Neutral earthing resistor

A.    areas of usage

1.      Common reasons for using neutral groundingresistor

a.       reducing single phase fault currents whichoccur in M.V. electrical networks to prevent damages on transformers andgenerators

b.      reducing temporary over voltage occurred bybraking instantaneous fault current, providing long-life for switchgear

c.       reducing step voltage to a harmless levelfor staff

Neutralgrounding resistors are used for resistance grounding of industrial powersystem. They are generally connected between ground and neutral of transfomers,generators and grounding transformers. Neutral grounding resistors are used inorder to limit maximum fault current to a value which will not damage theequipment in the power system, yet allow sufficient flow of fault current tooperate protective relays to clear the fault. Although it is possible to limitfault currents with high resistance neutral grounding resistors, phase toground short circuit currents can be extremely reduced. As a result of thisfact, protection devices may not sense the fault. Therefore, it is the mostcommon application to limit single phase fault currents with low resistanceneutral grounding resistors.

B.     Features

Stainless-steelresistor elements

Currenttransformer included (EN60044-1)

Bolted resistorelement connections instead of welded connections in order to be able toassemble spare parts on site immediately.

MINGRUI resistorsare designed to absorb a large amount of energy without exceeding temperaturelimitations defined in IEEE32. Neutral Grounding Resistors MINGRUI manufacturecan be used for indoor and outdoor and the neutral point is connected with aporcelain bushing or with a high voltage cable from the bottom, top or side.The most common protection degree preferred for Neutral grounding resistors isIP23 as it allows the resistor elements to cool easier and they can be usedboth at sea shores and deserts because the resistor elements are completelystainless steel and does not affected by extreme conditions. Neutral groundingresistors are shipped with maintenance and installation guide, in which,recommended relay settings for each Neutral grounding resistor are stated aswell. MINGRUI provides complete technical assistance in order to meet yourspecifications or site conditions.

B.a TechnicalSpecifications

Operation voltage:up to 110kV line to line systems

Rated current (A):up to 2000

Ambienttemperature :<55

Resistance alloy:stainless steel

Protection degree:IP23(outdoor) and others

Standards: IEEE32,IEC60137, IEC60298, IEC60273, IEC60071, IEC60060

C.     b

2mm hot dipgalvanized steel enclosure

Stainless steel oraluminum enclosures are available on demand

Typically, RAL7032paint for enclosure (other colors are available on demand)

Solid top coversloped to prevent water accumulation

Custom madelifting eye bolts for securing lifting

Front cover foreasy access to connection and inspection doors available on demand

Corrosionresistant stainless steel nameplate

B.c Options

Elevated supportstandard are provided for ground clearance and safety

Specially designedunits for hazardous and extreme locations

Stainless steel oraluminum enclosures on demand

Installation ofvoltage transformers

Installation ofprotection relays

Porcelain entrancebushings can be mounted on top or on the side of Neutral grounding resistor

Grounding transformerinstallation

Motorized ormanual single pole disconnector switches, load bank switches, surge arrestersand heaters in the Neutral Grounding Resistors

C. TESTS

C.a. Routine tests

Measurement ofinsulation resistance between enclosure and resistor

Withstand test ofdielectric strength at network frequency for one minute

Measurement oftotal DC resistance

Insulation test orresistor blocks

Galvanizationthickness test

Paint thicknesstest

C.b Type Test (ondemand)

Temperature risetest

Protection degreetest

Impulse voltagetest

Measurement of ACresistance

Seismic test