Mitsubishi Electric FR-A700 Series, Technical Manual

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247
2
P
ARAM
ETE
R
PARAMETER
(4) Torque boost [
Pr. 0
]
Second torque boost [
Pr. 46
]
Third torque boost [
Pr. 112
]
Allows the output voltage at the output frequency of
0Hz to be set to increase/decrease the motor starting
torque. Change the setting of the torque boost only
when the starting torque is not appropriate.
To perform the switch-over operation of two (or three)
motors by one inverter, the torque boost dedicated to
one motor can be set in [
Pr. 46 (Pr. 112)
]. (Active when
RT(X9) signal is ON.) Set 9999 (initial value) in [ Pr. 46
(Pr. 112) ] to set the same value in [ Pr. 0 ].
For , [ Pr. 112 ] is valid when both the RT and X9
signals are ON.
1) To increase the starting torque
The following figure shows the motor torque and
current characteristic examples in which the [
Pr.
13 Starting frequency ] is suppressed to a low value
and the torque boost is increased so that the
motor may be started at the starting current lower
than the stall prevention current.
When the torque boost setting is greater than the
initial setting, the continuously usable frequency
range is narrowed because the no-load current of
the motor increases. When the torque boost value
is 8%, for example, the frequency of 15Hz or less
cannot be used continuously.
Too high setting of the torque boost saturates the
magnetic flux of the motor iron core, which
increases the motor current and activates the
current limit function.
If the starting torque is insufficient when using the
serge voltage suppression filter (FR-ASF-H),
increase the [
Pr. 0 ] value.
2) To suppress motor vibration at low frequency
Vibration may be suppressed by setting the torque
boost value to lower than the factory setting (this
is applicable only when the motor capacity is
sufficient). In this case, the motor starting torque
is reduced.
Change the torque boost setting according to
actual operation and check that the above
problem does not occur.
3) When using an inverter dedicated motor
(constant-torque motor)
When using the inverter dedicated motor
(constant torque motor) and energy saving motor,
set the setting of [
Pr. 0 Torque boost ] as shown
below.
In addition, when the [ Pr. 71 Applied motor ] setting
is changed to the constant torque motor in the
initial setting status, the [
Pr. 0 ] setting is
automatically changed as shown below. The [ Pr.
0 ] setting is automatically changed also when the
constant torque motor setting is changed to the
standard motor setting.
Torque boost, motor torque and current examples
common
common
A700
A700
50
100
Torque boost = 8%
Torque boost = 4%
6Hz 4Hz
T
orque (%)
50
150
6Hz 4Hz
100
200
Speed [r/min]
0
0
Inverter overcurrent trip
activating current
Inverter stall prevention
or current limit function
activating current
Current (%)
[
Pr. 71
] Setting
Standard motor
(initial value)
Constant-torque
motor
0.75K or less 6% 6%
1.5K to 3.7K 4% 4%
5.5K
,
7.5K 3% 2%
11K to 37K 2% 2%
45K, 55K
2% 1.5% 2% 1.5%
75K or more 1% 1%
A700 F700 A700 F700