Abstract: A method for determining a direct current component in an electric device that is connected to a high-voltage supply network. The method includes the following steps: acquiring operating noises of the electric device with the aid of acoustic sensors that are part of a portable unit and that provide acoustic signals at the output; breaking the acoustic signals down into their frequency components by a Fourier transformation, yielding a frequency spectrum; determining odd and even frequency components of the frequency spectrum in dependence upon a basic frequency of the high-voltage supply network and setting them in a ratio to one another; concluding that a direct current component is present if the ratio exceeds a predefined threshold value.

Abstract: A method for detecting a direct current component in an inductive device, for example in a transformer or choke, includes using a computer for recording an oscillation signal, either of sound emitted from the device or of mechanical oscillation of the device, determining the frequency range of the oscillation signal, determining the value of at least one odd frequency in the frequency range, comparing the value of the odd frequency with the value of at least one even frequency in the frequency range, and determining a direct current component when the value of the odd frequency differs from the even frequency by a predefined amount. The method can be carried out without measuring equipment in the interior of an inductive device and without the involvement of an expert. A computer program product for carrying out the method is also provided.

Abstract: A method for drying a transformer which has a multistage cooling system, in particular a power transformer or a choke, has at least one transformer winding and at least one insulator for electrical insulation. Individual cooling stages of the cooling system are respectively associated with a loading state range of the transformer and are activated when the respective loading state range of the transformer is reached. The loading state range is a function which depends at least on a temperature of the transformer. The drying method is carried out during the operation of the transformer. An upper cooling stage, which lies above the lowest cooling stage, is or remains deactivated and the cooling stage which is situated directly below the upper cooling stage is or remains activated while the transformer is in the loading state range which is associated with the upper cooling stage.

Abstract: An assembly includes at least one winding and a housing in which the winding is disposed. The winding has at least one electrical conductor and a cellulosic or cellulose-containing insulation material at least partially surrounds the winding and/or the electrical conductor thereof. The housing is filled with a liquid coolant during operation so that the winding is located in a liquid coolant during operation. In addition to existing cellulose-containing insulation material which encloses the winding and/or the electrical conductor thereof for insulation purposes, the housing and/or a coolant circuit for the coolant contains at least one composition containing chemical compounds for reducing the aging of cellulose-containing insulation material. A method of reducing the aging of cellulosic insulation material of a winding is also provided.

Abstract: A method for operating a cooling system of a transformer, wherein the transformer is cooled via a cooling liquid that circulates in the cooling system that includes a heat-exchanger, devices for increasing heat exchange performance of the at heat-exchanger and a controller, where in a normal operating state, the controller adjusts power of the devices for increasing the heat exchange performance as a function of a measured upper temperature and where, irrespective of the measured upper temperature, the controller refrains from activating the devices and/or operates the devices at a reduced power relative to the normal operating state if the lower temperature of the cooling liquid lies below a lower threshold value during operation of the transformer to achieve improved characteristics of the cooling system during operation under low environmental temperatures of the transformer, particularly in the case of a turn-on operation following lengthy storage in a cold state.

Abstract: A winding arrangement for a transformer or for a reactor is provided. The winding arrangement includes an annular winding cover part disposed on the front face of a winding, wherein a side surface of the winding cover part overlaps a front surface of the winding, wherein the annular winding cover part is designed to be magnetically conductive at least in a partial area and comprises a convex side surface facing away from the winding.