100 Functional description CG Drives & Automation 01-7492-01r1
Motor I
2
t Current [232]
Sets the current limit for the motor I
2
t protection in percent
of I
MOT
.
Motor I
2
t Time [233]
Sets the time of the I
2
t function. After this time the limit for
the
I
2
t is reached if operating with 120% of the I
2
t current
value. Valid when start from 0 rpm.
Fig. 93 I
2
t function
Fig. 93 shows how the function integrates the square of the
motor current according to the “Mot I
2
t Curr [232]” and
the “Mot I
2
t Time [233]”.
When the selection Trip is set in menu [231] the AC drive
trips if this limit is exceeded.
When the selection Limit is set in menu [231] the AC drive
reduces the torque if the integrated value is 95% or closer to
the limit, so that the limit cannot be exceeded.
Example
In fig. 93 the thick grey line shows the following example.
• Menu “[232] Mot I
2
t Curr” is set to 100%.
1.2 x 100% = 120%
• Menu “[233] Mot I
2
t Time” is set to 1000 s.
This means that the AC drive will trip or reduce the current
(depending on the setting in menu [231]) after 1000 s if the
current is 1.2 times of 100% nominal motor current.
232 Mot I
2
t Curr
Default: 100% of I
MOT
Range: 0–150% of I
MOT
(set in menu [224])
NOTE: When the selection Limit is set in menu [231],
the value must be above the no-load current of the
motor.
NOTE: Not the time constant of the motor.
233 Mot I
2
t Time
Default: 60 s
Range: 60–1200 s
10
100
1000
10000
100000
1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2
t [s]
i / I2t-current
60 s (120%)
120 s (120%)
240 s (120%)
480 s (120%)
1000 s (120%)
Actual output current/ I
2
t-current
NOTE: If it is not possible to reduce the current, the
AC drive will trip after exceeding 110% of the limit.
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