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  1. K

    4160V Reduced Voltage Starter Question (run and shorting contactors are closed at the same time)

    Can someone give me some insight into what would happen at the motor terminals and on the line if 2K2 (run Contactor) and 2K3 (auto xfmr wye contactor) were to close simultaneously. There are interlocks to prevent this, but I would like to know out of curiosity. My theory is that you would have...
  2. K

    Voltage measurement on a Current Transformer (CT)

    I don’t know the ratio of the CT. I’m just looking for an explanation on this. I thought in order to measure output voltage you need to pass the current through a resistor and read the voltage drop. A co worker put 400a through the CT and measured 130v. Something just seems off to me. Can you...
  3. K

    Vacuum interrupter contacts and displacement current

    I’m self taught so I have a lot of holes in my understanding. I also have little to no mathematical understanding. Even though ironically, I tend to prefer to picture electricity as numbers rather than “water” in a pipe, etc. I’ve been studying displacement current recently and have a question...
  4. K

    Strange Ground Current Loop

    In the attached picture, I’ve drawn a crude schematic of the motor circuit. It is fed from a switchgear feeding 3 total motors. The feed contains 2 parallel conductors on each phase and ground. The equipment ground reads 12a going back to the switchgear, 6a per conductor. From the starter to...
  5. K

    DC Compound Motor Help

    What are the negative effects (if any) of running a compound DC motor with the series field open? I’m troubleshooting a 100hp recoiler motor on a metal slitter machine that constantly blows line and load fuses. It is on a DC drive. The drive has been replaced and the motor has been rewound. The...
  6. K

    Understanding surge capacitors

    I have a decent understanding of power factor caps, (far from perfect) but I’m not as clear on surge caps. Surge caps store transient voltages and discharge back into the system? Why are they tied to ground? And do they also provide capacitance in the motor circuit they are tied to providing...
  7. K

    Method for testing discharge resistors in 3 phase capacitors

    A couple of months ago I was troubleshooting a blown fuse on a power factor correction capacitor in a 4160v motor starter. While I was working through it I noticed that my DMM (fluke 289) would charge the capacitor to a certain degree while on the Ω function. The current from the meter would...
  8. K

    Help understanding auto transformer shorting

    Will someone please help me understand the significance of shorting an auto transformer? This feeds a motor. At reduced voltage, the motor starts at 65% of line voltage, a run contactor pulls in bypassing the transformer and the shorting contactor pulls in to take the transformer out of the...
  9. K

    Help with reducing AC Mains voltage sag at large chiller motor startup

    A 4160v chiller motor is drawing too much power at start-up. Utility company only lets them run it once or twice a year because of it. It dims all the lights etc.. It was originally a primary reactor starter (2 contactors). The PR was replaced with an auto-xfmr and wired the same. So now it’s a...
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