Influence Of Leakage Current Across Lines (In Case Of Thermal Relays); Influence Of Leakage Current Across Lines (In Case Of Ct And Ammeter) - Toshiba TOSVERT VF-AS3 Instruction Manual

Built-in noise filter
The 480 V models of this inverter has a built-in EMC noise filter, so the leakage current value in the
delta connection (single-phase grounding) power supply may become greater.

■ Influence of leakage current across lines (in case of 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
unnecessarily. When the wires are long (50 m or more) or in case of models with motors of low rated
current (several A (ampere) or less), especially the 480 V class low capacity (4.0 kW or less, 5.5 kW
or less with ND) models, it will be easy for the external thermal relay to activate unnecessarily,
because the ratio of leakage current against the motor rating will increase.
Leakage current path across wires
Power
supply
Here are some examples of measures against leakage current across lines.
• Use the electronic thermal of the inverter.
The setting of the electronic thermal is done with <tHrA: Motor overload protection current 1>. For
details, refer to [5. 1. 5].
• Decrease <F300: Carrier frequency>.
However, note that the motor magnetic noise is increased.
For details, refer to [6. 14].
• Install 0.1 to 0.5μF - 1000 V film capacitor to the input/output terminals of each phase in the ther-
mal relay.
Inverter
U/T 1
V/T 2
W/T 3

■ Influence of leakage current across lines (in case of 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 long (50 m or more) or in case
of models with motors of low rated current (several A (ampere) or less), especially the 480 V class
low capacity (4.0 kW or less, 5.5 kW or less with ND) models, it will be easy for the high frequency
component to pass through the externally connected CT and be superimposed on and burn the
ammeter, because the ratio of leakage current against the motor's rated current will increase.
Here are some examples of measures against leakage current across lines.
• Connect the ammeter to the terminal [FM] and terminal [AM] of the inverter.
Thermal relay
CT
Inverter
A
Thermal relay
2-59
E6582062
M
M
2. Installation and wiring
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3
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