Patent ID: 7355369

Claim:
An on-load transformer tap changing system in which a secondary or primary of a transformer includes at least one first tap and one second tap, the system comprising: a main connection circuit used to connect, in a steady state condition, the first tap or the second tap to an output terminal of the transformer secondary or primary; a first secondary connection circuit used to connect the first tap temporarily and directly to the output terminal of the transformer secondary or primary; and a second secondary connection circuit used to connect the second tap temporarily and directly to the output terminal, wherein each of the connection circuits comprises one or more insulated gate bipolar transistors, and wherein, when the first tap is connected to the output terminal via the first switching current, the central control circuit comprises a sequential operation enabling of following steps independently from the transformer load current value: conduction of the first secondary connection circuit to make a temporary parallel connection of the first tap to the output voltage, conduction of the second secondary connection circuit to make a temporary connection of the second tap to the output terminal, connection of the main connection circuit to the second tap, non-conduction of the first secondary connection circuit, conduction of the main connection circuit, and non-conduction of the second secondary connection circuit.