Transient equivalent analysis circuit of capacitor voltage transformer under lightning impulse

Abstract

The invention relates to a transient equivalent analysis circuit of a capacitive voltage transformer under lightning impulse, which comprises a capacitive voltage divider and an electromagnetic unit connected with the capacitive voltage divider, and is characterized in that the capacitive voltage divider is used for distributing high-voltage signals of a primary side power grid by utilizing a series capacitor voltage dividing principle; the capacitive voltage divider comprises a plurality of equivalent circuit units of a high-voltage capacitor element, an equivalent circuit unit of a medium-voltage capacitor element and an equivalent circuit unit of a transient capacitor element which are sequentially connected in series, and the electromagnetic unit comprises an intermediate transformer capacitance effect subunit, a composite reactance subunit and a damper. The intermediate transformer capacitance effect subunit is connected to the two ends of the equivalent circuit unit of the medium-voltage capacitor element through the composite reactance subunit, and the damper is connected to the secondary side of the equivalent circuit subunit of the intermediate transformer. Compared with the prior art, the method has the advantages that the actual electrical behavior of the capacitor voltage transformer under the lightning impulse can be accurately simulated, and the like.

Description

Technical Field

[0001] The invention relates to the technical field of electric power devices and testing, and in particular to a transient equivalent analysis circuit of a capacitive voltage transformer under lightning impulse. Background Art

[0002] Lightning is a high-voltage, high-current discharge phenomenon that occurs frequently in nature and has a significant impact on the safety of power equipment. Lightning overvoltage is mainly caused by lightning discharge. When lightning directly hits electrical equipment, or lightning hits the system to which the electrical equipment is connected (such as the grounding system) and breaks through the original insulation path to conduct to the electrical equipment, or lightning causes rapid changes in voltage / current in the surrounding area, causing the voltage of the electrical equipment to rise rapidly, overvoltage will be formed and threaten the safe operation of the electrical equipment. This overvoltage can damage electrical equipment, cause insulation breakdown or equipment failure, and in severe cases, trigger unstable operation of the power system.

[0003] Capacitor Voltage Transformer (CVT) is mainly used in power systems to measure, monitor and analyze voltage signals in power grids in real time, provide voltage signals for power system protection and control equipment, and assist in detecting and responding to faults. With climate change and the continuous increase in the scale of power systems, the losses and accidents caused by lightning overvoltage in CVT have increased significantly, such as the problem of inaccurate voltage measurement under lightning impulses.

[0004] On the other hand, 500kV CVT needs not only basic analysis models that consider long-term working voltage conditions, but also response analysis capabilities to lightning impulse voltage during design, operation, and maintenance. However, existing CVT analysis models are mostly focused on the physical structure of traditional CVT, including power frequency equivalent circuit models, harmonic transfer circuit models, etc., with only power frequency steady-state analysis, harmonic analysis, and frequency domain characteristic analysis capabilities, and do not have the ability to analyze lightning impulse transient high frequencies (0.1-100MHz), resulting in high-frequency response distortion, transient characteristic loss, and other problems. It is necessary to study transient equivalent analysis circuits suitable for 500kV CVT under lightning impulses. Summary of the invention

[0005] The purpose of the present invention is to provide a transient equivalent analysis circuit of a capacitor voltage transformer under lightning impulse, which can accurately simulate the actual electrical behavior of the capacitor voltage transformer under lightning impulse.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A transient equivalent analysis circuit for a capacitive voltage transformer under lightning impulse comprises a capacitive voltage divider and an electromagnetic unit connected thereto.

[0008] The capacitive voltage divider is used to distribute the high-voltage signal of the primary side power grid using the series capacitor voltage division principle. The capacitive voltage divider includes a plurality of equivalent circuit units of high-voltage capacitor elements, equivalent circuit units of medium-voltage capacitor elements and equivalent circuit units of transient capacitor elements connected in series in sequence.

[0009] The electromagnetic unit includes an intermediate transformer capacitance effect subunit, a composite reactance subunit and a damper. The transformer capacitance effect subunit is connected to both ends of the equivalent circuit unit of the medium voltage capacitor element via the composite reactance subunit. The damper is connected to the secondary side of the intermediate transformer capacitance effect subunit.

[0010] Furthermore, the equivalent circuit unit of the high-voltage capacitor element includes a high-voltage capacitor C1, a parasitic inductor L1 that affects the transient response of the circuit, and a parasitic resistor R1 that prevents oscillation caused by sudden changes in voltage or current. L1 , R C1 The parasitic inductance L1, the high voltage capacitor C1 and the parasitic resistance R C1 The high voltage capacitor C1 and the medium voltage capacitor element are connected in series, and the parasitic inductance L1 and the parasitic resistance R L1 Connect in parallel.

[0011] Furthermore, the equivalent circuit unit of the medium voltage capacitor element includes a medium voltage capacitor C2, a parasitic inductor L2 that affects the transient response of the circuit, and a parasitic resistor R2 that prevents oscillation caused by sudden changes in voltage or current. L2 , R C2 , the medium voltage capacitor C2 is connected in turn with the parasitic resistance R C2 and a parasitic inductance L2 connected in series, wherein the parasitic inductance L2 and the parasitic resistance R L2 Connect in parallel.

[0012] Furthermore, the equivalent circuit unit of the transient capacitor element includes a transient capacitor C3, a parasitic inductor L3 that affects the transient response of the circuit, and a parasitic resistor R that prevents oscillation caused by sudden changes in voltage or current. L3 , R C3 , the transient capacitor C3 is in turn connected to the parasitic resistor R C3 and a parasitic inductance L3 connected in series, wherein the parasitic inductance L3 and the parasitic resistance R L3 Connect in parallel.

[0013] Furthermore, the intermediate transformer capacitance effect subunit includes an intermediate transformer T, a stray capacitance C between the primary and secondary windings and the ground. T1p , C T2p , C T3p and the coupling capacitor C between the primary and secondary windings Ts2 , C Ts3, the stray capacitance C T1p Connected across the primary winding of the intermediate transformer T, the stray capacitance C T2p , C T3p It is connected in parallel across the secondary winding of the intermediate transformer T, and one end of each is connected to the ground.

[0014] Furthermore, the damper is connected to the secondary winding of the intermediate transformer T, and the damper includes a damping resistor R providing a damping effect. D And the reactor L to improve the frequency response D , the damping resistor R D And the reactor L D Series connection.

[0015] Furthermore, the intermediate transformer capacitance effect subunit also includes an excitation winding resistor R m and the excitation winding inductance L connected in series with it m , the field winding resistance R m and the field winding inductance L m The primary winding of the transformer T is connected across the middle, and the stray capacitance C T1p in parallel.

[0016] Furthermore, the composite reactance subunit includes a compensating reactor L k , Winding equivalent resistance R caused by skin effect K And the equivalent stray capacitance C caused by the inductance and capacitance effect in the high-frequency environment of lightning K , the winding equivalent resistance R K With compensation reactor L k connected in series, the equivalent stray capacitance C K The two-end circuit is connected to the winding equivalent resistance R K With compensation reactor L k Two ends of the circuit, and one end of the circuit is connected between the equivalent circuit unit of the high-voltage capacitor element and the equivalent circuit unit of the medium-voltage capacitor element, and the other end of the circuit is connected to the intermediate transformer T.

[0017] Furthermore, it also includes an equivalent inductance between the earth and the capacitive voltage divider, and the equivalent inductance is used to describe the inductive blocking effect of the earth on the lightning current under the lightning strike.

[0018] Furthermore, it also includes an equivalent resistance between the earth and the capacitive voltage divider, and the equivalent resistance is used to describe the resistive blocking effect of the earth on the lightning current under the lightning impulse.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention models the transient equivalent analysis circuit of a capacitive voltage transformer under lightning impulse. The constructed circuit includes an equivalent analysis circuit of electrical components such as a capacitive voltage divider, an intermediate transformer capacitive effect subunit in an electromagnetic unit, a composite reactance subunit, and a damper under lightning impulse. The circuit can accurately simulate the actual electrical behavior of the capacitive voltage transformer under lightning impulse and effectively capture the transient characteristics of lightning impulse.

[0021] (2) The transient equivalent analysis circuit of the present invention takes into account the parasitic parameters that affect the transmission of high-frequency voltage signals, designs and optimizes the 500kV CVT circuit model, and can effectively improve the time domain and frequency domain response accuracy of the 500kV capacitive voltage transformer under the transient high frequency of lightning impulse, providing a feasible analysis circuit for the analysis of lightning impulse conditions encountered in the actual application of capacitive voltage transformers.

[0022] (3) The transient equivalent analysis circuit model of the present invention is based on the electromagnetic transient simulation program and not only has the ability of power frequency steady-state analysis, harmonic analysis, and frequency domain characteristic analysis, but also has the ability of lightning impulse high-frequency transient response analysis, which makes up for the problems of high-frequency response distortion and transient characteristic loss of the traditional capacitive voltage transformer circuit model under lightning conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of a transient equivalent analysis circuit of a 500kV CVT of the present invention;

[0024] Figure 2 The electrical schematic diagram of the 500kV CVT of the present invention;

[0025] Figure 3 The input and measurement voltage signals of the 500kV CVT under lightning impulse of the present invention;

[0026] Figure 4 The lightning input of the 500kV CVT and the C3 measured voltage signal when the L3 parameter of the present invention changes;

[0027] Figure 5 R of the present invention k Lightning input of 500kV CVT and C3 measured voltage signal when parameters change;

[0028] Figure 6 L of the present invention g Lightning input of 500kV CVT and C3 measured voltage signal when parameters change. DETAILED DESCRIPTION

[0029] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0030] This embodiment provides a transient equivalent analysis circuit for a capacitive voltage transformer under lightning impulse, and the transient equivalent analysis circuit is applicable to a 500kV CVT. Figure 2 The 500kV CVT electrical schematic diagram shown in the figure shows that the 500kV CVT is mainly composed of a capacitor voltage divider and an electromagnetic unit. The part in the dotted box is the electromagnetic unit. The capacitor voltage divider is connected in series with a transient capacitor C3 based on the original high-voltage capacitor C1 and medium-voltage capacitor C2. The function of the capacitor voltage divider is to distribute the high-voltage signal of the primary side power grid using the series capacitor voltage division principle. The electromagnetic unit consists of an intermediate transformer T, a compensation reactor L k , and the damper R D Among them, T can transform the voltage obtained by C2 from the primary side to obtain the applicable standard voltage transformation that meets the secondary side measurement device; L k It can adjust the inductive and capacitive reactances in the circuit, which is helpful to reduce the impact on the accuracy of CVT. D The addition of is used to suppress the occurrence of ferromagnetic resonance. In the figure, a and n are the secondary winding lead-out terminals for measuring voltage signals; da and dn are R D Lead terminal; u is the primary input voltage of CVT, u c1 、u c2 、u c3 Represent the voltages on capacitors C1, C2, and C3 respectively.

[0031] The key step in implementing the path planning is to conduct transient equivalent analysis of the 500kV CVT according to the electrical schematic diagram. First, the voltage-dividing capacitors C1, C2, and C3 in the 500kV CVT are analyzed equivalently, including the parasitic inductances L1, L2, and L3 that affect the transient response of the circuit, and the parasitic resistance R that prevents oscillation caused by sudden changes in voltage or current. L1 , R C1 , R L2 , R C2 , R L3 , R C3 , forming multiple equivalent circuit units of high-voltage capacitor elements, medium-voltage capacitor elements and transient capacitor elements connected in series. L1 , R C1 , R L2 , R C2 , R L3 , R C3The transient high frequency of lightning impulse may cause measurement errors, affecting the measurement accuracy of 500kV CVT. L1 , R C1 , R L2 , R C2 , R L3 , R C3 The transient response of 500kV CVT under lightning impulse is more accurately simulated to simulate the actual electrical behavior of CVT under lightning impulse. In the equivalent circuit unit of high-voltage capacitor element, parasitic inductance L1 and parasitic resistance R C1 connected in series, the parasitic resistance R C1 The high voltage capacitor C1 is connected in series with the equivalent circuit unit of the composite reactance subunit and the medium voltage capacitor element, respectively. The parasitic inductance L1 and the parasitic resistance R L1 In the equivalent circuit unit of the medium voltage capacitor element, the medium voltage capacitor C2 is connected in series with the parasitic resistor R C2 and a parasitic inductance L2 connected in series, wherein the parasitic inductance L2 and the parasitic resistance R L2 The parasitic inductance L2 is connected in parallel with the equivalent circuit unit of the transient capacitance element. In the equivalent circuit unit of the transient capacitance element, the transient capacitance C3 is connected in sequence with the parasitic resistance R C3 and a parasitic inductance L3 connected in series, wherein the parasitic inductance L3 and the parasitic resistance R L3 Connect in parallel.

[0032] Secondly, the compensating reactor L in the 500kV CVT k Perform equivalence analysis, L k The equivalent circuit of the winding needs to take into account the equivalent resistance R caused by the skin effect. K And the equivalent stray capacitance C K The inductance and capacitance effects caused by lightning high frequency environment form a composite reactance subunit. In this subunit, the equivalent stray capacitance C K The two-end circuit is connected to the winding equivalent resistance R K With compensation reactor L k Two ends of the circuit, and one end of the circuit is connected between the equivalent circuit unit of the high-voltage capacitor element and the equivalent circuit unit of the medium-voltage capacitor element, and the other end of the circuit is connected to the intermediate transformer T.

[0033] Then, when analyzing the intermediate transformer in the 500kV CVT, in addition to the transformer primary winding leakage inductance L T1 , Winding resistance R T1 , secondary winding leakage inductance L T2 , Winding resistance R T2 , and the field winding resistance R m , field winding inductance Lm , the related capacitance effect of T caused by the change of transmission frequency must also be considered. Including the stray capacitance C of the winding on both sides to the ground T1p , C T2p , C T3p and the coupling capacitor C between the primary and secondary windings Ts2 , C Ts3 Then, considering that the 500kV CVT is mainly composed of capacitors and nonlinear inductance elements, it is easy to excite ferromagnetic resonance during transient processes. Therefore, when analyzing the damper in the 500kV CVT, the damping resistor R that provides the damping effect is also considered. D And the reactor L to improve the frequency response D In this subunit, the stray capacitance C T1p Connected across the primary winding of the intermediate transformer T, the stray capacitance C T2p , C T3p It is connected to the secondary winding of the intermediate transformer T, and one end of it is connected to the ground.

[0034] Finally, the proposed analysis circuit also considers the equivalent inductance L of the CVT external grounding conductor and the earth under lightning strike. g and resistor R g , the equivalent inductance L g and resistor R g By connecting with the equivalent circuit units of transient capacitor elements in sequence, accurate modeling can simulate the actual electrical behavior of 500kV CVT under lightning impulse, laying the foundation for the optimal design of 500kV CVT in practical applications.

[0035] The final formation is Figure 1 The 500kV CVT transient equivalent analysis circuit is shown.

[0036] The constructed transient equivalent analysis circuit is simulated and analyzed through the ATP-EMTP electromagnetic transient analysis simulation program to provide a reliable basis for evaluating the overvoltage monitoring level of the 500kV CVT under lightning conditions. First, the HEIDLER model is used as the lightning impulse wave model to generate a standard lightning voltage waveform with a wavefront time of 1.2μs and a half-peak time of 50μs as the input of the primary side of the 500kV CVT. Secondly, based on ATP-EMTP, the transient equivalent analysis circuit and the lightning impulse wave circuit are modeled, and the correctness and effectiveness of the proposed transient equivalent analysis circuit are verified according to the waveform response of C3 after the lightning voltage input. Figure 3The figure shows the transient response waveform of the primary side of a 500kV CVT under lightning impulse. The upper curve in the figure is the lightning impulse waveform, and the lower curve represents the voltage signal measured by C3. It can be found from the figure that when the primary side input is a standard lightning wave, the waveform response error of the transient capacitor C3 of the 500kV CVT after the lightning voltage input is ≤3%, which verifies the correctness and effectiveness of the proposed transient equivalent analysis circuit.

[0037] Based on the quantitative analysis method, the ATP-EMTP electromagnetic transient analysis simulation program is used to analyze the impact of changes in internal and external parameters of 500kV CVT on the transient response under lightning impulse. That is, while ensuring that other structural parameters remain unchanged, a certain parameter is changed one by one, and the waveform response of C3 after the lightning voltage input is analyzed. The specific operation method is as follows: Select L3 and R in the 500kV CVT transient equivalent analysis circuit. k , L g Parameters as an example for verification.

[0038] 1) Analyze the influence of L3 on the transient response of 500kV CVT under lightning impulse. When L3 changes alone, it is set as a single variable, with values ​​of 1μH, 5μH, and 10μH respectively, and other structural parameters remain unchanged. Figure 4 As shown in the figure, the CVT lightning input voltage signal and the measured output voltage signal when the L3 parameter changes. It can be seen from the figure that as L3 continues to increase, the transient response curve of C3 under lightning impulse basically coincides, and will not affect the transient response of CVT.

[0039] 2) Analysis of R k Impact on the transient response of 500kV CVT under lightning impulse. k When changing individually, the values ​​are 10Ω, 100Ω, and 200Ω respectively, and other structural parameters remain unchanged. Figure 5 As shown, R k CVT lightning input voltage signal and measured output voltage signal when parameters change. It can be seen from the figure that as R k As the voltage continues to increase, the transient response curve of C3 under lightning impulse basically coincides, which will not affect the transient response of CVT.

[0040] 3) Analysis of L g The impact on the transient response of 500kV CVT under lightning impulse. g When changing individually, the values ​​are 1μH, 20μH, and 60μH respectively. Figure 6 As shown, L g CVT lightning input voltage signal and measured output voltage signal when parameters change. It can be seen from the figure that as L gAs the inductance of the grounding lead and the earth increases, the transient response curve of C3 under lightning impulse shows an oscillation phenomenon, which indicates that the equivalent inductance of the grounding lead and the earth under lightning impulse will have a non-negligible influence on the transient response of CVT.

[0041] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0042] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A transient equivalent analysis circuit for a capacitive voltage transformer under lightning impulse, characterized in that: It includes a capacitive voltage divider and an electromagnetic unit connected thereto, The capacitive voltage divider is used to distribute the high-voltage signal of the primary side power grid using the series capacitor voltage division principle. The capacitive voltage divider includes a plurality of equivalent circuit units of high-voltage capacitor elements, equivalent circuit units of medium-voltage capacitor elements and equivalent circuit units of transient capacitor elements connected in series in sequence. The electromagnetic unit includes an intermediate transformer capacitance effect subunit, a composite reactance subunit and a damper. The transformer capacitance effect subunit is connected to both ends of the equivalent circuit unit of the medium voltage capacitor element via the composite reactance subunit. The damper is connected to the secondary side of the intermediate transformer capacitance effect subunit.

2. The transient equivalent analysis circuit of a capacitive voltage transformer under lightning impulse according to claim 1 is characterized in that: The equivalent circuit unit of the high-voltage capacitor element includes a high-voltage capacitor C1, a parasitic inductor L1 that affects the transient response of the circuit, and a parasitic resistor R that prevents oscillation caused by sudden changes in voltage or current. L1 , R C1 The parasitic inductance L1, the high voltage capacitor C1 and the parasitic resistance R C1 The high voltage capacitor C1 and the medium voltage capacitor element are connected in series, and the parasitic inductance L1 and the parasitic resistance R L1 Connect in parallel.

3. The transient equivalent analysis circuit of a capacitive voltage transformer under lightning impulse according to claim 1 is characterized in that: The equivalent circuit unit of the medium voltage capacitor element includes a medium voltage capacitor C2, a parasitic inductor L2 that affects the transient response of the circuit, and a parasitic resistor R that prevents oscillation caused by sudden changes in voltage or current. L2 , R C2 , the medium voltage capacitor C2 is connected in turn with the parasitic resistance R C2 and a parasitic inductance L2 connected in series, wherein the parasitic inductance L2 and the parasitic resistance R L2 Connect in parallel.

4. The transient equivalent analysis circuit of a capacitive voltage transformer under lightning impulse according to claim 1 is characterized in that: The equivalent circuit unit of the transient capacitance element includes a transient capacitance C3, a parasitic inductance L3 that affects the transient response of the circuit, and a parasitic resistance R that prevents oscillation caused by sudden changes in voltage or current. L3 , R C3 , the transient capacitor C3 is in turn connected to the parasitic resistor R C3 and a parasitic inductance L3 connected in series, wherein the parasitic inductance L3 and the parasitic resistance R L3 Connect in parallel.

5. The transient equivalent analysis circuit of a capacitive voltage transformer under lightning impulse according to claim 1, characterized in that: The intermediate transformer capacitance effect subunit includes an intermediate transformer T, a primary side winding and a secondary side winding to ground stray capacitance C T1p , C T2p , C T3p and the coupling capacitor C between the primary and secondary windings Ts2 , C Ts3 , the stray capacitance C T1p Connected across the primary winding of the intermediate transformer T, the stray capacitance C T2p , C T3p It is connected in parallel across the secondary winding of the intermediate transformer T, and one end of each is connected to the ground.

6. The transient equivalent analysis circuit of a capacitive voltage transformer under lightning impulse according to claim 5, characterized in that: The damper is connected to the secondary winding of the intermediate transformer T, and includes a damping resistor R that provides a damping effect. D And the reactor L to improve the frequency response D , the damping resistor R D And the reactor L D Series connection.

7. The transient equivalent analysis circuit of a capacitive voltage transformer under lightning impulse according to claim 5, characterized in that: The intermediate transformer capacitance effect subunit also includes the excitation winding resistance R m and the excitation winding inductance L connected in series with it m , the field winding resistance R m and the field winding inductance L m The primary winding of the transformer T is connected across the middle, and the stray capacitance C T1p in parallel.

8. The transient equivalent analysis circuit of a capacitive voltage transformer under lightning impulse according to claim 1, characterized in that: The composite reactance subunit includes a compensating reactor L k , Winding equivalent resistance R caused by skin effect K And the equivalent stray capacitance C caused by the inductance and capacitance effect in the high-frequency environment of lightning K , the winding equivalent resistance R K With compensation reactor L k connected in series, the equivalent stray capacitance C K The two-end circuit is connected to the winding equivalent resistance R K With compensation reactor L k Two ends of the circuit, and one end of the circuit is connected between the equivalent circuit unit of the high-voltage capacitor element and the equivalent circuit unit of the medium-voltage capacitor element, and the other end of the circuit is connected to the intermediate transformer T.

9. The transient equivalent analysis circuit of a capacitive voltage transformer under lightning impulse according to claim 1, characterized in that: It also includes an equivalent inductance between the earth and the capacitive voltage divider, and the equivalent inductance is used to describe the inductive blocking effect of the earth on the lightning current under the lightning strike.

10. The transient equivalent analysis circuit of a capacitive voltage transformer under lightning impulse according to claim 1, characterized in that: It also includes an equivalent resistance between the earth and the capacitive voltage divider, and the equivalent resistance is used to describe the resistive blocking effect of the earth on the lightning current under the lightning impulse.

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