CN103532123A - Protective circuit for switching over-voltage protection of dry air reactor - Google Patents

Abstract

The invention discloses a protective circuit for switching over-voltage protection of a dry air reactor, relates to an over-voltage protective circuit for the dry air reactor, and solves the following problems in the traditional reactor over-voltage protection: the capacitance volume is large and the production cost is high when a resistance-capacitance absorption circuit is singly used, and dispersibility of gap breakdown voltage is increased and service life of protective gap is reduced due to frequent actions of the protective gap when a gap protector is singly used. The protective circuit can be satisfied through choosing proper element parameters according to cut-off current; when the cut-off current is lower, a resistance-capacitance absorption device controls over-voltage amplitude values at two ends of the reactor to prevent the over-voltage amplitude values from reaching the breakdown voltage of the protective gap, the protective gap is in a disconnection state, and the reactor and respective resistance-capacitance elements form an RLC (Radio Link Control) oscillation circuit; when the cut-off current is higher, the over-voltage amplitude values at two ends of the reactor are higher, the protective gap is broken down, and a capacitor and a protective resistor thereof are short out; the protective circuit for the switching over-voltage protection of the dry air reactor is applied to the reactor protection field.

Description

A protection circuit for dry-type air-core reactor switching overvoltage protection

technical field

The invention relates to an overvoltage protection circuit of a dry-type air-core reactor.

Background technique

In the ultra-high-voltage large-capacity power grid, in order to compensate the reactive power of the grid, a certain number of reactors are required to be installed. Dry-type air-core reactor adopts multi-package and winding structure. Compared with iron-core reactor, it has technical advantages such as low price, simple structure, light weight, linear reactance value, low loss, and convenient maintenance. Since the 1990s, dry-type air-core reactors have been widely used in power systems. With the increase in the number and time of operation of dry-type air-core reactors, accidents have gradually increased, and they often catch fire, which has greatly affected the safe operation of the power system. Field investigation and anatomical research show that most of the dry-type air-core reactor faults are caused by inter-turn short circuit caused by inter-turn insulation defects. A large number of data show that various overvoltages are the main reasons that cause the inter-turn insulation defects of reactors and eventually lead to short circuits. Reducing the overvoltage level on the dry-type air-core reactor can not only effectively slow down the deterioration of the inter-turn insulation, but also avoid the breakdown of the inter-turn insulation caused by high-amplitude overvoltage, which is very necessary to improve the safe operation level of the dry-type air-core reactor.

According to the basic knowledge of electrical engineering theory, the energy cannot change suddenly, that is, the current on the inductor cannot change suddenly. During the continuous and rapid change of the current, a certain voltage value will be generated at both ends of the inductor, satisfying e=Ldi/dt. During the closing process of the reactor, due to the mechanical characteristics of the circuit breaker, there will be a bouncing phenomenon (the contact of the circuit breaker is combined, bounced, and in the process of combining). During the process of the contacts being combined, the current in the reactor has increased to a certain value (a certain amount of magnetic field energy is stored in the reactor), and during the process of the contacts bouncing, the current will generate multiple re-ignitions at both ends of the contacts Overvoltage. In the same way, in the process of reactor cut-off, a large rated current flows through the reactor before the cut-off (storing a certain magnetic field energy), and in the process of opening the circuit breaker (the description of overvoltage generated by switching and cutting), the current A cut-off overvoltage will be generated at both ends of the reactor.

Commonly used overvoltage protection methods mainly include zinc oxide arresters, resistance-capacitance absorption circuits, and protection gaps. Gapless metal oxide surge arresters have inherent thermal stability problems. They will age due to repeated overvoltage, and eventually lose thermal stability and be damaged or explode under continuous operating voltage or overvoltage. In addition, the insulation level of the reactor that has been in operation for many years will be reduced, and its insulation level may be lower than the protection voltage of the arrester, which cannot achieve a satisfactory protection effect. In the field of dry-type air-core reactor protection, in order to achieve the protection effect, the resistance-capacitance absorption method often requires a large capacitor with a higher rated voltage, and its volume and cost limit its wide-scale promotion in the power grid. The high-energy arc generated by the gap protection device when the gap breaks down will cause defects on the electrode surface, and frequent actions will increase the dispersion of the gap breakdown voltage, which will eventually damage the gap (generally, the gap protection has no resistance, resulting in a short circuit of the bus); Most of the protective gap devices have no resistance, and the breakdown current is large during operation, which may easily lead to ablation of the electrodes; in addition, a current transformer is installed in the circuit, the gap breaks down, the current changes suddenly, and the transformer sends a signal to control The system relay protection action, resulting in power failure.

Contents of the invention

The present invention aims to solve the problem that in the traditional reactor overvoltage protection, when the resistance-capacitance absorption circuit is used alone, the required capacitor volume is large and the cost is high. When the gap protection device is used alone, the frequent action of the protection gap will increase the dispersion of the gap breakdown voltage To reduce the life of the protection gap, the invention provides a protection circuit for dry-type air-core reactor switching overvoltage protection.

A protection circuit for dry-type air-core reactor switching overvoltage protection, which includes a circuit breaker, a first reactor, a second reactor, a third reactor, a first resistance-capacity absorption device, and a second resistance-capacity absorption device device, a third resistance-capacity absorption device, a first protection gap, a second protection gap and a third protection gap, the first resistance-capacity absorption device includes a first main resistance and a first absorption capacitance, and the second resistance The capacitive absorbing device includes a second main resistor and a second absorbing capacitor, and the third RC absorbing device includes a third main resistor and a third absorbing capacitor,

The three-phase input terminal of the circuit breaker is connected to the power grid, and the A-phase output terminal of the three-phase output terminal of the circuit breaker is connected to one end of the first reactor and one end of the first main resistor at the same time, and the circuit breaker Among the three-phase output terminals, the B-phase output terminal is simultaneously connected to one end of the second reactor and one end of the second main resistor, and the C-phase output terminal of the three-phase output terminals of the circuit breaker is simultaneously connected to one end of the third reactor and the second main resistor. One end of the three main resistors is connected, the other end of the first main resistor is connected to one end of the first absorbing capacitor and one end of the first protection gap at the same time, and the other end of the second main resistor is connected to the second absorbing capacitor One end of the first reactor is connected to one end of the second protection gap, the other end of the third main resistor is connected to one end of the third absorbing capacitor and one end of the third protection gap at the same time, the other end of the first reactor, the second The other end of a absorption capacitor, the other end of the first protection gap, the other end of the second reactor, the other end of the second absorption capacitor, the other end of the second protection gap, the other end of the third reactor, the third absorption The other end of the capacitor and the other end of the third guard gap are simultaneously connected to the power ground.

Principle analysis: A protection circuit for dry-type air-core reactor switching overvoltage protection described in the present invention works in two working modes, that is, the resistance-capacitance absorption mode and the protection gap-resistance mode.

(A): Resistance-capacitance absorption mode: When the intercepted current is low, the resistance-capacity absorption device can limit the overvoltage amplitude at both ends of the reactor, so that it cannot reach the breakdown voltage of the protection gap, and the protection gap is in an open circuit state, simplifying The circuit principle is shown in Figure 4,

When the circuit breaker is disconnected to generate cut-off, the reactor and the respective resistance-capacitance components form an RLC oscillation circuit, and the loop current equation satisfies:

$\mathrm{<span\; class="notranslate">\; LC</span>}\frac{{\mathrm{<span\; class="notranslate">\; di</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; RC</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; di</span>}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Among them, i represents the loop current;

R represents the resistance of the resistance element;

C represents the capacitance of the capacitive element;

L represents the reactance of the reactor;

的条件下，i₀为截流值，回路电流方程的解为：exist

Under the condition of , i ₀ is the cut-off value, and the solution of the loop current equation is:

$\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&delta;t</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

in:

为固有振荡角频率，

is the natural angular frequency of oscillation,

为衰减系数，

is the attenuation coefficient,

为实际振荡频率，

is the actual oscillation frequency,

When δ is small enough, ω=ω ₀ ;

but:

i=i ₀ e ^-δt sin(ωt+π/2) (3)

It can be seen that the current waveform flowing through the reactor is a decaying oscillatory wave.

The voltage e _{resistance capacitance} on the reactor is:

then there is,

It can be seen from formula (5) that the magnitude of the overvoltage generated on the reactor is directly proportional to the cut-off value of the circuit breaker, and inversely proportional to the 1/2 power of the capacitance of the snubber circuit. Apparently, the magnitude of the overvoltage can be reduced by setting the size of the absorbing capacitor.

(B): Protection gap-resistance mode: When the cut-off current is large, the resistance-capacitance absorption device can no longer limit the amplitude of the overvoltage, and the amplitude of the overvoltage at both ends of the reactor is relatively high, and the protection gap is broken down at this time , the capacitor and its protective resistor are short-circuited, and the protective gap and the main resistor at this time constitute a protective gap—resistive protection device. The simplified circuit principle is shown in Figure 5, and the principle is as follows:

过电压达到保护间隙击穿电压e_b时，保护间隙击穿，电抗器对电阻放电，i₀为截流值，则电抗器上的电流i_a变化为：Cut-off is formed when the circuit breaker is switched, and overvoltage is formed at both ends of the reactor.

When the overvoltage reaches the breakdown voltage e _b of the protection gap, the protection gap breaks down, and the reactor discharges to the resistance. I ₀ is the cut-off value, and the current i _a on the reactor changes as follows:

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Among them: t represents time;

The change law of the voltage e _gap on the reactor is:

then there is,

|e _gap |=i ₀ R (8)

It can be seen from the formula (8) that the magnitude of the voltage on the reactor is proportional to the size of the cut-off current, and increases with the increase of the resistance value of the protection resistor. By setting the size of the protection resistor, the amplitude of the overvoltage can be controlled within a certain range while meeting the requirements for busbar protection and absorbing the energy of the reactor.

Assuming that the limited overvoltage is 3 times the rated value, referring to the formula (8), it can be known that the resistance value of the protection resistor should be 3 times the impedance value of the protected reactor. 1/3 of the working time will not have any impact on the system.

的情况，i_m为额定电流的幅值，所以取截流电流

为两种保护方式的临界电流:It can be seen from the formula (5) and formula (8) that in the two protection methods, the size of the overvoltage is related to the size of the cut-off value, so a critical value can be determined according to the statistical data of the current value when the cut-off operation is complete. value. Through the determination of other circuit component parameters, when the cut-off current is less than the critical value, the protection gap does not break down, and the resistance-capacity absorption device undertakes the overvoltage protection work; when the cut-off current value is greater than the critical value, the protection gap breaks down , the overvoltage protection work is undertaken by the protection gap and the resistance. Taking the circuit connected to the A-phase output of the three-phase output of the circuit breaker as an example, the overvoltage amplitude limited by the protection gap is 3U _{L rated} , where U _{L rated} is the rated voltage of the reactor, that is, regardless of the resistance Whether it works in capacitive absorption mode or in protection gap mode, the amplitude of overvoltage always meets e≤3U _{L rating} . The maximum value of the overvoltage e _m =3U _{L rated} , the diameter and distance of the protective gap ball electrodes can be selected according to this value. Among the overvoltages generated by the switching reactor, the overvoltage generated during the cut-off process is much larger than that during the switching-in process. In the process of cutting off the reactor, no matter when it operates, most of them are completely disconnected near the zero crossing point of the current, and there are few cut-off currents.

In the case of , i _m is the magnitude of the rated current, so take the cut-off current

is the critical current of the two protection modes:

时，以阻容吸收方式工作，把截断电流

时，电抗器上过电压e_阻容=3UL_额定，代入公式（5）可得吸收电容

a. When

, it works in the resistance-capacitance absorption mode, and the cut-off current

, the overvoltage on the reactor e _{resistance capacitance} = 3UL _rated , substituting into the formula (5) can get the absorbing capacitance

时，阻容吸收方式已不能满足保护间隙过电压限定需要，保护球间隙击穿，以保护间隙的方式工作，当截断电流|i₀|=i_m时，把电抗器上过电压e_间隙=3U_L额定，代入公式入公式（8）可得电阻

b. When

, the resistance-capacitance absorption method can no longer meet the overvoltage limit requirements of the protection _gap , the protection ball gap breaks down, and works in _the protection gap mode. When the cut-off current |i ₀ | 3U _{L rated} , substituting the formula into the formula (8) can get the resistance

其中，i_m表示额定电流，被截断电流小于该临界值的概率为90%。由公式（5），与传统的过电压保护比，在把过电压控制在相同值的情况下，本发明的保护电路电容C_新型与传统单独采用阻容吸收装置中电容C_传统满足

这将大大的减小所需电容体积、降低成本；本发明的保护电路中间隙的动作次数减少为传统只采用保护间隙时的

同时由于主电阻的存在将减小保护间隙的电弧电流，从而大大的延长保护间隙的使用寿命和损坏概率。Suppose the critical value is

Among them, i _m represents the rated current, and the probability that the cut-off current is less than the critical value is 90%. According to the formula (5), compared with the traditional overvoltage protection ratio, under the condition that the overvoltage is controlled at the same value, the capacitance C _{of the new} protection circuit of the present invention and the capacitance C of the _traditional single resistance-capacitance absorbing device meet the requirements of

This will greatly reduce the required capacitor volume and reduce the cost; the number of actions of the gap in the protection circuit of the present invention is reduced to that of traditional protection gaps.

At the same time, due to the existence of the main resistance, the arc current of the protection gap will be reduced, thereby greatly prolonging the service life and damage probability of the protection gap.

According to the analysis of the above principles, the beneficial effects brought by the present invention can be obtained. The protection circuit for dry-type air-core reactor switching overvoltage protection according to the present invention requires small capacitance and low cost, which reduces the need for protection. The number of actions of the gap prolongs the service life and damage rate of the protection gap.

Description of drawings

FIG. 1 is a schematic diagram of the principle of a protection circuit for switching overvoltage protection of a dry-type air-core reactor according to the present invention.

Fig. 2 is a schematic diagram of the principle of a protection circuit for switching overvoltage protection of a dry-type air-core reactor described in the second embodiment.

Fig. 3 is a schematic diagram of the principle of a protection circuit for switching overvoltage protection of a dry-type air-core reactor described in Embodiment 3.

Fig. 4 is a schematic diagram of an equivalent principle of a protection circuit for switching overvoltage protection of a dry-type air-core reactor according to the present invention when the protection gap is an open circuit.

Fig. 5 is a schematic diagram of an equivalent principle of a protection circuit for switching overvoltage protection of a dry-type air-core reactor according to the present invention when the protection gap is broken down.

Detailed ways

Specific embodiment 1: Referring to Fig. 1 to illustrate this embodiment, a protection circuit for dry-type air-core reactor switching overvoltage protection described in this embodiment includes a circuit breaker QF and a first reactor DK-1 , the second reactor DK-2, the third reactor DK-3, the first RC absorption device, the second RC absorption device, the third RC absorption device, the first protection gap Ga, the second protection gap Gb and The third protection gap Gc, the first RC absorbing device includes the first main resistor R _SA and the first absorbing capacitor C _SA , the second RC absorbing device includes the second main resistor R _SB and the second absorbing Capacitor C _SB , the third RC absorption device includes a third main resistor R _SC and a third absorption capacitor C _SC ,

The three-phase input terminal of the circuit breaker QF is connected to the power grid, and the A-phase output terminal of the three-phase output terminal of the circuit breaker QF is simultaneously connected to one end of the first reactor DK-1 and one end of the first main resistor R _SA connection, the B-phase output terminal of the three-phase output terminal of the circuit breaker QF is connected to one end of the second reactor DK-2 and one end of the second main resistor R _SB at the same time, and the three-phase output terminal of the circuit breaker QF The C-phase output end is simultaneously connected with one end of the third reactor DK-3 and one end of the third main resistance R _SC , and the other end of the first main resistance R _SA is simultaneously connected with one end of the first absorption capacitor C SA and the first end of the first absorption capacitor C _SA . One end of a guard gap Ga is connected, and the other end of the second main resistor R _SB is simultaneously connected with one end of the second snubber capacitor _CSB and one end of the second guard gap Gb, and the third main resistor R _SC is The other end is connected to one end of the third absorption capacitor C _SC and one end of the third protection gap Gc at the same time, the other end of the first reactor DK-1, the other end of the first absorption capacitor C _SA , the first protection gap The other end of Ga, the other end of the second reactor DK-2, the other end of the second absorption capacitor _CSB , the other end of the second protection gap Gb, the other end of the third reactor DK-3, the third absorption capacitor The other end of C _SC and the other end of the third guard gap Gc are simultaneously connected to the power ground.

In this embodiment, the first main resistor R _SA in the first RC absorbing device, the second main resistor R _SB in the second RC absorbing device, and the third The main resistor R _SC plays the role of absorbing the energy of the overvoltage. It is a protection resistor under high overvoltage to prevent the short circuit of the busbar to ground when the protection gap breaks down, and absorb the energy of the reactor when the protection gap breaks down.

Specific embodiment 2: Refer to Fig. 2 to illustrate this embodiment. The difference between this embodiment and the protection circuit for dry-type air-core reactor switching overvoltage protection described in Embodiment 1 is that it also includes a first Protection resistor Ra, second protection resistor Rb and third protection resistor Rc;

The first protection resistor Ra is connected in series between the first main resistor R _SA and the first absorption capacitor C _SA , and the first protection resistor Ra and the first absorption capacitor C _SA are connected in series and connected in parallel with the first protection gap Ga ,

The second protection resistor Rb is connected in series between the second main resistor R _SB and the second absorption capacitor _CSB , and the second protection resistor Rb and the second absorption capacitor _CSB are connected in series and connected in parallel with the second protection gap Gb ,

The third protective resistor Rc is connected in series between the third main resistor R _SC and the third absorbing capacitor C _SC , and the third protective resistor Rc and the third absorbing capacitor C _SC are connected in series and connected in parallel with the third protective gap Gc .

Specific embodiment 3: Refer to Fig. 3 to illustrate this embodiment. The difference between this embodiment and the protection circuit for dry-type air-core reactor switching overvoltage protection described in Embodiment 2 is that it also includes a first Fuses FUa, second fuses FUb and third fuses FUc; the first fuse Fua is connected in series between the A-phase output terminal of the circuit breaker QF and the first main resistor R _SA , and the second fuse is disconnected The fuse FUb is connected in series between the B-phase output terminal of the circuit breaker QF and the second main resistor R _SB , and the third fuse FUc is connected in series between the C-phase output terminal of the circuit breaker QF and the third main resistor R _SC .

Specific Embodiment 4: Refer to Figures 1 and 2 to illustrate this embodiment. The difference between this embodiment and the protection circuit for dry-type air-core reactor switching overvoltage protection described in Embodiment 1 or 2 is that the The above-mentioned first reactor DK-1, second reactor DK-2 and third reactor DK-3 are all dry-type air-core reactors.

Claims (4)

1. A protection circuit for dry-type air-core reactor switching overvoltage protection, characterized in that it includes a circuit breaker (QF), a first reactor (DK-1), a second reactor (DK-2 ), the third reactor (DK-3), the first RC absorber, the second RC absorber, the third RC absorber, the first protection gap (Ga), the second protection gap (Gb) and the first Three protection gaps (Gc), the first RC absorbing device includes the first main resistor ( _RSA ) and the first absorbing capacitor (C _SA ), and the second RC absorbing device includes the second main resistor ( R _SB ) and the second snubber capacitor (C _SB ), the third RC snubber device includes the third main resistor (R _SC ) and the third snubber capacitor (C _SC ), the circuit breaker (QF) The three-phase input terminal is connected to the power grid, and the A-phase output terminal of the three-phase output terminal of the circuit breaker (QF) is connected to one end of the first reactor (DK-1) and one end of the first main resistor ( _RSA ) at the same time , the phase B output terminal of the three-phase output terminal of the circuit breaker (QF) is connected to one terminal of the second reactor (DK-2) and one terminal of the second main resistor ( _RSB ) at the same time, and the circuit breaker ( QF) Among the three-phase output terminals, the C-phase output terminal is connected with one end of the third reactor (DK-3) and one end of the third main resistance ( _RSC ) at the same time, and the other end of the first main resistance (R _SA ) One end is simultaneously connected with one end of the first snubber capacitor (C _SA ) and one end of the first guard gap (Ga), and the other end of the second main resistor (R _SB ) is simultaneously connected with the second end of the second snubber capacitor (C _SB ) One end is connected to one end of the second guard gap (Gb), and the other end of the third main resistor (R _SC ) is simultaneously connected to one end of the third snubber capacitor (C _SC ) and one end of the third guard gap (Gc) , the other end of the first reactor (DK-1), the other end of the first absorption capacitor (C _SA ), the other end of the first guard gap (Ga), the second reactor (DK-2) The other end, the other end of the second snubber capacitor (C _SB ), the other end of the second guard gap (Gb), the other end of the third reactor (DK-3), the other end of the third snubber capacitor (C _SC ) The other end of the third protection gap (Gc) is connected to the power ground at the same time. 2. A protection circuit for dry-type air-core reactor switching overvoltage protection according to claim 1, characterized in that it also includes a first protection resistor (Ra), a second protection resistor (Rb) and The third protective resistor (Rc); The first protection resistor (Ra) is connected in series between the first main resistor (R _SA ) and the first absorption capacitor (C _SA ), and the first protection resistor (Ra) and the first absorption capacitor (C _SA ) are connected in series connected in parallel with the first guard gap (Ga), The second protection resistor (Rb) is connected in series between the second main resistor (R _SB ) and the second snubber capacitor (C _SB ), and the second protection resistor (Rb) and the second snubber capacitor (C _SB ) are connected in series connected in parallel with the second guard gap (Gb), The third protective resistor (Rc) is connected in series between the third main resistor (R _SC ) and the third snubber capacitor (C _SC ), and the third protective resistor (Rc) is connected in series with the third snubber capacitor (C _SC ) Connected in parallel with the third guard gap (Gc). 3. A protection circuit for dry-type air-core reactor switching overvoltage protection according to claim 2, characterized in that it also includes a first fuse (FUa), a second fuse (FUb) and The third fuse (FUc); the first fuse (FUa) is connected in series between the A-phase output terminal of the circuit breaker (QF) and the first main resistor ( _RSA ), and the second fuse ( FUb) is connected in series between the B-phase output terminal of the circuit breaker (QF) and the second main resistor (RSB), and the third fuse (FUc) is connected in series between the C-phase output terminal of the circuit breaker (QF) and the second main resistor (R _SB ). between the three main resistors (R _SC ). 4. A protection circuit for dry-type air-core reactor switching overvoltage protection according to claim 1 or 2, characterized in that the first reactor (DK-1), the second reactor (DK-2) and the third reactor (DK-3) are both dry-type air-core reactors.

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