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  1. trevorm

    Harmonics and VFDs

    This thread has been most interesting and entertaining. I must admit that initially the reduced current had me thinking maybe Valvecrazy is onto something, until I realized that all that happened is that the load had been reduced and less work was being done. Naturally the amps will drop. The...
  2. trevorm

    Single Phase TX Configured in Three Phase

    The single phase fault current will remain the same. The phase to phase fault and three phase fault currents will depend on positive, negative and zero sequence network connections.
  3. trevorm

    Winch not starting under load

    If I understand correctly, a soft starter was mentioned. If this is a soft starter that works on the reduced voltage principle, the torque will be seriously affected. Torque is directly proportional to the square of the voltage. Reducing voltage to start will reduce the torque available. I...
  4. trevorm

    Transformer oil sampling under full-load conditions?

    To get accurate analysis of oil samples, the temperature the sample is taken at is important. I may be out of line on NFPA70E as it is not applicable in the country I operate in, if so I apologize in advance. My understanding is that where the work is done by qualified persons related to the...
  5. trevorm

    Determining CT ratio

    Maybe the 5A secondary is standard in certain parts of the world, please bear with me, my experience is only on systems in South Africa. Depending on the system, the secondary could be 1A or 5A. Many protection relays also give the option of selecting 1A or 5A. Whether a voltage TTR or...
  6. trevorm

    Determining CT ratio

    Primary Injection is the only accurate way to determine the ratio. Using the ampmeter sometimes is an option, but often the Protection and Metering circuits have different ratios. You also have to be aware that Protection and Metering CTs have different characteristics and different classes...

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