Littelfuse NGR User Manual
Protection Relays & Controls
Neutral Grounding
NGR SERIES
Neutral-Grounding-Resistor System
Description
Neutral-Grounding Resistors (NGRs) are used to ground power
systems by inserting a resistor between the system neutral and
ground. This lowers the prospective ground-fault current to a
predetermined value.
A properly designed resistance-grounded system provides benefits
over both ungrounded and solidly grounded systems. Because the
system is grounded, transient overvoltages do not occur and groundfault current can flow, allowing it to be detected and measured. Also,
because a resistor is used to ground the system, the very large and
destructive ground-fault currents of solidly grounded systems are
absent. Ground-fault relays (such as the SE-701) can be used on
feeders to provide selective coordination and the ability to quickly
locate or isolate the fault.
Applications
Resistance grounding is typically applied on transformers and
generators where safety and continuity of service are important. A
faulted feeder may remain in operation until it is safe to repair the fault,
where allowed by the local electrical code.
For information about the NGRM-ENC NGR Monitor Control Panel,
see Accessories.
Ordering Information
SYSTEM
LINE-NEUTRAL
VOLTAGE
NGR X
277, 347,…44000 AMPERES
Note: Order SE-325, SE-330, and SE-701 separately.
NGR
CURRENT
X – X – XXXX-RX
–
DUTY CYCLE
C = continuous
10 = 10 seconds E1 = EFCT-1
30 = 30 seconds
60 = 60 seconds C26 = SE-CS30-26
Benefits
g
Eliminate phase-to-ground arc-flash incidents
g
Eliminate transient overvoltages
g
Reduced point-of-fault damage
g
Can provide continuity of service during a ground fault
Features
g
ER-series Sensing Resistor and Current Transformer required for
NGR monitoring come pre-installed inside the enclosure
g
Can be packaged with a zigzag transformer to resistance ground an
ungrounded delta system, or a system with an inaccessible neutral
g
SE-325 or SE-330 NGR Monitor can provide continuous NGR
monitoring and ground-fault protection; NGR failure will render
current-sensing ground-fault protection inoperative
g
Stainless steel resistor elements prevent corrosion
DRAWING
NUMBER
Assigned
by factory
MONITORING COMPONENTS
IN NGR ENCLOSURE
–
X X – X – X
ER/ = Includes
Sensing Resistor
Blank = No
Sensing Resistor
CT = CT200
E26 = EFCT-26
C70 = SE-CS30-70
Contact factory
for other choices.
OTHER
OPTIONS
ZZ = Zigzag
transformer
(Note: may be
in separate N3R
enclosure)
Blank = None
OPEN = None
ENCLOSURE
STYLE
N3R = Galvanized
NEMA 3R
N3RSS = Stainless
Steel NEMA 3R
© 2013 Littelfuse Protection Relays & Controls
Littelfuse.com/ngr
Rev: 4-A-050213
Loading...