Why are synchronous motors grounded with reactance

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Discussion Overview

The discussion revolves around the grounding methods used for synchronous motors, specifically the use of reactance grounding compared to resistance grounding in alternators. Participants explore the implications of these grounding techniques for safety, stability, and electrical performance.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants question the meaning of "grounded" in the context of synchronous motors, suggesting it may relate to safety purposes.
  • There is a concern that grounding with reactance could lead to resonance issues and surges, particularly in motor applications.
  • One participant notes that in a Y-coupled synchronous motor, grounding can dampen higher harmonics in the neutral current, which may benefit nearby electronic devices.
  • Another participant discusses the differences in grounding regulations between the US and Europe, emphasizing that in Europe, no current should flow to ground under normal conditions.
  • Some contributions mention the use of high sensitive current relays (HFI-relays) for measuring ground current, indicating variations in safety practices in different regions.
  • A participant highlights that in the US, ground fault detection is typically performed at receptacles, which may differ from practices in other countries.
  • There is a reiteration of the original question regarding the rationale behind using reactance grounding for synchronous motors instead of resistance grounding, with a focus on potential ground faults in wye configurations.

Areas of Agreement / Disagreement

Participants express differing views on the implications and safety of reactance grounding versus resistance grounding. The discussion remains unresolved, with multiple competing perspectives on the topic.

Contextual Notes

Participants reference various grounding practices and regulations that may differ by region, indicating a lack of consensus on the best approach to grounding synchronous motors.

Who May Find This Useful

Electrical engineers, safety professionals, and students studying electrical systems may find this discussion relevant, particularly those interested in grounding techniques and their implications in different contexts.

arnab ghosh
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Why are synchronous motors reactance grounded and not resistance grounded like in alternators?
 
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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:
Hesch said:
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.
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 don't get why in case of motor , neutral is grounded through reactance . Will it not lead to resonance issues and surges?
 
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 ).
 
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.
 
Hesch said:
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.
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.
 
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Averagesupernova said:
detection is done at the receptacle.

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.
 
The receptacle is what you plug into. You would plug table lamp into a receptacle.
 
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arnab ghosh said:
Why are synchronous motors reactance grounded and not resistance grounded like in alternators?
basically 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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