- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I installed and commissioned so many 503s, in all of the the various iterations (Magnetek, Yaskawa, Saftronics, IDM, Omron, EMS, ElectroMotive, Unico...) its not even funny. It's not an Overload on the motor side, that displays as "OL1", and if it were an overload of the VFD itself, it displays as an "OL2" or "OL3" if it is torque related. If it is over heating because of poor heat sink ventilation, it displays "OH".
99.9999999% of the time when you get a "mysterious" intermittent OC fault, it's because you are experiencing an intermittent ground fault on the output. There is a Residual Ground fault circuit used in the output Hall Effect Transducer system that detects ground current flow up to 50% of the unit current rating and displays as "GF". But if there is an instantaneous increase in current flow to ground at over 50% Ir or the DC bus current jumps up to over 200% Ir, then the "OC" fault is triggered. I rarely witnessed the DC bus current issue in the wild, but the GF issue was relatively common.
Most likely you are using a 500V megger, am I right? The problem is, the DC pulses coming from a VFD that is getting 493V input are close to 700V, and if you have any standing waves being created by long lead lengths, they could be closer to 2000V. They could easily be punching through insulation in the motor windings or the motor circuit conductors, but not at a level low enough to be seen by the typical 500V megger. Get a 1000V megger and you may see the leakage.
By the way if you ARE using a 1000V megger and still saw nothing anomalous, another possibility is that because it WAS impacted with dust, one (or more) of the Darlington transistors has a cracked case. So under the right circumstances, it's leaking current to the heat sink, i.e. any slight condensation inside of the drive, or it started that way and now there is a carbon trace that makes it increasingly easier to happen each successive time. If that's the case, it's not worth fixing, you will chase the collateral damage into the rabbit hole and spend WAY more than the cost of a new drive.
99.9999999% of the time when you get a "mysterious" intermittent OC fault, it's because you are experiencing an intermittent ground fault on the output. There is a Residual Ground fault circuit used in the output Hall Effect Transducer system that detects ground current flow up to 50% of the unit current rating and displays as "GF". But if there is an instantaneous increase in current flow to ground at over 50% Ir or the DC bus current jumps up to over 200% Ir, then the "OC" fault is triggered. I rarely witnessed the DC bus current issue in the wild, but the GF issue was relatively common.
Most likely you are using a 500V megger, am I right? The problem is, the DC pulses coming from a VFD that is getting 493V input are close to 700V, and if you have any standing waves being created by long lead lengths, they could be closer to 2000V. They could easily be punching through insulation in the motor windings or the motor circuit conductors, but not at a level low enough to be seen by the typical 500V megger. Get a 1000V megger and you may see the leakage.
By the way if you ARE using a 1000V megger and still saw nothing anomalous, another possibility is that because it WAS impacted with dust, one (or more) of the Darlington transistors has a cracked case. So under the right circumstances, it's leaking current to the heat sink, i.e. any slight condensation inside of the drive, or it started that way and now there is a carbon trace that makes it increasingly easier to happen each successive time. If that's the case, it's not worth fixing, you will chase the collateral damage into the rabbit hole and spend WAY more than the cost of a new drive.
