

Product Range

	Power Resistors
	Neutral Grounding Resistors
	NGR & NIS Panels With CTs
	Loading Resistor & NGT Cubicles
	Dynamic Braking Resistors
	Load Banks
	Resistance Boxes
	Motor Starting Resistors and Starter Panels
	LAVT Cubicles
	Control Panels

NEUTRAL GROUNDING RESISTOR (NGR)

NEUTRAL GROUNDING RESISTOR (NGR) is used for the resistance grounding of Power Systems. Earthing through Resistor is the most common, economical and effective solution for impedance earthing. It is used, when the Neutral of the supply transformer is available and its own impedance is not enough to limit the fault current.

Inserting a Resistor between the Neutral of the Generator/Transformer and Ground serves to limit the maximum Fault Current to a predetermined value. This value is low enough to prevent damaging Fault Currents to the generating, distribution and other associated equipments; yet high enough to operate fault clearing relays.

RESISTANCE ASSEMBLY & ENCLOSURE :

Punched Stainless Steel (PSS) Grids are made of high resistance, non-aging and non-rusting stainless steel in grade AISI 304. The grid assembly is secured at both the ends by end brackets, to form a Resistance Tier. The whole assembly is rigid, shock resistant & vibration proof.

A number of resistance tiers, stacked one atop other and insulated from each other by interposing porcelain insulators, form a Resistance Bank. The Resistor Banks are mounted on Epoxy / Porcelain HT Post Insulators. The whole assembly is enclosed in a sheet steel enclosure, with adequate clearances.

A space heater alongwith a thermostat is provided to prevent condensation of moisture. Wherever required, Cable Box is provided on the enclosure to accommodate HT Terminal Bushings and CTs, alongwith a LT Terminal Box for housing Thermostat and MCB, Indicating Lamps & Terminals etc.

Wherever required, a Neutral Isolating Panel (NIS) is attached to the NGR Cubicle, for housing Manual / Motorised Isolator / Vacuum Contactor and HT CT's etc., in addition to HT Terminal Bushings & LT Terminal Box.

SALIENT FEATURES of NEUTRAL GROUNDING RESISTOR (NGR):

• The Enclosure is normally fabricated out of 2mm CRCA sheet in Panel Type construction; with hinged doors for easy accessibility, and to give it an aesthetic look.

• The Enclosure is Powder Coated after suitable metal pretreatment & surface preparation.

• Louvers are provided in the covers for ventilation and wiremesh is welded from inside, to ensure required degree of protection. No louvers are, however given for DOP of IP 55.

• For Outdoor Duty NGR, a sloped canopy is provided.

INBUILT BENEFITS OF LACHHMAN ELECTRONICS NEUTRAL GROUNDING RESISTOR (NGR)

Choice :
An extensive range of resistor elements allows selection of the most efficient and cost effective solution for any required duty. We manufacture NGRs for any system voltage or initial current and with rated times from a few seconds to continuous duty.

Stability :
The Resistance Value is set at the manufacturing stage and remains constant throughout the life of the NGR.

Reliability :
Punched Stainless Steel Grids offered by us are rigid, unbreakable, compact and corrosion resistance.
The intergrid connection is thru Z shaped surface to surface contact, held tightly by 2 nos. bolts per connection, ensuring a totally reliable contact.

Installation & Maintenance :
NEUTRAL GROUNDING RESISTOR (NGR) offered by us are naturally air cooled and are easy to install at site and they require virtually no maintenance and have a long life.

RANGE :

RATED FAULT CURRENT	:	From 1 A to 3000 Amp
RATED VOLTAGE	:	From 110 V to 36 KV
RATED TIME	:	Normal short time duty : 10 / 30 sec. Range available : Upto Cont. Duty
RESISTANCE TOLERANCE	:	± 10% (As per IEEE 32)
DEGREE OF PROTECTION	:	From IP 00 to IP 55 Commonly used : IP 21 - For Indoor Duty IP 33 - For Outdoor Duty
PERMISSIBLE TEMP. RISE (above ambient)	:	Normally 375° C / As per IEEE 32 / Lower Temp., as desired

As per IEEE-32 - For Neutral Grounding Resistors made from stainless steel resistance material, the allowable temperature rise for 10, 30 or 60 sec. time rating is 760°C ; 610° C for extended time rated and 385°C for continuous duty.

DESIGN PARAMETERS OF NEUTRAL GROUNDING RESISTOR (NGR):-

V :	Rated Line to Line Voltage
A :	Rated Fault Current
T :	Rated Time - Duration of the Fault Current
R :	Resistance Value (Ohms) :

TESTING AND STANDARDS :

We are an ISO 9001-2000 accredited manufacturing unit and stringent quality control is enforced through out the manufacturing process to ensure the quality. The Power Resistors are inspected and tested to ensure their compliance to the specifications. Test Results are documented and Test Certificates issued.

The NGRs are designed in accordance with international standards as per IEEE-32 / BS 587/ IS 12063. Our NGRs have been Type Tested at ERTL (N), New Delhi, for Temp. Rise Tests and for various Degrees of Protection.

HV WITHSTAND TEST ( For 1 minute 50 c/s AC Voltage ) :

For Voltage class below 600 Volts :

– 2 times of Line to Neutral Voltage + 1000 Volts

For Voltage class above 600 Volts :

– 2.25 times of Line to Neutral Voltage + 2000 Volts

Following Routine Tests are performed on each Neutral Grounding Resistor :

• Visual and Dimensional Check

• Resistance Value Check

• High Voltage Withstand Test

• Insulation Resistance Measurement

Following Type Tests can be performed on specific request :

• Temperature Rise Test as per IEEE 32 on a sample resistance grid assembly