The function can be enabled and disabled with the Operation setting. The corresponding parameter values are "On" and "Off".
The operation of MNSPTOC can be described by using a module diagram. All the modules in the diagram are explained in the next sections.
Level detector
The calculated negative-sequence current is compared to the Start value setting. If the measured value exceeds the Start value setting, the function activates the timer module.
Timer
Once activated, the timer activates the START output. Depending on the value of the set Operating curve type, the time characteristics are according to DT or IDMT. When the operation timer has reached the value set by Operate delay time in the DT mode or the maximum value defined by the inverse time curve, the OPERATE output is activated.
In a drop-off situation, that is, when the value of the negative-sequence current drops below the Start value setting, the reset timer is activated and the START output resets after the time delay of Reset delay time for the DT characteristics. For IDMT, the reset time depends on the curve type selected.
For the IDMT curves, it is possible to define minimum and maximum operate times with the Minimum operate time and Maximum operate time settings. The Machine time Mult setting parameter corresponds to the machine constant, equal to the I 22t constant of the machine, as stated by the machine manufacturer. In case there is a mismatch between the used CT and the protected motor's nominal current values, it is possible to fit the IDMT curves for the protected motor using the Current reference setting.
The activation of the OPERATE output activates the BLK_RESTART output. The deactivation of the OPERATE output activates the cooling timer. The timer is set to the value entered in the Cooling time setting. The BLK_RESTART output is kept active until the cooling timer is exceeded. If the negative-sequence current increases above the set value during this period, the OPERATE output is activated immediately.
T_ENARESTART indicates the duration for which the BLK_RESTART output remains active, that is, it indicates the remaining time of the cooling timer. The value is available in the monitored data view.
The timer calculates the start duration value START_DUR, which indicates the percentage ratio of the start situation and the set operation time. The value is available in the monitored data view.