Startco Engineering Ltd.
Page 1
SE-704 Earth-Leakage Monitor
Rev. 2
Pub. SE-704-M, January 18, 2008.
1. G
ENERAL
The SE-704 is a microprocessor-based earth-leakage
monitor for ac power supply systems that require earth-
leakage detection as low as 10 mA. It is uniquely suited
for very sensitive earth-fault protection on systems with
significant harmonic content. Its output relay can operate
in the fail-safe or non-fail-safe mode for undervoltage or
shunt-trip applications. The SE-704 has one output relay
with isolated normally open and normally closed contacts
for use in independent control circuits. Additional
features include LED trip and power indication, autoreset
or latching trips with front-panel and remote reset, trip
memory, test switch, self diagnostics, 0- to 5-V analog
output, CT verification with LED indication, digital
selector switches, and switch-selectable algorithms for
fixed-frequency or variable-frequency applications.
Earth-leakage current is sensed by an SE-CS30-series
core-balance earth-fault current transformer. The trip
level of the earth-leakage circuit is digital-switch
selectable from 10 to 500 mA. Trip time is digital-switch
selectable from 30 to 1,000 ms.
2. O
PERATION
2.1 C
ONFIGURATION
-S
WITCH
S
ETTINGS
See Fig. 1.
2.1.1 R
ELAY
O
PERATING
M
ODE
Switch 1 is used to set the operating mode of the output
relay. In the fail-safe mode, the output relay energizes
when the earth-leakage circuit is not tripped. In the fail-
safe mode, non-volatile memory retains the trip status of
the SE-704. If tripped, and the supply voltage is cycled,
the SE-704 will remain tripped, with the trip relay
de-energized and the TRIP LED on, until reset.
In the non-fail-safe mode, the output relay energizes
when an earth-leakage trip occurs. In the non-fail-safe
mode, trip status is not retained in non-volatile memory.
2.1.2 F
ILTER
S
ELECTION
Switch 2 is used to select the filtering algorithm for a
fixed-frequency (50/60
Hz) or variable-frequency
application. The FIXED FREQUENCY setting uses a
DFT filter that allows lower trip levels to be used by
rejecting harmonics that can cause nuisance tripping.
The VARIABLE FREQUENCY setting uses a peak-
detection algorithm with a wider band width for fault
detection in variable-frequency drive applications.
2.1.3 CT V
ERIFICATION
Switch 3 is used to enable CT verification. In the
ON position, a trip will occur if the SE-CS30 current
sensor is disconnected.
2.1.4 R
ESET
M
ODE
Switch 4 is used to select autoreset or latching trips.
See Section 2.2.3.
2.2 F
RONT
-P
ANEL
C
ONTROLS
2.2.1 E
ARTH
-L
EAKAGE
T
RIP
L
EVEL
The LEVEL (mA) selection switch is used to set the
earth-leakage trip level. For earth-leakage detection, the
earth-leakage trip level must be substantially below the
prospective earth-fault current. To avoid sympathetic
tripping, the trip level must be above the charging current of
the protected feeder.
2.2.2 E
ARTH
-L
EAKAGE
T
RIP
T
IME
The SE-704 has a definite-time trip characteristic. The
TIME (ms) selector switch is used to set the earth-leakage
trip time for coordination with upstream and downstream
earth-fault devices. Coordination requires the same trip
level for all earth-leakage devices in a system and the trip
time to progressively increase upstream. The amount of
equipment removed from the system will be a minimum if
the first earth-leakage device to operate is the one
immediately upstream from the fault.
2.2.3 R
ESET
If the Reset Mode switch is in the LATCHING
position, a trip remains latched until the RESET switch
is pressed or the remote-reset terminals (6 and 7) are
momentarily connected. In the non-fail-safe relay
operating mode, cycling the supply voltage will also
reset the SE-704.
If the Reset Mode switch is in the AUTORESET
position, a trip will reset when the fault is removed.
The reset circuit responds only to a momentary
closure so that a jammed or shorted switch will not
prevent a trip. The front-panel RESET switch is
inoperative when the remote-reset terminals are
connected.
2.2.4 T
EST
The TEST switch is used to test the earth-leakage
circuit, the indication, and the output relay. When the
TEST switch is pressed for one second, a test signal is
applied to the earth-leakage-detection circuit, the circuit
will trip, the TRIP LED will light, and the output relay
will operate.
