A transformer (100, 100′) is disclosed, comprising a first conducting element (110) having a first lobed portion (114) arranged to form a first plurality of lobes (116); and a second conducting element (120) having a second lobed portion (124) arranged to form a second plurality of lobes (126); wherein said first lobed portion (114) overlaps said second lobed portion (124) to define a plurality of enclosed areas (130). The transformer is adapted for applications requiring an autotransformer having a weak, negative magnetic coupling coefficient.

A power system can include a first tap changer for a first regulated transformer, where the first tap changer has a plurality of first positions. The power system can also include a second tap changer for a second regulated transformer, where the second tap changer has a plurality of second positions. The power system can further include at least one first instrument transformer coupled to the first regulated transformer. The power system can also include at least one second instrument transformer coupled to the second regulated transformer. The power system can further include a controller coupled to the at least one first instrument transformer and the at least one second instrument transformer, where the controller adjusts the first tap changer to a first adjusted position among the first positions based on the first measurements of the first regulated transformer and the second measurements of the second regulated transformer.

Downhole electrical energy harvesting and communication in systems for well installations having metallic structure carrying electric current, for example CP current. In some instances there is a harvesting module (4) electrically connected to the metallic structure (2) at a first location and to a second location spaced from the first location, the first and second locations being chosen such that, in use, there is a potential difference therebetween due to the electric current flowing in the structure (2); and the harvesting module (4) being arranged to harvest electrical energy from the electric current. In addition or alternatively, there may be communication apparatus (4, 5, 6) for communication by modulation of the current, for example CP current, in the metallic structure (2).

A switching arrangement (1), in particular a polarity switching means, for a control transformer (10) which comprises a first winding (2) for a phase of an AC power supply system, which phase is to be controlled, comprises—a first connection terminal (1.1) which can be connected to the winding (2);—a second connection terminal (1.2) which can be connected to a discharge line (3);—a vacuum interrupter (4);—an isolator (5);—a resistor (6) which is connected in series with the vacuum interrupter (4) and the isolator (5); wherein—the first connection terminal (1.1) is connected to the second connection terminal (1.2) by means of the series circuit.

Techniques are disclosed implementing a tunable transformer with additional taps in at least one of the three coils. The tunable transformer enables the resonant frequency within RF transceiver matching networks to be adjusted without substantially impacting the output power at resonance. The tunability of the transformer is partially driven by the insertion of additional coils within the transformer, which are selectively switched and may be further coupled with a tunable capacitance. The tunability of the transformer is further driven via the use of at least one multi-tap transformer coil, which allows electronic components to be coupled to different coil taps to thereby facilitate an adjustable DC inductance. Doing so counteracts changes in mutual inductance between the non-switched coils, and facilitates the stabilization of output power with shifts in resonant frequency.

The disclosure relates to a tap changer arranged to be connected to a regulating winding of a rated regulation voltage. The tap changer comprises a diverter switch, a tap selector and a set of tap changer contacts. The tap selector and the diverter switch are encapsulated in a shielding structure arranged to shield the tap selector and the diverter switch from an external electrical field, the shielding structure being arranged to be electrically connected to a connected tap of the regulating winding.

The disclosure further relates to transformer arrangement comprising at least one such tap changer.

Disclosed is an electric transformer that has variable impedance, optionally under load, which includes, in at least one of its transformation phases, a first impedance-varying auxiliary winding having inverse magnetic polarity arid a second impedance-varying auxiliary winding having inverse magnetic polarity, both auxiliary windings being divided into impedance circuit modules and being series connected by interposing the impedance circuit modules one by one, defining impedance variation modules that comprise impedance taps designed to be electrically coupled to a stepped-impedance-tap selector controlled by an impedance controller that allows the impedance of the transformation phase or of the electric transformer to be varied,

Transformer assembly has an input terminal, principal housing with main chamber for high voltage coil(s) having plurality of taps, low voltage coil(s) and retaining oil. An auxiliary housing extends outwardly from principal housing and is fluidly connected to main chamber so that auxiliary housing contains oil. A potential transformer; load tap changer having a controller, a motor and a plurality of switches; electrical wiring connected to taps, switches within auxiliary housing chamber are submerged by oil within auxiliary chamber; load tap change controller can adjust taps while the switches and electrical connections are submerged in oil of auxiliary housing chamber. The upper level of oil in the main housing chamber is at a level equal to or above the switches of the load tap changer. The auxiliary housing has an access opening and cover. System apparatus with frames, having beams, lattices and cable guides for routing cables for assembly.

Downhole electrical energy harvesting and communication in systems for well installations having metallic structure carrying electric current, for example CP current. In some instances there is a harvesting module (4) electrically connected to the metallic structure (2) at a first location and to a second location spaced from the first location, the first and second locations being chosen such that, in use, there is a potential difference therebetween due to the electric current flowing in the structure (2); and the harvesting module (4) being arranged to harvest electrical energy from the electric current. In addition or alternatively, there may be communication apparatus (4, 5, 6) for communication by modulation of the current, for example CP current, in the metallic structure (2).

Provided is a three-phase dry-type transformer. The three-phase dry-type transformer comprises three single-phase dry-type transformers connected to each other. Each single-phase transformer comprises an incoming line side high-voltage coil and an outgoing line side high-voltage coil, wherein the incoming line side high-voltage coil is provided with an incoming line end and an outgoing line end, and the outgoing line side high-voltage coil is provided with an incoming line end and an outgoing line end. The outgoing line end of the incoming line side high-voltage coil is connected to the incoming line end of the outgoing line side high-voltage coil, such that the incoming line side high-voltage coil and the outgoing line side high-voltage coil are connected in series. Further provided is an assembly method.