Method and device for prediction of a zero-crossing alternating current

An apparatus for predicting a zero-crossing of an alternating current after occurrence of a fault current in a current path for determining a suitable time for opening an electric switching device arranged in the current path for breaking the current in the current path, comprising:

• members adapted to detect the current in the current path, including an arrangement adapted to calculate the dc-level of the current, such as, and the decay of the dc-level with the time on the basis of values of the alternating current detected by said members,
• said arrangement being adapted to predict the time for a future zero-crossing of the alternating current on the basis of at least the current values obtained through said current detection, the calculated dc-level, the calculated dc-decay and information about the period time of the alternating current.

An arrangement for predicting a zero-crossing of an alternating current after occurrence of a fault current in a current path for determining a suitable time for opening an electric switching device arranged in the current path for breaking the current in the current path, comprising:

• a program module including a processor adapted to carry out program instructions to detect the current in the current path, to calculate the dc-level of the current represented by the displacement of the symmetry line of the alternating current with respect to the zero level thereof, and the decay of the dc-level with the time on the basis of detected values of the alternating current, and to predict a time for a future zero-crossing of the alternating current on the basis of at least current values obtained through said current detection, the dc-level calculated, the dc-decay calculated and the period time of the alternating current.

A computer program in combination with and embodied in a computer readable medium for carrying out a method of predicting a zero-crossing of an alternating current after occurrence of a fault current in a current path for determining a suitable time for opening an electric switching device arranged in the current path for breaking the current in the current path, comprising:

• instructions for influencing a processor to cause detection of the current in the current path, calculating of the dc-level of the current represented by the displacement of the symmetry line of the alternating current with respect to the zero level thereof, and the decay of the dc-level with the time on the basis of detected values of the alternating current, and predicting a time for a future zero-crossing of the alternating current on the basis of at least the current values obtained through said current detection, the dc-level calculated, the dc-decay calculated and the period time of the alternating current.