Mitsubishi Electric MELPRO-A Series Instruction Manual page 14

Operation value settings and using condition settings
1. Operation value settings
In general, the operation value settings are set as follow,
but these values should be set with due consideration
given to various conditions of the systems, such as
residual voltage and current, and protection coordination.
＜Setting examples＞
Power receiving point:
I =0.2～0.4A, V =5～10%, T=0.2～0.3s
0 0
Branch feeder:
I =Equivalent or smaller to power receiving point
0
V =5～10%, T=Instantaneous (Approx. 70ms)
0
For details, please consult with an electric power company.
In regard to V setting, set it more than V
0
in order to avoid unwanted operation.
Precautions for design and installation
＜Connection＞
(1) Test terminals of ZCT: The test terminals of ZCT (kt
and ℓt) 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 MDG-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
terminals of the relay (Z1, Z2, Y1, Y2, M, N), and
connect the shield to E terminal of the relay or D-
class grounding. The cable burden shall be 5Ω or
less for both ways. (In the case of 0.75mm
is about 100 meters.)
(3) Secondary wiring of ZCT: The secondary terminal (k,
ℓ), and the test terminal (kt, ℓt) are double nuts.
The wiring is connected between the nuts. When
connecting, do not loosen the inner side (ZCT side)
nut.
(4) Polarity: Polarity is very important to this relay.
Please pay attention to polarity for connecting from
ZCT and ZVT, and grounding point is also important.
(5) ZVT position: The position of ZVT does not affect
the characteristics or protection, either on the
power supply side or the load side of the CB.
(6) 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.
measured value
0
or more to connect to the
2
2. Using condition settings
For all using condition setting switches, factory settings
are set to a default of OFF.
(1) Frequency (SW1):
50Hz = ON, 60Hz = OFF
(2) Output contact (SW2):
Self-hold = ON, Auto-reset = OFF
(3) Maximum sensitivity angle (SW3):
Lead 10° (for reactor grounding system) = ON,
Lead 45° (for non-grounding system) = OFF
(7) 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.
(8) Grounding of ZVT: Please connect the "E" terminal of
MPD-3 type ZVT to A-class grounding.
(9) Grounding of MDG-A3V relay: Because the Z2 terminal
and Y2 terminal are internally short-circuited,
ground only one point of the Y2 terminal of the MPD-
3 type ZVT or the Y2 terminal of the MDG-A3V relay.
When the V
N terminal of the relay.
, one way (10) Connection to ZCT: Only one ZCT can be connected to
one MDG-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 and that the relay is disconnected from
ZVT.
(2) When the test is performed between the low-voltage
circuit and the earth, be sure to disconnect the
secondary side of VT, ZVT, and ZCT from the earth.
14
expansion terminal is used, ground only
0
JEP0-IL9554