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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)

    Baluncore — never looked at it that way. That correction will help. The difference in a power transformer and a current transformer being the voltage on the primary, there is no transformed voltage in a ct. But a voltage must still be present across the secondary for a current to flow.There is...
  3. K

    Voltage measurement on a Current Transformer (CT)

    Zoki - The only problem is that there are holes in my understanding. The question was more about helping me learn the relationship between E and I in a CT. The coworker and job really isn’t relevant. The GF system is malfunctioning, he checked the CT voltage to verify the condition of the CT...
  4. K

    Voltage measurement on a Current Transformer (CT)

    Since there appears to be no burden resistor internally, and a digital voltmeter will have a very high input impeadance , I would say there is no way to get an accurate measurement of the CT output by measuring voltage on the secondary only. Current and voltage may not be proptional. It will...
  5. K

    Voltage measurement on a Current Transformer (CT)

    That is all I can find so far. I’m having very little luck getting any real information.
  6. K

    Voltage measurement on a Current Transformer (CT)

    http://www.electricalpartmanuals.com/pdf/circuitBreaker/General%20Electric/Ground%20Fault%20Systems/GEI-86126H.pdf
  7. K

    Voltage measurement on a Current Transformer (CT)

    Yes. The manufacturer literature says to short “c” and “m” to prevent shock. It’s a 3 wire zero sequence CT for ground fault protection. The current from the CT energizes the trip coil. I’m just having a hard time reporting his 130v @ 400a to the customer because it seems wrong. The CT is a GE...
  8. K

    Vacuum interrupter contacts and displacement current

    Zoki the steady state capacitive current in AC is small and inherent in the circuit, but the displacement current through a capacitor equals the conduction current at the capacitor, correct?
  9. 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...
  10. K

    Vacuum interrupter contacts and displacement current

    And the same applies to both ac and dc correct? A charging or discharging dc capacitor will have a changing electric field which would cause the displacement? I’m an electrician, no one explains capacitors in this way. “A charge on one terminal pulls a charge from the other side” etc. (I’m...
  11. K

    Vacuum interrupter contacts and displacement current

    What allows it to pass through a capacitor dielectric at that frequency? The voltage at the capacitor plates would have the same frequency as an interrupter contact, right? Just curious. Thanks for the quick reply.
  12. 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...
  13. K

    Strange Ground Current Loop

    To answer the questions top to bottom, it is not an earthed neutal. It is on an equipment ground. the current is constant during operation. The ground is terminated in the peckerhead and does not enter the motor. If the grounds were open between the motor starter and switchgear I would expect...
  14. 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...
  15. K

    DC Compound Motor Help

    Tom, thank you very much for your reply. I’ve read about half so far, but I am currently working. Please allow me some time to review the rest of the information and I will get back promptly. Thank you for your speedy reply. I do have nameplate info and drive info. I will attach those in a bit
  16. K

    DC Compound Motor Help

    The DC drive has an output for the armature, and a separate output for the field. I’m not getting much information about the incidents, but I do know that at least 3 of the times it blew fuses at 300 feet per minute, 150 fpm, and 120fpm. All with “light load” as in, they were pulling thin gauge...
  17. 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...
  18. 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...
  19. K

    Method for testing discharge resistors in 3 phase capacitors

    What do the balancing resistors do?
  20. K

    Method for testing discharge resistors in 3 phase capacitors

    That’s what I was getting too. 24v give or take.I was just curious to see if I was missing anything. Thanks for the help
  21. K

    Method for testing discharge resistors in 3 phase capacitors

    Thanks a lot for the reply, it was informative. I don’t expect anyone to read this article (5min read:wink:) but it explains what I’m asking, only he is testing for cap discharge through leakage (very slow) and I’m testing for cap discharge through resistor. Of course a DMM would be a bad choice...
  22. K

    Method for testing discharge resistors in 3 phase capacitors

    Ah I just added the time bit to show that it was not discharging slow enough to make me think it was discharging through my meter, which had a high resistance.
  23. K

    Method for testing discharge resistors in 3 phase capacitors

    But 10uf was the capacitance of that particular capacitor
  24. K

    Method for testing discharge resistors in 3 phase capacitors

    Is the capacitance value necessary? It could be, I don’t know. But if you put a small current on it, it will charge to some value for however long you have that current present across the plates, right? It’s not the capacitor I’m testing here, it’s the discharge resistor installed to create a...
  25. 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...
  26. K

    Help understanding auto transformer shorting

    It’s alright though, I’ll chalk it up as a good learning experience and sleep like a baby.
  27. K

    Help understanding auto transformer shorting

    There’s probably a way to do it, although I don’t think the low voltage would provide the torque needed to turn the motor. Even if it would, they wouldn’t spend the money for it. After figuring out the problem, it turns out they are content with putting a reactor back in and only running that...
  28. K

    Help understanding auto transformer shorting

    I completely understand what you’re saying. But I’m really good at questioning myself to the point of confusion. I’ve found that my biggest revelations come from thinking out loud to one or many so to speak and piecing together the conversations. I’ve always thought there were no such thing as...
  29. K

    Help understanding auto transformer shorting

    I debated on even responding because it contradicts your post . Yeah but noted, I’ll take it as constructive criticism. I’m a newb to the forums. I learned more than one thing today though. Many thanks
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