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Discussion Starter · #1 ·
Hello everyone,
I have a NIDEC H300 that has had a reoccurring OI ac trip. We have the manual and have followed it’s recommended actions. We also have been in contact with NIDEC technical support trying to correct this issue.

It does not happen all of the time. It will run for months with no trips. Then it will trip multiple times. I believe it happens during start up.

Does anyone have any experience working with NIDEC “Emerson” VFDs?

Also, if anyone has any suggestions or extensive VFD knowledge I would greatly appreciate it. I’ll be happy to provide any details in regard to the tests and checks we have already done.

I’m typically used to working on Yaskawa, Benshaw and Robicon drives. This NIDEC has been interesting.....

Thank you in advance.
 

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What kind of motor and what environment is the motor in.

damp motor/connections ?
 

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Discussion Starter · #3 ·
What kind of motor and what environment is the motor in.

damp motor/connections ?
It serves a chilled water pump. The area is typically very dry. Also, we recently had the motor tested and it passed.
 

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Discussion Starter · #4 ·
What kind of motor and what environment is the motor in.

damp motor/connections ?
Sorry, I didn’t answer your entire question. I believe it’s just an induction motor and of-course inverter duty rated. It has high-pressed lugs bolted on stationary copper bus bar for each phase inside the junction box.
 

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Sorry, I didn’t answer your entire question. I believe it’s just an induction motor and of-course inverter duty rated. It has high-pressed lugs bolted on stationary copper bus bar for each phase inside the junction box.

No built in heater. Do you know how long the motor is shut down for? (they shut down at weekends and the problem only happens on a Monday kind of thing)
 

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Bilge Rat
motors and controls.........
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Has the noise level changed? Maybe it actually is overloading due to a bad bearing.

What speed does it usually run at?

Has anything in the water system changed?
 

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Discussion Starter · #7 ·
No built in heater. Do you know how long the motor is shut down for? (they shut down at weekends and the problem only happens on a Monday kind of thing)
Typically it runs twice a day. It’s weird though. It seems to always happen on the weekend. Then we find out about it Monday. We then troubleshoot it and it will run for days sometimes months with no problem.
 

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Does it have a fault log you could look at? Maybe pin down a time? Pin down how much current?
 

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Discussion Starter · #9 ·
Has the noise level changed? Maybe it actually is overloading due to a bad bearing.

What speed does it usually run at?

Has anything in the water system changed?
The noise hasn’t changed from what I can tell.

It typically runs around 80 percent. I’m not sure what RPM that is. I can find that out though.

Nothing in the system has changed that I know of. NIDEC Tech support told us that something in operations like a valve, ect. typically wouldn’t cause this trip. We always thought it would and it’s still hard to believe that.
 

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Discussion Starter · #10 ·
Does it have a fault log you could look at? Maybe pin down a time? Pin down how much current?
I can locate the last ten trips and their dates/times. Then there is a sub-trip that is supposed to help narrow the cause down. As far as displaying the current at the time of the trip. I believe we couldn’t locate that. I will look in the manual and try it again. It would make sense to list the current at the time of the trip.
 

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Bilge Rat
motors and controls.........
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80% on a centrifugal pump would be a fairly light load, not even close to an actual overload.

When it runs, can you look at current on the VFD display? The The display is more accurate than a typical clamp-on meter.
 

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80% on a centrifugal pump would be a fairly light load, not even close to an actual overload.

When it runs, can you look at current on the VFD display? The The display is more accurate than a typical clamp-on meter.
I agree. Its a variable torque load and for the drive to trip on OL will take some serious loading. But also these controls are usually reduced in size (current) for this reason.
I always trusted my amp clamp more than the display. The display is a not a direct current reading. Its a voltage across a resistor and then mathematically turned into current.
At least thats how I remember it.
 

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The noise hasn’t changed from what I can tell.

It typically runs around 80 percent. I’m not sure what RPM that is. I can find that out though.

Nothing in the system has changed that I know of. NIDEC Tech support told us that something in operations like a valve, ect. typically wouldn’t cause this trip. We always thought it would and it’s still hard to believe that.

The pump pulls the highest amps on start up until it builds up back pressure which can cause a overload problem but the manual states this is a instantaneous trip where the amps exceeded the drives max output so you are looking for a surge rather than a overload that the drive can deal with.

Ive seen old vfd's throw this code for no reason and ive seen motors that test good when warm test bad after they have cooled off.
 

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I agree. Its a variable torque load and for the drive to trip on OL will take some serious loading. But also these controls are usually reduced in size (current) for this reason.
I always trusted my amp clamp more than the display. The display is a not a direct current reading. Its a voltage across a resistor and then mathematically turned into current.
At least thats how I remember it.
Its reacting to what amps it thinks its pulling (that's why the display readings are important). Once i see what it thinks its doing then i can check to see if i agree with a meter at which point its probably not serviceable and will have to be replaced.
 

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Chief Flunky
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What is the insulation resistance using a digital megaohm meter tested at 500 V for 60 seconds from phase to ground after disconnecting from VFD? Also measure temperature in C when you do it. Watch readings. Is there any jitter? Does it jump up then flat light or rapidly increase then sort of level off but continue to increase?

Put multimeter in diode check mode. With drive off put one probe on DC+ and the other on L1, L2, L3, T1, T2, T3. Repeat with DC-. Then flip the probes and repeat again. Check to see that everything “looks right”. Readings should be about 0.3-0.7 V in one direction, open in the other. Check VFD capacitance. What is reading from DC+ to DC-?

Trying to determine if it’s an actual short either to ground or blown drive component.

How is drive speed or torque controlled?
 

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Discussion Starter · #16 ·
80% on a centrifugal pump would be a fairly light load, not even close to an actual overload.

When it runs, can you look at current on the VFD display? The The display is more accurate than a typical clamp-on meter.
I believe I can. I just need to scroll through and find it. We did put a Fluke power quality analyzer on the motor for a few days. The current was no where near an overload condition.
 

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Discussion Starter · #17 ·
The pump pulls the highest amps on start up until it builds up back pressure which can cause a overload problem but the manual states this is a instantaneous trip where the amps exceeded the drives max output so you are looking for a surge rather than a overload that the drive can deal with.

Ive seen old vfd's throw this code for no reason and ive seen motors that test good when warm test bad after they have cooled off.
It is very strange. I can say this. I have personally megger tested the motor at-least twice and it passed. We also just had another vender perform extensive motor testing and it passed again.

We also isolated the VFD output cables and megger tested them at 2000v per NIDEC’s recommendation. We tested each phase to ground. All passed. However, we did not test phase-phase. I asked the NIDEC support and they said we shouldn’t have to do that. They also initially told us to just replace all the VFD output cables as there is maybe a small short. We are finding that hard to believe.
 

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Discussion Starter · #18 ·
What is the insulation resistance using a digital megaohm meter tested at 500 V for 60 seconds from phase to ground after disconnecting from VFD? Also measure temperature in C when you do it. Watch readings. Is there any jitter? Does it jump up then flat light or rapidly increase then sort of level off but continue to increase?

Put multimeter in diode check mode. With drive off put one probe on DC+ and the other on L1, L2, L3, T1, T2, T3. Repeat with DC-. Then flip the probes and repeat again. Check to see that everything “looks right”. Readings should be about 0.3-0.7 V in one direction, open in the other. Check VFD capacitance. What is reading from DC+ to DC-?

Trying to determine if it’s an actual short either to ground or blown drive component.

How is drive speed or torque controlled?


I will look for the motor megger test results. The VFD output cables we recently tested phase-ground all tested in the T ohms except for one it was like 950 G ohms. However, we did not test phase-phase on the cables.

I will try taking those readings and see what the results are.
I did have a sub-trip number of 3000. It said something about the trip coming from power module 3. I can’t find in the manual what exactly the power module means. I asked the NIDEC support and they haven’t given me an answer.
I believe the drive is speed controlled.
 

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Chief Flunky
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It is very strange. I can say this. I have personally megger tested the motor at-least twice and it passed. We also just had another vender perform extensive motor testing and it passed again.

We also isolated the VFD output cables and megger tested them at 2000v per NIDEC’s recommendation. We tested each phase to ground. All passed. However, we did not test phase-phase. I asked the NIDEC support and they said we shouldn’t have to do that. They also initially told us to just replace all the VFD output cables as there is maybe a small short. We are finding that hard to believe.
Based on what they are telling you NIDEC is clueless. NIDEC is a motor company, a very large one. They are private labeling that VFD. NIDEC is asking you to do a DC test at 2000 V but the correct test if you were going to do what they are asking for is to measure the surge impedance at 2000 V. If you isolated the cables at both motor and drive end you can test insulation resistance.

I specifically asked what the readings were and told you what to watch for, for a reason. I have meggered plenty of motors that had ground faults but were considered "good" by people that don't know what to look for. 1 Megaohm is not good. 5 Megaohms is not good (raw reading). Even 100 Megaohms is not good if the reading shoots up to 100 Megaohms within a couple seconds then "flatlines" at that reading.

A common problem with VFD's is called reflected wave, but the problem can happen from other sources of surges in the system. If the electrical cable path between the VFD and the motor is long enough, it can puncture the cable insulation and cause the problem you are seeing. Meggering phase to phase and phase to ground should both be done. This means isolating at both ends. The cable is going to energize almost instantly so be ready for that.

Other issues are damaged IGBT's or SCR's or MOSFET's leading to intermittent shorts (at first) eventually building up to dead shorts, or a short in a cable, or damaged motor feeder cables. The drive DC link capacitors can be shorted too but the short doesn't show up until it gets near capacity.
 

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Discussion Starter · #20 ·
Based on what they are telling you NIDEC is clueless. NIDEC is a motor company, a very large one. They are private labeling that VFD. NIDEC is asking you to do a DC test at 2000 V but the correct test if you were going to do what they are asking for is to measure the surge impedance at 2000 V. If you isolated the cables at both motor and drive end you can test insulation resistance.

I specifically asked what the readings were and told you what to watch for, for a reason. I have meggered plenty of motors that had ground faults but were considered "good" by people that don't know what to look for. 1 Megaohm is not good. 5 Megaohms is not good (raw reading). Even 100 Megaohms is not good if the reading shoots up to 100 Megaohms within a couple seconds then "flatlines" at that reading.

A common problem with VFD's is called reflected wave, but the problem can happen from other sources of surges in the system. If the electrical cable path between the VFD and the motor is long enough, it can puncture the cable insulation and cause the problem you are seeing. Meggering phase to phase and phase to ground should both be done. This means isolating at both ends. The cable is going to energize almost instantly so be ready for that.

Other issues are damaged IGBT's or SCR's or MOSFET's leading to intermittent shorts (at first) eventually building up to dead shorts, or a short in a cable, or damaged motor feeder cables. The drive DC link capacitors can be shorted too but the short doesn't show up until it gets near capacity.
Thank you, I see what your saying. Unfortunately I can't find our in house motor megger test results. I can tell you this though. When we megger tested the motor we tested each phase for one minute at 500 V. When I am doing a one minute megger test I always make sure there is a steady incline in my readings. I also have seen motors megger tested and then fail once in service.

We also should be receiving reports soon from our motor testing contractor. I believe they did more extensive testing. I assume they did a PI and maybe a Hi-pot? I'll follow up with that when we receive the report.

However, based on your recommendations. I will do those checks. I will also will isolate the VFD output-motor cables and test them again and include phase-phase testing. If the cables results are a pass and the motor results all pass as they said they did. I would say its probably not a short in the cable or a problem with the motor?
 
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