Page 1
SE-134C Ground-Fault Ground-Check Monitor
Rev.
4
Pub. SE-134C-M, December 16, 2009.
1. G
ENERAL
The SE-134C is a microprocessor-based, combination
ground-fault and ground-wire monitor for resistance-
grounded systems. It has a switching power supply that
accepts a wide range of ac and dc voltages, its
specifications apply over an industrial temperature range
at high humidity, and it meets the IEEE surge-withstand-
capability tests (oscillatory and fast transient) for
protective relays and relay systems. Isolated, normally
open and normally closed contacts are provided for
contactor control or for shunt or undervoltage operation
in a breaker-trip circuit. All operating conditions are
clearly annunciated and two Form C contacts are
provided for remote indication. The SE-134C is housed
in an anodized extruded-aluminum enclosure, and all
connections are made with plug-in, wire-clamping
terminal blocks. Provision is made for both panel and
surface mounting.
The ground-fault circuit detects fundamental-
frequency, zero-sequence current with a window-type
current sensor and it verifies that the current sensor is
connected and not shorted. A definite-time characteristic
with 11 trip levels and 11 trip times allows coordination
in virtually any resistance-grounded system. Although
other current sensors may satisfy the verification circuit,
only SE-CS10-series sensors have characteristics that
meet system specifications. Current-sensor verification
can be disabled for a ground-check-only application.
The ground-check circuit has an open-circuit voltage of
24 Vdc, which is not a hazard to personnel, and it has an
output drive current above 100
mA for optimum
performance in slip-ring, commutated-load, and high-
induced-ac applications. Features include an externally
accessible ground-check fuse, a resistance-insertion test,
3-kV isolation between the ground-check loop and the
monitor electronics, and a PPI-600V accessory for
parallel-ground-path rejection. A PPI-600V will also
eliminate intermachine arcing and prevent stray ac and dc
currents from flowing in the monitored ground wire.
Unlike ground-check circuits using other termination
devices, and especially those with phase-reversal
switches, a ground-check circuit using a termination
device with a Zener characteristic is capable of loop
measurements that are independent of current in the phase
conductors. The SE-134C ground-check circuit
recognizes the SE-TA6A-series 5.6-volt Zener
characteristic as a valid end-of-line completion. This is
the only passive characteristic that will satisfy the ground-
check circuit’s multi-level drive, allow induced currents
to circulate in the ground-check loop, survive a phase-to-
ground-check fault, and clamp the ground-check voltage
during the fault. Although a standard 5.6-volt Zener
diode may engage the SE-134C’s ground-check circuit,
only an SE-TA6A-series termination assembly has the
compensation required to meet system specifications. In
select applications, a combination of an SE-TA12A and
SE-TA12B Termination Assemblies can be used to
monitor the cables of a splitter box (junction box) using a
single SE-134C Monitor. See Technical Note GC-11,
available at www.startco.ca.
2. O
PERATION
2.1 G
ROUND
-F
AULT
C
IRCUIT
2.1.1 GF
T
RIP
T
IME
S
ETTING
The ground-fault circuit has a definite-time
characteristic with 11 settings from 0.1 to 2.5 seconds.
Time-coordinated ground-fault protection requires the trip
time to be longer than the trip time of downstream
ground-fault devices.
2.1.2 GF
T
RIP
L
EVEL
S
ETTING
The trip level of the ground-fault circuit is switch
selectable with 11 settings from 0.5 to 12.5 A. A
minimum tripping ratio of 5 is recommended to achieve at
least 80% winding protection, and this requires the trip
level to be less than 20% of the grounding resistor let-
through current. Suggested trip-level ranges for 5-, 15-,
and 25-A neutral-grounding resistors are indicated on the
faceplate. A ground-fault trip is latched, requiring a reset.
A current-sensor failure will also cause a ground-fault
trip. See Section 3.1
If the SE-134C is operated in a ground-check-only
application and an SE-CS10 is not connected, connect
terminals 17 and 18 to disable sensor verification. See
Fig. 1.
2.2 G
ROUND
-C
HECK
C
IRCUIT
The ground-check loop consists of the outgoing
ground-check conductor, quick-coupler connections, the
SE-TA6A-series termination assembly, the SE-TA6A
connection to equipment frame or ground bus, the
ground-return path, and the SE-134C cable-ground-
terminal connection to substation ground.
The SE-134C detects a valid ground-check loop when
an SE-TA6A-series termination assembly is detected in
the loop and loop resistance is less than 28 ohms. The
loop is not valid if open (or high resistance), or if the
ground-check conductor is shorted to ground.
When the ground-check loop is valid, the SE-134C
ground-check circuit can be tested by pressing the GC
TEST switch or by shorting GC TEST terminals 11 and
12. This test invalidates the loop by inserting 47
Ω
in the
ground-check loop and a trip should occur in less than
250 ms.
The ground-check circuit is usually operated in the
non-latching mode; however, it can be operated in the
latching mode by connecting terminals 14 and 15.
The ground-check circuit is protected by a 1.5-A time-
delay fuse (F1).