Influences Of Leakage Currents And Measures Against It - Toshiba TOSVERT VF-P7 Instruction Manual

1.4.3 Influences of leakage currents and measures against it

An electric current can leak through an input or output cable of the inverter because of its insufficient
capacitance and, sometimes, affects the peripheral systems. The amount of a leakage current depends
on the carrier frequency, the length of the input/output cable, etc. It is advisable to take the following
measures to prevent leakage currents.
(1) Influences of a current leaking into other systems via the ground
An electric current can leak not only into other circuits of an inverter but also into other
inverters through grounding wires. Such a leakage current can exerts influences on various
electronic devices, for example, malfunction of ground leakage breakers or relays, ground
relays, fire alarms, sensors, etc., noise on CRTs and display of incorrect current values on a
CRT screen.
Power
supply
Measures to be taken:
1. Lower the PWM carrier frequency.
Use parameter  to lower the PWM carrier frequency.
2. Use high frequency-ready ground leakage breakers (e.g., Esper Mighty series(manufactured
by Toshiba Schneider Electric Ltd.)). When these ground leakage breakers are installed,
there is no need to lower the PWM carrier frequency.
3. If sensors and CRTs are affected, they can be restored by lowering the PWM carrier
frequency as described in 1 above. However, if lowering the PWM carrier frequency results
in an increase in magnetic noise, contact your Toshiba dealer.
(2) Influences of a current leaking from a cable into other cables
① Thermal relay
If a current leaks from an output cable of an inverter to other cables because of its
insufficient capacitance, the high-frequency elements of the leakage current sometimes
increase the effective current value, and thus cause external relays to malfunction. For a
model with relatively long cables (longer than 50 m), the external thermal relays can
malfunction more easily because a leakage current can be too large as compared with the
current rating of the motor.
Warning
Inverter
Inverter
A-11
IM
IM