SE437096B - DEVICE FOR REDUCING THE EARTH FLOW IN NON-DIRECT POWER - Google Patents

Abstract

1. A device for limiting earth leakage currents in a three-phase supply network with a compensator connected between a neutral point in the network and earth, said compensator generating in case of an earth fault a complementary current adjustable independently of amplitude and phase position for compensation of the reactive and active components of the earth leakage current, characterized in that the compensator consists of two controllable three-phase transformers fed on their primary sides by a separate three-phase current source.

Description

8401365-5 3. General information on compensation In power networks, both in the event of disturbance-free operation and in the event of a ground fault, all currents to ground add up to zero (Kirchhoff I).

Thus, the earth fault current in an uncompensated network constitutes the zero complement to the drain currents of the healthy phase conductors. The fact that a corresponding complement current can be generated at other, more suitable points in the power system is used to limit the earth fault current and thus the risk of damage in the fault location. The capacitive component of the earth fault current is compensated, for example, by means of an adjustable inductance at the zero point of the power system (Petersen coil). Normal variations in the divert currents, however, mean that there is usually a certain reactive residual current remaining.

In addition to this reactive residual current, there is also an active current in the fault point which the Petersen coil does not compensate for even with accurate tuning.

The present invention relates to a device for compensating both the reactive and the active component in the earth fault current. The device can then preferably be used for residual current compensation in parallel with an existing Petersen coil. Description of the patent-pending compensator The invention is described in more detail in connection with the accompanying drawings, in which: Figure 1 shows the diagram for compensating for the earth-fault current exemplified in the event of an earth fault in the T-phase.

Figure 2 shows the associated pointer diagram.

Figure 3 shows an embodiment of a compensating device according to the invention.

In order to compensate for the current shown in Figure 1 in the fault location (I;), a compensator consisting of two controllable phase shifting transformers is arranged according to the invention in the zero point of the power system or its equivalent. DJ Figure 3 shows an exemplary embodiment of such a compensating device. The device has a three-phase design for obtaining three variable secondary voltages with a mutual phase shift of 120 degrees.

In the event of a ground fault, the control and monitoring equipment switches one of these secondary voltages between the zero point of the main system and the ground. The preset secondary voltage shall then generate the complementary current LK shown in Figure 1 and Figure 2, respectively, which satisfies the tuning condition (IF: 0): if - lCD + Ina is the sum of the two fault-free phase conductors' discharge currents in the event of an earth fault. lg is the possible Petersenspolen power contribution.

As a phase shifting transformer, it is advantageous to use an ordinary slip ring asynchronous motor where the rotor can be fixed in any adjustable position. The phase shift between primary and secondary voltage is determined by the relative position of the rotor in the stator.

By secondary-side parallel or series connection of two such three-phase transformers, three secondary voltages can then be generated where, in addition to the phase position, the amplitude can also be changed steplessly. However, the mutual phase shift of the three voltages then remains constant.

In this context, it is irrelevant whether the winding of the stator or rotor constitutes the primary and secondary side of the transformer, respectively.

The primary side is connected to a power supply with the same frequency as the main system. The connection of the compensation device to a high-voltage system can take place as shown in figure 3 via an auxiliary transformer at the zero point, a separate zero point generator or the Petersen coil's secondary winding.

Literature references (1) Petersen, Waldemar: The limitation of the earth-end current and the suppression of the earth-end arc during the earth-end coil.

ETZ Heft 1 s.5 ff 1919. (2) Willheim, Raoul: Das Erdsohlussproblem in Hoch- spannungsnetzen s.1Ä8 ff Springer Verlag 1936.

Claims (1)

1. 5401365-5 PATENT CLAIMS Device for reducing the earth fault current in non-earthed power networks is characterized by two earth fault faults to the zero point of the power network or its equivalently connected, controllable phase shifting transformers which by means of a separate power supply generate it for compensating active component required complement current between the zero point of the power grid and earth.