Excessive Leakage Current?

[adamscb]

Forum,

We have a VFD for a 350hp, 480v motor that's connected to a resistance-grounded wye system. The other day our HRG alarms were going off, so we began to troubleshoot. Phase-to-phase and phase-to-ground voltages looked fine, the current was evenly distributed along all three phases, but one thing stood out to me: the GND wire was carrying 4.8 - 5.0A of current. Is this excessive leakage current? I looked for filters and the VFD has a line filter, but not a load one. This is either a Toshiba G9 or an H9, can't remember which one exactly. I was looking through the manual and I think the root cause is the grounding capacitors are not set-up properly for an HRG system. Could this be a root cause? Let me know, thanks

 

[kwired]

Forum,

We have a VFD for a 350hp, 480v motor that's connected to a resistance-grounded wye system. The other day our HRG alarms were going off, so we began to troubleshoot. Phase-to-phase and phase-to-ground voltages looked fine, the current was evenly distributed along all three phases, but one thing stood out to me: the GND wire was carrying 4.8 - 5.0A of current. Is this excessive leakage current? I looked for filters and the VFD has a line filter, but not a load one. This is either a Toshiba G9 or an H9, can't remember which one exactly. I was looking through the manual and I think the root cause is the grounding capacitors are not set-up properly for an HRG system. Could this be a root cause? Let me know, thanks

Grounding capacitors??

Too high of input voltage might cause MOV's on the input lines to shunt some current to ground, or you could actually have a fault in the front end of the drive. Load side of drive shouldn't really have much impact on this.

 

[adamscb]

See attached pictures

 

[adamscb]

The second attachment more aligns with what you're saying, in that the problem might be on the input of the drive. If that is the case, these Grounding Capacitors have two settings: High and Low capacitance, what are your thoughts as to which setting I should choose?

 

[kwired]

See attached pictures

I would think that is something associated with output side of drive and should have minimal amount of current flowing - it is part of noise reduction components and not something that should be carrying any significant power levels. 5 amps @ 277 volts is quite a bit of power, for something that shouldn't be carrying any significant power, especially if there is a HRG resistor in series with it. Are you measuring same current back at the HRG resistor? What is voltage across resistor? What is voltage between HRG and each ungrounded conductor? The lowest reading is the one with any fault on it.

 

[adamscb]

I would think that is something associated with output side of drive and should have minimal amount of current flowing - it is part of noise reduction components and not something that should be carrying any significant power levels. 5 amps @ 277 volts is quite a bit of power, for something that shouldn't be carrying any significant power, especially if there is a HRG resistor in series with it. Are you measuring same current back at the HRG resistor? What is voltage across resistor? What is voltage between HRG and each ungrounded conductor? The lowest reading is the one with any fault on it.

Phase-to-ground voltages measured a consistent 286v on all phases to ground, with phase-to-phase being 498v. I haven't measured voltage across the HRG though.

Could this be capacitive coupling between the windings in the motor and ground?

 

[kwired]

Phase-to-ground voltages measured a consistent 286v on all phases to ground, with phase-to-phase being 498v. I haven't measured voltage across the HRG though.

Could this be capacitive coupling between the windings in the motor and ground?

Not all that convinced capacitive coupling would yield 5 amps of current.

 

[GoldDigger]

Not all that convinced capacitive coupling would yield 5 amps of current.

And unless triplen harmonics are involved a balanced ground capacitor set should not produce any neutral (or in this case ground) current. (Of course that depends on the capacitor tolerance and value matching.)

Sent from my XT1585 using Tapatalk

 

[Jraef]

Forum,

We have a VFD for a 350hp, 480v motor that's connected to a resistance-grounded wye system. The other day our HRG alarms were going off, so we began to troubleshoot. Phase-to-phase and phase-to-ground voltages looked fine, the current was evenly distributed along all three phases, but one thing stood out to me: the GND wire was carrying 4.8 - 5.0A of current. Is this excessive leakage current? I looked for filters and the VFD has a line filter, but not a load one. This is either a Toshiba G9 or an H9, can't remember which one exactly. I was looking through the manual and I think the root cause is the grounding capacitors are not set-up properly for an HRG system. Could this be a root cause? Let me know, thanks

It's more likely Common Mode Noise rather than "leakage current". All VFDs produce common mode noise as a result of the PWM firing of DC pulses that comprise the output pseudo-sine wave. This is one reason why it's not a good idea to connect VFDs directly to HRG (or Delta) power systems. The correct fix for this is to use a "Drive Isolation Transformer" that is a 1:1 ratio, but the secondary is a solidly grounded Wye feeding just that one drive input, giving the CM noise a path to ground that doesn’t go through the HRG system.