Grounding method and system for power distribution network through voltage arc suppression coil

Abstract

The application discloses a grounding method and system of a distribution network through a voltage arc-extinguishing coil. The method comprises: grounding of the distribution network through the voltage arc-extinguishing coil, wherein the voltage arc-extinguishing coil at least comprises an air-gap core and two winding coils wound on the air-gap core, one end of a first winding coil is grounded through a damping resistor or directly grounded, the other end is connected to a neutral point or a phase line or a grounding transformer tapping of the distribution network, and a second winding coil applies voltage. Under normal operation conditions of the distribution network, the voltage arc-extinguishing coil tracks changes of a ground capacitance of the distribution network to realize automatic tuning; under a grounding fault condition of the distribution network, the second winding coil injects a reverse voltage into a fault phase power supply to regulate voltage size and phase, implement voltage arc-extinguishing, force a fault point voltage to be less than a fault arc reignition voltage, and achieve the arc extinguishing purpose. The technical scheme provided by the application can realize zero-voltage arc-extinguishing and zero-current voltage reduction safe operation of the distribution network fault through only one voltage arc-extinguishing coil.

Description

Technical Field

[0001] This invention relates to power distribution network grounding technology, and particularly to a grounding method and system for power distribution networks via voltage arc suppression coils. Background Technology

[0002] The use of electricity has become deeply integrated into people's daily lives. Medium and low-voltage distribution networks play a crucial role in the power grid system. However, these networks, so closely related to people's lives, experience frequent faults, leading to countless accidents such as electric shocks, equipment fires, and forest fires. Early distribution networks were small-scale, and their neutral points used ungrounded systems. Over the years, neutral point grounding methods have developed rapidly, and can now be broadly categorized into two types: low-current grounding and high-current grounding. Different countries around the world employ different grounding methods, gradually forming two major camps: Europe's low-current grounding and the United States' high-current grounding. Low-current grounding includes ungrounded methods, high-resistance grounding, and resonant grounding, while high-current grounding includes direct grounding or low-current grounding.

[0003] In the case of a neutral-point ungrounded system, the grounding current is small during a fault, allowing it to operate with the fault for up to 2 hours; however, the voltage between the non-faulty phases and ground will increase. Over time, this can easily lead to intermittent arcing overvoltages during grounding faults, posing safety hazards such as electric shock and fire. While a neutral point with an arc suppression coil can effectively reduce grounding current and provide rapid line selection, location, and section isolation for both transient and permanent faults, the arc suppression coil cannot compensate for the active and harmonic components of the fault current, easily resulting in intermittent arcing overvoltages. Grounding the neutral point with a small resistor can reduce zero-sequence impedance and increase fault current, but the protection sensitivity is only a few hundred ohms, rendering it ineffective against high-resistance faults and leading to an increased tripping rate.

[0004] In summary, existing distribution network grounding technologies cannot guarantee the reliability of the distribution network and cannot meet the needs of power grids and power companies. Summary of the Invention

[0005] The purpose of this invention is to provide a grounding method for arc suppression coils that can better balance reliability and economy, specifically a grounding method and system for distribution networks via voltage arc suppression coils.

[0006] Therefore, the present invention provides the following technical solution:

[0007] The present invention provides a grounding method for a distribution network via a voltage arc suppression coil. The voltage arc suppression coil includes at least an iron core with an air gap and two coil windings wound on the iron core. One end of the first coil winding is grounded via a damping resistor or directly grounded, and the other end is connected to the neutral point, phase line, or grounding transformer tap of the distribution network. The second coil winding is connected to the power supply.

[0008] Under normal operating conditions of the distribution network, the voltage arc suppression coil tracks the changes in the distribution network's capacitance to ground to achieve automatic tuning; under the condition of a ground fault in the distribution network, voltage arc suppression is performed, that is, the second winding injects the reverse voltage of the fault phase power supply, adjusts the voltage magnitude and phase, and forces the voltage at the fault point to be less than the fault arc reignition voltage, thereby achieving the purpose of extinguishing the arc.

[0009] This invention proposes for the first time to connect a second winding, which is powered, to an arc-suppression coil, making its primary winding the first winding. The upper end of the first winding is connected to the system neutral point, phase line, or grounding transformer tap, and the lower end is grounded via a damping resistor or directly. The primary side then functions as an arc-suppression coil, achieving primary compensation for the ground capacitance current of the distribution network system. Furthermore, by simply applying a power supply of appropriate magnitude and phase to the second winding, the voltage arc-suppression effect can be achieved.

[0010] Alternatively, the amplitude of the reverse voltage injected into the second winding may be controlled using any of the following three methods:

[0011] First: Change the output value of the independent power electronic power supply, wherein the two ends of the second winding are connected to the independent power electronic power supply;

[0012] Second: Adjust the voltage by changing the impedance value, wherein the second winding has a series impedance in the injection voltage circuit;

[0013] Third: Adjust the tap position of the injection voltage circuit of the second winding. Several taps are set on the second winding, and different taps correspond to different tap positions.

[0014] The injected voltage circuit is applied to the terminals of the second winding and is used to apply voltage to the second winding.

[0015] That is, during the voltage arc suppression process, the power supply to the second winding can come from the fault phase power supply voltage extracted from the secondary side of the grounding transformer, or it can be the fault phase power supply voltage generated by an independent power electronic power supply.

[0016] Alternatively, the voltage control strategy for voltage arc suppression of the voltage arc suppression coil is as follows:

[0017] After the ground fault stabilizes, the first stage of voltage arc suppression is implemented: zero-voltage arc suppression control at the fault point. This involves controlling the voltage amplitude and phase injected into the second winding of the voltage arc suppression coil to ensure that the neutral point voltage is equal in magnitude and opposite in phase to the fault phase power supply, thereby forcing the fault point voltage to approach zero and achieving fault arc suppression.

[0018] After the arc is reliably extinguished, the second stage of voltage arc suppression is implemented to detect and control the arc extinguishing at the fault point. This involves changing the voltage amplitude and phase injected into the second winding of the voltage arc suppression coil and detecting whether the zero-sequence current injected into the neutral point changes linearly with the zero-sequence voltage.

[0019] If the change is linear, i.e. the arc is extinguished, the second winding of the voltage arc suppression coil stops injecting voltage, and the power distribution network resumes normal operation.

[0020] Otherwise, implement the third stage of voltage arc suppression, which is zero-current voltage reduction safety operation control at the fault point. This involves adjusting the magnitude and phase of the voltage injected into the second winding of the voltage arc suppression coil to reduce the voltage at the fault point until the current at the fault point is zero.

[0021] During or after the third stage of control, the fault point boost protection control enters the fourth stage of voltage arc suppression. This involves controlling the voltage amplitude and phase injected into the second winding of the voltage arc suppression coil to raise the fault point voltage to a level greater than the line voltage but less than twice the phase voltage. This causes the fault point resistance to decrease, and the grounding current at the fault point to increase nonlinearly and rapidly. This triggers the selective line protection or overcurrent protection to quickly clear the fault and achieve rapid isolation of permanent faults.

[0022] Here, "approaching" or "close to" both refer to a certain range that meets the accuracy requirements. This range can be adjusted according to experiments and accuracy requirements. For example, the range that approaches zero can be specified within the interval [0, 500V].

[0023] The current arc suppression control strategy of the arc suppression coil targets the grounding current and can only compensate for reactive current, not active current, resulting in residual current. The voltage arc suppression control strategy provided by this invention targets the fault phase voltage, reducing it to zero to achieve voltage arc suppression. Consequently, the grounding current is also reduced to zero, achieving complete extinguishing of the grounding arc. That is, only a power supply of appropriate magnitude and phase needs to be applied to the second winding to achieve the effect of voltage arc suppression, completely suppressing the fault arc. It can achieve zero-voltage arc suppression for transient faults, zero-current voltage reduction for permanent faults, and voltage boost protection for high-resistance grounding faults. This effectively reduces the power outage rate, meets the needs of the power grid and power companies, and effectively reduces losses caused by distribution network grounding faults.

[0024] Further optionally, the tuning methods of the voltage arc suppression coil include the following three:

[0025] The first method involves changing the air gap of the iron core. In this invention, the voltage arc suppression coil includes an iron core with an adjustable air gap. This air-gap iron core has a large magnetic reluctance, resulting in a low excitation impedance for the voltage arc suppression coil. This characteristic determines that the first winding of the voltage arc suppression coil can act as the inductor of the arc suppression coil. The iron core consists of two parts: a stationary and a moving part. The stationary iron core is at the bottom, and the moving iron core is at the top. By changing the position of the moving iron core, the size of the air gap between the moving and stationary iron cores is altered, thereby changing the inductance value of the first winding to achieve the tuning goal. Increasing the air gap reduces the excitation impedance of the voltage arc suppression coil, thus reducing the inductance of the first winding; conversely, decreasing the air gap increases it.

[0026] The second method is to change the number of turns of the first winding coil, wherein several turn taps are set on the first winding, and different turn taps correspond to different coil turns;

[0027] The third method involves adding a third winding to the iron core. The terminals of this third winding are externally connected to an inductor or capacitor, and tuning is achieved by changing the inductance or capacitance values. Specifically, the equivalent inductance of the first winding is altered by controlling the connection of the capacitor and inductor in the third winding via a switch, thus achieving the tuning goal. Specifically, increasing the connection of the capacitor decreases the inductance of the first winding; increasing the connection of the inductor increases the inductance of the first winding.

[0028] Alternatively, since normal line switching and other operations cause changes in the ground capacitance parameters, the technical solution of the present invention performs tracking and tuning during normal operation. Therefore, under fault conditions, the direct arc suppression coil is closest to the state of full compensation, and the grounding current is minimized, which can effectively reduce the harm of grounding faults.

[0029] The first winding of the voltage arc suppression coil acts as an arc suppression coil, achieving primary compensation for the ground capacitance current of the distribution network system. If the first air gap adjustment tuning method is adopted, based on the full compensation requirement, the required core air gap size during tuning is:

[0030]

[0031] Where, μ δ Let μ be the permeability of the air gap. Fe Where is the permeability of the iron core, A is the cross-sectional area of ​​the iron core, N1 is the number of turns of the first winding, C0 is the system capacitance to ground, a is the height of the iron core, b is the length of the iron core base, ω is the system power frequency angular frequency, and L... m It is the excitation reactance of the voltage arc suppression coil.

[0032] The required air gap size for full compensation is calculated, and the most suitable air gap setting is adjusted accordingly.

[0033] Further, based on the full compensation requirement, the number of turns of the first winding during tuning is:

[0034]

[0035]

[0036] Where N1 is the number of turns of the first winding, Λ m For iron core magnetic permeability, R m C0 is the core reluctance, ω is the system capacitance to ground, and μ is the system power frequency. δ Let μ be the permeability of the air gap. Fe Let be the magnetic permeability of the iron core, a be the height of the iron core, b be the length of the iron core base, A be the cross-sectional area of ​​the iron core, and δ be the size of the air gap in the iron core.

[0037] The number of turns taps is adjusted based on the calculated number of turns required for full compensation.

[0038] Alternatively, based on the full compensation requirement, the capacitance value required during tuning is:

[0039]

[0040] Among them, L m N1 is the excitation reactance of the voltage arc suppression coil, N3 is the number of turns of the first winding of the voltage arc suppression coil, C0 is the system capacitance to ground parameter, and ω is the system power frequency angular frequency.

[0041] The appropriate capacitor setting is adjusted based on the calculated equivalent capacitance required for full compensation.

[0042] In addition, the present invention also provides a voltage arc suppression coil for a power distribution network, the voltage arc suppression coil comprising at least an iron core with an air gap and two coil windings wound on the iron core; wherein, the first winding of the two coil windings is located on the primary side of the iron core, one end of the first winding is grounded through a damping resistor or directly grounded, and the other end is connected to the neutral point of the power distribution network or a phase line or a tap of a grounding transformer; the second winding of the two coil windings is located on the secondary side of the iron core and is connected to a power source.

[0043] Further optionally, the core of the voltage arc suppression coil is air gap adjustable and / or the secondary side of the voltage arc suppression coil is also provided with a third winding coil, which is connected to the RC switch branch to achieve the purpose of arc suppression coil tuning.

[0044] In this case, the lower end of the first winding of the voltage arc suppression coil is grounded through a damping resistor. If a third winding is provided, the damping resistor can also be installed in the third winding and connected in parallel with the capacitor or inductor branch.

[0045] Alternatively, the second and third windings can be set independently to form a three-winding voltage arc suppression coil; or the second and third windings can form an autotransformer winding to form an autotransformer voltage arc suppression coil.

[0046] The power supply connected to the second winding comes from the fault phase power supply voltage extracted from the secondary side of the grounding transformer, or it can be the fault phase power supply voltage generated by an independent power electronic power supply. When the power supply voltage comes from the secondary side of the grounding transformer, the grounding transformer can adopt any of the connection types ZNy11 and YNDx, where x can be 3, 5, 7, 9, or 11. Different connection types have different switching control methods, allowing the secondary side output line voltage to be either opposite or in the same direction as the fault phase power supply voltage. The number of turns in the first and second windings of the voltage arc suppression coil are N1 and N2, respectively, and the number of turns on the high-voltage and low-voltage sides of the grounding transformer are N4 and N5, respectively. Therefore, N1:N2≈N4:N5.

[0047] Furthermore, the power supply of the second winding is connected to the second winding via a step-down impedance. The step-down impedance is connected in parallel with a switch. After a fault occurs, the second stage switch for voltage arc suppression is opened, and the step-down impedance is engaged. Adjusting the magnitude of the variable step-down impedance can reduce the amplitude and phase of the voltage injected into the second winding.

[0048] Furthermore, the present invention also provides an injection device based on the voltage arc suppression coil, comprising: the voltage arc suppression coil, and an independent power electronic power supply or a reverse power supply of the power distribution network.

[0049] Beneficial effects

[0050] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0051] 1. Compared with the traditional arc suppression coil grounding method, the grounding method provided by the present invention, with a similar cost to the arc suppression coil, only requires a second winding to apply a power supply of appropriate magnitude and phase to achieve the effect of voltage arc suppression, completely suppressing the fault arc; it can achieve zero-voltage arc suppression at the fault point for transient faults, zero-current voltage reduction for safe operation at the fault point for permanent faults, and voltage boost protection at the fault point for high-resistance grounding faults, effectively reducing the power grid outage rate, meeting the needs of the power grid and power companies, and effectively reducing losses caused by distribution network grounding faults.

[0052] 2. Compared with similar grounding methods using voltage arc suppression devices, the grounding method provided by this invention has the advantage that the low excitation impedance of the voltage arc suppression coil means that the first winding can act as the inductor of the arc suppression coil, saving the footprint and cost of one arc suppression coil. The automatic tuning function of the voltage arc suppression coil itself can reduce the magnitude of the zero-sequence current, thereby reducing the capacity requirement of the power supply device connected to the second winding coil. Based on achieving reliable power supply arc suppression, it has advantages in terms of operational reliability and economy. Furthermore, if a grounding fault occurs, the reduction in zero-sequence current can effectively reduce the damage caused by the fault. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the grounding method for a power distribution network via a voltage arc suppression coil.

[0054] Figure 2 A grounding method that involves adding a third winding to the voltage arc suppression coil to form a three-winding system;

[0055] Figure 3 A wiring method in which a third winding is added to the voltage arc suppression coil and connected as an autotransformer winding;

[0056] Figure 4 The equivalent circuit (a) and simplified diagram (b) for the voltage arc suppression coil with a third winding are shown.

[0057] Figure 5 A flowchart illustrating the arc suppression process using a voltage-based arc suppression coil grounding method in a power distribution network.

[0058] Figure 6 The waveform diagram of the fault phase voltage after implementing the first stage of voltage arc suppression control and zero-voltage arc suppression control;

[0059] Figure 7 To implement the second stage of voltage arc suppression control, the curve of the zero-sequence current changing with the zero-sequence voltage is shown.

[0060] Figure 8 The fault current (a) and fault phase voltage waveforms (b) after the implementation of the third stage of voltage arc suppression control with zero current reduction for safe operation;

[0061] Figure 9 The fault current (a) and fault phase voltage waveforms (b) after the fourth stage of voltage arc suppression control is implemented to control the boost protection of the fault point. Detailed Implementation

[0062] The present invention will be further described below with reference to embodiments.

[0063] This invention provides a grounding method and system for a distribution network via a voltage arc suppression coil. Specifically, the voltage arc suppression coil includes at least an iron core with an air gap and two coil windings wound around the iron core. One end of the first winding is grounded via a damping resistor or directly grounded, and the other end is connected to the neutral point, phase line, or tap of the grounding transformer in the distribution network. A voltage is applied to the second winding. Under normal operating conditions of the distribution network, the voltage arc suppression coil automatically tunes by tracking changes in the distribution network's capacitance to ground. Under grounding fault conditions, voltage arc suppression is performed, i.e., the second winding injects the reverse voltage of the fault phase power supply, adjusts the voltage magnitude and phase, and implements voltage arc suppression, forcing the fault point voltage to be less than the fault arc reignition voltage, thereby achieving the purpose of extinguishing the arc.

[0064] like Figure 1 As shown, These are the three-phase power supply electromotive forces of the system, and Y0 is the system's ground parameter, where Y0 = 1 / jωC0, R f For a single-phase ground fault, T1 is the grounding resistance. T1 is a grounding transformer connected in a ZNy11 configuration. The low-voltage side of the grounding transformer is controlled by a1, a2, b1, b2, c1, c2 to output the secondary side voltage in either the reverse or same direction as the fault phase power supply. Z n To reduce the voltage impedance, it is controlled by switch S2.

[0065] The voltage is controlled by connecting the upper end of the first winding of the arc suppression coil to the system neutral point O via S0. R is the neutral point voltage of the system. S It is a damping resistor, controlled by switch S1, and connected to ground at the lower end of the first winding.

[0066] Depend on Figure 1 It can be seen that, Figure 1 The voltage arc suppression coil in the circuit has two coil windings. One end of the first winding is grounded through a damping resistor, and the other end is connected to the neutral point of the distribution network. The second winding is connected to the secondary side of the grounding transformer to obtain the applied power supply.

[0067] Other feasible embodiments, such as Figure 2 As shown, a third winding is also provided on the voltage coil. This third winding is connected to the RC switch branch to achieve the purpose of tuning the arc suppression coil. Among them, Figure 2 In the RC switch branch, each branch consists of a capacitor connected in series with the switch, and in parallel with other capacitor-switch branches, connected across the third winding. Figure 2 In this configuration, the second and third winding coils are independently arranged in parallel on the secondary side of the voltage arc suppression coil, wherein the first, second, and third winding coils constitute a three-winding connection.

[0068] In other feasible embodiments, such as Figure 3As shown, the second winding coil and the third winding coil share the same set of winding coils. A tap is provided on the second winding coil, and the third winding coil is the winding from the tap to the winding end of the second winding coil.

[0069] Based on the above circuit structure, if a grounding fault occurs, the present invention provides the following grounding method:

[0070] During normal operation of the distribution network, switches S0, S1, and S2 are all closed, while switches a1, a2, b1, b2, c1, and c2 are open. The damping resistor and the first winding of the voltage arc suppression coil are connected to the system. In a fault condition, switch S1 is open. After 0.5–2 seconds, the first stage of voltage arc suppression control is implemented, closing two sets of switches a1, a2, b1, b2, c1, and c2. This causes the secondary side of the grounding transformer to output a voltage opposite in phase to the fault phase power supply. The amplitude and phase of the voltage injected into the second winding are adjusted to force the fault phase voltage to satisfy the condition that the neutral point voltage is equal in magnitude and opposite in phase to the fault phase power supply, forcing the fault point voltage as close to zero as possible to achieve complete arc suppression. After 6–10 seconds, the second stage of voltage arc suppression control is implemented, namely, the detection control for the extinction of the fault point arc. This involves changing the amplitude and phase of the voltage injected into the second winding of the voltage arc suppression coil to detect… Whether the zero-sequence current injected at the neutral point changes linearly with the zero-sequence voltage, if it does, it is determined that the arc is extinguished, the second winding of the voltage arc suppression coil stops injecting voltage, and the distribution network resumes normal operation; otherwise, the third stage of voltage arc suppression control is implemented, namely the zero-current voltage reduction safety operation control at the fault point, which adjusts the magnitude and phase of the voltage injected by the second winding of the voltage arc suppression coil to make the fault point current zero and the fault phase voltage as close as possible to the normal voltage; during the third stage of control, the fourth stage of voltage arc suppression control can also be entered, namely the fault point voltage boost protection control, which controls the magnitude and phase of the voltage injected by the second winding of the voltage arc suppression coil to raise the fault point voltage to a value between the line voltage and twice the phase voltage, causing the fault point resistance to decrease, the fault point grounding current to increase nonlinearly and rapidly, and the line selection protection or overcurrent protection to be activated, quickly clearing the fault and achieving rapid isolation of permanent faults.

[0071] Regarding automatic tuning, the tuning methods for the voltage arc suppression coil provided by this invention include the following three methods:

[0072] The first method involves changing the air gap in the iron core. In this case, the air gap is adjustable. Based on the full compensation requirement, the required air gap size for tuning is:

[0073]

[0074] Where, μ δ Let μ be the permeability of the air gap. FeWhere is the permeability of the iron core, A is the cross-sectional area of ​​the iron core, N1 is the number of turns of the first winding, C0 is the system capacitance to ground, a is the height of the iron core, b is the length of the iron core base, ω is the system power frequency angular frequency, and L... m It is the excitation reactance of the voltage arc suppression coil.

[0075] The second method involves changing the number of turns in the first winding coil. Several turn taps are set on the first winding, and different turn taps correspond to different coil turn numbers. Based on the full compensation requirement, the number of turns in the first winding coil during tuning is:

[0076]

[0077]

[0078] Where N1 is the number of turns of the first winding, Λ m For iron core magnetic permeability, R m C0 is the core reluctance, ω is the system capacitance to ground, and μ is the system power frequency. δ Let μ be the permeability of the air gap. Fe Let be the magnetic permeability of the iron core, a be the height of the iron core, b be the length of the iron core base, A be the cross-sectional area of ​​the iron core, and δ be the size of the air gap in the iron core.

[0079] The third method involves adding a third winding to the iron core. The terminals of this third winding are externally connected to an inductor or capacitor, and tuning is achieved by changing the inductance or capacitance value. Based on the full compensation requirement, the capacitance value required for tuning is:

[0080]

[0081] Among them, L m N1 is the magnetizing reactance of the voltage arc suppression coil, N3 is the number of turns in the first winding of the voltage arc suppression coil, C0 is the system capacitance to ground parameter, and ω is the system power frequency.

[0082] like Figure 2 As shown, the secondary side capacitor circuit is equipped with 4 capacitors, satisfying the relationship C1 = 2. 0 C1, C2 = 2 1 C1, C3 = 2 2 C1, C4 = 2 3 C1. This allows for the first-position switch to be engaged without closure. x =0, the second switch K1 is closed and C is engaged. x =C1, third position closed, switch K2 is engaged in C x =2C1, fourth position closed, switches K1 and K2 are engaged in C. x =3C1………to the 16th position, close switches K1, K2, K3 and 3K4 to engage C. x=15C1. The capacitance value and range allocation of the capacitor input can be calculated based on the settings of the RC switch circuit. After calculating the required capacitance value under full compensation according to the above formula, the corresponding switches are activated according to the design of the RC switch branch to achieve or closely approximate the calculated capacitance value (resulting in the converted equivalent capacitance C). n ′).

[0083] It should be noted that the adjustment rules for overcompensation and undercompensation during the tuning compensation process are shown in Table 1 below:

[0084] Table 1

[0085] Running state Over compensation Under compensation Adjusting capacitance Increasing input capacitance Decreasing input capacitance Adjusting air gap Decreasing air gap Increasing air gap Adjusting number of turns Increasing number of turns Decreasing number of turns

[0086] Regarding voltage arc suppression:

[0087] The control methods for switches a1, a2, b1, b2, c1, and c2 in the first and fourth stages of the voltage arc suppression process are shown in the table below:

[0088] Faulty phase A phase fault B phase fault C phase fault Output reverse voltage a2, c1 b2, a1 c2, b1 Output same direction voltage a1, c2 b1, a2 c1, b2

[0089] It should be noted that in the above example, the power supply loaded on the second winding is obtained through the output of the secondary side of the grounding transformer. In other feasible embodiments, the power supply loaded on the second winding can also be provided by an independent power electronic power supply.

[0090] There are three methods to change the voltage amplitude and phase injected into the voltage arc suppression coil in the second stage control during the voltage arc suppression process: changing the output value of the independent power electronic power supply, changing the taps of the second winding coil (where several taps are set on the second winding, and different taps correspond to different tap positions); or disconnecting switch S2 to engage the step-down impedance Z. n By changing its impedance value, the voltage injected into the second winding can be controlled through voltage division.

[0091] In the second stage of control during voltage arc suppression, whether the zero-sequence current injected at the neutral point changes linearly with the zero-sequence voltage can determine the fault type. If it changes linearly, the ground fault type is a transient ground fault; otherwise, it is a permanent ground fault. The basis for this judgment is as follows:

[0092] In the second stage, when adjusting the amplitude and phase of the injected voltage,

[0093] If the ground fault is transient, and the ground fault no longer exists after the arc is extinguished, then the system zero-sequence current... The zero-sequence current and the zero-sequence voltage are linearly related.

[0094] If the ground fault is permanent, and the ground fault still exists after the arc suppression is completed, then the zero-sequence current... The zero-sequence current and the zero-sequence voltage are not linearly related.

[0095] In summary, the linear relationship between zero-sequence current and zero-sequence voltage can be used as a criterion for fault type.

[0096] Figure 4 X′ T1σ 、X′ T2σ 、X′ Tm This is the converted grounding transformer reactance parameter, X′ 2σ and X′ 3σ This is the converted leakage reactance of the second and third windings of the arc suppression coil, X. m It is the magnetizing reactance of the voltage arc suppression coil, Z in X is the equivalent internal impedance of the grounding transformer. 1σ It is the leakage reactance of the first winding of the voltage arc suppression coil, C n ′ is the equivalent capacitance of the third winding after conversion, where n takes values ​​from 1 to 16. This is a virtual power source for the fault point; if phase C is faulty, then... 3R f The fault resistance is given; neglecting leakage reactance, the grounding transformer section and the injected voltage are simplified using Thevenin's theorem and Norton's theorem to obtain... Figure 4 In Figure (b), the fault phase voltage under fault conditions is... It can be represented as:

[0097]

[0098] Injection voltage Power supply voltage of the faulty phase It is the opposite, so by controlling the injection voltage of the second winding of the voltage arc suppression coil, the magnitude of the fault phase voltage can be adjusted, reducing the fault point voltage to be as close to zero as possible, thus achieving complete arc suppression of the fault.

[0099] In addition, the present invention also provides an injection device based on the voltage arc suppression coil, comprising: the voltage arc suppression coil, and an independent power electronic power supply or a reverse power supply of the power distribution network.

[0100] The above details the entire process of arc suppression in a distribution network via a voltage arc suppression coil grounding method. To verify the arc suppression method described in this invention, it was validated using PSCAD simulation software. An ungrounded 10kV distribution network system, as shown in the figure, was built within the system, with the following system parameters: The system's capacitance to ground C0 = 1.5 [μF], the line's resistance to ground R0 = 12 [kΩ], the grounding transformer capacity is 170 kVA, the high-voltage side-to-ground voltage ratio is 6.062:0.4, the distribution network frequency is 50 Hz, the voltage arc suppression coil capacity is 3.15 [MVA], the voltage ratio of the first, second, and third windings is 6.062:0.4:1, and the no-load current percentage is 2.899%.

[0101] The fault is set to occur in phase C, and the fault occurs in 0.3s. After 0.5s, the voltage arc suppression coil implements voltage arc suppression. The control time of switches C1 and A2 on the low-voltage side of the grounding transformer is set to 0.5s to control the input voltage, and the grounding resistance is set to 1000Ω.

[0102] The voltage waveform of the fault phase after implementing the first stage of voltage arc suppression control and zero-voltage arc suppression control at the fault point is shown in the figure below. Figure 5 As shown, the voltage of the fault phase drops rapidly to 0 after 0.5s, which means that the first stage of voltage arc suppression control is achieved.

[0103] Six to eight seconds after the first stage of voltage arc suppression control ends, the second stage of voltage arc suppression, which involves detecting and controlling the extinction of the arc at the fault point, is implemented. The step-down resistor R... S The switching on is controlled by switch S2. Simulations show the resistance of the step-down resistor ranging from 0.1Ω to 3Ω, with each adjustment being 0.1Ω. Several zero-sequence voltage and zero-sequence current data points are obtained, and the zero-sequence current variation with zero-sequence voltage is shown below. Figure 6 As shown, if a transient ground fault occurs in the system, the zero-sequence current changes linearly with the zero-sequence voltage.

[0104] Based on the relationship between the zero-sequence current and the zero-sequence voltage obtained from the second stage of voltage arc suppression control, if the relationship is not linear, it is determined to be a permanent grounding fault, and the third stage of voltage arc suppression control is initiated. Figure 7 The waveforms of fault current (a) and fault phase voltage (b) after implementing the zero-current voltage reduction safe operation control at the fault point in the third stage of voltage arc suppression are shown.

[0105] During or after the third stage of control, the fault point voltage boosting protection control enters the fourth stage of voltage arc suppression, causing the fault point voltage to rise to a level greater than the line voltage but less than twice the phase voltage. This causes the fault point resistance to decrease, and the fault point grounding current to increase nonlinearly and rapidly. This triggers the selective line protection or overcurrent protection to quickly clear the fault and achieve rapid isolation of permanent faults. Figure 8 The fault current (a) and fault phase waveform (b) after the fault point boost protection control in the fourth stage of voltage arc suppression can be clearly seen. After the fault phase voltage is increased, the fault current also increases significantly. With the help of line selection protection or overcurrent protection, the fault can be quickly cleared and permanent faults can be quickly isolated.

[0106] In summary, the method provided by this invention can achieve zero-voltage arc suppression and zero-current voltage reduction for safe operation of distribution networks in the face of grounding faults in medium and low voltage distribution networks. Simulation results show that the grounding method of the distribution network via a voltage arc suppression coil provided by this invention can effectively eliminate grounding fault arcs, effectively reduce the power outage rate, meet the needs of the power grid and power companies, and reduce losses caused by distribution network grounding faults.

[0107] It should be emphasized that the examples described in this invention are illustrative rather than limiting. Therefore, this invention is not limited to the examples described in the specific embodiments. Any other embodiments derived by those skilled in the art based on the technical solutions of this invention, without departing from the spirit and scope of this invention, whether modifications or substitutions, are also within the protection scope of this invention.

Claims

1. A grounding method for a power distribution network via a voltage arc suppression coil, characterized in that: The voltage arc suppression coil includes at least an iron core with an air gap and two coil windings wound on the iron core. One end of the first coil winding is grounded via a damping resistor or directly grounded, and the other end is connected to the neutral point, phase line, or tap of the grounding transformer in the power distribution network. The second coil winding is connected to the power supply. Under normal operating conditions of the distribution network, the voltage arc suppression coil tracks the changes in the distribution network's capacitance to ground to achieve automatic tuning; under the condition of a ground fault in the distribution network, voltage arc suppression is performed, that is, the second winding injects the reverse voltage of the fault phase power supply, adjusts the voltage magnitude and phase, and forces the voltage at the fault point to be less than the fault arc reignition voltage, thereby achieving the purpose of extinguishing the arc. The voltage control strategy for voltage arc suppression of the voltage arc suppression coil is as follows: After the ground fault stabilizes, the first stage of voltage arc suppression is implemented: zero-voltage arc suppression control at the fault point. This involves controlling the voltage amplitude and phase injected into the second winding of the voltage arc suppression coil to ensure that the neutral point voltage is equal in magnitude and opposite in phase to the fault phase power supply, thereby forcing the fault point voltage to approach zero and achieving fault arc suppression. After the arc is reliably extinguished, the second stage of voltage arc suppression is implemented to detect and control the arc extinguishing at the fault point. This involves changing the voltage amplitude and phase injected into the second winding of the voltage arc suppression coil and detecting whether the zero-sequence current injected into the neutral point changes linearly with the zero-sequence voltage. If the change is linear, i.e. the arc is extinguished, the second winding of the voltage arc suppression coil stops injecting voltage, and the power distribution network resumes normal operation. Otherwise, implement the third stage of voltage arc suppression, which is zero-current voltage reduction safety operation control at the fault point. This involves adjusting the magnitude and phase of the voltage injected into the second winding of the voltage arc suppression coil to reduce the voltage at the fault point until the current at the fault point is zero. During or after the third stage of control, the fault point boost protection control enters the fourth stage of voltage arc suppression. This involves controlling the voltage amplitude and phase injected into the second winding of the voltage arc suppression coil to raise the fault point voltage to a level greater than the line voltage but less than twice the phase voltage. This causes the fault point resistance to decrease, and the grounding current at the fault point to increase nonlinearly and rapidly. This triggers the selective line protection or overcurrent protection to quickly clear the fault and achieve permanent fault isolation.

2. The method according to claim 1, characterized in that: The amplitude of the reverse voltage injected into the second winding is controlled using any one of the following three methods: First: Change the output value of the independent power electronic power supply, wherein the two ends of the second winding are connected to the independent power electronic power supply; Second: Adjust the voltage by changing the impedance value, wherein the second winding has a series impedance in the injection voltage circuit; Third: Adjust the tap position of the injection voltage circuit of the second winding. Several taps are set on the second winding, and different taps correspond to different tap positions. The injected voltage circuit is applied to the terminals of the second winding and is used to apply voltage to the second winding.

3. The method according to claim 1, characterized in that: The tuning methods for the voltage arc suppression coil include the following three: The first method is to change the air gap in the iron core; The second method is to change the number of turns of the first winding coil, wherein several turn taps are set on the first winding, and different turn taps correspond to different coil turns. The third method involves adding a third winding to the iron core. The terminals of the third winding are connected to an external inductor or capacitor, and the tuning is achieved by changing the inductance or capacitance value.

4. The method according to claim 3, characterized in that: Based on the requirement of full compensation, the required air gap size of the iron core during tuning is: ， in, Let be the permeability of the air gap. Let be the magnetic permeability of the iron core, and A be the cross-sectional area of ​​the iron core. The number of turns of the first winding. Here are the system's capacitance to ground parameters. a For the core height, b The length of the iron core base The system's power frequency angular frequency; The required air gap size for full compensation is calculated, and the most suitable air gap setting is adjusted accordingly.

5. The method according to claim 3, characterized in that: Based on the requirement of full compensation, the number of turns of the first winding during tuning is: ， ， in, The number of turns of the first winding. For iron core magnetic permeability, For iron core magnetic reluctance, Here are the system's capacitance to ground parameters. The system's power frequency angular frequency, Let be the permeability of the air gap. Let be the magnetic permeability of the iron core. a For the core height, b Where A is the length of the iron core base and A is the cross-sectional area of ​​the iron core. This refers to the size of the air gap in the iron core; The number of turns taps is adjusted based on the calculated number of turns required for full compensation.

6. The method according to claim 3, characterized in that: Based on the requirement of full compensation, the capacitance value required during tuning is: ， in, For the excitation reactance of the voltage arc suppression coil, This refers to the number of turns in the first winding of the voltage arc suppression coil. This refers to the number of turns in the third winding. Here are the system's capacitance to ground parameters. The system's power frequency angular frequency; The appropriate capacitor setting is adjusted based on the calculated equivalent capacitance required for full compensation.

7. A voltage arc suppression coil for a power distribution network, characterized in that: The voltage arc suppression coil includes at least an iron core with an air gap and two coil windings wound on the iron core; wherein, the first winding of the two coil windings is located on the primary side of the iron core, one end of the first winding is grounded through a damping resistor or directly grounded, and the other end is connected to the neutral point of the distribution network or a phase line or a tap of the grounding transformer; the second winding of the two coil windings is located on the secondary side of the iron core and is connected to a power supply; the voltage arc suppression coil is controlled by the method described in any one of claims 1-6.

8. The voltage arc suppression coil according to claim 7, characterized in that: The core of the voltage arc suppression coil is air gap adjustable and / or the secondary side of the voltage arc suppression coil is also provided with a third winding coil, which is connected to the RC switch branch to achieve the purpose of tuning the arc suppression coil.

9. An injection device based on the voltage arc suppression coil of claim 7, characterized in that: include: The voltage arc suppression coil, and the independent power electronic power supply or the reverse power supply of the distribution network.

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