RU2478216C1 - Device for determining vacuum circuit breaker characteristics - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device includes a charger, a capacitor battery, an auxiliary and tested circuit breaker, a discharge circuit, an instrument shunt and a voltage divider. Charger is connected in series to capacitor battery. Discharge circuit is double-frequency and consists of two inductance coils and one capacitor. One of the inductance coils is connected in series to other parallel connected inductance coil and capacitor, the common wire of which is grounded. Auxiliary and tested circuit breakers are connected in series between capacitor battery and discharge circuit. Capacitor battery is connected to grounding through the instrument shunt; voltage divider is connected to the discharge circuit input. Primary natural frequency of the current flowing in the circuit exceeds by an order the industrial frequency after auxiliary circuit breaker is switched on. After the tested circuit breaker is switched off, low-frequency oscillations in discharge circuit are 2…5 kHz.

EFFECT: reduction of overall dimensions, enlarging functional capabilities, reduction of requirements for operation synchronisation of circuit breakers, and increasing probable occurrence of repeated ignitions.

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Description

The invention relates to electrical engineering and can be used to determine the slew rate (K) and decrease (K _sn ) of the electrical strength of vacuum circuit breakers (BB), which determine the likelihood of re-ignition (PZ) in the contact gap of the circuit breaker and dangerous overvoltage during shutdown and inclusion of inductive load - transformers and rotating electrical machines.

A device for determining the characteristics of explosives [Y. Matsui, T. Yokoyama, E. Umeya. Reignition current interruption characteristics of the vacuum interrupter. - IEEE Transactions on Power Delivery, Vol.3, No.4, October 1988], consisting of capacitor banks for charge storage, a discharge circuit including three inductors and one capacitance, a measuring shunt, a voltage divider, a test and test switch, a charger . The initiation of re-ignitions in the device occurs when the tested circuit breaker switches off the current of 50 or 100 Hz flowing from the storage capacitor through the discharge circuit, and at the time of re-ignition, a high-frequency current is generated that flows through the switch due to the presence of a high-frequency oscillating circuit in the discharge circuit.

The disadvantages of this technical solution are the large dimensions of the installation, the significant capacitance of the used capacitor bank for storing electrical energy, the difficulty of synchronizing the start of tripping of the tested circuit breaker after turning on the auxiliary circuit breaker due to the low oscillation frequency of the main frequency, and the inability to determine the reduction rate (K _sn ) of the electric the durability of the contact gap of the test explosive when the load is turned on, high requirements for the accuracy of the device control and synchronization of switches, low probability of occurrence of repeated ignitions.

A device for determining the characteristics of explosives is also known [Roguski A.T. Experimental investigation of the dielectric recovery strength between the separating contacts of vacuum circuit breakers. - IEEE Transactions on Power Delivery, Vol. 4, No. 2, April 1989], consisting of a charger, an energy storage device (capacitor bank), a test switch, a switch control circuit, voltage dividers, a measuring shunt. In this device for determining the characteristics of an explosive, the speed of restoration of the electric strength of an explosive is measured by measuring the voltage and time of repeated ignitions that occur when the explosive is disconnected from the capacitor bank.

The disadvantages of this device are the high requirements for the operation of the control and synchronization devices of the circuit breaker, the large installation dimensions due to the large capacitance of capacitor banks, the low probability of the occurrence of a short circuit, the absence of high-frequency free oscillations in the circuit breaker current that are typical for many power supply circuits when the load is connected via power cable / overhead line, the inability to measure the speed of reduction of the electric strength of the switch when the load is turned on and.

The closest technical solution is a device for determining the characteristics of explosives [Y.H.Fu, R.P.P.Smeets. An experimental investigation on high-frequency vacuum arc interruption at small gap length. - IEEE Transactions on Plasma Science, Vol.19, No. 5, October 1991] (prototype), consisting of a capacitor bank of a large capacity, an auxiliary switch connected between the capacitor bank and the two-frequency discharge circuit, a test switch included in the high-frequency generation circuit of the two-frequency discharge circuit, a measuring shunt. The prototype allows measuring the speed of restoration of the electric strength of a vacuum circuit breaker and the maximum rate of change of the breaking current di / dt when the explosive is turned off.

The disadvantages of this device are the large dimensions of the device due to the use of a capacitor bank of large capacitance for the formation of the main frequency of free oscillations f ₀ = 50 Hz, high requirements for the accuracy of synchronization of the auxiliary and test switches, insufficiently wide functionality, namely the lack of the ability to determine the reduction rate (K _sn ) electric strength of the test explosive when it is turned on due to the peculiarities of connecting the test switch, the low probability of occurrence of reignition due to the fundamental frequency of free oscillations of the current equal to f ₀ = 50 Hz. To initiate repeated ignitions in a vacuum arcing chamber, the time interval between the moment of opening of the contacts until the moment of primary current interruption (t ₀ ) should be minimal (tenths of a millisecond). Estimation of the maximum time t ₀ (without taking into account the fact that the re-ignition of the intercontact gap occurs not at the maximum of the oscillations of the intercontact voltage, but somewhat earlier [V. Kachesov. Estimation of the probability of escalation of overvoltages when disconnecting inhibited electric motors. - Electrical Engineering, No. 4, 2006] ) is performed by the expression:

t _{0, max} = 2U ^* ₀ / KT _LF / 2,

where U ^* ₀ is the voltage on the capacitor bank at the time of the initial current interruption,

T _LF - period of free low-frequency oscillations after opening the contacts of the tested circuit breaker.

For the proposed range, K = 20 ... 60 kV / ms, U ^* ₀ = 10 kV and T _LF = 0.2 ... 0.5 μs (f _LF = 2 ... 5 kHz) t ₀ , _max = 0.75 ms. Therefore, the duration of the current flow in the test switch (after turning on the auxiliary switch) should be in the range

t _leak = n · T ₀ /2-t ₀ , _max ... n · T _0/2 ,

where T ₀ = 1 / f ₀ ,

n is the number of half-periods of oscillations T _0/2 .

In connection with the frequency of 50 Hz (T ₀ = 20 ms) noted when turning off the current, a complex control system is required with high requirements for the accuracy of the delay between the operation of the test and auxiliary switches. Due to the technical complexity of creating control devices and precise synchronization by circuit breakers having dispersions of their own on / off times, the probability of repeated ignitions ( _Pz ) when the explosive is turned off is low. Her score is

The objective of the invention is to reduce the dimensions of the device for determining the characteristics of explosives, increase the likelihood of repeated ignitions during operation of the installation, reduce the accuracy requirements for synchronizing the operation of auxiliary and test switches, expand the functionality of the installation to determine the characteristics of vacuum circuit breakers, namely, provide a measure of the rate of decrease in electric strength.

The objective of the invention is achieved in that in the proposed device comprising a charger, a capacitor bank, auxiliary and test switch, a discharge circuit, a measuring shunt, a voltage divider, the charger being connected in series with the capacitor bank, the auxiliary and test switches are connected in series between the capacitor bank and a discharge circuit, the capacitor bank is grounded through a measuring shunt, a voltage divider is connected at the input of the discharge circuit, moreover, the discharge circuit is made of two-frequency, consisting of two inductors and one capacitor, the main frequency of free oscillations in which after turning on the auxiliary switch is an order of magnitude higher than the industrial frequency, and after the test switch is turned off, the low-frequency oscillations in the discharge circuit are 2 ... 5 kHz, control devices for the test and auxiliary switch connected to the synchronization unit.

Figure 1 shows the electrical circuit of the proposed device; figure 2 - voltage at the contact of the tested switch when it is turned on; figure 3 - voltage at the contact of the tested circuit breaker when it is turned off; figure 4 - waveform of the current in the tested circuit breaker.

A device for determining the characteristics of vacuum circuit breakers (Fig. 1) consists of a charger 1, a discharge circuit 2, a capacitive energy storage 3 (capacitor bank C _BC ) having a low intrinsic inductance, a test switch 4 (V _and ) connected in series, and an auxiliary switch 5 (B ₁ ), control devices 6 and 7 (УУ ₁ and УУ _И ) by auxiliary switch 5 and test switch 4, synchronization unit 8 (BS), voltage divider 9 (DN) and measuring shunt 10 (R _Ш ), connected in series with b Tara capacitor 3 (C _BC).

The charger 1 (charger) includes a voltage source 11, an adjustable step-up transformer 12 (T), a rectifier 13 (D) that connects a step-up transformer 12 and a capacitor bank 3 (C _BC ) through a protective resistor 14.

The discharge circuit 2 includes elements L (15), C (16), L ₁ (17). The parameters of the parallel circuit 16-15 (CL) are calculated so that after opening the contacts of the test switch 4 (V _and ), the free voltage fluctuations at the output of the coil 15 (L) have a frequency f _LF = 2 ... 5 kHz. The inductance value of the 17 (L ₁ ) discharge circuit is determined from the condition for the existence of free high-frequency (HF) current oscillations with a frequency of - f _HF = (2π (L ₁ C) ⁰⁵ ) ^-1 = 100 ... 500 kHz after repeated ignitions in the contact gap of the tested circuit breaker 4 ( _VI ).

The value of the inductance 15 (L) is determined from the condition:

I _{max L} >> I ₀ ,

where I ₀ is the maximum value of the cutoff current of the test explosive.

The value of I ₀ can be taken equal to 5 A,

. Для обеспечения высокой вероятности повторных зажиганий емкость конденсаторной батареи 3 (С_БК) определяют из условия формирования основной частоты свободных колебаний, возникающих после включения вспомогательного выключателя 5 (B₁), в 10 раз превышающей промышленную С_БК=1/((50·10)²·4π²L). При этом одновременно обеспечивается условие для поддержания многократных зажиганий в межконтактном промежутке выключателя благодаря условию С_БК>>С.

. To ensure a high probability of repeated ignitions, the capacitance of the capacitor bank 3 (C _BK ) is determined from the conditions for the formation of the main frequency of free oscillations that occur after the auxiliary switch 5 (B ₁ ) is turned on, 10 times higher than the industrial C _BK = 1 / ((50 · 10) ² 4π ² L). At the same time, a condition is provided for maintaining multiple ignitions in the contact gap of the circuit breaker due to condition C _BK >> C.

The device operates as follows. In the initial state in the determination of the law and the rate of reduction of dielectric strength By and maximum rate of change of the interrupted current di / dt of the vacuum switch contacts 4 _(VI) are in the closed state. When you turn on the voltage source 11, the capacitor bank 3 (C _BK ) is charged through the resistance 14 (R3) and the rectifier 13 (D) from the transformer 12 (T) to the test voltage U ₀ .

At receipt of the switching signal to perform synchronization unit 8 (BS) is formed of commands switching of the auxiliary switch 5 (B ₁₎ and switch off the test 4 _(VI) with a time delay t _zd. The delay time t _zd programmed in block sync 8 starting from the expression t = t _{zd vklV1} -t _otklVi + t _{has elapsed,} where t _vklV1 - ON time of the auxiliary switch 5 (B _1), t _otklVi - switch-off time of the test _(VI) , t _leaked is the required current flow time with frequency f ₀ along the discharge circuit. Commands from the synchronization unit 8 receives the control devices 6 and 7 (W ₁ and W _i) with the t _zd, then the auxiliary switch 5 is activated (B _1), a time t _{has elapsed} after the test switch 4 is switched off (in _and out). The tripping of the test switch 4 ( _VI ) is accompanied by the presence of numerous repeated ignitions, which makes it possible to determine the rate of restoration of electric strength and the maximum current cut-off speed di / dt.

In this case, the highest frequency of free oscillations of the current in the two-frequency circuit during repeated ignitions of the arc is 100 ... 500 kHz, the variation of which allows determining the maximum switch-off speed di / dt.

Using the main frequency of free vibrations f ₀ ≅500 Hz allows the use of a capacitor bank 3 (C _BK ) of small capacity and an inductance coil 15 (L) of small inductance, which leads to a significant reduction in the dimensions of the device for determining the characteristics of vacuum circuit breakers. Due to the reduction of the arc burning time from the moment of opening the contacts of the tested switch 4 (V _and ) to the initial interruption of the current (t ₀ ), which is limited by the half-period of the main free frequency (T _0/2 ), it is significant (in accordance with (1) - approximately 10 times) the probability of occurrence of repeated ignitions increases and the required time for obtaining the necessary measurement data is reduced.

The interruption by the test switch 4 of an increased frequency current (~ 500 Hz) does not change the mechanism for the occurrence of repeated ignitions (voltage escalation), since switch 4 (V _and ) is capable of breaking off currents of disproportionately higher frequencies (hundreds of kHz). Therefore, the measurement data obtained using the proposed device will correspond to the data obtained when turning off the current of industrial frequency.

When determining the law and the rate of decrease (K _SN ) of electric strength in the initial state, switch 5 (B ₁ ) is in the closed state, the capacitor bank 3 (C _BK ) is charged from charger 1 (charger) to the test voltage U ₀ . When a command is received to the control device 4, the switch 4 (B _and ) is turned on. The proximity of the contacts in the vacuum chamber leads to the breakdown of the intercontact gap and the formation in the circuit 3-15-16 (С _БК -L ₁ -С) of a high-frequency current oscillation, which breaks off when it passes a zero value. The charge remaining on the plates of the capacitor 15 (C) after the interruption of the high-frequency current in the oscillatory process flows through the inductance 15 (L), and reduces the voltage from one of the contacts of the switch, increasing the recovery voltage on the contracting gap, which, when the electric strength is reached, causes repeated breakdown and arc ignition. Thus, the inclusion of the switch 4 (B _and ) in the circuit shown in figure 1, is accompanied by numerous breakdowns, allowing to determine the law and the rate of decrease in electrical strength of the tested switch.

Figure 2 shows the waveform of the voltage on the coil 17 (L ₁ ). According to the voltage waveform, by approximating the stresses of the prebreakdowns, using, for example, the Lagrange method [Hamming R.Kh. Numerical methods. 2nd ed. - M: Nauka, 1972], the average rate of decrease in the electric strength of the contact gap is determined (in figure 2 - K _SN = 60 kV / ms).

Figure 3 shows the waveforms of the voltage (u) on the coil 17 (L ₁ ) and current (i) in the test switch (capacitor 3 (C _BC )). Performing the approximation of the re-ignition voltages from the measuring waveform, the average slew rate of the electric strength of the intercontact gap of the tested circuit breaker is determined (in figure 3, K = 45 kV / ms). According to the waveform of the current (Fig. 4), the rate of its change (di / dt) is determined before interruption. It was 100 A / μs.

Thus, the dimensions of the device for determining the characteristics of vacuum circuit breakers are reduced due to the use of a two-frequency oscillatory circuit, with an increased main frequency of oscillations and due to the use of a lower capacitance of the capacitor bank and inductance of the inductor, the functionality of the installation for determining the characteristics of vacuum circuit breakers is expanded, namely, measurement the rate of decrease in electric strength due to the sequential inclusion of the test switch I with the battery and capacitor discharge circuit, increased probability of re-ignition and reduced requirements for synchronizing the operation of auxiliary and test switches by the use of elevated free oscillations of the fundamental frequency f _0.

Claims (1)

A device for determining the characteristics of vacuum circuit breakers, comprising a charger, a capacitor bank, an auxiliary and test switch, a discharge circuit, a measuring shunt, a voltage divider, characterized in that the charger is connected in series with a capacitor bank, the discharge circuit is made of two-frequency, consisting of two inductance coils and one capacitor, and one of the inductors is connected in series with the second inductance connected in parallel to the second In particular, with a capacitor, the common wire of which is grounded, the auxiliary and test switches are connected in series between the capacitor bank and the discharge circuit, the capacitor bank is grounded through the measuring shunt, the voltage divider is connected to the input of the discharge circuit, the discharge circuit is double-frequency, the main frequency of free oscillations of the current flow in which after turning on the auxiliary switch, the order of magnitude exceeds the industrial frequency, which is formed by the capacitor bank and an inductor connected in parallel to the capacitor in the discharge circuit, and after the test switch is turned off, low-frequency oscillations in the discharge circuit are 2 ... 5 kHz, which are formed due to oscillations between the capacitor and inductance in the discharge circuit, connected in parallel to each other, the control device of the test and auxiliary switch connected to the synchronization unit.

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