Actually the majority of the damage was in the area of the control circuitry which drives the gate of the solid-state switches (SCR/thyristor).
We had an interesting development yesterday in which we saw similar damage as a result of over-currenting the switching device during the motor startup...
Thanks for everyone's comments/suggestions.
Yes, the damage is only to my box and not to the motor. Currently the electronics in my box are grounded. I have considered a floating neutral for the electronics, contained inside an grounded enclosure for safety. I'll give it some more thought.
In...
Bill,
Thanks for your reply. I'm a bit out of my element, but does this implementation have an effect on the floating delta, or just provide me a safe vantage point from which to observe it?
I would still need surge suppression on the lines of the floating delta, and I'm not clear on what I can...
Hi,
I think I have some of the same issues described in thread238-227276. I hope you can help.
I'm working to develop a device to monitor and control an oilwell pumpjack and its motor. My device takes its power from the 480V/3-phase supply that runs the motor. Lately I've had a rash of...
Hi All,
As suggested, I turned off the motor and used the Dranetz to measure THD of the voltage. I'm seeing about 39 V in the 300 Hz component out of a total RMS of 480 V. At another well in the same area (although maybe 2 miles away), the 300 Hz component is only 21 V out of 480 V. I don't know...
All,
Thank you very much for your replies.
- I will return to the well to record the voltage with the motor turned off, as Bill suggested.
- The pumpjack motor has a cyclical load. It varies between no-load and 120% of full-load with a period of about 8 seconds. Whether lightly loaded or heavily...
Hi All,
I'm working in a west Texas oilfield. The motor that drives the pumpjack is 460V, 3-ph, 60 HP. It is powered directly from the grid: no generators or VFDs, etc. Looking at the current to the motor on a scope, I can see a lot of 5th-harmonic (300 Hz) content distorting the current...
Thanks to everyone for your replies.
Thanks for pointing out my error regarding frequency. I assumed that the frequency of the generated energy would be a function of the speed of the overspeeded motor.
Yes, in this application, it is possible that the pumpjacks are not optimally balanced and...
Hi,
Pumpjacks in the oil fields use 3-phase induction motors. During a certain portion of the pumping cycle, the weight of the falling masses can force the motor to rotate at above its synchronous speed, thereby turning it into a generator. There is a belief that this briefly (~ 1 second out of...
