Mitsubishi Electric FR-A700 Technical Manual page 491

(3) Countermeasure
unnecessary operation of earth leakage
circuit breaker and thermal relay due to
earth leakage current
1) Countermeasure to be taken for unnecessary
operation of earth leakage circuit breaker
(a) Use an earth leakage circuit breaker (or earth
leakage relay) for which high frequency
components have been considered.
Use the earth
developed for use with an inverter, e.g.
Mitsubishi's products designed for harmonic
and surge suppression or set a large
sensitivity current to prevent unnecessary
operation.
(b) Provide dedicated ground cable.
Provide the motor with a dedicated ground
cable to divide current, thereby reducing to-
ground leakage current.
2) Countermeasure to taken for thermal relay malfunction
(c) Use the electronic thermal relay function built
into the inverter.
Inverter detects output current after cutting
high frequency components. And thermal
relay function is rarely affected by leakage
currents.
Examples of countermeasure to be taken to prevent
unnecessary operation
(a) Use harmonic/surge reduction NV.
Power
supply
(f) Minimize wiring length.
Earth leakage
circuit breaker
Effects of countermeasure
Countermeasure marked
No. Phenomenon
Surge Reduction
Operation of
(a) circuit breaker in
the same line
1)
Operation of
(b) circuit breaker in
the other line
Thermal relay
2)
operation
Symbol meaning
to be taken for
leakage circuit breaker
(e) Reduce carrier frequency.
Earth leakage
circuit breaker
Inverter
(a) Use harmonic/surge reduction NV.
(f) Use cables of small capacitance/minimize wiring length.
are recommended for phenomena occurring due to the influence of leakage current.
a) Harmonic /
b) Dedicated
Ground Cable
Breaker
:Adequate effect, :Effect produced,
(d) Increase the setting of the external thermal
relay.
When the electronic thermal relay cannot be
used, e.g. when two or more motors are
connected to one inverter and thermal relays
are installed individually, increase the setting
of each external thermal relay by the
equivalence of the leakage current to make
them difficult to be actuated.
Motors of 11kW or more capacity rarely have
leakage current to make them difficult to be
actuated.
3) Countermeasure to be taken for unnecessary
operation of earth leakage circuit breaker and
thermal relay.
(e) Set the carrier frequency of the inverter to a
low value.
Decrease leakage current by setting the
carrier frequency of the inverter to a low value
using the relevant parameter.
However, it should be noted that the decrease
in carrier frequency increases noise during
motor running.
(f) Decrease the to-ground and line-to-line
capacitances.
Wire cables of smaller capacitances between
the inverter power supply side and motor side
to minimize the wiring length.
(f) Minimize wiring length.
Use cables of small capacitance.
(c) Use electronic thermal relay.
c) Use of d) Thermal
Electronic Relay Setting
Thermal Relay Change
:No effect
525
SELECTION
(d) Increase thermal relay setting.
Motor
(b) Use dedicated
ground cable for wiring.
Motor
e) Carrier f) Reduction
Frequency of
Change Capacitance
3