A transformer arrangement includes a transformer having a winding and a surge arrester arrangement connected thereto. The SAA includes a surge arrester (SA) connected across at least a section of the winding and a switch operable between a closed and open state. In the closed state, SA is electrically connected across at least the section, and in the open state, the SA electrically disconnected from at least the section. The SAA includes at least one further SA .sub.arranged to be connected across at least one further section and at least one further switch, operable between a closed and open state, wherein in the closed state the further SA is electrically connected across the at least one further section, and in the open state, the at least one further SA is electrically disconnected from the further section. A method for electrically connecting/disconnecting the transformer to/from the SAA—is also described.

An electrical appliance for connecting to a high voltage includes an active part, which is provided with a magnetizable core and at least one winding assembly, surrounding a respective core section of the core and having windings that are inductively coupled to one another. A tank, which can be filled with an insulating fluid, encases the active part. The tank has two end casings and a central part arranged between the end casings. The electrical appliance is compact and has a low tare weight. The active part is mechanically connected to the boiler only at the end casings and the end casings are supported on fasteners. The central part is produced from a light material.

A medium frequency transformer for a DC/DC converter includes: a core having an air gap and a coil surrounding a core section and having a plurality of windings; a medium voltage electric insulation, surrounding the coil each winding including a first and second termination, and a conductor wound around a portion of the core in at least one turn between the first and second termination; a plurality of terminals provided outside the insulation, each connected to a different first termination by one of a plurality of connectors, a channel extending from an outside of the insulation into and at least partially through said electric insulation, wherein the connectors extend through the channel and are insulated against one another by means of a low voltage insulation within the channel. The second terminations are connected to one another within or inside the insulation and connected to a second terminal outside of the insulation by a second connector.

A high voltage (HV) apparatus insulated with an insulating gel includes at least two electrically conductive elements, such as a head transformer cover, a head housing base, a core casing, a primary conductor, bottom external housing, a bottom support flange, and/or a core. At least one of the electrically conductive elements has a coating made of solid insulating material separating the surface of the conductive element from the insulating gel and adapted for limiting electron emission from the conductive elements into the insulating gel.

The present invention relates to the use, for the retrofilling of a transformer, of at least one dielectric fluid of general formula (1):

(A−X).sub.n−B  (1)

in which A and B, which are identical or different, represent, independently of each other, an optionally substituted aromatic ring, X represents a spacer group and n represents 0, 1, 2 or 3.

The invention also relates to a transformer containing at least one dielectric fluid of general formula (1) and an amount of PCBs of less than 20%.

A dry high voltage (HV) instrument transformer in the form of a HV current transformer includes a core casing having a secondary winding, a top housing, a primary winding, and a dry bushing, wherein the core casing comprises an insulation containing an electrically insulating material made of PES nonwoven impregnated and cured with low viscosity epoxy. The dry HV instrument transformer in the form of a HV voltage transformer includes a bottom tank housing, a cast of a primary winding module with an embedded screen surrounding the primary winding, a field grading disc, and a core, wherein the cast of the primary winding module is made of an insulating composite containing an electrically insulating material made of PES nonwoven impregnated and cured with low viscosity epoxy.

The present invention refers to HV apparatus, in particular a HV dry current transformer, insulated with an insulating gel, or a voltage transformer, insulated with an insulating gel. The dry HV current transformer comprises at least two electrically conductive elements i.e. a head transformer cover, a head housing base, a core casing and a primary conductor. In the dry HV current transformer at least one of the electrically conductive elements has a coating made of solid insulating material separating the surface of the conductive elements from the insulating gel and adapted for limiting the electron emission from the conductive elements into the insulating gel. The voltage transformer comprises a bottom external housing, a bottom support flange, a core. In the voltage transformer at least one of the electrically conductive elements has a coating made of solid insulating material separating the surface of the conductive elements from the insulating gel and adapted for limiting the electron emission from the conductive elements into the insulating gel.

Techniques for assessing a health of a transformer breather are provided. The transformer breather contains a desiccant and is in fluid communication with an expansion tank of a fluid-insulated transformer. A weight measurement that is dependent on a weight of the transformer breather or of a component or sub-assembly thereof is processed to assess the health of the transformer breather.

There is provided a pressboard for high-voltage devices, the pressboard having a density of 0.6-1.3 g/cm.sup.3 according to IEC60641-2, and including 1-15% microfibrillated cellulose, MFC, based on the total dry weight of the pressboard. There is also provided an insulation element including such pressboard, wherein the pressboard is impregnated with an electrically insulating compound. There is also provided use of such insulation element in a high-voltage device as well as a high-voltage device comprising such insulation element, wherein the high-voltage device may be a power transformer.

A system and a method for predicting a remaining useful life of a transformer are provided. The system includes the transformer and a processing device. The transformer includes a liquid insulating material and a solid insulating material. The processing device is configured to establish, through a machine learning method, a life prediction model based on status data and corresponding life loss data of the liquid insulating material and the solid insulating material, and the processing device uses the life prediction model to predict the remaining useful life of the transformer based on operating data of the transformer.