Mitsubishi FR - S500 instruction manual To-ground leakage currents, Line-to-line leakage currents

1.5.4 Leakage current and installation of earth leakage circuit breaker

Due to static capacitances existing in the inverter I/O wiring and motor, leakage currents flow through them. Since their values depend on the static capacitances, carrier frequency, etc., take the following counter measures.

(1) To-ground leakage currents

Leakage currents may flow not only into the inverter's own line but also into the other line through the ground cable, etc.

These leakage currents may operate earth leakage circuit breakers and earth leakage relays unnecessarily.

Counter measures

If the carrier frequency setting is high, decrease the carrier frequency (Pr. 72) of the inverter.

Note that motor noise increases. Selection of Soft-PWM control (Pr. 70) will make it unoffending. (Factory setting)

By using earth leakage circuit breakers designed for harmonic and surge suppression (e.g. Mitsubishi's Progressive Super Series) in the inverter's own line and other line, operation can be performed with the carrier frequency kept high (with low noise).

(2) Line-to-line leakage currents

Harmonics of leakage	NFB	Thermal relay	Motor
currents flowing in static	Power	Inverter	IM
capacities between the
	supply

inverter output cables	Line static
may operate the external
	capacitances
thermal relay
	Line-to-Line Leakage Current Path
unnecessarily.

Counter measures

Use the electronic overcurrent protection of the inverter.

Decrease the carrier frequency. Note that motor noise increases. Selection of Soft-PWM (Pr. 70) makes it unoffending.

To ensure that the motor is protected against line-to-line leakage currents, it is 1 recommended to use a temperature sensor to directly detect motor temperature.

Installation and selection of no-fuse breaker

On the power receiving side, install a no-fuse breaker (NFB) to protect the primary wiring of the inverter. Which NFB to choose depends on the power supply side power factor (which changes with the power supply voltage, output frequency and load) of the inverter. Especially as the completely electromagnetic type NFB changes in operational characteristic with harmonic currents, you need to choose the one of a little larger capacity. (Check the data of the corresponding breaker.) For the earth leakage circuit breaker, use our product designed for harmonic and surge suppression (Progressive Super Series). (Refer to page 13 for the recommended models.)

CAUTION

Choose the NFB type according to the power supply capacity.

15