RU2337449C1 - Device for equipment overvoltage protection - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device contains current-limiting elements 1-5, every of which is serially connected into one of wires 6-10 of protected equipment 11 lines, overvoltage limiters 12-16, every of which is connected with its inlet to one of wires 6-10 of protected equipment 11 lines. Overvoltage limiters 12-16 are connected between each other with their outlets as star, the common point of which is connected to grounding lead 17, through condenser 18, capacity of which is selected under the following condition: time constant Tcharge of condenser 18 charge circuit through current-limiting elements 1-5 should exceed minimum duration of overvoltage and current induced by lightning discharge and other sources. Additional overvoltage limiter 19 is connected parallel to condenser 18 (for instance, discharger), actuation voltage of which is selected as exceeding voltage of measuring instrument (not pictured), which is used for measurement of insulation resistance or instrument of short circuit monitoring Uovervoltage limiter>Umeasuring instrument, and actuation voltage of other overvoltage limiters 12-16 is selected as lower than the voltage of mentioned measuring instrument Uovervoltage limiter>Umeasuring instrument.

EFFECT: increase of reliability, durability and expansion of technological resources of device.

5 cl, 5 dwg

Description

The invention relates to the field of electrical engineering, mainly to protection schemes for low-current, for example, telecommunication equipment against excessive voltage on communication lines that respond to voltage above normal, without disconnecting the protected equipment from communication lines.

A device is known for protecting against lightning impulses of overvoltages of a two-wire communication line, comprising a spark gap included in each of the wires, which is connected to each of the input terminals and the ground loop, isolation electrical resistances made in the form of reactors connected in series in each of the wires, two-sided semiconductor voltage limiters connected between the output terminals and the ground loop (RU No. 2050663, 1995).

Its disadvantage is limited functionality, as it is intended only for two-wire communication lines.

A device for protecting equipment from overvoltages is known, containing a group of current-limiting elements, each of which is connected in series to one of the wires of the lines of the protected equipment, a group of surge suppressors, each of which is connected by an input to one of the wires of the lines of the protected equipment, and the outputs of the surge suppressors are interconnected by a star , the common point of which is connected to the ground terminal (RU No. 2190916, 2002, prototype).

The disadvantages of the prototype are as follows.

In the known scheme, each operation of surge arresters such as a gas spark gap in the line-to-ground circuit leads to a short-circuit of the line to ground. For a number of circuits of protected equipment, the short-circuit mode is emergency and it is desirable to reduce the frequency of occurrence of such modes. If overvoltages are caused by relatively long currents, for example, 10/350 μs in duration with a direct lightning discharge, then the protection implemented in the prototype by creating a closed circuit from the line directly to the ground is justified, because such a current must be taken to the ground along a circuit with low resistance. However, in practice, short-term overvoltages and currents occur much more often than long-term ones. Short-term overvoltages are caused by relatively short currents, for example, a duration of 8/20 μs when exposed to induced overvoltages of relatively short duration and amplitude, for example, from a lightning discharge. Accordingly, short-circuit conditions often occur, which degrades the operational characteristics of the protection device and reduces its reliability and durability.

In addition, during the operation of cable lines and equipment to be protected, there is a need for periodic (or constant) measurement of insulation resistance with measuring instruments with a high value of the measuring voltage (for example, using a megger with a measuring voltage of 500 V). A number of circuits use devices for continuous monitoring of the absence of a line short to ground by applying a measurement voltage to the line-to-ground circuit. In order for the circuits with surge suppressors not to influence the measurement and control results, the operating voltage of surge suppressors Uopn in the line-to-ground circuit must exceed the measuring voltage of the insulation tester or the insulation tester Uip, i.e. the condition Uopn> Uip must be satisfied. In this case, the protective device made according to the prototype effectively limits overvoltages only if their level exceeds Uip, and therefore does not provide low-level protection, i.e. has limited functionality.

An object of the invention is to provide an effective surge protection device and expanding the arsenal of surge protection devices.

The technical result that provides a solution to the problem consists in increasing reliability and durability by eliminating the short-circuit condition for short-term overvoltages and currents, as well as in expanding the functionality by expanding the range of limiting overvoltages to lower their levels and making the device circuit non-critical to Uip .

The essence of the invention lies in the fact that the device for protecting equipment from overvoltages contains a group of current-limiting elements, each of which is connected in series to one of the wires of the lines of the protected equipment, a group of surge arresters, each of which is connected by an input to one of the wires of the lines of the protected equipment, and the outputs are limiters the overvoltages are interconnected by a star, the common point of which is connected to the ground terminal, while the common point of the star is connected to the ground terminal of the capacitor, the capacitance of which is chosen from the condition: the time constant of the capacitor charging circuit through the current-limiting elements must be greater than the minimum duration overvoltages.

Preferably, an additional surge suppressor is connected in parallel with the capacitor, wherein the operating voltage of the additional surge suppressor is selected to be higher than the voltage of the measuring device used to measure the insulation resistance or the short-circuit monitoring device, and the operating voltage of the remaining surge suppressors is selected to be lower than the voltage of the specified measuring instrument.

In special cases of implementation, the device contains current-limiting elements from the composition: a resistor, an inductor, their combination, surge suppressors from the composition: arresters, varistors, a combination of arresters and varistors, semiconductor surge suppressors, and an additional surge suppressor is made in the form of a surge arrester.

Figure 1 shows a schematic diagram of a device for limiting overvoltage using surge arresters as surge suppressors, in Fig.2 - with varistor surge suppressors, in Fig.3 - with combined surge suppressors: varistors and surge arresters connected in series with them, in Fig. 4 - with current-limiting elements in the form of an inductor, Fig. 5 - with current-limiting elements in the form of an inductor with a series-connected resistor.

The surge protection device in this example contains five current-limiting elements 1, 2, 3, 4, 5, each of which is connected in series to one of the wires 6, 7, 8, 9, 10 of the protected equipment lines 11, limiters 12, 13, 14, 15, 16 overvoltages, each of which is connected by an input to one of the wires of 6-10 lines of the protected equipment (device) 11. The outputs of the limiters 12-16 overvoltages are interconnected by a star, the common point of which is connected to the ground terminal 17, characterized in what is the common point of a star related to in grounding output 17 through a capacitor 18, the capacitance of which is selected from the condition: the time constant Tzar of the charge circuit of the capacitor 18 through current-limiting elements 1-5 should be longer than the minimum duration of overvoltages and currents induced by a lightning discharge and other sources. For most sources of short-term overvoltage, sufficient for the realization of the latter requirement is, for example, the condition Tzar> 100 μs.

In parallel with the capacitor 18, an additional overvoltage limiter 19 is connected (for example, a surge arrester), and the operating voltage of the additional overvoltage limiter 19 is selected to be higher than the voltage of the measuring device (not shown) used to measure the insulation resistance or the monitoring device for the presence of a short circuit Uop> Uip, and the operation voltage of the remaining limiters 12-16 overvoltage is selected lower than the voltage of the specified measuring device Uopn <Uip.

As current limiting elements 1-5, resistors, inductors, and combinations thereof can be used.

As surge suppressors, arresters, varistors, a combination of surge arresters and varistors, semiconductor surge suppressors can be used.

On the input line of the device, input terminals 20, 21, 22, 23, 24 are connected to current-limiting elements 1-5. The output terminals (not indicated) are connected to the equipment 11.

A device for surge protection works as follows.

The device using as limiters 12-16 overvoltage arresters, as shown in figure 1, works as follows.

When a short-duration overvoltage pulse is supplied via a wire from the communication line or the power supply cable at the input of the protection device via any of the wires 6-10 to the input terminals 20-24, one or more surge suppressors (for example, 12), the operating voltage of which is selected from the condition Uopn <Uyp (for example, Uopn is equal to 90 V, and the megohmmeter measuring voltage Uyp is chosen equal to 500 V). The pulse current from the overvoltage source flows from the line through the input terminal 20, through the current-limiting element 1, the voltage limiter 12, the capacitor 18 to the ground. If the pulse is short (for example, a pulse with a voltage of 4000 V and a duration of 1/50 μs from a test generator with an internal impedance of 2 Ω) and the condition Tzar> 100 μs is selected (for example, the current-limiting element 1 is made in the form of resistors with a resistance of 1 Ω, and the capacitor capacitance is 18 equal to 100 μF), then the voltage across the capacitor 18 will be significantly less than in the line (in our example, the voltage from 4000 V will decrease to approximately 300 V). If gas arresters are chosen as voltage limiters 12-16, then the voltage at the output terminals 1-5 and, accordingly, at the protected equipment 11 (with respect to the ground) will be approximately equal to the voltage at the capacitor 18, i.e. will be limited to 300 V. If the measuring voltage of the device - megohmmeter Uyp is chosen equal to 500 V, and the voltage of the surge suppressor 19 (surge arrester) is 600 V, then by the condition Uopn> U, the operation of the surge suppressor 19 will not occur, i.e. Short circuit to ground will not occur. With the parameters of the circuit elements described in the example, the protection device will operate when the amplitude of the voltage pulses is more than 90 V, but at the same time, the state of its insulation can be checked with a voltage of 500 V.

Only at voltages close to 10 kV, which corresponds to the limit values of the amplitude of the induced lightning overvoltages according to GOST 13109-97 for a low-voltage power supply network, the voltage across the capacitor 18 reaches 600 V and the spark gap 19 can trip. Thus, the optimal choice of circuit protection device parameters can eliminate the operation of the surge suppressor 19 with a line to ground fault for most types of overvoltage with the most common parameters, but at the same time provide a sufficiently low level of surge suppression at the input of the protected device 11.

When a surge voltage pulse is received from the communication line or the power supply cable at the input of the protection device via any wire to the input terminals 20-24, one or more surge arresters 12-16 (for example, 12), the operating voltage of which is selected from the condition Uopn <Uyp (for example, Uopn is 90 V, and the megohmmeter measuring voltage Uyp is chosen to be 500 V). The pulse current from the overvoltage source flows from the line through the input terminal 20, through the current-limiting element 1, the voltage limiter 12, the capacitor 18 to the ground. If the pulse is long (for example, a current pulse of 20 kA and a duration of 10/350 μs from a test generator simulating a direct lightning discharge), the voltage across the capacitor 18 will increase and in our example will exceed 600 V, after which the overvoltage limiter 19 will operate and the wires 6 will be closed -10 to the ground. If gas arresters are selected as surge arresters 12-16, then the voltage at the output terminals 20-24 and, accordingly, the protected equipment 11 (with respect to the ground) will be approximately equal to the voltage drop across the arresters 12-16 in their on state.

When checking the insulation resistance, the megohm meter is connected between one of the input terminals 20-24 or the output terminals 20-24 and ground. Voltage limiters 12-16, if they are selected with a limiting voltage (for example, 90 V), lower than the megohmmeter measuring voltage (for example, 500 V), operate, and the voltage limiter 19 does not work. Under such conditions, the megohmmeter will objectively measure the insulation resistance of the device with respect to the ground.

A device with varistor (VR) surge arresters 12-16, as shown in figure 2, operates as follows.

When a short-duration overvoltage pulse arrives at the input of the protection device from the communication line or cable at the input of the protection device 20-24 through any of the wires 6-10, one or more varistor surge arresters 12-16 are triggered, for example, the operating voltage of which is selected from the condition Uopn <Uip (for example, Uopn is 90 V, and the measuring voltage of the megger Uip is chosen to be 500 V). The pulse current from the overvoltage source flows through the input terminal 20, through the current-limiting element 1, the overvoltage limiter 12, the capacitor 18 to the ground. If the pulse is short (for example, a pulse with a voltage of 4000 V and a duration of 1/50 μs from a test generator with an internal impedance of 2 Ohms) and the condition Tzar> 100 μs is selected (for example, current-limiting elements 1-5 are made in the form of resistors with a resistance of 1 Ohm, and the capacitance capacitor 18 is equal to 100 μF), then the voltage across capacitor 18 will be significantly less than in the line (in our example, the voltage from 4000 V will decrease to approximately 275 V). If varistors are chosen as voltage limiters 12-16, then the voltage at the output terminals and, accordingly, on the protected device (with respect to the ground) will be equal to the voltage across the capacitor 18 plus the voltage drop across the varistor, and in our example it will be limited to approximately 475 V. If the megohmmeter measuring voltage Uyp is chosen equal to 500 V, and the operating voltage of the surge suppressor 19 (arrester) is 600 V, then by the condition Uopn> U, the operation of the surge suppressor 19 will not occur, i.e. Short circuit to ground will not occur. With the parameters of the circuit elements described in the example, the protection device will operate when the amplitude of the voltage pulses is more than 90 V, but at the same time, the state of its insulation can be checked with a voltage of 500 V.

Only at voltages close to 10 kV, which corresponds to the limit values of the amplitude of the induced lightning overvoltages according to GOST 13109-97 for a low-voltage power supply network, the voltage across the capacitor 18 reaches 600 V and the spark gap 19 can trip. Thus, the optimal choice of circuit protection device parameters can eliminate the operation of the surge suppressor 19 with a line to ground fault for most types of overvoltage with the most common parameters, but at the same time provide a sufficiently low level of surge suppression at the input of the protected device.

When a surge voltage pulse is received from the communication line or the power supply cable at the input of the protection device to the input terminals 20-24 and via any of the wires 6-10, one or more varistor surge arresters 12-16 (for example, 12), the operating voltage which are selected from the condition Uopn <Uip (for example, Uopn is 90 V, and the measuring voltage of the megger Uip is chosen to be 500 V). The pulse current from the overvoltage source flows through the input terminal 20 through a current-limiting element 1, a voltage limiter 12, a capacitor 18 to ground. If the pulse is long (for example, a current pulse of 20 kA and a duration of 10/350 μs from a test generator simulating a direct lightning discharge), the voltage across the capacitor 18 will increase and in this example will exceed 600 V in about 30 μs, after which the overvoltage limiter 19 and close the wires 6-10 to the ground. If varistors are chosen as voltage limiters 12-16, then the voltage at the output terminals and, accordingly, on the protected device 11 (with respect to the ground) will be approximately equal to the voltage drop across the discharger 19 in its switched on state plus the voltage drop across the varistors 12-16.

When checking the insulation resistance, a megohm meter is connected between one of the input terminals 20-24 or the output terminals and ground. Voltage limiters 12-16, if they are selected with a limiting voltage (for example, 90 V) lower than the megohmmeter measuring voltage (for example, 500 V), are triggered, and the voltage limiter 19 does not work. Under such conditions, the megohmmeter will objectively measure the insulation resistance of the device with respect to the ground.

Similarly to the circuit shown in FIG. 2, a circuit can be implemented with the replacement of varistors by semiconductor surge arresters 12-16. The algorithm of its operation is similar to the algorithm described for the circuit with varistors.

A device with combined surge arresters 12-16 (varistors and series connected arrester), shown in figure 3, works as follows.

When a short-duration overvoltage pulse arrives via a wire from the communication line or the power supply cable at the input of the protection device via any of the wires to the input terminals 20-24, one or more combined surge arresters 12-16 (for example, 12), the total voltage of the varistor and the arrester selected from the condition Uopn <Uip (for example, Uopn in the sum is 90 V, and the measuring voltage of the megger Uip is chosen to be 500 V). The pulse current from the overvoltage source flows through the input terminal 20, through the current-limiting element 1, the voltage limiter 12, the capacitor 18 to the ground. If the pulse is short (for example, a pulse with a voltage of 4000 V and a duration of 1/50 μs from a test generator with an internal impedance of 2 Ω) and the condition Tzar> 100 μs is selected (for example, the current-limiting element 1 is made in the form of resistors with a resistance of 1 Ω, and the capacitor capacitance is 18 equal to 100 μF), then the voltage across the capacitor 18 will be significantly less than in line 1 (in our example, the voltage from 4000 V will decrease to approximately 275 V). For combined voltage limiters 12–16 at the varistors and arresters, the voltage at the output terminals and, respectively, at the protected device 11 (with respect to the ground) will be approximately equal to the voltage at the capacitor 18 plus the voltage drop across the varistor of the limiter 12, and in our example it will be limited to approximately 475 V. If the megohmmeter measuring voltage Uyp is chosen equal to 500 V, and the response voltage of the surge suppressor 19 (arrester) is 600 V, then by the condition Uopn> Uyp of the limiter 19 prot voltage does not occur, ie, Short circuit to ground will not occur. With the parameters of the circuit elements described in the example, the protection device will operate when the amplitude of the voltage pulses is more than 90 V, but at the same time, the state of its insulation can be checked with a voltage of 500 V.

Only at voltages close to 10 kV, which corresponds to the limit values of the amplitude of the induced lightning overvoltages according to GOST 13109-97 for a low-voltage power supply network, the voltage across the capacitor 18 reaches 600 V and the spark gap 19 can trip. Thus, the optimal choice of circuit protection device parameters can eliminate the operation of the surge suppressor 19 with a line to ground fault for most types of overvoltage with the most common parameters, but at the same time provide a sufficiently low level of surge suppression at the input of the protected device.

When a surge voltage pulse is received from the communication line or the power supply cable at the input of the protection device to the input terminals 20-24 and via any of the wires 6-10, one or more combined voltage limiters 12-16 (for example, 12), total the operating voltage of which is selected from the condition Uop <Uip (for example, Uopn is 90 V, and the measuring voltage of the megger Uip is chosen to be 500 V). The pulse current from the overvoltage source flows through the input terminal 20, through the current-limiting element 1, the overvoltage limiter 12, the capacitor 18 to the ground. If the pulse is long (for example, a current pulse of 20 kA and a duration of 10/350 μs from a test generator simulating a direct lightning discharge), the voltage across the capacitor 18 will increase and in our example will exceed 600 V in about 30 μs, after which the overvoltage limiter 19 and closes line 1 to the ground. For combined voltage limiters 12–16 at the varistors and arresters, the voltage at the output terminals and, respectively, at the protected device 11 (with respect to the ground) will be approximately equal to the voltage drop across the arrestor 19 when it is on, plus the total voltage drop across the varistors and arresters at the limiters 12– 16.

When checking the insulation resistance, a megohm meter is connected between one of the input terminals 20-24 or the output terminals and ground. Voltage limiters 12-16, if they are selected with a limiting voltage (for example, 90 V) less than the megohmmeter measuring voltage (for example, 500 V), they work, and the voltage limiter 19 does not work. Under such conditions, the megohmmeter will objectively measure the insulation resistance of the device with respect to the ground.

Similarly to that shown in the diagram of FIG. 3, a circuit can be implemented with the replacement of varistors by semiconductor surge arresters.

The operation of the device circuit using, as current-limiting elements, an inductor or inductor with a series-connected resistor (Figs. 4, 5) does not fundamentally differ from the work described for the circuits in Figs. 1-3.

Thus, an effective surge protection device was created and the arsenal of surge protection devices was expanded.

At the same time, reliability and durability are improved due to the exclusion of the short circuit mode for short-term overvoltages and currents, as well as expanded functionality by expanding the range of limiting overvoltages in the direction of lowering their levels and making the device circuit uncritical with respect to Uyp.

Claims (5)

1. A device for protecting equipment from overvoltages, containing a group of current-limiting elements, each of which is connected in series to one of the wires of the lines of the protected equipment, a group of surge suppressors, each of which is connected by an input to one of the wires of the lines of the protected equipment, with the outputs being connected to each other a star whose common point is connected to the ground terminal, characterized in that the common point of the star is connected to the ground terminal through a capacitor, capacitance is chosen from the condition: the time constant circuit of the capacitor charge through the current-limiting elements must be greater than the minimum duration overvoltages. 2. The device according to claim 1, characterized in that an additional surge suppressor is connected in parallel with the capacitor, moreover, the operating voltage of the additional surge suppressor is selected to be higher than the voltage of the measuring device used to measure insulation resistance or a short-circuit monitoring device, and the response voltage of the remaining surge suppressors is selected less voltage of the specified measuring device. 3. The device according to any one of claims 1 and 2, characterized in that it contains current-limiting elements from the composition: resistor, inductor, their combination. 4. The device according to any one of claims 1 and 2, characterized in that it contains surge suppressors from the composition: arresters, varistors, a combination of arresters and varistors, semiconductor surge suppressors. 5. The device according to any one of claims 1 and 2, characterized in that the additional surge suppressor is made in the form of a spark gap.

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