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.
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:
- 203Bh:3h Threshold – specifies the limit in mAs that determines whether the maximum current or rated current is switched to.
- 203Bh:4h CalcValue – specifies the calculated value that is compared with the threshold for setting the current.
- 203Bh:5h LimitedCurrent – shows the momentary current value that was set by I2t.
- 203Bh:6h Status:
- Value = "0": I2t deactivated
- Value = "1": I2t activated
Closed loop must be activated, (bit 0 of object 3202h set to "1", see also chapter Closed Loop). To activate the mode, the three object entries mentioned above (2031h, 203Bh:1h, 203Bh:2h) 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.
Function of I2t
From the specification of rated current, maximum current and maximum duration of the maximum current, an I2tLim is calculated.
The motor can run with maximum current until the calculated I2tLim 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 t1Lim, I2tLim 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 I2tLim is reached more quickly than in time t1.