Neutral grounding resistor

A.     areas of usage

1.      Common reasons for using neutral grounding resistor

a.       reducing single phase fault currents which occur in M.V. electrical networks to prevent damages on transformers and generators

b.      reducing temporary over voltage occurred by braking 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.

MINGRUI resistors are designed to absorb a large amount of energy without exceeding temperature limitations defined in IEEE32. Neutral Grounding Resistors MINGRUI manufacture can be used for indoor and outdoor and the neutral point is connected with a porcelain bushing or with a high voltage cable from the bottom, top or side. The most common protection degree preferred for Neutral grounding resistors is IP23 as it allows the resistor elements to cool easier and they can be used both at sea shores and deserts because the resistor elements are completely stainless steel and does not affected by extreme conditions. Neutral grounding resistors are shipped with maintenance and installation guide, in which, recommended relay settings for each Neutral grounding resistor are stated as well. MINGRUI provides complete technical assistance in order to meet your specifications or site conditions.

B.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

C.     b

2mm hot dip galvanized steel enclosure

Stainless steel or aluminum enclosures are available on demand

Typically, RAL7032 paint for enclosure (other colors are available on demand)

Solid top cover sloped to prevent water accumulation

Custom made lifting eye bolts for securing lifting

Front cover for easy access to connection and inspection doors available on demand

Corrosion resistant stainless steel nameplate

B.c 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

C.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

C.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)