Mitsubishi Electric FATEC FR-A800 Manual page 118

7
REVIEW OF INSTALLATION ENVIRONMENT
(2) Line-to-line leakage current
Type
Effect and
countermeasure
Undesirable
current path
Table 7.5 Effects and countermeasures of line-to-line leakage current
• This leakage current flows via a static capacitance between the inverter output cables.
• Harmonics of the leakage current 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
(7.5 kW or lower), the external thermal relay is likely to operate unnecessarily because
the ratio of the leakage current to the rated motor current increases.
●Countermeasures
• Use H000 (Pr.9) Electronic thermal O/L relay.
• If the carrier frequency setting is high, decrease E600 (Pr.72) PWM frequency selection
setting.
Note that the motor noise increases. Selecting E601 (Pr.240) Soft-PWM operation
selection makes the sound inoffensive.
To ensure that the motor is protected against line-to-line leakage current, it is
recommended to use a temperature sensor to directly detect motor temperature.
MCCB MC
Power
supply
Effect and countermeasure
Thermal relay
Inverter
Line-to-line
static capacitances
Line-to-line leakage currents path
Motor
IM
7.2 Noise
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