Mitsubishi Electric FR-F740 EC Instruction Manual page 83

Wiring
Fig. 3-36: Line-to-line leakage currents
● Countermeasures
– Use Pr. 9 "Electronic thermal O/L relay".
– 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 selec-
tion" makes the sound inoffensive. To ensure that the motor is protected against line-to-
line leakage currents, it is recommended to use a temperature sensor (e.g. PTC element)
to directly detect motor temperature.
● Selecting a power supply circuit breaker:
You can also use a circuit breaker (MCCB) to protect the power supply lines against short
circuits and overloads. However, note that this does not protect the inverter (rectifiers, IGBT).
Select the capacity of the circuit breaker on the basis of the cross-sectional area of the power
supply lines. To calculate the required mains current trip point you need to know the power
required by the inverter (refer to rated input capacity in appendix A, specifications) and the
mains supply voltage. Select a circuit breaker with a trip point that is slightly higher than
calculated, particularly in the case of breakers with electromagnetic tripping, since the trip
characteristics are strongly influenced by the harmonics in the power supply line.
The earth leakage breaker must be either a Mitsubishi earth leakage breaker (ELB, for
harmonics and surges) or an ELB with breaker designed for harmonic and surge suppres-
sion that is approved for use with frequency inverters.
FR-F700 EC
Power
supply
Electromagnetic compatibility (EMC)
Line-to-line
Thermal
leakage currents
relay
Inverter
Line-to-line static
capacitances
path
M
3~
I001043E
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