13
JEP0-IL9555
Precautions for design and installation
＜
Connection
＞
(1) Test terminals of ZCT: The test terminals of ZCT
(kt and
ℓ
t) are used only for the operation test
and keep them open after the test. (Do not short
the test terminals.)
(2) Wiring material: Since the MGR-A3V relay is a high
sensitivity digital type relay, it is necessary to
suppress surge and noise from the main circuit and
other lines.
Therefore, use 2-core shielded cables with a
diameter of 0.75mm
2
or more to connect to the Z1-Z2
terminals of the relay (ZCT circuit), and connect
the shield to E terminal of the relay or D-class
grounding. The cable burden shall be 5
Ω
or less
for both ways. (In the case of 0.75mm
2
, one way is
about 100 meters.)
(3) Secondary wiring of ZCT: The secondary terminal (k,
ℓ
), and the test terminal (kt,
ℓ
t) are double nuts.
The wiring is connected between the nuts. When
connecting, do not loosen the inner side (ZCT side)
nut.
(4) Shield grounding of power cable: When an electric
power cable is used at the primary side of ZCT, pay
attention to the shield grounding as shown in
JEAC8011 regulations.
(5) Handling of power cable: Please handle with care
not to damage the outer sheath of ZCT primary
cable.
The bending radius should be more than 10 times the
conductor outer diameter. Please locate the three-
phase cable symmetrically in the ZCT through hole.
(6) Alarm circuit: For MGR-A3T-R type relay, the output
contact is auto-reset type. If you want to use the
alarm circuit as self-hold type, please build a
circuit as shown in Fig. 3-7.
(7) Connection to ZCT: Only one ZCT can be connected to
one MGR-A3V relay. If two or more ZCTs are
connected in parallel, correct detection may not be
possible.
＜
Caution on withstand voltage test
＞
(1) After the relay is mounted into the panel, when the
test is performed between the high-voltage circuit
and the earth/the low-voltage circuit, be sure to
check that the secondary side of VT and ZCT are
grounded.
(2) When the test is performed between the low-voltage
circuit and the earth, be sure to disconnect the
secondary side of VT and ZCT from the earth.
＜
Precautions for use
＞
(1) This ground relay uses only the current of the zero-
phase current transformer and does not have
directionality. If the ground capacitance on the load
side is large (the cable is laid over a long distance),
please consider using the MDG-A3 type directional
earth fault relay.
(2) When using the MGR-A3T-R type relay, please check the
matching of the impedance characteristics of the
internal reactor of the relay (R=4.5
Ω
, L=2.9mH) and
that of the trip coil of the circuit-breaker. Please
use a combination that allows the tripping current
to flow 3A or more. In the case of VCB of our company,
the impedance is matched.
Fig. 3-6 Earth method of cable shield
Fig. 3-7 Alarm circuit of self-hold type
MGR
MGR
Power
source
side
Power
source
side
MGR-A3 type relay
Alarm circuit
X
B1
B2
Y
Y
BZ
Y
AC100/110V
(For resetting
from self-hold
state)
E
PB
Buzzer
