User:Halebp

A Neutral Grounding Resistor (NGR) is a grounding device for non-isolated systems, which is used to connect the neutral point of the transformer to earth through resistance. Neutral Grounding Resistors are used to protect equipment, such as, power transformers and power generators against 50/60 Hz faults (short circuit) and transient phenomena (lightning). Neutral Grounding Resistors are used in industrial power systems for resistance grounding of wye connected generators and transformers. A neutral grounding resistor limits the fault current to a value which is sufficient enough to operate protective relays, yet prevent unwanted fault damage.

Advantages
The purpose of resistance grounding is to provide protection of a transformer/generator by solving the problem of transient over-voltages thereby reducing equipment damage. It accomplishes this by allowing the magnitude of fault current to be predetermined by Ohms law I=V/R where I=fault current, V=line to neutral voltage, R= Ohmic value of resistor. In addition, limiting fault current to predetermined maximum values permits the designer to selectively co-ordinate the operation of protective devices, which minimizes system disruption and allows quick location of the fault.

Neutral grounding resistors will save money by reducing magnitude of transient over-voltages, thereby reducing equipment damage, simplifying ground fault location, improving system and equipment fault protection, reducing maintenance time and expense, creating improved safety for personnel, improving lightning protection and reducing fault frequency.

When the neutral of a system is not grounded destructive overvoltages appear from line to ground during normal switching of circuits. It has been shown that these overvoltages cause aging and insulation failure at various locations throughout the system. As a result, a line to ground fault can cause considerable damage, interruption of service and difficulty in fault location.

Advantages of Neutral Grounding Resistors Include:


 * Reduced overvoltages.
 * Reduced equipment damage.
 * Isolation of faulted circuit.
 * Increased protection of transformers, generators and auxiliary equipment.
 * Reduced operation/maintenance expense.
 * Increase safety.
 * Improved reliability.
 * Reduced frequency of faults.
 * Quicker fault location.
 * Increased lightning protection.