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PROTECTIVE FUNCTIONS
Note: 1. Resetting the inverter initializes the internal heat integrating data of the electronic overcurrent
protection.
Note: 2. When an instantaneous power failure occurs, the alarm display and alarm output are not provided,
but the inverter performs protective operation to prevent a fault from occurring in itself. In some
operating status (load size, acceleration/deceleration time setting, etc.), overcurrent or other
protection may be activated upon power restoration.
Operation Panel
Indication
E.THM FR-PU04 Motor Ovrload
Name Motor overload shut-off (electronic overcurrent protection) (Note 1)
Description
The electronic overcurrent protection in the inverter detects motor overheat due to
overload or reduced cooling capability during constant-speed operation. When 85%
of the preset value is reached, pre-alarm (TH indication) occurs. When the specified
value is reached, the protective circuit is activated to stop the inverter output. When
a special motor such as a multi-pole motor or two or more motors are run, provide a
thermal relay in the inverter output side since the motor(s) cannot be protected by
the electronic overcurrent protection.
Check point Check the motor for use under overload.
Corrective action
• Reduce the load weight.
• For a constant-torque motor, change the Pr. 71 setting to the constant-torque
motor setting.
Operation Panel
Indication
E.THT FR-PU04 Inv. Overload
Name Inverter overload shut-off (electronic overcurrent protection) (Note 1)
Description
If a current of more than 150% of the rated output current flows and overcurrent
shut-off does not occur (200% or less), inverse-time characteristics cause the
electronic overcurrent protection to be activated to stop the inverter output in order
to protect the output transistors.
(Overload immunity 150%, 60s.)
Check point Check the motor for use under overload.
Corrective action Reduce the load weight.
Operation Panel
Indication
E.IPF FR-PU04 Inst. Pwr. Loss
Name Instantaneous power failure protection (Note 2)
Description
If a power failure occurs for longer than 15ms (this also applies to inverter input
shut-off), the instantaneous power failure protective function is activated to stop the
inverter output in order to prevent the control circuit from malfunctioning. At this
time, the alarm warning output contacts open (across terminals B-C) and close
(across terminals A-C). (Note 2) If a power failure persists for longer than 100ms,
the alarm warning output is not provided, and the inverter restarts if the start signal
is on upon power restoration. (The inverter continues operating if an instantaneous
power failure is within 15ms.)
Check point Find the cause of instantaneous power failure occurrence.
Corrective action
• Remedy the instantaneous power failure.
• Prepare a backup power supply for instantaneous power failure.
• Set the function of automatic restart after instantaneous power failure. (Refer to
page 96.)
