A system includes conductive windings extending around a magnetic core and impedance-varying windings extending around the magnetic core. The impedance-varying windings include positive windings and negative windings. The conductive windings and the impedance-varying windings conduct electric current around the magnetic core. The system includes a first impedance tap changer that is electrically coupled with the positive windings of the impedance-varying windings and a second impedance tap changer electrically coupled with the negative windings of the impedance-varying windings. A controller controls the first impedance tap changer and the second impedance tap changer to change an impedance of the system by changing which portion of the positive windings and which portion of the negative windings are conductively coupled with the conductive windings, and which portion of the positive windings and which portion of the negative windings are disconnected from the conductive windings.

An on-load tap-changer switches, without interruption, between winding taps of a tapped transformer. The on-load tap-changer includes fixed contacts, which include a first fixed contact, which is configured to connect to a first winding tap of the tapped transformer; and a second fixed contact, which is configured to connect to a second winding tap of the tapped transformer. The on-load tap-changer also includes a first selector arm, which is configured such that it can contact each of the fixed contacts; a second selector arm, which is configured such that it can contact each of the fixed contacts; and a diverter switch configured to perform a switch from the first fixed contact to the second fixed contact of the on-load tap-changer; a connection contact arranged additionally to the fixed contacts; and an auxiliary contact, which configured to selectively contact the connection contact or one of the fixed contacts.

An apparatus for a load tap changer includes a first primary winding electrically connected to a first contact, the first contact configured to connect to one of a plurality of taps in a load tap changer; a second contact, the second contact configured to connect to one of the plurality of taps in the load tap changer; a magnetic core; and a control circuit including: a secondary winding configured to magnetically couple to the first primary winding and the magnetic core; and an electrical network electrically connected to the secondary winding, the electrical network being configured to prevent magnetic saturation of the magnetic core during switching of the first or second contact.

The subject of the application is a power electronic tap changer module for transformer using power electronic elements connected to sections of a primary winding of the transformer. The power electronic tap changer module is equipped with valves having a pair of a thyristor or transistors connected with a controller and the valves are connected in series with the fuses, respectively. The module is equipped with an additional oversized tap line having an oversized valve rated for short circuit current, which valve is connected with an overvoltage triggering circuit. The oversized valve is equipped with a pair of thyristor or transistors connected with a thermally protected voltage suppressing device.

An on-load tap changer is provided having a plurality of modules, each of which is operable to change taps in a transformer winding. The tap changer includes a motor connected to rotate at least one shaft. The at least one shaft is connected to the tap change modules and is operable upon rotation to cause the tap change modules to each perform a sequence of operations that effectuate a tap change. A multi-turn absolute encoder is connected to the at least one shaft. A monitoring system is connected to the encoder and is operable to determine from the position of the at least one shaft where the tap change modules are in the sequence of operations.

The following steps are performed in order to test a tap changer of a transformer which tap changer is designed to change a transmission ratio of the transformer: generating a test signal which is supplied to a winding of the transformer and to the tap changer, repeatedly actuating the tap changer in order to change the transmission ratio with each actuation, determining a curve of an electrical measurement variable (I; I.sub.1; I.sub.2) of the transformer over time (t) for each actuation of the tap changer depending on the test signal filtering the curves in order to prevent at least one of the curves from being output outputting the filtered curves.

The present application discloses a method to optimize operation of a transformer cooling system, the corresponding cooling system, and a method to determine the capacity of Variable Frequency Drives (VFD) that are used in the transformer cooling system. The method comprises: preprocessing the initial data input by user; collecting the on-line data, and calculating the optimized control command to meet the requirement of the transformer loss, top-oil temperature variation and noise; and executing the control actions by controlling a controllable switch and/or sending a control command to a VFD. Compared with the existing prior arts, the proposed solutions are much more intuitive and practical in the field of the cooling system.

An on-load tap changer that includes an actuator configured to adjust a turn ratio of the transformer, and a processing unit configured to control the actuator and to communicate with a control device via a digital signal connection. The processing unit is further configured to receive a status detected by a sensor. A method of manufacturing the on-load tap changer is also disclosed. Embodiments according to the present disclosure provide a digitalized on-load tap changer that allows various statuses to be monitored or controlled, by which various advantages can be achieved. For example, the life of a contact of the transformer can be predicted. Other data can be used to determine whether it is safe to adjust the contact of the transformer. Moreover, the optical fibers between the on-load tap changer and an external device enable an isolated transmission of control and data signals that almost eliminates interferences.

A switch apparatus (10) for a measuring device (30) for a transformer includes controllable switch device (14) which are configured to short-circuit respectively assigned terminals (11) of one of a plurality of windings of the transformer. A test apparatus (40) including the switch apparatus (10) and a method (50) for operating the switch apparatus (10) are also disclosed. With apparatuses (10, 40) and methods (50) according to the exemplary embodiments, the work effort, time expenditure and errors and inaccuracies can be reduced through an automated testing of transformers.

A transformer configured to receive a primary incoming voltage and provide at least two secondary output voltages. The transformer includes at least one secondary output assembly which includes at least two secondary voltage stabs, the number of voltage stabs being the same as the number of secondary output voltages, connected and configured to provide access to a respective secondary output voltage. The chosen secondary output voltage is connected by coupling a tap change link between a lug landing and either of the at least two secondary voltage stabs. Another of the secondary output voltages is provided by connecting coupling the tap change link between the lug landing and the other of the at least two secondary voltage stabs.