Abstract: A protection system for a transformer system that includes three single phase transformers with auxiliary secondary windings, respectively. The auxiliary secondary windings are connected to form an open delta configuration. The protection system is connected into the open delta configuration, between the auxiliary secondary windings of two of the transformers. The protection system includes a circuit having an element with a threshold voltage and current characteristic connected in series with a thermal protection device and a resistor.

Abstract: The subject of the invention is an indicator of presence of AC voltage in medium or high voltage conductors and/or conducting elements of transmission and distribution systems, whose basic AC voltage detecting and indicating element is a liquid crystal display (1). The indicator according to the invention is characterized in that its housing (8) has the shape of a frame closed by a transparent plate (9) on the front and by a conducting element (10) on the back. At least one row of circumferential ribs (11) is positioned around the frame window. The liquid crystal display (1) is placed hermetically between the transparent plate (9) of the frame window and the conducting element (10) and it has electrodes in the form of conducting segments.

Abstract: The subject of the invention is a protecting system for medium-voltage potential transformers, finding application in the attenuation of ferroresonant states occurring in at least one of three potential transformers in a three-phase medium-voltage network. The system according to the invention features an element with a threshold voltage and current characteristic (1) and a thermal fuse (2), which are connected in series between an attenuating resistor (R1) and the output of the auxiliary secondary winding of one of the single-phase transformers.