Method of operating parallel transformers

A method of controlling parallel operation of N transformers in a parallel circuit in which a respective tap changer of each transformer has a respective control sensor and all of the control sensors are connected together by a communications connection, N being equal to or greater than 2, the method comprising the steps of:

• generating a measurement with each of the control sensors;
• transferring at least one of the measurements of the control sensors of the transformers by the communications connection to the N−1 remaining control sensors;
• calculating a controlling deviation caused by a circuit reactive current for each control sensor on the basis of the measurements of the control sensors;
• actuating the tap changer associated with each transformer by the respective control sensor as a function of the calculated controlling deviation such that minimization of the circuit reactive current is carried out for the respective transformer;
• detecting absence of at least one signal of at least one of the control sensors caused by interruption of the communications connection at an instant and reporting the absence of the at least one signal of the at least one control sensor to all remaining control sensors;
• and
• determining the controlling deviation required for minimization of the circuit reactive current of the at least one control sensor affected by the interruption of the communications connection on the basis of the measurements from at least one further control sensor of at least one further transformer of the N transformers not affected by the interruption of the communications connection and received by the communications connection prior to the instant;
• and
• including with the at least one further control sensor affected by the interruption the individual instantaneously measured measurements of its respective transformer in the determination.