Impedance Earthing with Generators.

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Tushar Mogre Participant Join Date: Jan 2008 Location: Mumbai, India Posts: 2	Impedance Earthing with Generators. 01/25/2008 6:25 AM
	Would like to know the reasons for providing inductor (reactance) in Neutral Earthing path of a Generators. Specifically 1MVA to 20MVA a fixed inductor is observed but with higher rating, even an earthing transformer usage is seen which provides variable values of impedances. Is the only reason for limiting the short circuit levels with earth faults or any other reasons too. If so any design criteria?
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Anonymous Poster	#1 Re: Impedance Earthing with Generators. 01/26/2008 4:13 AM
	Hi, 1. Resonant Grounded. The ground-fault neutralizer is a neutral reactor having characteristics such that the capacitive charging current during a line-to-ground fault is neutralized by an equal component of inductive current contributed by the ground-fault neutralizer. 2. Low-Inductance Grounding. The value of the inductor in ohms is less than that required for resonant grounding. A generator system - grounded through an inductor may have the following desirable features: - Limits transient overvoltages on the unfaulted phases. - Allows the application of lower rated surge arresters - Allows differential and ground relay operation for fast clearing of ground faults. - Limits the line-to-ground fault current to values less than those caused by 3-phase faults. A major disadvantage of low-inductance grounding is that the relatively high ground-fault currents increase the possibility of iron-core damage for internal faults.
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angelayanmei Participant Join Date: Mar 2011 Location: China Posts: 4	#3 In reply to #1 Re: Impedance Earthing with Generators. 03/17/2011 4:09 AM
	Hi, how are you? I find your summery about groud-fault-neutralizer is clear and to the point. I am in the field of neutral ground resistor cabinet, I am not sure if there is any difference between the two? Could neutral ground resistor take the place of ground-fault-neutralizer for the function of preventing grounding hazards? Thank you
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Paata Active Contributor Join Date: Jan 2008 Posts: 20	#2 Re: Impedance Earthing with Generators. 02/09/2008 9:34 AM
	Hello, In addition to other reasons: In parallel operation of synchronous generators and in interconnected systems with grounded neutrals, the third harmonics will produce circulating currents in the neutral that may reach values of up to 60 %rated current. These harmonic currents are superimposed on the phase currents, thus causing thermal overload of the stator winding. As a remedy the neutral current can be reduced to appr. 15 - 20 % rated current by means of neutral reactors. In this case it must be observed that the voltage drop at the reactor will not exceed the maximum admissible value.
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