Troublesome electrical issues

cpedersen

Member
Location
USA
Occupation
Facilities Mgr
1. Work with the utility to replace upgrade pole transformers: Done
2. Upsize ground wires and rebond to ground rods: Done
3. Check and bond the grounds on the drive cables: Done, ish.

There is a junction box between the drive and the motor that splits signals to a computer. The junction box is track mounted and has ground pins on the cable. I know that each end of the cable shielding is supposed to be grounded, but I don't know how the shield grounding of each cable at the junction is accomplished.

The cable from the drive to the junction, I verified the ground at the drive. From the junction to the motor, I verified the ground at the motor.


4. Look into easy start components to introduce between before the power supplies. <---- Here
5. Investigating upsizing the 240/400 transformer.
6. After grounding investigate via Emerson's on board scope to see if DC ripple is occuring
7. Ensure The secondary Y is separately derived and has a GEC to the ground rod (#6 max to the ground rod may meet code idk). The transformer secondary has a system bonding jumper that connects the neutral, the GEC, all other Earth ground systems nearby, the building steel, and the equipment grounding system.
8. Start to panic !
9. Investigate EMC filters
10. Investigate Line reactor(s).
11. Thermal Scanning
 

cpedersen

Member
Location
USA
Occupation
Facilities Mgr
12.
There are 28 30 amp vfd's connected to one ground bar. And I believe the AWG of that ground bar is 8 gage. Seems to me that ground wire size is too small. Judging from this chart, 1645536139897.png
Shouldn't the AWG be 4?
 

__dan

Senior Member
Just upping the EGC size from 8 to 4, by itself I would not expect to relieve drive fault tripping. Under normal operating conditions the EGC is not carrying heavy current. Same for the GEC, it has to be done properly, but probably not causing the drive to trip.

Location of the ground bar makes a difference, line side / load side. It's probably bonded to everything and in parallel with conduit / cabinet EGC's.

The drive to motor cable, when that has a bad shield connection and it's in parallel with the motor encoder data cable, that can give the noisy encoder drive fault trip. I've seen specs that, for that problem, the manufacturer may recommend an additional redundant, heavier than normal, EGC from the drive to the motor. That's for Emerson to call for. They have the experience with their installed fleet. Also, the equipment manufacturer may have experience with the problem. I would give them a call.

It's a process of elimination. After what has been looked at and mitigated to date, are you still having trouble. What fault codes from the drive are you still getting. I would be pretty quick to call Emerson and run it by them for their experience with the application.
 

xformer

Senior Member
Location
Dallas, Tx
Occupation
Master Electrician
So we have a piece of equipment that requires 310 amps at 400 V. It is the only piece of equipment on the circuit.

The primary side is supplied by the utility with 240 nominal high leg delta. The transformer is a 225 KVA delta / Wye transformer.
The secondary side is 400 volts WYE. No neutral has been brought to the equipment only three hots and a ground.

The equipment has 30 VFD's with low duty cycles, each rated at 30 Amps. Peak current (200ms) has been 120Amps on each leg.

I have monitored the power for the last month. During this time in operation we consistently get the ground showing intermittent 5.5V. Also current, but I cannot recollect amount (an amp or two?) Internal to equipment there is a transformer 400/24 transformer. The VFDs are fed by a power supply, measuring from the VFD to the ground bar, I show 45 ohms while running. The metal case (also supposedly grounded to the bar) only shows 2.6 Ohms.

Total harmonic distortion (current) ranges from 45-70% - which I think contribute to the voltage on the ground.

When turning on, random VFD's will trip going into error conditions. This goes on for about 45-135 minutes. After which the equipment runs all day without incident.

Random problems always brings to mind grounding issues.

I suspect that the voltage on the ground is causing the trips.

Question: What avenue would you attack this?
1). Bring a neutral, with the idea that this would allow us to cleanup the ground? (Does that even make sense?)
2). Install line reactors, with the idea that lowering the harmonic distortion by 10% would result in less voltage on the ground.
3). Same argument as #2, except active filtering would lower the distortion down to 5-8%. (much more expensive).
4). Something else?


Appreciate the thoughts
Is this a single phase or a 3 phase transformer?
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
The equipment is self contained. Data cables run from a computer, to control cards, which go from there to each of the components, predominantly VFD motors. All drawn on common power and ground.

How do you initially start up the machine? Is it done from a user interface panel that allows the operation of the machine to be controlled, or is there only a start/stop switch that powers it all up? I'm just asking to see whether a reset or other initialization procedure can be done to get the machine up and running correctly.
 

cpedersen

Member
Location
USA
Occupation
Facilities Mgr
How do you initially start up the machine? Is it done from a user interface panel that allows the operation of the machine to be controlled, or is there only a start/stop switch that powers it all up? I'm just asking to see whether a reset or other initialization procedure can be done to get the machine up and running correctly.
Kind of both?

A start / stop switch powers on all the drives, and the computer. But it powers into a "stop" mode, which needs a manual release, which then transfers control to the computer.

But electrically speaking all the drives turn on at the same time, and it does cause a 10-20% voltage drop.
 

cpedersen

Member
Location
USA
Occupation
Facilities Mgr
Location of the ground bar makes a difference, line side / load side. It's probably bonded to everything and in parallel with conduit / cabinet EGC's.

The drive to motor cable, when that has a bad shield connection and it's in parallel with the motor encoder data cable, that can give the noisy encoder drive fault trip. I've seen specs that, for that problem, the manufacturer may recommend an additional redundant, heavier than normal, EGC from the drive to the motor. That's for Emerson to call for. They have the experience with their installed fleet. Also, the equipment manufacturer may have experience with the problem. I would give them a call.

It's a process of elimination. After what has been looked at and mitigated to date, are you still having trouble. What fault codes from the drive are you still getting. I would be pretty quick to call Emerson and run it by them for their experience with the application.
There are four primary ground buses. One for frames, one for rapiers & colors, etc.
All of the busses tie back to the main ground, although I haven't verified as its inaccessable.

Within the frame bus, the driver and the motor tie to the same bus. (AKA line side/ load side are the same bus).

Between the driver and the motor there are junction boxes where the signal is split off to the computer.
They are track mounted. On the frames that track is grounded; I am following up on the rapier track as it doesn't seem to be.

We have involved nidec into the equation (Emerson), they have been helpful, but still no solution as yet.

I'll update error messages from the drives in a bit.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
The Wye is grounded to a ground bar in the disconnect switch, which itself is tied to the ground rod outside. The ground rod shows 30 Ohms.


The cable from the disconnect switch to the ground rod is too small. Fixing that is underway. I haven't sized the grounding cable from the transformer to the disconnect switch, nor from the transformer to the equipment.
is this connected to the incoming and outgoing equipment grounding conductors?
 

__dan

Senior Member

I have monitored the power for the last month. During this time in operation we consistently get the ground showing intermittent 5.5V. Also current, but I cannot recollect amount (an amp or two?) Internal to equipment there is a transformer 400/24 transformer. The VFDs are fed by a power supply, measuring from the VFD to the ground bar, I show 45 ohms while running. The metal case (also supposedly grounded to the bar) only shows 2.6 Ohms.

Appreciate the thoughts

This, the floating Voltage on the grounding system. If you can find two grounded points with 5.5 V raised between them, that's evidence of a problem. It is not necessarily a matter of just jumpering them together with a heavy enough wire. I would want an understanding of why the Voltage difference could exist. It should not be possible, and if you discover why, it's necessary data in my opinion, the why.

The 225 kVA isolating transformer. It's a matter of opening the front cover and visually inspecting for the system bonding jumper, the secondary Y, neutral to ground bar jumper. I would take a peek at the GEC at the same time, but a missing GEC would not cause the type of trouble a floating neutral would. Again, not a matter of upsizing a wire that's already there. It's a matter of verifying the EGC's and system bonding jumper, what you need to run, is there.

Great photos. The orange cables are the drive to motor power cables and the green ones are the encoders. The encoder is high speed bit data and sensitive to noise. Just routing them parallel on the same path is questionable. Normally they would be separated by distance or metal raceway. Yes I know, each is separately shielded. The power cable shield is kind of hokey and unfamiliar to a lot of electricians. The way the shield connects at the drive or at the intermediate j box on tracks, must be done properly, or poor shielding of the drive motor cable will inject noise into the encoder data cable.

Both cables take a parallel path and terminate in parallel from drive to motor. Any bad shield connection on the power cable will be taken up by the shield on the data cable, making it noisy. How they did the shielding at that hokey floating track mounted j box would merit special attention.

Emerson and the equipment manufacturer should have special insight, experience, into what problems cause the drive fault codes you're getting.

The EGC GEC grounding issues with your finding undersize or not to code wiring. Code violations are like potato chips, you never eat just one. If you're finding code violations it would indicate non pro work performed (mechanics doing wiring), when the problems you're experiencing would call for a really knowledgeable electrician, a ghostbuster, to look at and diagnose. Yes running a wire from point A to point B might work, but the guy running the wire should know why.

Yes. All the drives are Emerson M700s; most are 28 are 30 amp and there are 1x32, 3x27, 4x5A and I think a 7.5 amp. I have more info on the drives. Pics attached.

I have not checked voltages between the drive and the motor. But the ground shield seems to be well done and grounded at both ends.

The units include a small module about half the size of a dollar bill that is billed as an EMC filter. I see nothing on heat syncs, however, the units are in a climate controlled cabinet that is kept around 27C.

View attachment 2558491 View attachment 2558490 View attachment 2558492
 

cpedersen

Member
Location
USA
Occupation
Facilities Mgr
TripOI ac
Value3
Short description


This trip indicates that the instantaneous drive output current has exceeded the drive over current threshold.
Sourcexxyzz
Control system00000: Instantaneous over-current trip when the measured a.c. current exceeds over current threshold
Power systemPower module number000: Instantaneous over-current trip when the measured a.c. current exceeds over current threshold.
The over current threshold is the maximum current the drive can measure and is defined by VM_DRIVE_CURRENT[MAX].
Recommended actions:
  • Acceleration / deceleration rate is too short.
  • If seen during auto-tune reduce the voltage boost.
  • Check for short circuit on the output cabling.
  • Check integrity of the motor insulation using a Megger.
  • Check feedback device wiring.
  • Check feedback drive mechanical coupling.
  • Check feedback signals are free from noise.
  • Check motor cable is within limits for the frame size.
  • Reduce the speed loop gains ([menu3.html#10]Speed Controller Proportional Gain Kp1 (03.010), [menu3.html#11]Speed Controller Integral Gain Ki1 (03.011), [menu3.html#12]Speed Controller Differential Feedback Gain Kd1 (03.012)).
  • Check that the phase angle auto-tune has been completed (RFC-S mode only).
  • Reduce the current loop gains (RFC-A and RFC-S modes only).
TripPhasing Error
Value198
Short description


If position feedback is being used this trip indicates that the phase offset angle in [menu3.html#25]Position Feedback Phase Angle (03.025) (or [menu21.html#20]M2 Position Feedback Phase Angle (21.020) if the second motor map is being used) is incorrect and that the drive is unable to control the motor correctly.
Recommended actions:
  • Check the encoder wiring.
  • Check the encoder signals for noise with an oscilloscope.
  • Check encoder mechanical coupling.
  • Perform an auto-tune to measure the encoder phase angle or manually enter the correct phase angle into [menu3.html#25]Position Feedback Phase Angle (03.025).
  • Spurious Phasing Error trips can sometimes be seen in very dynamic applications. This trip can be disabled by setting [menu3.html#8]Over Speed Threshold (03.008) to a value greater than zero.
If sensorless control is being used this indicates that significant instability has occurred and the motor has accelerated without control. For low saliency motors ([menu5.html#66]Active Saliency Torque Mode (05.066) < 2) this operates in the same way as when position feedback is used, based on the speed of the motor and the voltages applied. For high saliency motors ([menu5.html#66]Active Saliency Torque Mode (05.066) = 2) this type of detection cannot be used and the over-speed trip should be used instead. However this trip is used for high saliency motors when low speed control using current injection is being used ([menu5.html#66]Active Saliency Torque Mode (05.066) = 2) and control is lost because the motor has become non-salient. The saliency of most permanent magnet motors reduces with load, and so [menu5.html#71]Low Speed Sensorless Mode Current (05.071) must be set to a level to limit the current so that the motor remains salient enough for control.
Recommended actions:
  • Ensure that the motor parameters are set-up correctly.
  • Reduce the speed controller gains.
  • If high seliency control is being used ensure that [menu5.html#71]Low Speed Sensorless Mode Current (05.071) is set to a low enough level, so that the motor remains salient at low speeds and higher loads.
  • This trip can be disabled by setting [menu3.html#8]Over Speed Threshold (03.008) to a value greater than zero.
TripEncoder 1
Value189
Short description


Drive position feedback interface power supply overloaded. Terminals 13 & 14 of the 15 way D-type connector can supply a maximum current of 200mA at 15V or 300mA at 5V.
Recommended actions:
  • Check encoder power supply wiring.
  • Disable the termination resistors ([menu3.html#39]P1 Termination Select (03.039) set to 0) to reduce current consumption.
  • For 5V encoders with long cables, select 8V ([menu3.html#36]P1 Supply Voltage (03.036)) and fit a 5V voltage regulator close to the encoder.
  • Check the encoder specification to confirm it is compatible with the encoder port power supply current capability.
  • Replace the encoder.
  • Use an external power supply with higher current capability.
 

topgone

Senior Member
12.
There are 28 30 amp vfd's connected to one ground bar. And I believe the AWG of that ground bar is 8 gage. Seems to me that ground wire size is too small. Judging from this chart, View attachment 2559551
Shouldn't the AWG be 4?
That chart is used for sizing equipment grounding conductor based on a normal system that doesn't have high harmonics contents, IMHO (assume one phase is lost and the current imbalance appears on the neutral). 4/0 is good for a circuit protected by a 1600A breaker, not #4.
If you have 28 -30A CBs and each circuit exhibit 45-70% THDi, my quick calcs here tells me your neutral current due to harmonics could go as high as 1,156A!
 
Last edited:

__dan

Senior Member
The fault code list and the troubleshooting hints is very informative but I'm sure it takes some familiarity to read what the list is saying. The fault codes basically break down into initial drive setup checks and parameter setting, and then looking into noise in the encoder wiring.

Roughly summarized as:

Meg the motor (for the overcurrent trip, basic first check).

Verify or reenter the motor nameplate data.

Verify the proper accel deecel settings, indicated loop gain speed parameters.

Force the drive to autotune to the motor.

If you still get trips you can try to loosen parameters for accel deecel, loop gain parameters (as indicated in the troubleshooting list), in consultation with the factory. The default settings could be too tight for the application. The encoder noise (phasing error?) could be params set too tight (consult the factory).

That's the basic easy first pass, has to be done anyway, and could have been missed at commissioning. After that, wiring issues and noise on the encoder data pathway is indicated as (possible cause to check).

Separately, survey power wiring and grounding conductors for Voltage and current. Don't know how to say this but you should already know what values are expected before doing the Voltage and Amp clamp checks. In prior posts irrc reported 20% Voltage drop and Voltage on the ground bus bar. Verify and eliminate. The running load Voltage drop is of concern, not the instantaneous turn on drop.

Rinse and Repeat. For things like this, don't always get them on the first pass. Process of elimination. Keep going down the list making the list smaller until the problem goes away.

Could be more than one problem or same problem repeated. Likely the problem is indicated in the fault code troubleshooting list.
 
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