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Recent content by Marke

  1. Marke

    VFD increasing the motor winding temperature

    Harmonic currents and other distortion currents in the stator will induce additional currents in the rotor. For each repetitive cyclic current, there will be an effective rotating torque field set up in the stator which will be rotating (or stationary) and this in turn will induce a current in...
  2. Marke

    Currant imbalance submersible pump

    We recently had a case of quite bad imbalance, one phase current high and earth current. Pump 100M down the hole. Pump was lifted and reconnected using the same cables, in a test well. All cables were just coiled up on the ground. Almost perfect balance, so not cables. Pump was reinstalled...
  3. Marke

    Currant imbalance submersible pump

    This is a common problem. When the pump was lowered down the well casing, the four conductors (three phase plus earth) need to be dead vertical and not rotate around the riser pipe. If any one phase conductor is allowed to move around the riser by a partial turn, you will get a transformer...
  4. Marke

    Does anyone use NTC resistors to limit inrush current on single phase AC motors as a soft start?.

    I have seen it done on very small machines, but then you could argue that it is not necessary as the current is always so low. Mark Empson Advanced Motor Control Ltd
  5. Marke

    Inexplicable motor failures

    When you say that the pump is unloaded, are you sure that mechanically the load reflected to the pump is actually reduced? What type of pump is this and how are you controlling the load? If it is a turbine pump, or a moving cavity pump, or some multi stage pumps, closing down the discharge side...
  6. Marke

    VSD Starting and Line Transfer

    Open transition switching is always going to result in transients to flux the iron. If switching is too son after the disconnect, the rotor will still be generating and depending on the phase relationship between the "generated voltage" and the line voltage, and the magnitude of the generated...
  7. Marke

    IEEE 399 - Motor starting studies thumb rule

    Waross Yes I agree.Have gone to 40% plus on many occasions. It depends on the generator set up and configurations. If a three phase averaging AVR is used, plus external excitation (permanent magnet generator for excitation) you can commonly go to full voltage starting with some sag, but no...
  8. Marke

    Current present in Earthing wire of 3 phase motor, what is an acceptable leakage current?

    I have seen a high earth current in a number of installations of bore hole pumps with a steel riser. If the cables down the well to the motor are not perfectly fed down the bore with the motor, you can end up with a partial turn of one phase around the riser and it acts like a short circuited...
  9. Marke

    VFD Resonance With AC Grid

    Hello Guilhermebr This could be Middlebrook instability. Do you have a harmonic filter in series with the input to the VFD? Do you have a Hi Z impedance on the input to the VFD? I usually find Middlebrook in a rural installation with a single VFD on a dedicated transformer and many KM of...
  10. Marke

    Softstarter/Motor troubleshooting

    Well said Jeff. In addition to Jeffs comments, there are major differences in start characteristics due to the variation in High Slip characteristics of different induction motors. Typically, you will need to develop around 40% torque initially to start the pump, and usually you would look at 3...
  11. Marke

    Harmonics in 250kW VFD

    Hi Lionel That is a good summary from a suppliers perspective and I believe would be pretty well the defacto attitude towards harmonics across the board. Here, in New Zealand, we do have rural areas where the accumulation of the harmonic currents on the local network can result in harmonic...
  12. Marke

    Harmonics in 250kW VFD

    A three phase rectifier that is balanced will draw ODD harmonics minus the triplens, so expect to see 5th, 7th, 11th, 13th .... with the amplitude reducing as the harmonic number increases. (multiples of 3 balance out.) Harmonic mitigation may be required by regulation. - it is needed in some...
  13. Marke

    A question about a sentence in a AC drive manual.

    Hi A bit more information would be a great help in providing the best advice. If the manufacturer recommends that you do an ID Run, then there could be a valid reason for this. 1. There are many variations on two themes when it comes to the waveform generation within the drive. Essentially...
  14. Marke

    A question about a sentence in a AC drive manual.

    The drive runs a routine called ID Run, or Auto-Tune whereby it feeds different waveforms/frequencies to the motor in order to determine what the motor characteristics are. Often, there are two choices, a static ID Run where the motor does not turn, and a rotating ID Run where the motor tunes...
  15. Marke

    What possible root cause Phase C current spiked two time of Phase A & B current?

    Part of the bus charging mechanism of the VFD?? Rotate the phases around and see if the trip moves to a different phase. Mark Empson Advanced Motor Control Ltd
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