Generally connected between ground and neutral of transformers, ners reduce the fault currents to a maximum predetermined value that avoids a network shutdown and damage to equipment, yet allows sufficient flow of fault current to activate protection devices to locate and clear the fault. Grounding system theory and practice ced engineering. This is the basic theory of earting transformer, the operation and other features of an earthing transformer is described as follows. What is earthing transformer or grounding transformer. Advantage and disadvantage of grounded and ungrounded neutral system if this is the first time for you then please read my previous post about electric earthing system.
Current rating of this transformer is the maximum neutral current in amperes that the transformer is designed to carry in fault condition for a specific time. If the grounding transformer is lost, a linetoground causes high phasetoneutral voltages on the unfaulted phases, and load unbalances can also cause neutral shifts and overvoltages. D static power converter for devices such as rectifiers and inverters, the system grounding is determined by the grounding of the output stage of the converter. It provides a low impedance path to the neutral and also limits the transient overvoltage when the ground faults occur in the system. Grounding transformers used as the only ground source to a distribution circuit should be in service whenever the threephase power source is in service. The neutral of the earthing transformer shall be solidly earthed to provide earthed neutral in the 33 kv systems. Grounding transformer the grounding transformer is used to provide a path to an ungrounded system or when the system neutral is not available for some reason, for example, when a system is delta connected. Because the reactance of source generator or transformer impedance is in series with the neutral circuit, this system cannot be considered a zeroimpedance circuit. The earthing transformer shall have impedance to restrict earth fault current.
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