Specifications
NGR is used to protect transformer, generator and other associated equipment in power system against short circuit and lightning
A. Areas of usage
1. Common reasons for using neutral grounding resistor
a. Reducing single phase fault currents which occurs in M.V. electrical networks to prevent damages on transformer and generators
b. Reducing temporary over voltage occurred by braking in instantaneous fault current, providing long-life for switchgear
c. Reducing step voltage to a harmless level for staff
Neutral grounding resistors are used for resistance grounding of industrial power system. They are generally connected between ground and neutral of transfomers, generators and grounding transformers. Neutral grounding resistors are used in order to limit maximum fault current to a value which will not damage the equipment in the power system, yet allow sufficient flow of fault current to operate protective relays to clear the fault. Although it is possible to limit fault currents with high resistance neutral grounding resistors, phase to ground short circuit currents can be extremely reduced. As a result of this fact, protection devices may not sense the fault. Therefore, it is the most common application to limit single phase fault currents with low resistance neutral grounding resistors.
B. Features
Stainless steel resistor elements
Current transformer included (EN60044-1)
Bolted resistor element connections instead of welded connections in order to be able to assemble spare parts on site immediately
a. Technical Specifications
Operation voltage: up to 110kV line to line systems
Rated current (A): up to 2000
Ambient temperature :<55
Resistance alloy: stainless steel
Protection degree: IP23(outdoor) and others
Standards: IEEE32, IEC60137, IEC60298, IEC60273, IEC60071, IEC60060
b. Options
Elevated support standard are provided for ground clearance and safety
Specially designed units for hazardous and extreme locations
Stainless steel or aluminum enclosures on demand
Installation of voltage transformers
Installation of protection relays
Porcelain entrance bushings can be mounted on top or on the side of Neutral grounding resistor
Grounding transformer installation
Motorized or manual single pole disconnector switches, load bank switches, surge arresters and heaters in the Neutral Grounding Resistors
C. Tests
a. Routine tests
Measurement of insulation resistance between enclosure and resistor
Withstand test of dielectric strength at network frequency for one minute
Measurement of total DC resistance
Insulation test or resistor blocks
Galvanization thickness test
Paint thickness test
b Type Test (on demand)
Temperature rise test
Protection degree test
Impulse voltage test
Measurement of AC resistance
Seismic test
D. Selection details
System voltage
Line to neutral voltage
Desired current rating
Desired resistance level
Maximum time ON (seconds)
Bushing entry or cable entry
Current transformer ratio (if applicable)
Disconnector switch (if applicable)
Special options (if applicable)
