Mitsubishi Electric FR-A700 Technical Manual page 113

1.5.3 Overcurrent protection (OC1 to OC3)
To protect IGBT from overcurrent, the following protective
functions are activated by detecting the output current of
the inverter.
1) Rated output current (100%)
2) Overload current rating (150%)
3) Current limit operation
(stall prevention (overcurrent) operation)
Overcurrent shut-off (
A700
*1 120% or more
F700
*2 170% or more,
F700
200% or more,
1.5.4 Stall prevention (overcurrent) function and fast response current limit function
common
(common)
Both functions are activated against the output current (output
torque under Real sensorless vector control and vector
control). If a rise in current is sharp, the overcurrent protection
is activated because the stall prevention function cannot
suppress the current. Better for current suppression (limit)
capability than the stall prevention function, the fast response
current limit function has a less possibility of activating the
overcurrent protection, thus ensuring operation highly
resistant to overload.
You can activate these functions using [Pr. 156].
Note that if an overload state is continued, the electronic
thermal relay (E.THT) may be operated. Unlike the stall
prevention (overvoltage), the current limit function does not
function against regenerative overvoltage during deceleration.
(1) Stall prevention
acceleration,
operation)
common
The inverter has a function for limiting the motor
current. If the current reaches or exceeds [Pr. 22 Stall
prevention operation level], the inverter lowers the
output frequency during acceleration operation to
reduce the load current and waits for the decrease of
the load current. The inverter decreases the output
frequency during constant speed operation and waits
for decrease of the load current. When the current
returns to within [Pr. 22 Stall prevention operation level]
etc., the inverter increases the frequency again,
accelerates and operates at the set frequency.
The current limit
overcurrent shut-off if the current changes suddenly
as in a short circuit occurring in the output side.
*1
220% or more)
*2
230% or more,
E700 D700
(overcurrent) (during
during constant-speed
function may not prevent
common
(common)
1) Rated output current
Maximum current allowed to flow continuously.
2) Overload current rating
Current allowed to flow one minute continuously.
Sufficient cooling time is required for repeated
use.
3) Current limit operation
The current limit is activated.
4) Overcurrent shut-off
Activates the protective circuit instantaneously to
shut off the transistor gate. Causes the electronic
thermal relay to shut off the gate to protect the
transistor if a current smaller than this value flows
continuously for a long time.
(2) Stall prevention
deceleration)
If the current reaches or exceeds [Pr. 22 Stall prevention
operation level] etc., the inverter increases the output
frequency to reduce the load current and waits for the
decrease of the load current. When the current returns
to within [Pr. 22 Stall prevention operation level] etc., the
inverter decreases
decelerates to the set frequency or stops.
(3) Fast-response current limit
When the output current exceeds the specified value
(independently of [Pr. 22]), the inverter shuts off the
outputs, decelerates to the specified value and
cancels the output shut-off. Action is the same
regardless of acceleration, constant speed, and
deceleration operation. Although response speed is
fast, the output torque also decreases rapidly due to
the rapid decrease of output voltage.
During acceleration
Stall prevention activated
Operation at stall prevention (overcurrent)
106
SPECIFICATIONS
(overcurrent)
common
the frequency again
common
During
constant-speed
During deceleration
operation
[Pr. 22], etc.
100%
(during
and
Time
Time