SU817851A1 - Device for overvoltage protection of multiphase circuits - Google Patents

Description

(54) DEVICE FOR PROTECTION AGAINST OVERVOLTAGE OF MULTIPHASE CHAINS

one

The invention relates to electrical engineering, in particular, to overvoltage protection devices of high voltage circuits.

Valve gaps are known, made according to the four-beam star scheme, in each beam of which there is a non-linear resistor and a spark gap 1 connected in series with it.

The disadvantage of such a device is the relatively high level of interphase overvoltages limited by them, due to the presence of a spark gap in each ray of a star (at least 2lj, where is the linear voltage of the network).

It is also known an overvoltage protection device for multiphase AC circuits, containing highly linear resistors connected between each phase and ground, made in the form of two series-connected parts, the midpoints of which are interconnected through spark gaps connected according to the star 2 scheme.

The level of restriction of interphase overvoltages by such a device is lower than that of valve gaps included in the four-beam star scheme, and is approximately 1.8 Q,

However, the required further reduction of this level is imitated by the spread of the breakdown characteristics of the spark gaps, as well as by the random nature of the change in the potential of the star of the spark gaps. The purpose of the invention is to reduce the limiting level of inter-phase switching overvoltages.

The goal is achieved by the fact that the overvoltage protection device of multiphase AC circuits contains a highly linear resistors connected between each phase of the circuit and the ground, made in the form of two series-connected parts, the midpoints of which are interconnected through spark gaps connected according to the star circuit , an additional capacitor is inserted, connected between the star neutral of the aforementioned spark gaps and the ground.

Claims (2)

The drawing shows the proposed device. Between the phases of the protected three-phase AC circuit 1 and the ground: the high linear resistors are included, consisting of two series-connected parts — resistors 2 and. 3, Common points of resistors 2 and 3 of all phases are interconnected through spark gaps 4 connected by a star. The resistances of the spark gaps 4 at the frequency uJ of the switching overvoltages are equal to Z, and r4o "Neutral 5 stars of the spark gaps 4 are connected to ground through a capacitor 6, whose resistance at frequency c) is T, and Zj, Z |. The device works as follows. In the normal operating mode, due to the symmetry of the phase voltages of the protected circuit 1, the voltage of the neutral 5 is zero, the current through the capacitor 6 does not flow. Spark gaps 4 are not pierced, the series-connected resistors 2 and 3, forming a three-beam star, operate stably in the normal operating mode, since the current flowing through them is small. When a switching overvoltage asymmetrical in phases 1 occurs in the circuit 1, the values of K reach the common point of resistors 2 and 3, the spark gaps 4 form with the capacitor 6 a divider with arms Z and Z, the voltage gaps 4 affect the spark gaps 4 (Ze + Z ), and neutral 5 is voltage KZ, / (Z о + Z). The smaller Zo in comparison with Z ,, TeM is closer to zero the voltage on the neutral 5 and, consequently, the smaller the influence of various random factors on the volt-second characteristics of the spark gaps 4. When the voltage applied to the spark gaps 4 exceeds them breakdown voltage, they will break and switch the three-beam star into a four-beam star, ensuring efficiently. and limiting interphase overvoltages. In overvoltage limiting mode, the dynamic resistance of the resistor 3 -,. Therefore, the presence of capacitor 6 will not significantly reduce the voltage at the point where, after the breakdown of the gap 4, resistors 3 of all phases are combined, i.e. voltage at one end of a four-beam star connected to earth. As a consequence, the presence of a connection between the neutral 5 and the ground through the capacitor 6 does not reduce the effectiveness of limiting the interfacial overvoltages. The use of the invention allows, by stabilizing the breakdown voltage of the spark gaps, to reduce its upper limit and thereby improve the protective characteristics of the device in modes of limiting interphase overvoltages (to the extreme, approximately 1.6-9.7). The use of the proposed device makes it possible to reduce the interphase distance in substations and in high-voltage apparatuses. The claims of the device for protection against overvoltages of multiphase ac circuits, comprising high-reliant successively connected resistors connected between each phase and ground, the connection points of which are interconnected through spark gaps connected according to the star circuit, characterized in that limiting the interphase switching overvoltages, a capacitor is inserted in it that is connected between the star neutral of the aforementioned spark gaps and the ground. Sources of information taken into account during the examination 1. German patent number H80039, cl. 21 p 72, 1964. 2. USSR author's certificate number 603029, cl. H 01 T 5/00, 1978. RrRgRg RrRgRg