Mitsubishi Electric FR-A820-00046 (0.4K), Instruction Manual

Page: 145 / 1218

Precautions for use of the inverter Electro-magnetic interference (EMI) and leakage currents
FR-A800 3 - 1
3 Precautions for use of the inverter
3.1 Electro-magnetic interference (EMI) and leakage currents
3.1.1 Leakage currents and countermeasures
Capacitances exist between the inverter I/O cables, other cables and earth and in the motor, through
which a leakage current flows. Since its value depends on the static capacitances, carrier frequency,
etc., low acoustic noise operation at the increased carrier frequency of the inverter will increase the
leakage current. Therefore, take the following countermeasures. Select the earth leakage current
breaker according to its rated sensitivity 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 earthing (grounding) cable, etc. These leakage currents may operate earth leakage circuit break-
ers and earth leakage relays unnecessarily.
●
Suppression technique
– 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).
●
To-earth (ground) 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. 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 capacitances 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 models (FR-A840-00250(7.5K) or lower), the external thermal relay is
likely to operate unnecessarily because the ratio of the leakage current to the rated motor current in-
creases.