Hello,
My father recently encountered a problem. There is a pump drive that is very old and it recently started tripping the circuit breaker after about 30min of operation. After carefully examining the problem he discovered that the pump drive has a lower and lower efficiency as it ages. He increased the circuit breaker to 100A and the pump drive and pump now run fine (yes, he did check the pump and wire).
But it was difficult to observe the problem at first because it took several hours before it would occur.
I thought about this and wondered, as a purely academic question how this might have been observed from the beginning without having to sit there and observe the pump and pump drive.
A shunt resistor with a multimeter and a camera would have worked well I thought, but I've no idea how much voltage shunt resistors are rated for (we're talking a 3-phase to pump, 2-phase into pump drive circuit @ 240V), there's also the matter of derating which I've not yet had to do because my projects have all been low voltage and amperage DC.
I tried to search for this online but the only help I could find was wikipedia which simply said: "All shunts have a derating factor for continuous (2+ minutes) use, 66% being the most common, so the example shunt [ 500A 75 mV ] should not be operated above 330 A (and 50 m drop) longer than that..... [citation needed]"
That's not very clear (What about +2h? At what voltage?) and there's no reference to read either. Normally resistors have wattage and voltage rating, and after some searching of ebay, shunt resistors never seem to have one. Nor have I found one that explicitly states a derating factor.
Any advice?
Thanks
My father recently encountered a problem. There is a pump drive that is very old and it recently started tripping the circuit breaker after about 30min of operation. After carefully examining the problem he discovered that the pump drive has a lower and lower efficiency as it ages. He increased the circuit breaker to 100A and the pump drive and pump now run fine (yes, he did check the pump and wire).
But it was difficult to observe the problem at first because it took several hours before it would occur.
I thought about this and wondered, as a purely academic question how this might have been observed from the beginning without having to sit there and observe the pump and pump drive.
A shunt resistor with a multimeter and a camera would have worked well I thought, but I've no idea how much voltage shunt resistors are rated for (we're talking a 3-phase to pump, 2-phase into pump drive circuit @ 240V), there's also the matter of derating which I've not yet had to do because my projects have all been low voltage and amperage DC.
I tried to search for this online but the only help I could find was wikipedia which simply said: "All shunts have a derating factor for continuous (2+ minutes) use, 66% being the most common, so the example shunt [ 500A 75 mV ] should not be operated above 330 A (and 50 m drop) longer than that..... [citation needed]"
That's not very clear (What about +2h? At what voltage?) and there's no reference to read either. Normally resistors have wattage and voltage rating, and after some searching of ebay, shunt resistors never seem to have one. Nor have I found one that explicitly states a derating factor.
Any advice?
Thanks