RU43109U1 - PULSE OVERVOLTAGE PROTECTION DEVICE - Google Patents

Abstract

The utility model relates to the field of electric power and electrical engineering and can be used to protect consumers of direct current electricity from surge surges that occur in the mains when switching its loads in operational and emergency conditions and from atmospheric surges. A device is proposed that protects consumers of electric power of direct and alternating current from switching and atmospheric overvoltages. In the surge protection device, consisting of a varistor and a surge arrester connected in parallel, a second varistor is added, connected in series with the surge arrester.

Description

The utility model relates to the field of electric power and electrical engineering and can be used to protect consumers of electric power of direct and alternating currents from surge surges that occur in the mains when switching its loads in operational and emergency conditions and from atmospheric surges.

A device for surge protection [Schwab A. Electromagnetic compatibility. - M .: Energoatomizdat, 1995, pp. 165, Fig. 4.18], which provides the limitation of impulse overvoltage due to the use of a varistor which is always switched on under the mains voltage. The principle of operation of the device is to limit the overvoltage pulse when it exceeds the value of the residual voltage of the varistor, determined from the current-voltage characteristics of the varistor.

The disadvantage of this device is that the voltage limitation during the entire exposure time of the pulse occurs at a practically constant level that exceeds the maximum continuous voltage at the installation site of the device by at least 1.8 times, which is explained by the properties of modern varistors. That is, the protected load during the entire time of exposure to the pulse is under the indicated excess voltage.

A device for protection against surge voltage [Technique of high voltage. Under the total. ed. D.V. Razeviga - M .: Energia, 1976, p. 293, Fig. 16.7], consisting of a series-connected spark gap and a varistor having a non-linear current-voltage characteristic. This device operates as follows. When exposed to an overvoltage pulse, a spark gap breaks through and connects

a varistor limiting the overvoltage pulse in accordance with its current-voltage characteristic.

The disadvantage of this device is the dependence of the breakdown voltage of the spark gap on the slew rate of the applied overvoltage pulse. With a high slew rate of the overvoltage pulse, this leads to the fact that the voltage before the spark gap is triggered can take unacceptably high values for the protected load.

Closest to the claimed utility model (prototype) [Schwab A. Electromagnetic compatibility. - M .: Energoatomizdat, 1995, p. 183, fig. 4.24] is a surge protection device consisting of a varistor and a spark gap connected in parallel. When an overvoltage pulse appears at the input of the device, the varistor, which has a higher speed than the arrester, starts working first. Under the influence of the residual voltage of the varistor, after a statistical delay time, a spark gap breaks through, limiting the overvoltage pulse to the value of the arc burning voltage in the spark gap (20-30 V).

The disadvantage of this device is the inability to use it in low-resistance circuits (especially in DC circuits), due to the high accompanying current through the arrester, which thermally destroys it. The operation of the arrester leads to a significant decrease in the voltage at the protected load, which may be unacceptable for the protected load.

The objective of the utility model is to protect consumers of electricity from surge surges. The technical result of the utility model is the ability of the device to independently suppress the accompanying currents, the absence of voltage dips caused by the operation of the protection device and increased reliability.

The problem is solved using the proposed surge protection device, consisting of a parallel-connected varistor of the arrester, as well as a second varistor, connected in series with the arrester.

In FIG. A diagram of a surge protection device is shown, where it contains a varistor 1 (VI) connected in parallel to a second varistor 2 (V2) and a spark gap 3 (FV) connected in series.

In accordance with the proposed scheme, the device operates as follows. In the steady state operation mode (in the absence of overvoltage pulses), currents do not flow through the protective elements. This is because varistor 1 is selected from the condition that it can operate for a long time at an operating voltage, and the second varistor 2 is separated from the network by a surge arrester 3. The limiting voltage of the second varistor 2 is selected below the limiting voltage of varistor 1. The second varistor 2 can have a maximum long-term allowable voltage less than the mains voltage, since in normal mode almost all the operating voltage of the network is applied to the arrester 3. Varistor 1 is connected to the supply voltage, so the voltage at the output of the device p Avo network voltage.

When exposed to an overvoltage pulse, the device will work as follows. The first overvoltage pulse will limit the varistor 1. The restriction will be made at a level of approximately equal to 1.8 of the maximum continuous mains voltage at the installation site of the device. Then, under the influence of the residual voltage of varistor 1, after a statistical delay time, a spark gap 3 breaks through and the voltage decreases to approximately the voltage level of the limitation of the second varistor 2, which, with the appropriate choice of the long-term allowable voltage of the second varistor 2, can have a value close to the mains voltage. Since varistor 1 only works during the statistical delay time of the arrester 3, and the second varistor 2

If it absorbs the main part of the pulse energy, then the energy intensity of varistor 1 can be chosen much lower than the energy intensity of the second varistor 2.

After the termination of the overvoltage pulse, the current flowing through the second varistor 2 will be several milliamps. Arrester 3 is able to repay this current on its own. The device goes into the steady state described above.

The proposed utility model has the following set of advantages that none of the known technical solutions has:

- the ability to suppress the accompanying currents, which allows its use in low-resistance circuits of constant and alternating currents;

- the exception of the possibility of damage to the arresters due to accompanying currents, which increases the reliability of the device;

- the absence of voltage dips caused by the operation of the protection device;

- the restriction level only at the first instant of protection operation is approximately 1.8 of the maximum long-term voltage of the network at the installation site of the protection device, and then after a few microseconds it decreases to a voltage close to the network voltage;

- the absence of dependence of the voltage limiting the protection device from the slew rate of the overvoltage pulse.

Claims (1)

A surge protection device consisting of a varistor and a surge arrester connected in parallel, characterized in that a second varistor, connected in series with the arrester, is additionally introduced into it.