I'm on a facility where every single 480V VFD is simultaneously faulting on over-voltage. :thumbsdown: I have roughly 20 pumps and fans on drives, varying HP size. This fault isn't consistent, but this is the second time it's happened. The first time we wrote it off to a potential lightning hit, but there hasn't been any storms in the area lately and it happened again last night.
VFD Info:
The drives are all AB PowerFlex 753 AC Drive, Open Type, 480V, 3 PH, Frame 2, Filtered, CM Jumper Removed, DB Transistor. I've verified VFD frame sizes for their respective load, cable sizes, VD, grounding, etc. and I cannot see anything out of the norm.
Site distribution:
The site power distribution consists of two, 20MVA, 13.2/4160 Virginia transformers from an on-site substation. These dual feeds go into one, main-tie-main, 4160V, 3P, 3W switchgear which then feeds the plant load from the two main busses. There are three main 480V MCC buildings, each with their own 1MVA, 4160/480 step down transformer for plant load, including the feeds for the VFD's that are tripping. One low voltage MCC building contains a 4160V, RVSS for a 6100HP compressor that has not been commissioned yet. Additionally, there is one 4160V MCC Building that houses: two RVSS's for two 800HP compressors; One Toshiba sync VFD for three, 3750HP compressors; and an additional Toshiba sync VFD for three, 1250HP compressors.
Additional Comments:
So am I looking at an inrush issue? Harmonics Issue? All of the above? :?
All comments and information are welcome and I thank you in advance. I'll provide any information necessary to help me out.
Regards,
RT
VFD Info:
The drives are all AB PowerFlex 753 AC Drive, Open Type, 480V, 3 PH, Frame 2, Filtered, CM Jumper Removed, DB Transistor. I've verified VFD frame sizes for their respective load, cable sizes, VD, grounding, etc. and I cannot see anything out of the norm.
Site distribution:
The site power distribution consists of two, 20MVA, 13.2/4160 Virginia transformers from an on-site substation. These dual feeds go into one, main-tie-main, 4160V, 3P, 3W switchgear which then feeds the plant load from the two main busses. There are three main 480V MCC buildings, each with their own 1MVA, 4160/480 step down transformer for plant load, including the feeds for the VFD's that are tripping. One low voltage MCC building contains a 4160V, RVSS for a 6100HP compressor that has not been commissioned yet. Additionally, there is one 4160V MCC Building that houses: two RVSS's for two 800HP compressors; One Toshiba sync VFD for three, 3750HP compressors; and an additional Toshiba sync VFD for three, 1250HP compressors.
Additional Comments:
- I'm having my field techs pull the time logs, but I'm wondering if I'm getting the spike if/when we have a process shutdown of either our 3750 or 1250 compressors, and that sudden drop in load is causing the energy to flow into the smaller loads. We did have a process shutdown around the same time, hence pulling the fault times to see if they're somehow related. FYI, a process shutdown for this facility is rapid shutdown, sort of like an ESD but without killing everything on site. What happens to our large sync VFD's is that they will open the bypass contactor on the across the line motor and ramp down immediately (-5sec) on the motor that is still under VFD control. The third motor in each compressor set is future.
- No other devices are faulting that are fed from circuit breakers, including motor starters that are on E1 Overload's.
- The upstream substation's two main 751 protection relays are not recording any over voltage events, so I would have a hard time believing that I'm getting any spike from the Utility. The substation is running just a little high @ 4300V, but that's well within IEEE tolerance.
So am I looking at an inrush issue? Harmonics Issue? All of the above? :?
All comments and information are welcome and I thank you in advance. I'll provide any information necessary to help me out.
Regards,
RT
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