Soft start fault
Soft start fault
(OP)
Interesting problem today. We had a big mill go down several times last night due to a phase loss fault monitored by a Motortronics MVC Plus 4160v soft start. Pulling the data from the event recorder in the MVC shows that the amperage at the time of the fault was 242, 154, 151, and the the voltage was 4220, 4219, 4214, on phase A, B, C. Interesting thing also was the recorded power factor was 1.21.
We also monitor this motor with a Multilin 469 and SPM combo. Neither one of these units recorded any type of problem. The 469 and MVC don't share the same CT's so I'm thinking the there is a possible intermittent problem with the Temp/CT board in the SCR stacks in the medium voltage compartment.
Previously we were getting all of our readings in the control room off of the 469 and the SPM through a modbus connection. We hooked up the MVC today so we could monitor it's metering data also. I'm hoping that we can isolate the problem by comparing the readings. We opened the medium voltage compartments and checked the wiring and the connections, but couldn't find any obvious problems, and there was a rush to run the machine. It's running OK right know, but I'd like to find the problem as soon as they're down.
We also monitor this motor with a Multilin 469 and SPM combo. Neither one of these units recorded any type of problem. The 469 and MVC don't share the same CT's so I'm thinking the there is a possible intermittent problem with the Temp/CT board in the SCR stacks in the medium voltage compartment.
Previously we were getting all of our readings in the control room off of the 469 and the SPM through a modbus connection. We hooked up the MVC today so we could monitor it's metering data also. I'm hoping that we can isolate the problem by comparing the readings. We opened the medium voltage compartments and checked the wiring and the connections, but couldn't find any obvious problems, and there was a rush to run the machine. It's running OK right know, but I'd like to find the problem as soon as they're down.





RE: Soft start fault
RE: Soft start fault
LOL
Do you have an offset neutral?? We had a problem with a soft start tripping on voltage phase shift. The utility had a very long (maybe 20 miles) of two phase plus neutral distribution line. Our plant was the last on the three phase line. The heavy neutral currents and the reactance of the lines gave us quite a bit of current on the neutral.
Can you safely check your phase to neutral voltages? In my experience, I see more voltage difference phase to neutral than phase to phase. Your soft start may be responding to a low phase to neutral voltage or annunciating a voltage phase shift as loss of phase. In this condition, the phase to neutral voltages are no longer at 120 degrees to each other.
Bill
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RE: Soft start fault
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RE: Soft start fault
What could cause a device to read a power factor of 1.21 anyway. I believe that MVC reads a power factor of .020 or something like that while it's running also. The 469 shows the expected .96 - .98.
RE: Soft start fault
The Temp/CT board is just an interface that accepts the Temperature Sensor from the stack heat sink and the CT secondary signal as analog values, then digitizes them through an A/D chip. Then it also does the fiber optic conversion for sending the values back up to the mP in the control unit, isolating the mP from any noise that could be introduced if wires were used. No other MV RVSS manufacturer does it this way so nobody else is going to understand what a "Temp/CT board" is by the way.
As I think about it more, the problem couldn't be the entire Temp/CT board or the fiber optic connection however, because you would get the same problem on the temperature sensor; it would tell you that the heat sink was 65,536 degrees C (the max value). So it is likely either a bad connection from the CT to the Temp CT board or a bad CT. Motortronics makes their own CTs, they have had internal quality problems in the past so it's not unheard of. It could also be a bad A/D chip on that board as well, that has happened too.
Those boards are not terribly expensive and are very easy to swap out, have you tried contacting Motortronics?
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RE: Soft start fault
RE: Soft start fault
RE: Soft start fault