Device for measuring system capacitance current by using injection method

Abstract

The utility model discloses a device for measuring system capacitance current by using an injection method. The device comprises a measurement and signal generator and an integrated injection transformer, the measurement and signal generator internally comprises an H-bridge inversion unit, an LCL filter circuit, a power supply and a controller; the integrated injection transformer comprises a boosting transformer, a voltage transformer and a current transformer; the output end of the controller is connected with the controlled end of the H-bridge inverter unit; the power supply, the H-bridge inverter unit and the LCL filter circuit are sequentially connected in series, the output end of the H-bridge inverter unit is connected to the boosting transformer through the LCL filter circuit, and the other end of the boosting transformer is a signal output end X. According to the utility model, signals with different frequencies are injected into the system, and the capacitance current of the system is calculated by establishing a loop equation according to different zero sequence loop impedances of the system under different frequencies; as the measurement and signal generator and the boosting transformer are large in capacity, the requirement for accurate back measurement after signal injection is met, and therefore the measurement accuracy is high.

Description

Technical Field

[0001] This invention relates to the field of automatic tracking devices for resonant grounding systems in power distribution networks, and in particular to a system capacitance current measuring device. Background Technology

[0002] In power distribution networks, a common grounding method is to ground the neutral point through an arc suppression coil. By adjusting the tap position of the arc suppression coil, the system capacitive current is calculated using the tuning curve method and the incremental method before and after the tap change. Then, the inductive reactance of the arc suppression coil is adjusted to approximately equal the system capacitive reactance. When a ground fault occurs, the grounding point current is compensated, achieving the purpose of extinguishing the arc. Therefore, accurate calculation of the capacitive current is crucial. The tap adjustment method for calculating the system capacitive current is a passive measurement method. When the system imbalance is very small, this method has a very large calculation error, making it difficult to accurately track and compensate.

[0003] As the capacity of power distribution networks increases, the amount of cables used also increases, leading to a larger system capacitive current while the system imbalance decreases. This undoubtedly increases the difficulty of calculating the capacitive current using the tap-adjustment method. In mountainous and long-distance transmission systems, overhead lines are still used, resulting in significant system imbalance. To suppress series resonance, arc suppression coils require high-resistance damping resistors with very high damping ratios. The tuning curve of the arc suppression coils is very smooth, leading to large errors in calculating the system capacitive current using the tap-adjustment method, and making it impossible for arc suppression devices to accurately track the current.

[0004] Another method for measuring system capacitive current is to calculate the capacitive current by injecting a signal through an open delta PT. However, this method is limited by the small secondary capacitance of the PT, resulting in a very small injected signal and poor measurement accuracy. Furthermore, the PT harmonic suppressor and arc suppression coil need to be disconnected during measurement, limiting its application scenarios. Utility Model Content

[0005] The technical problem to be solved by this invention is to provide a device for measuring system capacitance current using the injection method, thereby improving the accuracy of system capacitance current calculation.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows.

[0007] An apparatus for measuring system capacitive current using an injection method includes a measuring and signal generator and an integrated injection transformer. The measuring and signal generator internally includes an H-bridge inverter unit, an LCL filter circuit, a power supply, and a controller. The integrated injection transformer includes a step-up transformer, a voltage transformer, and a current transformer. The input terminal of the controller is connected to the signal terminals of the voltage transformer and the current transformer, respectively, and the output terminal of the controller is connected to the controlled terminal of the H-bridge inverter unit. The power supply, the H-bridge inverter unit, and the LCL filter circuit are connected in series. The output terminal of the H-bridge inverter unit is connected to the primary side of the step-up transformer via the LCL filter circuit. One end of the secondary side of the step-up transformer is grounded via the current transformer, and the other end of the secondary side of the step-up transformer is the signal output terminal X.

[0008] Preferably, the LCL filter circuit includes a first inductor, a capacitor, and a second inductor. The first inductor and the second inductor are connected in series between one input terminal of the step-up transformer and one output terminal of the H-bridge inverter unit. One end of the capacitor is connected to the junction of the first inductor and the second inductor, and the other end is connected to the other input terminal of the step-up transformer and the other output terminal of the H-bridge inverter unit, respectively.

[0009] The technological advancements achieved by this utility model are as follows, due to the adoption of the above technical solutions.

[0010] This invention injects signals of different frequencies into the system using a measuring and signal generator. Utilizing the different zero-sequence loop impedances at different frequencies, the system's capacitive current is calculated by establishing loop equations. Because of the injected signal, the calculation of the system capacitive current is unaffected by system unbalanced voltage; even if the unbalanced voltage is zero, the system capacitive current can still be calculated. Furthermore, the measuring and signal generator and the step-up transformer have large capacities, meeting the requirement for accurate backtesting after signal injection, thus resulting in high measurement accuracy. Attached Figure Description

[0011] Figure 1 This is a structural block diagram of the present invention;

[0012] Figure 2 This is an application diagram of the present invention connected to the neutral point of a parallel capacitor system;

[0013] Figure 3 for Figure 2 The zero-order equivalent diagram of the system;

[0014] Figure 4 This is an application diagram of the present invention connected to the neutral point system of the arc suppression coil;

[0015] Figure 5 for Figure 4 The zero-order equivalent diagram of the system;

[0016] Figure 6This is an application diagram of the parallel capacitor neutral point measurement system with arc suppression coil of this utility model;

[0017] Figure 7 This is a diagram showing the impedance conversion between series and parallel.

[0018] Wherein: L1. First inductor, C. Capacitor, L2. Second inductor, HQ. H-bridge converter, DY. Power supply, KZQ. Controller, B. Step-up transformer, PT. Voltage transformer, LH. Current transformer. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0020] A device for measuring system capacitive current using an injection method, the structure of which is as follows: Figure 1 As shown, it includes a measurement and signal generator and an integrated injection transformer. The measurement and signal generator is used to generate signals of different frequencies to inject into the system, and to establish loop equations to calculate the system capacitance current based on the different zero-sequence loop impedances of the system at different frequencies; the integrated injection transformer injects the different frequency signals generated by the measurement and signal generator into the system.

[0021] The measurement and signal generator internally includes an H-bridge inverter unit HQ, an LCL filter circuit, a power supply DY, and a controller KZQ. The integrated injection transformer includes a step-up transformer B, a voltage transformer PT, and a current transformer CT.

[0022] The input terminals of the controller KZQ are connected to the signal terminals of the voltage transformer PT and the current transformer CT, respectively, to collect the voltage and current changes of the system. The output terminal of the controller KZQ is connected to the controlled terminal of the H-bridge inverter unit HQ, to send control signals of varying frequencies to the H-bridge inverter unit, and can calculate the zero-sequence loop impedance based on the collected voltage and current changes, and at the same time establish loop equations at different frequencies to calculate the capacitor current.

[0023] The power supply DY, H-bridge inverter unit HQ, and LCL filter circuit are connected in series. The output terminal of H-bridge inverter unit HQ is connected to the primary side of step-up transformer B through LCL filter circuit. One end of the secondary side of step-up transformer B is grounded through current transformer CT, and the other end of the secondary side of step-up transformer B is the signal output terminal X.

[0024] The LCL filter circuit includes a first inductor L1, a capacitor C, and a second inductor L2. The first inductor L1 and the second inductor L2 are connected in series between one input terminal of the step-up transformer B and one output terminal of the H-bridge inverter unit HQ. One end of the capacitor C is connected to the junction of the first inductor L1 and the second inductor L2, and the other end is connected to the other input terminal of the step-up transformer B and the other output terminal of the H-bridge inverter unit HQ.

[0025] When this invention is applied to a neutral-point ungrounded system, the system is equipped with a compensation capacitor. The signal output terminal X of the device can be connected to the neutral point of the compensation capacitor for measurement. Figure 2 As shown, its zero-sequence equivalent diagram is as follows: Figure 3 As shown, where: U s X is the voltage of the variable signal source. CB To compensate for the capacitor reactance, X LB X is the reactance of the series reactor, Is is the output current of the signal source, and X is the reactance of the series reactor. c For the system's ground capacitance that needs to be solved, R sys Let U0 be the system resistance to ground that needs to be solved, U0 be the voltage injected into the system side by the signal source, and I0 be the current injected into the system side by the signal source. The system parallel impedance parameters include the system capacitive reactance X. c and system-to-ground resistance R sys .

[0026] During normal system operation, the measuring device injects a fixed frequency f1 (corresponding to angular frequency ω1) and an amplitude of U into the system. s The voltage signal is used to acquire the injected current I in the system through a current transformer. s ; By principle Figure 3 The zero-sequence loop current I0 on the system side can be calculated, which is also the current injected into the system side by the variable signal source.

[0027]

[0028] The system-side voltage can be directly calculated based on the system-side voltage, current, and compensation capacitor impedance. .

[0029]

[0030] The system impedance is:

[0031]

[0032] Among them: Z P1 The system-side complex impedance calculated when the signal source outputs frequency f1; R Pω1 For the system-side complex impedance Z P1 The real part of X; Pω1 For the system-side complex impedance Z P1 The imaginary part of ; j is a unit vector.

[0033] Then, by impedance transformation, the parallel impedance parameter of the actual system—the system capacitive reactance X—can be obtained. c and system-to-ground resistance R sys The impedance series-to-parallel conversion principle diagram is as follows: Figure 7 As shown.

[0034]

[0035]

[0036] Where: X Cω1 The system's capacitive reactance to ground at frequency f1; R SYS R is the system's resistance to ground. Pω1 For the system-side complex impedance Z P1 The real part of X; Pω1 For the system-side complex impedance Z P1 The imaginary part.

[0037] The system's capacitive reactance to ground at power frequency is obtained by performing frequency transformation:

[0038]

[0039] Where: X Cω1 The system's capacitive reactance to ground at frequency f1; X C This represents the system's capacitive reactance to ground at a frequency of 50Hz.

[0040] The system capacitor current can be calculated by dividing the system bus phase voltage by X. C get.

[0041] When this invention is applied to a system equipped with an arc suppression coil, the signal output terminal X of the device can be connected to the neutral point of the grounding transformer for measurement, such as... Figure 4 As shown, its zero-sequence equivalent diagram is as follows: Figure 5 As shown; alternatively, the signal output terminal X of the device can be connected to the neutral point of the configured compensation capacitor for measurement, such as... Figure 6 As shown. The system ground capacitive reactance can be calculated using the prior invention patent application "202510473787.1 A method for calculating zero-sequence loop impedance using frequency conversion signal", and then the system capacitive current can be calculated by dividing the system bus phase voltage by the system ground capacitive reactance.

[0042] This invention injects signals of different frequencies into the system using a measurement and signal generator. By utilizing the different zero-sequence loop impedances of the system at different frequencies, the system capacitance current is calculated by establishing loop equations. This overcomes the limitations of calculating capacitance current using the PT open-delta injection method. The measurement is not affected by the system PT characteristics, and the injection power can be greatly increased, improving the energy of the injected signal, making the backtest signal more accurate, and thus improving the accuracy of the system capacitance current.

[0043] This invention can measure not only neutral-point ungrounded systems, but also systems grounded by a single arc suppression coil and systems with multiple arc suppression coils connected in parallel, thus expanding its application range. The measurement results can be transmitted to the arc suppression coil as a basis for adjusting its settings, and can also be used as an instrument to measure the system's capacitive current, assisting operators in understanding changes in the system's capacitive current.

Claims

1. An apparatus for measuring the capacitive current of a system using injection, characterized in that: The system includes a measurement and signal generator and an integrated injection transformer. The measurement and signal generator internally includes an H-bridge inverter unit (HQ), an LCL filter circuit, a power supply (DY), and a controller (KZQ). The integrated injection transformer includes a step-up transformer (B), a voltage transformer (PT), and a current transformer (CT). The input terminals of the controller (KZQ) are connected to the signal terminals of the voltage transformer (PT) and the current transformer (CT), respectively, and the output terminal of the controller (KZQ) is connected to the controlled terminal of the H-bridge inverter unit (HQ). The power supply (DY), the H-bridge inverter unit (HQ), and the LCL filter circuit are connected in series. The output terminal of the H-bridge inverter unit (HQ) is connected to the primary side of the step-up transformer (B) through the LCL filter circuit. One end of the secondary side of the step-up transformer (B) is grounded through the current transformer (CT), and the other end of the secondary side of the step-up transformer (B) is the signal output terminal X.

2. The apparatus for measuring the capacitive current of a system using injection method according to claim 1, characterized in that: The LCL filter circuit includes a first inductor (L1), a capacitor (C), and a second inductor (L2). The first inductor (L1) and the second inductor (L2) are connected in series between one input terminal of the step-up transformer (B) and one output terminal of the H-bridge inverter unit (HQ). One end of the capacitor (C) is connected to the junction of the first inductor (L1) and the second inductor (L2), and the other end is connected to the other input terminal of the step-up transformer (B) and the other output terminal of the H-bridge inverter unit (HQ).

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