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Why are synchronous motors grounded with reactance

  1. Apr 29, 2015 #1
    Why are synchronous motors reactance grounded and not resistance grounded like in alternators?
     
  2. jcsd
  3. Apr 29, 2015 #2

    Hesch

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    What do you mean by "grounded"? As a safety-purpose?

    I don't think that is permitted. I think that the motor (shield) must be shortcircuited to ground.

    Where is the safety if the resistor/inductor is blown? Then you could act as reserve-impedance to the blown resistor/inductor.
     
    Last edited: Apr 29, 2015
  4. Apr 29, 2015 #3
    Grounded as in the neutral is connected to the ground by reactor in case of motor . In case of generator , since neutral is grounded with resistance , it helps to control the current and hence suppress stability issues. But I donot get why in case of motor , neutral is grounded through reactance . Will it not lead to resonance issues and surges?
     
  5. Apr 29, 2015 #4

    Hesch

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    If a Y-coupled synchronous motor is connected to neutral (not "grounded"), the higher harmonics (if present) in the neutral current will be dampened, so that nearby radios, mobile telephones, etc. will work proporly.

    I don't know the rules/laws in US in case of "grounding" things, but in Europe no current may flow to "ground" under normal conditions. The purpose of grounding things is to protect people in case of an electric failure ( isolation in motor shortcircuited ).
     
  6. Apr 29, 2015 #5

    Hesch

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    I've tried to google "HFI-relay+US". There is not much to be found. "HFI-relay" means: "High sensitive current relay" that is measuring the ground-current (if any), using Kirchhoffs current law: Ia+Ib+Ic+Ineutral = -Iground. If Iground is above ≈20 mA, the relay will break everything (except ground) in your installation.

    I think you have other rules/laws in US regarding safety, so I cannot answer your question.
     
  7. Apr 29, 2015 #6

    Averagesupernova

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    Concerning breaking connections here in the U.S.A., neutral is virtually never broken. At least residentially, most ground fault detection is done at the receptacle. This is because most often it is the most inexpensive way to go. Not always though. The same is true in the U.S.A. concerning the ground wire. The green or bare wire and what they are connected to all the way back to the service is never meant to carry anything except a fault.
     
  8. Apr 29, 2015 #7

    Hesch

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    Thank you for the answer, but what is the "receptacle". My dictionary tells me, that it some kind of container?

    Please describe it more detailed.
     
  9. Apr 29, 2015 #8

    Averagesupernova

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    The receptacle is what you plug into. You would plug table lamp into a receptacle.
     
  10. Apr 30, 2015 #9

    donpacino

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    Basicly with motors you would get a ground fault with a resistive load in a wye configuration. When all three phases are closed you would have a short to ground
     
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