I²t Motor overload protection

The goal of I²t motor overload protection is to protect the motor from damage and, at the same time, operate it normally up to its thermal limit.

This function is only available if the controller is in the closed loop mode (bit 0 of object 3202_h must be set to "1").

There is an exception: If I²t is activated in open loop mode, the current is limited to the set rated current, even if the set maximum current is larger. This function was implemented for safety reasons so that one can switch from closed loop mode with very high, brief maximum current to open loop mode without damaging the motor.

The following objects indicate the current state of I²t:

Closed loop must be activated, (bit 0 of object 3202_h set to "1", see also chapter Closed Loop). To activate the mode, the three object entries mentioned above (2031_h, 203B_h:1_h, 203B_h:2_h) must have been appropriately specified. This means that the maximum current must be greater than the rated current and a time value for the maximum duration of the maximum current must be entered. If these conditions are not met, the I²t functionality remains deactivated.

From the specification of rated current, maximum current and maximum duration of the maximum current, an I²t_Lim is calculated.

The motor can run with maximum current until the calculated I²t_Lim is reached. The current is then immediately reduced to the rated current.

The relationships are illustrated again in the following diagram.

In the first section, t1, the current value is higher than the rated current. At time t1_Lim, I²t_Lim is reached and the current is limited to the rated current. A current that corresponds to the maximum current then occurs for a period of time t2. Hence, the value for I²t_Lim is reached more quickly than in time t1.