46
• Take ambient temperature, relative humidity, altitude, air quality, and other environmental
conditions into account when selecting and installing the transformer.
• The overall technical requirements of the box-type LV cabinet are as follows:
– The breaking capacity of the branch molded case circuit breaker (MCCB) and air cir-
cuit breaker (ACB) of the box-type LV cabinet should be greater than the short circuit
current at the LV side of the transformer. For example, the LV side short-circuit current
of a boost transformer with a rated capacity of 3200 kVA and a short-circuit resistance
of 7% can be calculated in the following way: I = 3200 *1.1/0.8/1.732/0.07 = 36.29 kA.
Thus the MCCB Icu of the LV cabinet branch circuit should be no less than 36.29 kA
at 880Vac. The LV side short-circuit current of a boost transformer with a rated ca-
pacity of 4480kVA and a short-circuit impedance of 8% can be calculated in the fol-
lowing way: I = 4480 * 1.1 / 0.8 / 1.732 / 0.08 = 44.46 kA. Thus the MCCB lcu of the
LV cabinet branch circuit should be no less than 44.46kA at 880Vac.
– The temperature and altitude derating should be taken into account when a circuit
breaker is working, and a LV cabinet temperature rise test report is required.
– When designing a LV cabinet, must pay attention to the impact of the diffused MCCB
electric arc on the cabinet and other branch circuit MCCBs, thus the interior of the
cabinet needs to be insulated. A third-party test report of the circuit-breaking perform-
ance of the whole machine in an event of a short-circuit on the LV side is also re-
quired. It is recommended to adopt graduated protection to ensure that in an event of
a single short-circuit fault on the LV side of the box, the corresponding branch MCCB
trips normally while the general ACB does not trip.
– When PLC communication is adopted, the box-type LV power distribution room
needs to be equipped with a fuse switch disconnector or a circuit breaker. The recom-
mended specification of the cable connecting to the EMU200 is 4 mm
2
- 10 mm
2
, the
cable voltage specification is 1.8 / 3 kV, and the cable distance from the EMU200 to
the box's LV bus should be no more than 10 m.
• When Anti-PID is enabled, the AC output common mode voltage of the inverter is 906V,
and the following requirements should be met:
– The LV side winding of the transformer, AC cables, and secondary devices (including
protective relay, detection and measurement instruments, and related auxiliary devi-
ces) must withstand the voltage to ground of at least 906 V.
– If the LV side winding is in Y shape, neutral point grounding is prohibited.
– Surge protective devices (SPD) for the AC combiner box and on the LV side of the
transformer are recommended to be connected in the "3+1" manner, as shown in the
figure below. The Min. continuous operating voltages of M1 - M4 are 680 Vac.
5 Electrical Connection User Manual
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