Mitsubishi Electric fr-e700 series, Instruction Manual

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Electromagnetic compatibility (EMC) Wiring
3 - 48
3.9 Electromagnetic compatibility (EMC)
3.9.1 Leakage currents and countermeasures
Mains filters, shielded motor cables, the motor, and the inverter itself cause stationary and variable
leakage currents to PE. Since its value depends on the capacitances, carrier frequency, etc., low acous-
tic noise operation at the increased carrier frequency of the inverter will increase the leakage current.
Therefore, take the following measures. Select the earth leakage breaker according to its rated sen-
sitivity current, independently of the carrier frequency setting.
To-earth (ground) leakage currents
Leakage currents may flow not only into the inverter's own line but also into the other lines through
the earth (ground) cable, etc. These leakage currents may operate earth (ground) leakage circuit
breakers and earth leakage relays unnecessarily.
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Countermeasures
– If the carrier frequency setting is high, decrease the Pr. 72 "PWM frequency selection" setting.
Note that motor noise increases. Selecting Pr. 240 "Soft-PWM operation selection" makes the
sound inoffensive.
– By using earth leakage circuit breakers designed for harmonic and surge suppression in the
inverter's own line and other line, operation can be performed with the carrier frequency kept
high (with low noise).
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To-earth leakage currents
– Take caution as long wiring will increase the leakage current. Decreasing the carrier frequency
of the inverter reduces the leakage current.
– Increasing the motor capacity increases the leakage current.
– Shielded motor cables significantly increase the leakage current to PE (approx. double the
value generated with unshielded motor cables of the same length).
– The leakage current of the 400 V class is larger than that of the 200 V class.
Line-to-line leakage currents
Harmonics of leakage currents flowing in static capacities between the inverter output cables may
operate the external thermal relay unnecessarily. When the wiring length is long (50 m or more) for
the 400 V class small-capacity model (FR-E700-170SC or less), the external thermal relay is likely to op-
erate unnecessarily because the ratio of the leakage current to the rated motor current increases.