FR-A701 INSTRUCTION MANUAL (Applied) - Automation Systems ...

EMC and leakage currents3.1 EMC and leakage currents3.1.1 Leakage currents and countermeasuresCapacitances exist between the inverter I/O cables, other cables and earth and in the motor, through which a leakagecurrent flows. Since its value depends on the static capacitances, carrier frequency, etc., low acoustic noise operationat the increased carrier frequency of the inverter will increase the leakage current. Therefore, take the followingmeasures. Select the earth leakage circuit breaker according to its rated sensitivity current, independently of the carrierfrequency setting.(1) To-earth (ground) leakage currentsLeakage 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 relaysunnecessarily.• Suppression technique⋅ If the carrier frequency setting is high, decrease the Pr. 72 PWM frequency selection setting. Note that motor noiseincreases. 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 andother 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 inverterreduces the leakage current.⋅ Increasing the motor capacity increases the leakage current. The leakage current of the 400V class is larger thanthat of the 200V class.(2) Line-to-line leakage currentsHarmonics of leakage currents flowing in static capacitances between the inverter output cables may operate theexternal thermal relay unnecessarily. When the wiring length is long (50m or more) for the 400V class small-capacitymodel (7.5K or less), the external thermal relay is likely to operate unnecessarily because the ratio of the leakagecurrent to the rated motor current increases.• Line-to-line leakage current data example (200V class)Motor Capacity(kW)Rated MotorCurrent(A)Leakage Currents(mA)Wiring length 50m Wiring length 100m3.7 12.8 440 6305.5 19.4 490 6807.5 25.6 535 725⋅Motor SF-JR 4P⋅Carrier frequency: 14.5kHz⋅Used wire: 2mm 2 , 4coresCabtyre cable*The leakage currents of the 400V class are about twice as large.MCCBMCThermal relayMotorPowersupplyInverterIMLine-to-line staticcapacitancesLine-to-line leakage currents path• Measures⋅ 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 noiseincreases. Selecting Pr. 240 Soft-PWM operation selection makes the sound inoffensive. To ensure that the motor isprotected against line-to-line leakage currents, it is recommended to use a temperature sensor to directly detectmotor temperature.• Installation and selection of moulded case circuit breakerInstall a moulded case circuit breaker (MCCB) on the power receiving side to protect the wiring of the inverter inputside. Select the MCCB according to the inverter input side power factor (which depends on the power supply voltage,output frequency and load). Especially for a completely electromagnetic MCCB, one of a slightly large capacity mustbe selected since its operation characteristic varies with harmonic currents. (Check it in the data of the correspondingbreaker.) As an earth leakage circuit breaker, use the Mitsubishi earth leakage circuit breaker designed forharmonics and surge suppression.38