Cut Sheet
Protection Relays & Controls
© 2015 Littelfuse Protection Relays & Controls
Neutral-Grounding-Resistor Monitoring
Description
The SE-330 is an advanced ground-fault and neutral-grounding-
resistor monitoring relay. It measures neutral current, neutral-to-
ground voltage, and neutral-to-ground resistance. It provides
continuous monitoring of the neutral-to-ground path to verify
that the neutral-grounding resistor (NGR) is intact. This is of
utmost importance—an open NGR renders current-sensing
ground-fault protection inoperative and could result in a false
belief that the system is functioning properly. The SE-330 can be
used with low- and medium-voltage transformers and
generators with low- or high-resistance grounding used in
processing, manufacturing, chemical, pulp and paper, petroleum,
and water-treatment facilities. For high-voltage applications, use
the SE-330HV. For applications that require conformance to
Australian standard AS/NZS 2081.3:2002, use the SE-330AU.
Resistor Monitoring
The SE-330 combines the measured values of resistance,
current, and voltage to continuously determine that an NGR
is intact. It is able to detect a resistor failure with or without
a ground fault present. Sensing resistors are matched to the
system voltage and are used to monitor NGRs on systems up
to 72 kV.
Ground-Fault Monitoring
The SE-330 uses an application-appropriate current transformer
to reliably detect ground-fault currents as small as 100 mA. DFT
filtering ensures that false trips due to harmonic noise from
adjustable-speed drives do not occur. Should the resistor open
and a ground fault subsequently occur, the SE-330 will detect
the fault through voltage measurement, while other current-only
sensing relays would be ineffective.
Pulsing Ground-Fault Location
The SE-330 is capable of controlling a pulsing contactor, which is
used to switch the NGR resistance in a pulsing-compatible NGR
package. The resulting ground-fault current is distinguishable
from charging currents and noise and will only appear upstream
of the ground fault, making fault location fast and easy, even
without isolating feeders or interrupting loads.
SE-330, SE-330HV SERIES
Neutral-Grounding-Resistor Monitor - New Revision
Simplified Circuit Diagram
NGR
L2
CT
L1
SE-330 SERIES
ER SERIES
(Sensing Resistor)
(NGR Monitor)
A
B
ORDERING
NUMBER
POWER
SUPPLY
COMM
K4 UNIT HEALTHY
CONTACT
SE-330 - X X - 0
X
SE-330
for all apps.
35 kV or less
SE-330HV
for 72 kV
apps.
0=120/240
Vac/Vdc
2=48 Vdc
0=USB Only
1=DeviceNet
3=
EtherNet
(Dual RJ45)
4=
EtherNet
(SC Fiber & RJ45)
5=
EtherNet
(Dual SC Fiber)
6=
IEC61850
(Dual RJ45)
7=
IEC61850
(SC Fiber & RJ45)
8=
IEC61850
(Dual SC Fiber)
0=Normally Open
1=Normally Closed
NOTE: For Australian applications, see the SE-330AU.
Ordering Information
ACCESSORIES REQUIREMENT
ER Series Sensing Resistor Required
Current Transformer Required
SE-IP65CVR-G Optional
SE-MRE-600 Optional
RK-332 Optional
NGRM-ENC Optional
PGA-0520 Optional
SE-330-SMA Optional
Littelfuse reserves the right to make product changes, without notice. Material in this document is as accurate as known at the time of publication. Visit Littelfuse.com for the most up-to-date information.
© 2017 Littelfuse Protection Relays & Controls
Littelfuse.com/se-330 Littelfuse.com/se-330hv
ER Series Sensing Resistor
Required interface between the power system
and the SE-330/SE-330HV. Eliminates hazardous
voltage levels at the relay.
EFCT Series Ground-Fault Current Transformer
Sensitive ground-fault current detection (5 A primary).
SE-CS30 Series Ground-Fault Current Transformer
Sensitive ground-fault current detection (30 A primary).
Other Current Transformer
For low-resistance NGRs choose a CT primary
approximately equal to the NGR rating. Inputs
are provided for 1- and 5- A- secondary CTs.
SE-IP65CVR-G Hinged Transparent Cover
Watertight cover, tamper resistant, IP65 protection.
Accessories
A
B
For detailed wiring diagram, see adjacent page.
Rev: 4-D-102017
Based on SE-330 Manual Rev: 10-P-101817
Based on SE-330 HV Manual Rev: 5-M-101817