RU2304835C1 - Overvoltage protective gear - Google Patents

Abstract

FIELD: electrical engineering; power switching devices; overvoltage protection of electrical equipment.

SUBSTANCE: proposed overvoltage protective device has controllable discharge gap connected in series with working resistor. Controllable discharge gap is made in the form of controllable vacuum discharger. Working resistor is made in the form of parallel-connected nonlinear resistor R with U_pr < KU_m, where 1 < K < 1.8; K is ratio; U_pr is remaining limiting voltage; U_m is peak value of mains rated voltage. Line impedance Z incorporates resistive and reactive components and its value meets following inequality: U_ov/I_ov > Z > U_pr/I_max, where I_max is current through R at U = U_pr = U_pr; I_ov is current through R at which current-voltage characteristic transfers from conductance region to accompanying current region; U_ov is voltage across R at current I = I_ov.

EFFECT: enlarged operating voltage range, enhanced admissible pulse currents and electric strength recovery rate upon disconnection of accompanying current, enhanced reliability and service life.

1 cl, 2 dwg

Description

The invention relates to the field of electrical engineering, namely to power switching equipment, and is intended to protect electrical equipment from overvoltage.

To protect electrical equipment from lightning and switching overvoltages, devices are used that limit the level of overvoltage by shunting the protected equipment at dangerous voltage levels for the latter.

Known valve arresters containing series-connected spark gaps and operating resistance with a non-linear current-voltage characteristic [1]. The protective characteristics of such a spark gap are determined by the breakdown voltage of the spark gaps and the coefficient of nonlinearity of the working resistance.

The disadvantage of this device is the instability of the breakdown voltage and its change due to violation of the tightness of the spark gap, the complexity of the design and limited life with prolonged transmission of discharge current.

Known surge suppressor (arrester), containing resistance with a high degree of nonlinearity based on zinc oxide (ZnO) [2]. The arrester limits the amplitude of the overvoltage in the same way as a gate arrester, but due to a higher degree of nonlinearity it can be used without spark gaps. The surge arrester provides the limitation of switching overvoltages to the level of _Upr = 1.8 U _m and lightning overvoltages to the level of _Upr = 2.4 U _m , where U _protr is the remaining limiting voltage of the arrester, U _m is the amplitude of the rated mains voltage.

The disadvantage of this device is that it is not able to limit overvoltages significantly below twofold.

The closest technical solution to the proposed one is a device containing an air gap with a control electrode connected in series with the working resistance [3].

The disadvantages of this device are a narrow range of operating voltages, a significant voltage drop across the arrester in the open state, low breaking capacity and, as a result, a small resource and low reliability.

The technical result of the proposed solution is a significant expansion of the range of operating voltages, an increase in permissible pulse currents and the speed of restoration of electric strength after switching off the accompanying current, as well as an increase in reliability and service life.

The technical result is achieved by the fact that in a surge protection device containing a controlled discharge gap connected in series with a working resistance, a vacuum controlled spark gap is used as a controlled discharge gap, and the working resistance is made in the form of parallel connected non-linear resistance R and linear resistance Z containing active and reactive component, and nonlinear resistance is used with _Uash <KU _m ,

where 1 <K <1.8, _Upr is the remaining limiting voltage, U _m , is the amplitude of the nominal network voltage, and the value of the linear resistance must satisfy the inequality:

U _per / I _per >Z> U _prot / I _max ,

where I _max is the current through R at U = _Uash , I _per is the current value in R (reference current) at which its current-voltage characteristic passes from the conductivity region 2 (Fig. 2) to the region of the accompanying current 1, U _per is the voltage on R at current I = I _per .

The invention is illustrated in figure 1, which shows a schematic diagram of a device for limiting overvoltage. Figure 2 shows a typical current-voltage characteristic of a nonlinear element.

The device contains a vacuum spark gap 1 with a start block 2 and a working resistance 3 connected in series with the spark gap, which consists of a non-linear resistance R - 4 and a linear resistance Z - 5 connected in parallel. Such a device is connected in parallel to the protected object in each phase of the mains voltage.

The device operates as follows.

The vacuum arrester 1 is switched on using the start block 2, which, after supplying a control pulse, gives an ignition pulse to the control electrode with the specified voltage and current parameters.

Vacuum spark gap 1 is able to reliably turn on in a wide range of operating voltages (0.01-1) U _nom and for a long time to pass discharge current. After the arrester is switched on, a pulsed current flows through it, the value of which is limited by the operating resistance 3. When the current approaches zero, the arrester disables the current and the mains voltage is restored on it.

Non-linear resistance 4 serves to limit the level of overvoltage when the arrester is switched on. The protective level in the proposed circuit can be selected close to the rated voltage on the protected equipment, i.e. overvoltage ratio K <1.8. As a result, the energy dissipated in resistance 4 during the flow of the discharge current will be significantly less than in the circuit without a vacuum spark gap.

Parallel connection with non-linear resistance 4 of linear resistance 5 also allows to reduce the energy released in the non-linear resistance. The value of the linear resistance Z is selected based on the criterion of the optimal distribution of energy absorbed in the resistances R and Z from the ratio:

U _per / I _per >Z> U _prot / I _max ,

where I _max is the current through R at U = _Uash , I _per is the current value in R at which its current-voltage characteristic passes from the conductivity region 2 (Fig. 2) to the region of the accompanying current 1, U _per is the voltage across R at the current I = I _per = 1-20 mA.

If Z> U _per / I _per , in this case Z exceeds R in all real modes and the bulk of the energy is dissipated in R.

If Z <U _prot / I _max , then almost all the current flows through Z and R practically does not work.

The indicated ratio determines the range of linear resistance Z. The optimal value of R is selected from this range based on an engineering calculation. The objective of this calculation is to choose a linear resistance of such a magnitude that most of the energy is absorbed in it, and at the same time, that this resistance has acceptable overall and cost indicators.

Information sources

1. Chunikhin A.A., Zhavoronkov M.A. High voltage apparatuses. M .: Energoatomizdat, 1985, p. 395.

2. Series capacitors for power system. Part 2: Protective equipment for series capacitor banks. IEC 143-2: 1994, P.75.

3. Kurekhin VV Network protection from dangerous levels of switching overvoltages // Management of electromechanical objects in the mining industry. Kemerovo: Book. Publishing House, 1982, p. 27 (prototype).

Claims (1)

An overvoltage protection device comprising a controllable discharge gap connected in series with a working resistance, characterized in that a vacuum controlled discharger is used as a controlled discharge gap, and the working resistance is made in the form of parallel connected non-linear resistance R and linear resistance Z containing active and reactive component, and nonlinear resistance with _Upr / KU _m , where 1 <K <1.8, K is the overvoltage ratio, U _def is the remaining limiting voltage; U _m - the amplitude of the nominal voltage of the network, and the value of the linear resistance must satisfy the inequality U _per / I _per >Z> U _prot / I _prot , where I _max is the current through R at U = _Uash , I _per is the current value in R at which its current-voltage characteristic passes from the conduction region to the region of the accompanying current, U _per is the voltage across R at the current I = I _per .

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