Toshiba Tosvert VF-AS1 - Manual (Page 33)

E6581301
A-17
1
1.4.3 What to do about the leak current
Warning
Current may leak through the inverter's input/output wires because of insufficient electrostatic capacity on the motor with bad
effects on peripheral equipment. The leakage current's value is affected by the carrier frequency and the length of the input/output
wires. Test and adopt the following remedies against leakage current.
(1) Effects of leakage current across ground
Leakage current may flow not just through the inverter system but also through ground wires to other systems.
Leakage current will cause earth leakage current breakers, leakage current relays, ground relays, fire alarms and
sensors to operate improperly, and it will cause superimposed noise on the CRT screen or display of incorrect current
values during current detection with the CRT.
Leakage current path across ground
Power supply
inverter
inverter
Remedies:
1. Reduce PWM carrier frequency.
The setting of PWM carrier frequency is done with the parameter EH.
2. If there is no radio-frequency interference or similar problem, detach the built-in noise filter capacitor.
⇒ Refer to Section 1.3.3. (For inverters of certain capacities, the PWM carrier frequency (EH) must be set at
4 kHz or below.)
3. 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.
4. If the sensors and CRT are affected, it can be remedied by reducing the PWM carrier frequency described in
1 above, but if this cannot be remedied because of the increase in the motor's electric magnetic noise, please
consult with your supplier.
* Cautions for applying models with a built-in noise filter.
For the models with a built-in noise filter, the leakage current value at power supply of ∆ (delta) connecting wire
(single-phase earth) can be larger than normal inverter, so be careful.
VFAS1-2004PL~2150PM: Approx. 15mA
VFAS1-2185PM~2450PM: Approx. 1mA
(2) Affects of leakage current across supply lines
Power supply inverter
Thermal relay
Leakage 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
motor cables are more than 50m long, external thermal relay may operate improperly with models having motors
of low rated current, especially the 400V class low capacity (3.7/4.0kW or less) models, because the leakage
current will be high in proportion to the motor rating.