Time to end this thread:
I've got the OEM engineer answering all of my questions with, "NO!" and angered some in here but I got the nerve to start and run it under load and was successful. I was wary because I replaced the the shorted SCR in the original soft start and its unshorted twin but...
Mr. Skogsgurra, in reference to your earlier suggestion that the surge test may not be needed because the high current is only during start and not run was correct. I had the motor "surge test" tested by professionals and it passed. The OEM stated that was something they would do under similar...
I got called away by a whining and whimpering one horse motor.
Thanks to everyone for their inputs. The voltage of the switchgear that powers the motor is 500V and this would be adding some to the current but to be on the safe side I am calling in a professional to do the surge comparison test...
The ramp is controlled by a nine position switch with position 1 meaning six seconds which is factory default. I do not have information as what the different steps mean on the switch but I set it to 3 and used a stop watch. The ramp was 7 seconds and the highest current reading was 2450A. I...
Ramp is OEM set to 6 seconds. I will lengthen that value to say 10 seconds and do a test. I will try this and see what happens but suspect that the current will remain large because I now think there is a motor fault.
Motor FLA is 754A. I checked the thyristor data chart and the first amps listed is "I TRMSM" and it is 2800A. The motor is also uncoupled and 2863A during start is way too high. I have already done two start and run tests but I watched B phase only during start. After start the current fell to...
I have just been thinking the same thing. I think the thyristors are rated in the area of 2800A. I did not monitor the other two phases but only the B phase during start. After thinking about it, somewhere in the area of 1500A is what it should have peaked at during start. Would you agree that...
Motor passed smoke test and will be coupled to the load next. Current on the B phase (where SCR short was occuring) ramped up to 2863A and then dropped extremely fast to 144A once up to speed.
itsmoked, I apologize for sounding cavalier with respect to safety. I am very safety conscious but...
I have installed a good soft start from another unit and will probably do the smoke test in the next few hours. I was going to rebuild the old soft start and use the 5 HP motor to test it. I know that even at locked rotor it cannot short the SCR.
Instead of rebuilding the old soft start I...
Mr. Skogsgurra, I thought about gating early on but do not have a way to test it. I came up with the idea of after making the swap and repairing the original soft star to power a 5HP motor with it and check current on all three motor taps. With a good motor they must be less than 10% deviation...
I only wish to prove that it is the soft start that caused the recent SCR fault. I can buy a new soft start but it needs to be running Monday morning so I want to make the swap. The main CB of the circuit is 1200A and the fuses in the switchgear are 1500A so I expected the CB to trip before a...
Thanks for the information. Here is a short description of the problem. It was a OEM Maintenance Support Manager that suggested the surge test as a comparison test. Both terms I was not familiar with.
700HP motor soft start shorted a B phase SCR (cathode to anode) for no apparent reason...
I have a 700HP 460V induction motor that I have been asked to perform a surge test on. The motor megs good with a regular hand crank megger set to 500V but I am unfamiliar with the term "surge test". Would someone describe exactly what this entails? Thanks
