Combined DC Circuit Breaker Short-Circuit Current Breaking Test Circuit and Parameter Configuration Method

Abstract

The present invention discloses a combined DC circuit breaker short-circuit current breaking test circuit and a parameter configuration method. The test circuit includes: a current source circuit, which includes a full-bridge circuit unit composed of fully controlled power semiconductor devices, a resonant reactor, and a starting switch, wherein a charging capacitor is connected across the center of the two series bridge arms of the full-bridge circuit unit; a test sample switch circuit, which includes a breaking branch, an oscillating branch, and a dissipating branch, and the three are connected in parallel. A fast-opening mechanical switch is arranged on the breaking branch, and a charging capacitor, an inductor, and an electronic trigger switch module are arranged on the oscillating branch; a voltage source circuit, which includes a charging capacitor, a resonant reactor, and a starting switch. Among them, the short-circuit current breaking test of the double-line combined DC circuit breaker is split into two single-line short-circuit current breaking tests. The present invention can provide positive and negative currents without changing the charging direction and the circuit wiring method, and at the same time realize the parameter configuration of the test circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage power transmission and transformation equipment, and particularly relates to a short-circuit current breaking test circuit and parameter configuration method for a combined DC circuit breaker. Background Art

[0002] The high-voltage DC circuit breaker is a key device in a flexible DC power grid. As a key component for selective isolation of DC-side faults in a DC power grid, the DC circuit breaker plays a dual role of control and protection in a multi-terminal high-voltage DC power transmission system.

[0003] With the multi-terminal development trend of DC power grids, compared with hybrid DC circuit breakers, the technical route of combined high-voltage DC circuit breakers has become an economical solution for multi-terminal flexible DC power grids (specifically refer to Chinese patent document CN115241850 B). However, the performance index assessment tests for them are still blank at home and abroad, which belongs to a technical problem.

[0004] In the case of insufficient direct test capacity for high-voltage level circuit breakers, to evaluate the breaking ability of the above-mentioned combined high-voltage DC circuit breaker under various faults and meet the requirements of operation performance index assessment tests, it is necessary to design a breaking test circuit and simulate different fault scenarios, such as short-circuit or over-current conditions, and record the response time of the circuit breaker, short-circuit current breaking, and other related parameters. By analyzing the test results, the reliability and performance of the circuit breaker can be evaluated, and then necessary improvement measures can be taken to improve its breaking ability. Summary of the Invention

[0005] The purpose of the present invention is to provide a short-circuit current breaking test circuit and parameter configuration method for a double-line combined DC circuit breaker, which can meet the test requirements for the breaking ability of the combined high-voltage DC circuit breaker under various faults by equivalent the current, voltage, and energy conditions in the actual DC system.

[0006] To this end, the present invention provides a short-circuit current breaking test circuit for a dual-line combined DC circuit breaker, including: a current source circuit for providing positive and reverse currents, comprising a full-bridge circuit unit composed of fully controlled power semiconductor devices, a resonant reactor Li, and a starting switch Ki, wherein a charging capacitor Ci is connected across the center of the two series bridge arms of the full-bridge circuit unit; a test sample switch circuit including a breaking branch, an oscillating branch, and a dissipating branch, which are connected in parallel. A fast-opening mechanical switch is provided on the breaking branch, and a charging capacitor C, an inductor L, and an electronic trigger switch module are provided on the oscillating branch; a voltage source circuit including a charging capacitor Cu, a resonant reactor Lu, and a starting switch Ku. The current source circuit, the test sample switch circuit, and the voltage source circuit are connected in parallel. The short-circuit current breaking test of the dual-line combined DC circuit breaker is split into two single-line short-circuit current breaking tests. During each single-line short-circuit breaking test, the breaking branch of the test sample switch circuit is connected to the breaking branch of the test sample switch circuit.

[0007] The present invention also provides a method for configuring parameters of a short-circuit current breaking test circuit for a dual-line combined DC circuit breaker, which is used to provide different short-circuit current amplitudes, different short-circuit current rising rates, and different breaking voltages. The circuit parameters include capacitance values, inductance values, pre-charging voltage values, and switching times. The method for obtaining the circuit parameters is as follows: According to the parameters of the combined DC circuit breaker to be subjected to the short-circuit current breaking test, calculate its short-circuit current and breaking recovery voltage, and then obtain the parameters of the current source circuit and the voltage source circuit of the test circuit, and configure the test circuit parameters accordingly.

[0008] The present invention equivalentizes the current, voltage, and energy conditions in the actual DC system, and utilizes the action characteristics of the circuit breaker and the variation law that the voltage and current at both ends of the contact appear at different times during the short-circuit current breaking process. The short-circuit current and the recovery voltage during the short-circuit current breaking process of the circuit breaker are provided by two sets of independent power sources respectively, and the voltage and current are superimposed on the test sample according to the standard requirements.

[0009] Compared with the prior art, the present invention has the following technical advantages / effects:

[0010] 1) In the current source circuit of the present invention, the current source resonates through a pre-charging capacitor and an inductor. There is a full-bridge circuit unit based on fully controlled power semiconductor devices around the capacitor. By means of diagonal triggering, it is possible to provide positive and reverse currents without changing the charging direction and the circuit wiring method.

[0011] 2) In the test circuit of the present invention, a calculation method for the circuit parameters is given, and then the parameter configuration of the test circuit can be realized. Furthermore, different short-circuit current amplitudes, different short-circuit current rising rates, and different breaking voltages can be provided to meet different short-circuit conditions corresponding to the combined circuit breaker.

[0012] In addition to the purposes, features and advantages described above, the present invention has other purposes, features and advantages. The present invention will be further described in detail below with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0014] Figure 1 is a schematic diagram of a typical topology of the combined DC circuit breaker proposed in an embodiment of the present invention;

[0015] Figure 2 is a schematic diagram of a short-circuit current breaking test circuit of the combined DC circuit breaker in an embodiment of the present invention;

[0016] Figure 3 is a schematic diagram of the action logic of the short-circuit current breaking test in an embodiment of the present invention;

[0017] Figure 4 is a schematic diagram of the stress analysis circuit structure of the combined DC circuit breaker in an embodiment of the present invention;

[0018] Figure 5 is a waveform diagram of the current in the breaking branch in an embodiment of the present invention;

[0019] Figure 6 is a waveform diagram of the oscillating current of the current source in an embodiment of the present invention;

[0020] Figure 7 is a waveform diagram of the oscillating current of the voltage source in an embodiment of the present invention;

[0021] Figure 8 is a waveform diagram of the resonant voltage on the resonant branch of the test switch in an embodiment of the present invention;

[0022] Figure 9 is a waveform diagram of the voltage across the contact in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0024] The typical topology of the dual-line combined DC circuit breaker is shown in Figure 1 and includes: a resonant branch (main breaking branch), a dissipative branch, two breaking branches, and two auxiliary branches.

[0025] The main breaking path, that is, the electronic trigger switch in the resonant branch, adopts a controlled resonant type main breaking switch, which includes an electronic trigger switch module composed of multiple stages of half-bridge / full-bridge sub-modules (four stages of full-bridges are shown in the figure, corresponding to the 50KV voltage level) connected in series, a resonant inductor L, and a pressure-bearing capacitor C. Each stage of the sub-module is independently powered. The breaking branch switch is only composed of a fast mechanical switch, and the auxiliary branch switch is also only composed of a fast mechanical switch. The electronic switch device only conducts the resonant current and does not break the system current.

[0026] The superiority of the combined DC circuit breaker is reflected in that it can use a set of circuits to break the short-circuit current in both directions of two branches by cooperating with the resonant branch and the breaking branch switches (CB1, CB2), and the auxiliary switches (CB3, CB4).

[0027] Due to the improvement of the topology structure, correspondingly, the fault conditions it faces have also changed compared with traditional DC circuit breakers. The fault conditions and their breaking strategies can be briefly described as the following situations:

[0028] (1) Single-pole line fault situation: One pole line operates normally, and the other pole line fails. At this time, a tripping operation can be performed on the faulty branch.

[0029] (2) Double-pole line fault situation 1: When the peak value of the oscillating current in the oscillating branch is greater than the sum of the short-circuit currents of the two faulty breaking branches, a zero-crossing tripping operation is simultaneously performed on the two faulty breaking branches. Otherwise, a zero-crossing tripping operation is performed on each faulty branch separately;

[0030] (3) Double-pole line fault situation 2: When the time difference between the faults of the two breaking branches is within the set threshold, after the mechanical switches in the two breaking branches trip successfully, the electronic trigger switch in the oscillating branch is started to work to complete the tripping operation of the two breaking lines;

[0031] (4) Double-pole line fault situation 3: When the time difference between the faults of the two breaking branches is greater than the set threshold, after the tripping operation of the breaking branch with the earlier fault is completed, the tripping operation of the other breaking branch is responded to.

[0032] It can be seen from the above analysis that for the double-line combined DC circuit breaker, the maximum short-circuit current that may appear in each branch in the four fault situations is the same and is the maximum short-circuit current of a single line. At the same time, their corresponding timing logics are similar to the single-line short-circuit current breaking test. Only the single-line short-circuit current breaking test is required below.

[0033] When the direct test capacity of high-voltage circuit breakers is insufficient, the action characteristics of the circuit breaker and the variation law of the voltage and current at both ends of the contacts during the short-circuit current breaking process are usually utilized. The short-circuit current and the recovery voltage during the short-circuit current breaking process of the circuit breaker are provided by two independent power supplies respectively, and the voltage and current are superimposed on the test sample according to the standard requirements.

[0034] Considering the particularity of its topology, the current source test circuit and the voltage source test circuit to be configured are different from those of traditional mechanical circuit breakers and hybrid circuit breakers. As shown in the appendix Figure 2 The short-circuit current breaking test circuit of the double-line combined DC circuit breaker mainly consists of three parts, namely the current source circuit, the test sample switch circuit, and the voltage source circuit.

[0035] Among them, the current source circuit designs a full-bridge circuit unit based on fully controlled power semiconductor devices, which can provide positive and negative currents. Each arm of the full-bridge circuit unit can be composed of IGBT or IGCT. At the same time, due to the characteristics of the combined DC circuit breaker, the test sample switch circuit includes the breaking branch, the oscillation branch, and the energy-consuming branch of the combined DC circuit breaker itself. The action logic of the entire test circuit is as follows:

[0036] Taking the opening of the single-line forward short-circuit current as an example, the action timing of the entire breaking test is as Figure 3 shown. Define the initial moment t 0 of the entire test logic. At this time, the charging capacitor C i of the current source circuit, the pre-charging capacitor C 0 in the test sample switch electronic trigger switch module, and the charging capacitor C v of the voltage source circuit are respectively charged with voltages U Ci , U 0 , and U Cv . The main switch K of the breaking branch is in the closed state, and the starting switch Ki of the current source circuit and the starting switch Ku of the voltage source circuit are in the open state.

[0037] 1) At the moment t 0 , close the starting switch K i of the current source circuit, trigger V 1 and V 4 . The charging capacitor C i of the current source circuit discharges to the test sample switch through the resonance reactor L i of the current source circuit, generating a forward discharge current;

[0038] 2) At the moment t 1 , the current I breaker of the breaking branch reaches the rated current value of the breaking branch, and then continues to rise until the current I breaker of the breaking branch is detected.The amplitude reaches the expected value, and the system determines that a short-circuit fault has occurred and simultaneously issues an instruction to the circuit breaker.

[0039] 3) Assume that after △T 1 time (the time for the fault current to rise to the preset value + the control and protection determination time + the time for transmitting the instruction to the circuit breaker), at time t 2 moment (at time t 1 and after △T 1 time), the circuit breaker starts to trip.

[0040] 4) At time t K1 moment (at time △T2 after time t2, (△T2 is determined by the average opening time of the main switch K of the breaking branch)), the fast-opening mechanical switch reaches the just-opened position and an arc starts to appear.

[0041] 5) At time t 3 moment, after the command is issued, the electronic trigger switch module of the test sample switch starts to act, alternately generating resonant current in this cycle until the current in the breaking branch passes through zero.

[0042] 6) At time t 4 moment, when it is detected that the current I breaker in the breaking branch is continuously less than the set value for 50 μs, it is determined that the mechanical switch has extinguished the arc and the electrical connection of the breaking branch has been disconnected. At this time, the closing voltage source loop starts the switch K u to supplement the TRV, and the charging capacitor C u of the voltage source loop passes through the resonant reactor L u of the voltage source loop and discharges to the resonant capacitor of the test sample switch until the arrester acts to consume energy and the tripping is successful.

[0043] Before conducting the short-circuit current breaking test, the present invention solves the above technical problems through the following technical means:

[0044] First, it is necessary to analyze the stress parameters of the circuit breaker to be subjected to the short-circuit current breaking test. As shown in the appendix Figure 4 and according to its characteristic parameters, the short-circuit current expression under different working conditions of short-circuit faults is obtained, as shown in Equation 1-1.

[0045]

[0046] In the formula, I main is the short-circuit current of the breaking branch, U main is the ideal DC power supply voltage, R main is the load resistance value, R Fault is the fault resistance, and L main is the inductance value of the current-limiting reactor in the breaking branch.

[0047] When building a circuit for equivalent short - circuit breaking test, the most severe working condition should be taken as a reference to input the short - circuit current under the most severe working condition. Based on Equation 1 - 1, a current - source test circuit is built according to the expression of the short - circuit current. Through the capacitance C of the current - source branch i and the inductance L of the current - source branch i resonate to generate a resonant current as shown in Equation 1 - 2:

[0048]

[0049] In the formula, I i is the current value of the current - source branch, is the pre - charging voltage value of the capacitance of the current - source branch, C i is the capacitance value of the current - source branch, L i is the inductance value of the current - source branch.

[0050] The first quarter - cycle of the generated current is intercepted. The starting time is and its amplitude is When, that is When, the ending time is determined by the rated breaking capacity of the circuit breaker (the maximum short - circuit current amplitude it can break), that is When. Among them is the input time of the current - source branch, is the output time of the voltage - source branch.

[0051] For the voltage - source circuit, when the voltage - source circuit is input, the mechanical switch of the breaking branch has been disconnected. At this time, it is equivalent to the process in which the voltage - source circuit resonates with the resonant inductance L and the resonant capacitance C in the resonant branch of the combined DC circuit breaker. It can be known that the resonant current generated in this process is as shown in Equations 1 - 3 and 1 - 4:

[0052]

[0053]

[0054] In the formula, I v is the current value of the voltage - source branch, is the pre - charging voltage value of the capacitance of the voltage - source branch; is the residual voltage on the resonant capacitance C in the resonant branch of the combined DC circuit breaker when the voltage - source branch is input; C v is the capacitance value of the voltage - source branch; L v is the inductance value of the current - source branch.

[0055] At this time, the voltage on the mechanical switch contact of the breaking branch is the sum of the voltage across the resonant capacitance C and the transient voltage induced by the resonant inductance L. The expression of the contact voltage is:

[0056]

[0057] As can be seen from the above analysis, according to the parameters of the modular DC circuit breaker to be subjected to the short-circuit current breaking test, the short-circuit current and the recovery voltage of the contact can be deduced, and then the parameters of the test current source and voltage source circuits can be obtained.

[0058] Taking the modular DC circuit breaker with a rated voltage of 50 kV and a maximum short-circuit breaking current of 30 kA as an example, the present invention has carried out an example verification. The schematic diagrams of voltage and current in the test are as Figures 5 - 7 shown, which are respectively the short-circuit current waveform diagram of the breaking branch, the oscillating current waveform diagram of the current source, the oscillating current waveform diagram of the voltage source, the resonant voltage waveform diagram on the resonant branch of the test product switch, and the contact voltage waveform diagram.

[0059] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A parameter configuration method for a short-circuit current breaking test circuit of a dual-line combined DC circuit breaker, characterized in that: Used to provide different short-circuit current amplitudes, different short-circuit current rise rates, and different break voltages. The short-circuit current breaking test circuit of the dual-line combined DC circuit breaker includes: a current source circuit for providing forward and reverse currents, including a full-bridge circuit unit composed of four fully controlled power semiconductor devices, a resonant reactor L i , start switch K i The center of the two series bridge arms of the full-bridge circuit unit is connected across a charging capacitor C i ; The switch circuit of the test product includes a disconnecting branch, an oscillating branch, and an energy-consuming branch, which are connected in parallel. The disconnecting branch is provided with a fast-disconnecting mechanical switch, and the oscillating branch is provided with a charging capacitor C, an inductor L, and an electronic trigger switch module; the voltage source circuit includes a charging capacitor C u , resonant reactor L u , start switch K u , wherein the current source circuit, the test switch circuit and the voltage source circuit are connected in parallel, and the short-circuit current breaking test of the dual-line combined DC circuit breaker is divided into two single-line short-circuit current breaking tests, and in each single-line short-circuit breaking test, its breaking branch is connected to the breaking branch of the test switch circuit, The loop parameters include capacitance value, inductance value, pre-charge voltage value and switching time. The loop parameters are obtained by calculating the short-circuit current and the break recovery voltage of the combined DC circuit breaker to be tested for short-circuit current breaking according to the parameters of the combined DC circuit breaker to be tested for short-circuit current breaking, and then obtaining the parameters of the current source circuit and the voltage source circuit of the test circuit, and configuring the test circuit parameters accordingly. The method for obtaining the loop parameters comprises the following steps: S1. Perform stress parameter analysis on the circuit breaker to be tested for short-circuit current breaking, and obtain the short-circuit current expression under different working conditions of short-circuit fault according to its characteristic parameters: -------------（1-1） In the formula To disconnect the branch short-circuit current, is the ideal DC power supply voltage, is the load resistance value, is the fault resistance, is the inductance value of the current limiting reactor of the disconnecting branch; S2. Build a current source test circuit according to the short-circuit current expression. and the current source branch inductance The resonance produces a resonant current: -------------------------（1-2） In the formula is the current value of the current source branch, is the pre-charge voltage value of the current source branch capacitor, is the capacitance value of the current source branch, is the inductance of the current source branch; S3, intercept the first quarter of the current it generates, the starting time is Its amplitude is When End time Determined by the rated breaking capacity of the circuit breaker, that is When That is the moment when the current source branch is put into operation. That is the moment when the voltage source branch is launched.

2. The parameter configuration method of the short-circuit current breaking test circuit of the dual-line combined DC circuit breaker according to claim 1 is characterized in that: The method for obtaining loop parameters also includes the following steps: S4, when the voltage source circuit is put into operation, the mechanical switch of the disconnecting branch has been disconnected. At this time, the voltage source circuit has a negative impact on the resonant inductance in the resonant branch of the combined DC circuit breaker. and resonant capacitor Resonance is performed, and the resonant current generated in this process is: ----------------（1-3） -----------------------------（1-4） In the formula is the voltage source branch current value, The voltage source branch capacitor pre-charge voltage value; When the voltage source branch is put into operation, the resonant capacitor of the combined DC circuit breaker resonant branch Residual pressure on is the capacitance value of the voltage source branch; is the inductance of the current source branch; S5. The voltage on the disconnecting branch mechanical switch is the resonant branch capacitance. The voltage across the resistor and the resonant inductor The sum of the induced transient voltages and the fracture voltage expression are: 。 3. The parameter configuration method of the short-circuit current breaking test circuit of the dual-line combined DC circuit breaker according to claim 1 is characterized in that: The capacitance value and the inductance value of the voltage source branch and the current source branch are determined according to the capacitor and inductor selection.

4. The parameter configuration method of the short-circuit current breaking test circuit of the dual-line combined DC circuit breaker according to claim 1 is characterized in that: By controlling the gating state of the fully controlled power semiconductor devices of the full-bridge circuit unit, the current source loop generates a forward current or a reverse current.

5. The parameter configuration method of the short-circuit current breaking test circuit of the dual-line combined DC circuit breaker according to claim 1 is characterized in that: The electronic trigger switch module is composed of a multi-stage half-bridge sub-module, and each half-bridge sub-module has a pre-charge capacitor C0.

6. The parameter configuration method of the short-circuit current breaking test circuit of the dual-line combined DC circuit breaker according to claim 1 is characterized in that: The electronic trigger switch module is composed of a multi-stage full-bridge sub-module, and each full-bridge sub-module has a pre-charge capacitor C0.

7. The parameter configuration method of the short-circuit current breaking test circuit of the dual-line combined DC circuit breaker according to claim 5 or 6, characterized in that: Before the initial time t0 of the entire test, the charging capacitor Ci, the pre-charging capacitor C0 in the electronic trigger switch module of the test switch and the charging capacitor Cv of the voltage source circuit are charged to the voltages UCi, U0 and UCv respectively, so that the main switch K of the disconnecting branch is in the closed state, and the current source circuit starting switch Ki and the voltage source circuit starting switch Ku are in the open state.

8. The parameter configuration method of the short-circuit current breaking test circuit of the dual-line combined DC circuit breaker according to claim 7, characterized in that: The switch action timing control strategy in the short-circuit current breaking test is as follows: 1) At t0, the closing current source circuit starts switch K i , triggering the full-bridge circuit unit, so that the current source loop charges the capacitor C i Through the current source loop resonant reactor L i Discharge to the test switch to generate a forward discharge current; 2) At time t1, the branch current is disconnected Reach the rated current value of the disconnected branch, and then continue to rise until the disconnected branch current is detected When the amplitude reaches the expected value, the system determines that a short circuit fault has occurred and sends instructions to the circuit breaker at the same time; 3) At t2, the circuit breaker starts to open, where t2 is the time △T1 after t1, △T1 = the time when the fault current rises to the preset value + the control and protection judgment time + the time when the command is transmitted to the circuit breaker; 4) t K1 At this moment, the quick-opening mechanical switch reaches the just-opening position and an arc begins to appear. K1 The time is △T2 after the time t2, △T2 is determined by the average disconnection time of the main switch K of the disconnected branch; 5) At t3, after the command is issued, the electronic trigger switch module of the test switch starts to operate, alternately generating resonant current in this cycle until the current of the disconnected branch passes through zero; 6) At t4, the disconnected branch current is detected When the value is less than the set value for 50μs continuously, the mechanical switch is judged to be arc-extinguished and the electrical connection of the disconnected branch has been disconnected. At this time, the closing voltage source circuit starts the switch K u To supplement TRV, the voltage source loop charges the capacitor C u Through the voltage source loop resonant reactor L u Discharge the resonant capacitor of the test switch until the arrester operates to consume energy and the switch is opened successfully.

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