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 ].
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
& 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
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
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
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.
# 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
# Any other standard as
A ] ROUTINE TEST :
Following tests are conducted.
a] Visual and Dimentional
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.
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
d. Chemical Composition of
e. Any other test as