PowerFlex 400 trips on Ground Fault

phuz

Member
Join Date
Jun 2008
Location
Mohnton, PA
Posts
1,043
A customer has a 25hp well pump on a PowerFlex 400 VFD. Supposedly this has been happening for a while, but I offered to look into it. The timing seems random. Sometimes the pump will run through it's cycle fine and others it will trip with a Ground Fault. Yesterday it happened at least 6 times. Electricians inspected the motor and said it was fine and passed the megger. This particular well install is only 3 years old, but the electricians are ready to pull new wire to the motor. The 480 3-ph comes into the panel, goes through a line reactor, to the VFD, to an AC filter (looks exactly like another line reactor), and then about 75' to the motor itself.

I suggested swapping VFDs with one of the other wells to eliminate a VFD issue. Thoughts?
 
Thanks. Lots of info in there. Strange that none of those came up in my google searches.
I'll pass these along. Much appreciated!🍻
 
Electricians inspected the motor and said it was fine and passed the megger. This particular well install is only 3 years old, but the electricians are ready to pull new wire to the motor.
I suggested swapping VFDs with one of the other wells to eliminate a VFD issue. Thoughts?

I wonder how the electricians can determine that the motor is fine. There are a lot of things that can be wrong with a motor that meggers good. Since the fault it intermittent, the motor could also megger good, intermittently.

However, most of the time I have seen intermittent ground faults have been due to moisture in conduits and junctions boxes with bad splices, or wires with bad insulation, usually in or near the peckerhead. I'd let the electricians pull new wire before I'd swap VFDs.
 
Drives are often much better at finding faults than simple test systems. One thing that can happen is that there are tiny pin holes in the insulation caused by corona discharge due to standing waves in the VFD output that are going phase to phase, but not to ground, until there is sufficient moisture in the conduit, ie condensation. When you use a megger in the simplest form, tying all three leads together and measuring to ground, it doesn’t show up unless you just happen to do it when the moisture is present. It’s also possible that they used a 500V megger and the discharge takes place at a much higher voltage level (standing waves can get up to 2-1/2x the line voltage). That’s why a higher voltage megger is recommended.
 
If this is a deep well then that bore pump could be over a hundred feet deep. Changing cable is not a cheap or easy exercise. But it sounds like your pump is above ground?

I have seen faulty current sensors on a drive also cause this issue, and it was also intermittent. It was a large drive so we replaced a few circuit boards with the CTs as directed by the drive manufacturer. Problem solved.

If it's possible to change the drive I'd try that first, after inspecting any terminals, disconnects or accessible cable between the drive and the well head. Most of our drive suppliers here have loan units if you ask nicely. Or as you say if you can swap for another good known one from another well and see if the problem follows the drive or the motor.
 
Last edited:
1000V megger is certainly a must. Also, if 460V power is delta-sourced, you must either install a delta-wye drive isolation transformer or turn off the Ground Fault and Short Circuit Fault as they will be nothing but false alarms in a floating delta environment
 
I've seen several pump motors that Meg fine when they cool down... And Overcurrent or Ground Fault when they get up to temperature. The trick in these cases was to get the leads disconnected quickly, and Meg it while it's still hot... Ding, Ding, Ding... A bad motor.

Another good reason why we should be Megging motors at 2000V these days.
 

Similar Topics

Hello I have a powerflex 400 of 25HP for a 60amp 25HP motor, the motor have a belt that move the clarifier of milk. It is a process that requires...
Replies
11
Views
4,165
Does anyone know what the RJ45 pinouts are for the DSI port on PowerFlex 400 drive? I want to connect a Modbus 485 master to it. Thx
Replies
6
Views
2,744
Gentlemen; Have a bit of an odd one - a customer has a PF400 running a vacuum pump motor. They said they changed the motor out 3 months ago, and...
Replies
30
Views
12,407
I have a controls system that has multiple PF400's. All of them are older series A drives. They all communicate with 22-comm-e's with a...
Replies
1
Views
1,544
We have a F04 UnderVoltage fault on a PowerFlex 400 drive, which does not want to reset. It was running normally for months. We checked input...
Replies
10
Views
6,052
Back
Top Bottom