Toshiba VF-S15 Instruction Manual page 39

(2) Influence of leakage current across lines
Power
supply
Leakage current path across wires
(1) Thermal relays
The high frequency component of current leaking into electrostatic capacity between inverter out-
put 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 leakage current will increase in proportion to the motor rating.
Remedies:
1. Use the electronic thermal built into the inverter. (Refer to section 5.6)
The setting of the electronic thermal is done using parameter , .
2. Reduce the inverter's PWM carrier frequency. However, that will increase the motor's magnetic
noise.
The setting of PWM carrier frequency is done with the parameter . (Refer to section 6.18)
3. This can be improved by installing 0.1μ to 0.5μF - 1000V film capacitor to the input/output terminals
of each phase in the thermal relay.
U/T1
V/T2
W/T3
(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), especially the 500V class low capacity (4.0kW or less) models, because the leakage
current will increase in proportion to the motor's rated current.
Thermal relays
CT
Inverter
A
Thermal relays
A-27
E6581611
M
M
1