Abstract: The invention relates to a method for detection of a ground fault (18), which occurs in the vicinity of a neutral point (22), in a polyphase electrical device which is operated at a fundamental frequency, in particular an electrical machine (10) or a transformer which has a number of windings (11, 12, 13), which are associated with the individual phases, one end of each of which windings (11, 12, 13) is connected to the neutral point (22) and the other end of each of which windings (11, 12, 13) is connected directly to a power supply network via a power supply system connection (14, 15, 16). Simple and reliable detection is achieved in that the change in the physical variables which is associated with a ground fault (18) is measured in the immediate vicinity of the ground fault (18), and is evaluated.

Abstract: A generator for producing high voltages and having at least one generator winding (12) is connected via a generator circuit (10) to a network (19), which generator circuit has means (15, . . . , 17) for protection against overvoltages. Improved protection against higher voltages is achieved in that the at least one generator winding (12) is subdivided into a number of winding sections (12a-c) whose winding insulation is designed such that the insulation level is graduated, and in that the overvoltage protection means have a number of overvoltage protection elements (15, . . . , 17), which are associated with the respective individual winding sections (12a-c) and whose response levels are matched to the requirements of the associated winding section.

Abstract: In a plant containing a turbo-generator the magnetic circuit of the turbo-generator is included in an electric generator which directly supplies a high supply voltage of 20-800 kV, preferably higher than 36 kV. The insulation of the generator is built up of a cable (6) comprising one or more current-carrying conductors (31) with a number of strands (36) surrounded by outer and inner semiconducting layers (34, 32) and intermediate insulating layers (33). The outer semiconducting layer (34) is at earth potential. The phases of the winding are Y-connected. The Y-point may be insulated and protected from over-voltage by means of surge arresters, or else the Y-point may be earthed via a suppression filter.

Abstract: The magnetic circuit of a generator in a hydro-generator plant is arranged to directly supply a high supply voltage of 20-800 kV, preferably higher than 36 kV. The generator is provided with solid insulation and its winding includes a cable (6) comprising one or more current-carrying conductors (31) with a number of strands (36) surrounded by at least one outer and one inner semiconducting layer (34, 32) and intermediate insulating layers (33). The outer semiconducting layer (34) is at earth potential. The stator winding may be produced with full or fractional slot winding, the phases of the winding being Y-connected. The Y-point may be insulated and protected from over-voltage by means of surge arresters, or else the Y-point may be earthed via a suppression filter. The invention also relates to a hydro-generator plant, a generator included in the plant and a procedure for building such a plant.

Abstract: An electric high voltage AC machine intended to be directly connected to a distribution or transmission network (16) comprises at least one winding. This winding comprises at least one current-carrying conductor, a first layer having semiconducting properties provided around said conductor, a solid insulating layer provided around said first layer, and a second layer having semiconducting properties provided around said insulating layer. In addition grounding means (18, 24, 26, 28) are provided to connect at least one point of said winding to ground.

Abstract: The invention relates to a method for detection of a ground fault (18), which occurs in the vicinity of a neutral point (22), in a polyphase electrical device which is operated at a fundamental frequency, in particular an electrical machine (10) or a transformer which has a number of windings (11, 12, 13), which are associated with the individual phases, one end of each of which windings (11, 12, 13) is connected to the neutral point (22) and the other end of each of which windings (11, 12, 13) is connected directly to a power supply network via a power supply system connection (14, 15, 16). Simple and reliable detection is achieved in that the change in the physical variables which is associated with a ground fault (18) is measured in the immediate vicinity of the ground fault (18), and is evaluated.

Abstract: A generator for producing high voltages and having at least one generator winding (12) is connected via a generator circuit (10) to a network (19), which generator circuit has means (15, . . . , 17) for protection against overvoltages. Improved protection against higher voltages is achieved in that the at least one generator winding (12) is subdivided into a number of winding sections (12a-c) whose winding insulation is designed such that the insulation level is graduated, and in that the overvoltage protection means have a number of overvoltage protection elements (15, . . . , 17), which are associated with the respective individual winding sections (12a-c) and whose response levels are matched to the requirements of the associated winding section.