
2.SELECTION METHODS CONFIGURATIONS AND SELECTION B-65332EN/01
2.1.2 Overload Duty Characteristic
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A Dis series motor can be used intermittently, even out of its rated
continuous operating area, when the maximum torque is not exceeded.
The overload duty characteristic represents the duty ratio (%) and "on
time" for which the motor runs under a given overload condition. The
conditions for the "on time" and "off time" of the motor can be
calculated as follows:
<1> Obtain the overload ratio using the following expression:
Overload ratio = load torque ÷ rated continuous torque
Then, the duty ratio (%) and on time of the motor can be
determined from the overload ratio and overload duty cycle
characteristic curves (shown on the next and subsequent pages).
Example:
To run the D3000/150is (liquid cooling) with a load torque
of 1440 Nm at very low speed for one minute:
Overload ratio = 1440 ÷ 1200 = 1.2 (120%)
because the rated continuous force of the D3000/150is is
1200 Nm.
From the overload duty characteristic curve for liquid
cooling, the duty ratio (%) is determined to be 68% when
the motor runs with an overload ratio of 120% for one
minute.
<2> Obtain the off time of the motor using the following expression.
Off time = on time × (100 ÷ duty ratio (%) - 1)
Example:
From the value obtained in the example in <1>:
Off time=1×(100÷68-1)
0.47 minutes (about 28 seconds)
Therefore, it is necessary to keep the motor stopped for at
least 28 seconds after it runs for one minute under the
conditions described above.
The curves of overload duty chractaristics are as follows.