the insulation, it is important to check it at or above a level where it normally operates. Since a 480VAC sinewave reaches 660V at its peak, that would be the max on a sinewave. PWM power from a drive can reach as much as 1600V momemtarily due to ringing and other high frequency effects. Thus the 1000V megger.