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  1. moose2

    Earth current limiting Resistor

    I work at an old mining installation that uses reactors on the star point of all underground transformers to limit earth fault currents. Why use a reactor instead of resistors? I would have thought reactors would create problems with transients/harmonics during earth fault protection switching...
  2. moose2

    vacuum contactor transients

    I was actually thinking about putting a R-C network across the earth reactor to help quench the transients. We are limited to 5A earth fault current, hence the reactor. That is out of the hazardous zone inside the substation so it might be worth a go. If I get an earth fault trip and THEN the...
  3. moose2

    vacuum contactor transients

    The contactors are in a flame proof enclosure that is very (read VERY) tight. No room for any monitoring equipment unless you can get a 'scope the size of a matchbox.
  4. moose2

    vacuum contactor transients

    So, as of night shift this is what we now have. One shuttle car has another, new/rewound motor on it.PLUS we have changed out the vacuum contactors for air break contactors. The other car has a new/rewound motor but it still has the vacuum contactors. Now I just have to sit back and wait and see...
  5. moose2

    vacuum contactor transients

    yeah just checked out a farnell catalogue, HV proves are only AUS$250 for a scopemeter. Thanks
  6. moose2

    vacuum contactor transients

    Just had a meeting with the manufacturers of the shuttle cars and they refuse to believe the contactors are to blame. There are no suppressors on the contactors so I assume they are doped pole faces. The information I have received point to transients at up to 2.5Mhz and 10-15 times L-L...
  7. moose2

    vacuum contactor transients

    The motors in question are AC 2 speed consequent pole constant torque used to drive a chain conveyor, not traction. To make matters more difficult they are in a hazardous zone which makes condition monitoring very difficult. 'H' class insulation is standard on these flame proof motors. I will...
  8. moose2

    vacuum contactor transients

    Yeah I have to careful what I say. Mining guys have a tough skin though. Sorry to confuse, we are a coal mine using rubber tyred shuttle cars for loading from the miner onto the belt. As for pumps, water is a huge issue at my mine. We have many dedicated pumping engineers and I do not enter...
  9. moose2

    vacuum contactor transients

    I just had a thought this was not an isolated mining issue. And mining guys aren't that smart.... hehehe Sorry I didn't mention that the motors drive a chain conveyor on the car and the cars are rubber tyred. Thanks Dave, if i don't get any useful info from the gurus here then I'll contact you.
  10. moose2

    vacuum contactor transients

    I'm having some problems with 2 speed consequent pole constant torque motors dying from earth faults. They are rated at 12.5/25HP, from memory 15A FLC. They are on brand new shuttle cars, which are used in underground coal mining, and nearly identical to other cars on site. The only differrence...

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