Inverter Peripheral Circuit And Inverter Operation At Instantaneous Power Failure - Mitsubishi Electric FATEC FR-A800 Manual

7
REVIEW OF INSTALLATION ENVIRONMENT
7.1.7 Inverter peripheral circuit and inverter operation at instantaneous
power failure
(1) For a magnetic contactor (MC) at the inverter's input line
When the instantaneous power failure time is short and both the magnetic contactor MC and
relay RA do not trip (start signal STF remains ON), the operation is as described in
Subsection 7.1.6.
When only the magnetic contactor MC trips, the motor coasts to a stop. Therefore, when
restarting the inverter after a power restoration, turn on MC again or use the instantaneous
power failure function after the motor coasts to a stop (coasting interlock timer is necessary).
(2) For magnetic contactors (MC) at both the inverter's input line and the output line
When the instantaneous power failure time is short and both the magnetic contactor MC1
and relay RA do not trip (start signal STF remains ON), the operation is as described in
Subsection 7.1.6.
When only the magnetic contactor MC1 trips, the motor coasts to a stop. Therefore, when
restarting the inverter after a power restoration, turn on MC1 again or use the instantaneous
power failure function after the motor coasts to a stop (coasting interlock timer is necessary).
When only the magnetic contactor MC2 trips, the motor coasts to a stop. However, the
inverter continues to output depending on the instantaneous power failure time, or only the
inverter restarts after resetting at the power restoration. Therefore, when MC2 is turned on
again, the motor starts directly with the inverter output frequency, and this may cause an
inverter trip due to overcurrent.
1) Even though an instantaneous power failure occurs at the receiving end, an instantaneous
power failure is unlikely to occur (completely) at the low voltage side inverter input terminal
(R, S, T) and voltage drops instantaneously. (Undervoltage protection operations)
2) An inverter has the instantaneous power failure protective function and the undervoltage
protection. The protective function is activated when the DC circuit voltage of the inverter is
under a certain value for a certain time. Therefore, when the power supply drops
instantaneously, the protective function may be activated for an inverter whose load output
(kW) is large, and the operation may continue for an inverter whose load output is small.
3) On the other hand, the magnetic contactors or relays may not trip due to an instantaneous
voltage drop, if once it is turned on. In general, it trips when the voltage is equal to or lower
than 30% to 50% of coil rating.
7.1 Power supply of inverter (harmonics and instantaneous power failure)
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MCCB
MC
RA
MC 1
MCCB
RA
Inverter
STF
SD
MC 2
Inverter
STF
SD
M
M