logo S. R. NARKHEDE ENGINEERING PVT. LTD.

a.gif (47 bytes)

 a.gif (47 bytes)

NEUTRAL GROUNDING RESISTORS

Neutral Grounding Resistor Panel upto 66 KV

PURPOSE : Neutral Grounding Resistor are connected between the neutral & the earth so that it will limit the earth fault current to a safe value [ Normally full load current of the generator, transformer, etc. thereby protecting the transformer, generator system ].


TYPICAL RESISTANCE ELEMENT USED

OPERATION: Consider two conditions.

1. No Earth Fault : Continuous current ( 5 % to 10 % of full load current) may pass through the resistor due to system unbalance.

2. Earth Fault Condition: Restricted fault current passes through the resistor protecting the system till automatic protection takes place. The earth pressure (Rated Voltage) is absorbed by the resistor protecting the winding etc.

IMPORTANT PARAMETERS & CONSTRUCTIONS :

  • Rated Voltage : For neutral grounding resistor rated voltage means line-to neutral voltage ( System Voltage divided by 1.732).

  • Rated Current : Means initial current that will flow through resistor when it is cold. Normally rated current value is same as full load current.

  • Duty rating or Time Rating : It is length of time for which NGR must tolerate rated voltage.

  • Short Time  Rating : Normally it is 10 or 30 or 60 seconds depending on design parameters of protection system. If fault is immediately cleared and system made healthy then chances of fault repetition should be considered. IS-3043 recommends 30 sec. rating.

  • Continuous Rating : It is normally 10 % of full load current for healthy system neutral grounding resistor to be designed for continuous rating of 5% to 10 % of full load current ( if required).

  • Temperature Rise Allowed : Normally Temp. rise is restricted to 375 deg.c. as per BS 587. It can be 760 deg.c. as per IEEE-32. We can offer NGR of any other temp. rise as per requirement.

  • Enclosure : For outdoors application enclosure designed to give degree of protection of IP 33 is normally used. Enclosure upto  IP 65 protection are offered. Enclosure material can be Mild Steel, Aluminium or Stainless Steel. Painting / Galvanising or Hot Dip Galvanising or Powder Coating is offered as per requirement. safety screen enclosure is provided if required. For continous rating enclosure protection is not above IP 43.

  • Material of Resistance Element : we offer resistor elements made from any stainless steel or fecral or cast iron or CU-NI or NI-CR or any other resistance material as per requirement. Normally formed stainless steel element are best and economical for NGRS.

  • Construction : NGR include resistor assembly , plus required insulators, internal connections and hardware.

  • Options/Accesories : Few of the following are usually incorporated. Current Transformers, Potentials Transformers, Grounding Transformers, Two bushing, Elevating Stands, Manual/ Electrical operated/ Motorised Isolator, earth leakage relay, Lightning arrestors, auxiliary control wiring terminal box with cable glands, termination kit, stand off insulator, space heater with thermostat control are also offered.

  • Cabling/ Termination : Suitable arrangement is provided for termination of cable, flats or bus duct as per requirement. Incase of XLPE cable terminal box with suitable clearance and undrilled removable gland plate is provided.

Standards Followed :

# IEEE-32, IS-3043 & BS 162 for neutral grounding resistor.

# Is 2147 or IS 12063 of 1987 for degree of protection for enclosure.

# IS 5 for paint shade.

# Any other standard as required.

TESTS:

A ] ROUTINE TEST : Following tests are conducted.
a] Visual and Dimentional
b] Meger test using 1000 V Meger
c] Resistance measurement
d] High voltage test as per IEEE - 32

B] TYPE TEST : Temperature rise test or ( Heat run test ) of following rating can be conducted in house.
a] 2000 AMP, 40/80 Volts, 1 Phase, 60 SEC.
b] 415/230 Volts, 100 KW, 3 Phase, Continuous.

C] SPECIALS TEST : Our resistors are tested for following tests on prototype unit

a. Temperature rise test : C.P.R.I Bangalore, test certificate for temperature rise test for continuous & short time rating. 

b. Protection Test : ARAI, Pune, test Certificate for IP33, IP 55 and IP 65 protection Test as per IS 2147 or IS 12063 of 1987.

c. Tensile strength of resistance material.

d. Chemical Composition of resistance material.

e. Any other test as required.

NEUTRAL GROUNDING RESISTOR

ELEMENTS

    

 

BACK