Toshiba VF-nC1 - Manual (Page 21)

E6581090
A-12
1
Remedies:
1. Reduce PWM carrier frequency.
The setting of PWM carrier frequency is done with the parameter H.
2. Use high frequency remedial products for earth leakage breakers. If you use equipment like
this, there is no need to reduce the PWM carrier frequency.
3. If the sensors and CRT are affected, it can be remedied using the reduction of PWM carrier
frequency described in 1 above, but if this cannot be remedied since there is an increase in
the motor's magnetic noise, please consult with Toshiba.
(3) Affects of leakage current across lines
Power
supply
Inverter
Thermal relay
CT
A
M
Leak current path across wires
① Thermal relays
The high frequency component of current leaking into electrostatic capacity between inverter
output wires will increase the effective current values and make externally connected thermal
relays operate improperly. If the wires are more than 50 meters long, it will be easy for the
external thermal relay to operate improperly with models having motors of low rated current
(several A(ampere) or less), because the leak current will increase in proportion to the motor
rating.
Remedies:
1. Use the electronic thermal built into the inverter.
The setting of the electronic thermal is done using parameter QNO & VJT.
2. Reduce the inverter's PWM carrier frequency. However, that will increase the motor's
magnetic noise. Use parameter H for setting the PWM carrier frequency.
3. This can be improved by installing 0.1 µ~0.5µF-1000V film capacitor to the input/output
terminals of each phase in the thermal relay.
② CT and ammeter
If a CT and ammeter are connected externally to detect inverter output current, the leak
current's high frequency component may destroy the ammeter. If the wires are more than 50
meters long, it will be easy for the high frequency component to pass through the externally
connected CT and be superimposed on and burn the ammeter with models having motors of
low rated current (several A(ampere) or less) because the leak current will increase in
proportion to the motor's rated current.
Remedies:
1. Use a multi-function programmable output terminal for the inverter’s control circuit.
A current can be put out via the FM/OUT terminal.
If the meter is connected, use an ammeter of 1mAdc full scale or a voltmeter of 7.5V-1mA full
scale.
2. Use the monitor functions built into the inverter.
Use the monitor functions on the panel built into the inverter to check current values.
U/T1
V/T2
W/T3
IM
Thermal relay