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Recent content by waross

  1. waross

    Phase-earth fault in YNd11 step-up transformer while operating at no load

    The neutral connection is probably providing ground current detection. What are the primary voltages? Line to line and line to neutral? It is possible to have equal line to neutral voltages along with unequal line to line to line voltages. This is quite common in long rural lines with mostly...
  2. waross

    Phase-earth fault in YNd11 step-up transformer while operating at no load

    Any unbalance in the incoming power and the delta will cause a neutral current. This may be misinterpreted as a ground fault be the protection.
  3. waross

    Phase-earth fault in YNd11 step-up transformer while operating at no load

    Unbalanced primary phase voltages or pri9mary phase angles.
  4. waross

    Corrosion on cable trays.

    We always used Spray on Electrical Insulating Varnish on all ground connections. The bolt corrosion appears to be atmospheric corrosion. Try Stainless steel bolts.
  5. waross

    DC Motor Drive - Imbalanced input (line/neutral) and output (motor + / - ) current

    The most likely cause, but not the only possibility: Someone servicing the brushes accidentally caused a short to ground from one of the brush holders.
  6. waross

    DC Motor Drive - Imbalanced input (line/neutral) and output (motor + / - ) current

    Yes. Common practice and a requirement of most codes. Yes. First at the motor. Note, there may be an alternate ground path if the motor is mounted on steel connected to structural steel. If the tech's have a DC clamp meter, measure the current in the PE conductor. A long shot, disconnect the...
  7. waross

    Commutator marks in DC Motors

    Does that make the commutator burning a design issue? Rule of thumb for sparking/arcing at the commutator. Move the brushes to cover the sparks. So when we cover those sparks may we expect sparking at every second alternate bar? Or, do we split the difference and go with minimum sparking at each...
  8. waross

    Spain and Portugal power grid collapse

    Is this a new name for "Pole Slipping"?
  9. waross

    Commutator marks in DC Motors

    Yes, general causes of sparking but mostly not applicable to sparking at every second bar. Look for something inducing an AC ripple on the generated DC.
  10. waross

    Commutator marks in DC Motors

    The first thing that comes to mind is a mismatch between rotor slots and field width and or spacing. Energize the field with 120 VAC. The voltage at the brushes should be zero or very close to zero. Slowly turn the rotor while monitoring the armature voltage. Any variation of the voltage at the...
  11. waross

    Power Transformer Rating

    Designed for anticipated load growth. Actual rating depends on installed equipment. Selection of operating cooling mode by thermostat(s).
  12. waross

    DC Motor Drive - Imbalanced input (line/neutral) and output (motor + / - ) current

    I suspect either a ground fault somewhere, OR Someone has grounded the neutral in one or more locations. Look for the missing current on the protective earth conductor. If you find the missing Amps on the PE, then try to follow the current back to either the drive or the motor, or possibly both...
  13. waross

    35kV Line Reactors

    One solution may be to run both bus to a common equi-distant location and from there together back to the transformer. Old text books, 80 to 100 or more, described a wireless reactor used for transformer impedance matching and load sharing on 110/220 Volt secondaries. Transformer life was 20...
  14. waross

    Air India 787 crashes on take off

    This is more of an anecdote that you may find amusing more than useful. The fishing boats in Central America typically have 32 Volt starting systems and 12 Volt radios and navigation. They Use 24 volt bulbs in the engine room. The 32 Volts is connected to the engine room lights which are not...
  15. waross

    How to protect against frequent breakdown of soft starters at a water pumping station?

    I have seen this many times in Central America, The missing/blown fuse is feed the distribution circuit. Wye/delta transformer banks were common. A wye/delta bank will backfeed into a dead primary phase and try to pickup the upstream load on the missing phase. The back EMF of a motor will do the...
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