Transmission Line Current Sensor

Abstract

The present invention discloses a power transmission line current sensor, comprising: a Rogowski coil module, whose output signal is a differential voltage signal of the measured current; an integrator module, which converts the differential voltage signal into a voltage signal of the measured current; a DC isolation amplifier module, which filters out DC from the voltage signal of the integrator module, amplifies it, and outputs a power frequency signal and a high-frequency current signal; a high-pass filter module, which filters out the power frequency and its harmonics from the high-frequency current signal, and outputs a high-frequency current signal with a large and small amplitude. The sensor monitors and measures the power frequency current, high-frequency lightning current, and high-frequency partial discharge current of the power transmission and distribution line in real time. The advantage of the present invention is that faults can only be detected by detecting these currents, allowing for effective and real-time monitoring of the safe operation of the line.

Description

Technical Field

[0001] The present invention relates to a current sensor, in particular to a transmission line current sensor. Background Art

[0002] The transmission and distribution grid is complex, and the normal power frequency currents carried within it require monitoring and protection. Lightning strikes generate high-frequency lightning currents, while fallen trees on power lines generate high-frequency partial discharge currents. These high-frequency currents are considered fault currents. Only by detecting these fault currents can the corresponding faults be detected and the safe operation of the power lines effectively and in real time be monitored.

[0003] A Rogowski coil is a wire evenly wound around a non-ferromagnetic structure of uniform size. The coil induces electromotive force, and its output signal is a differential voltage signal of the measured current. It needs to pass through an integrator to be restored to the measured signal. It has the characteristics of high bandwidth and low saturation, overcoming many shortcomings of traditional electromagnetic current transformers, and is very suitable for measuring current in power transmission and distribution systems. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a power transmission line current sensor that effectively monitors line safety.

[0005] In order to solve the above technical problems, the present invention provides a transmission line current sensor, comprising

[0006] Rogowski coil module: The output signal is the differential voltage signal of the measured current;

[0007] Integrator module: converts the differential voltage signal into the voltage signal of the measured current;

[0008] DC isolation amplifier module: filters out DC from the voltage signal of the integrator module, then amplifies it and outputs power frequency signal and high-frequency current signal;

[0009] High-pass filter module: filters out the power frequency and its harmonics in the high-frequency current signal and outputs a high-frequency current signal with large and small amplitudes;

[0010] The above modules monitor and measure the power frequency current, high frequency lightning current and high frequency partial discharge current of the transmission and distribution lines in real time. Only by detecting these currents can faults be detected, and the safe operation of the lines can be effectively monitored in real time.

[0011] The high-frequency current signal with a small amplitude output by the high-pass filtering module is output via the high-gain amplification module.

[0012] The Rogowski coil module is a high-frequency Rogowski coil module, and its bandwidth is at least 2 MHz.

[0013] The signal output by the integrator module passes through a DC isolation circuit composed of capacitors and resistors and reaches the non-inverting end of the non-inverting amplifier. The output signal of the DC isolation amplifier module is adjusted by an adjustable resistor to calibrate the output accuracy.

[0014] The high-pass filter module includes a fourth-order high-pass filter and a third-order high-pass filter. The fourth-order high-pass filter filters out the low-frequency signal and outputs a high-frequency current signal with a large amplitude. The third-order high-pass filter filters out the low-frequency signal and outputs a high-frequency current signal with a small amplitude.

[0015] The superior effects of the present invention are:

[0016] 1) This invention outputs power frequency current and high frequency current separately, simplifying the analysis of power frequency and high frequency, providing effective technical support for detecting effective current and fault current, and greatly facilitating signal processing. The power frequency output can continuously monitor the normal current level in the line.

[0017] 2) The high-frequency current output portion of the present invention filters out the power frequency signal, greatly facilitating high-frequency analysis. The power frequency content in the traveling wave is very small, so filtering out the power frequency will not significantly affect the analysis of the original waveform. However, the presence of the power frequency makes waveform interception difficult, so filtering out the power frequency can effectively capture the traveling wave signal.

[0018] 3) The magnitude of traveling waves varies greatly, ranging from hundreds of kiloamperes to just a few amperes. The two-range output can separate large and small faults, facilitating detailed fault analysis.

[0019] 4) The sensor of the present invention needs to be used with a high-frequency Rogowski coil, which increases the natural frequency of the Rogowski coil itself and improves the entire acquisition frequency band. General current sensors cannot reach such a high frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0021] Figure 1 It is a circuit principle block diagram of the present invention;

[0022] Figure 2 A circuit diagram of the present invention;

[0023] Description of the numbers in the figure

[0024] P1—integrator module; P2—DC isolation amplifier module;

[0025] P3—fourth-order filter; P4—third-order filter;

[0026] P5—High gain non-inverting amplifier. DETAILED DESCRIPTION

[0027] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0028] Figure 1 FIG. 1 shows a circuit block diagram of an embodiment of the present invention. Figure 2 FIG. 1 shows a circuit diagram of an embodiment of the present invention. Figure 1 and Figure 2 As shown, the present invention provides a transmission line current sensor, such as Figure 2 The upper, middle and lower outputs shown correspond to the power frequency output, high frequency large range output and high frequency small range output respectively; including the Rogowski coil module, integrator module P1, DC isolation amplifier module P2, fourth-order high-pass filter P3, third-order high-pass filter P4 and high-gain non-inverting amplifier P5.

[0029] The Rogowski coil module is a high-frequency Rogowski coil, and its bandwidth must be at least 2 MHz. Due to its hollow characteristics, the frequency can be very high, which is not possible for general current sensors.

[0030] The integrator module P1 converts the differential voltage signal used by the high-frequency Rogowski coil into a voltage signal reflecting the original current, and is placed between the high-frequency Rogowski coil and the DC isolation amplifier module. Figure 2 As shown, the two output terminals of the high-frequency Rogowski coil are respectively connected to the non-inverting and inverting input terminals of the operational amplifier U1A. R1 and C1 jointly determine the integration time. R2 is a DC gain limiting resistor that limits the DC gain caused by the offset voltage of the operational amplifier.

[0031] The DC-blocking amplifier module P2 removes DC from the voltage signal generated by the integrator module, then amplifies it and calibrates the output accuracy by adjusting adjustable resistors. It is located between the integrator module and the high-pass filter module. After the signal is output from the integrator module, it passes through a DC-blocking circuit composed of capacitors and resistors before reaching the non-inverting terminal of the non-inverting amplifier. DC-blocking is necessary because the DC gain caused by the offset voltage of the previous integrator circuit can cause the output signal to be offset from the center point. The high-impedance input of the non-inverting amplifier also prevents crosstalk between the various channels. The output signal is regulated by adjustable resistors RX1, RX2, and RX3 to calibrate the output accuracy. C2 and R3 form the DC-blocking circuit for the power frequency channel, C3 and R7 form the DC-blocking circuit for the high-frequency, large-range range, and C8 and R14 form the DC-blocking circuit for the high-frequency, small-range range. RX1, RX2, and RX3 adjust the amplification factor of each of the three output channels, respectively.

[0032] The fourth-order high-pass filter P3 is located on the high-frequency current large-range channel. It filters the power frequency and its harmonics, leaving a pure high-frequency current signal for easy analysis. After filtering the signal output by the DC isolation amplifier module, it directly outputs a high-amplitude high-frequency current. Capacitors C4, C5, C6, and C7 and resistors R8, R9, R10, and R11 jointly determine the inflection point frequency. By setting the inflection point frequency of 1 kHz, the corresponding value is obtained from the coefficient table of the Chebyshev filter, achieving a balance between the Q value and the frequency attenuation slope.

[0033] The third-order high-pass filter P4 is located on the high-frequency current small-range channel. It also filters out the power frequency and its harmonics, leaving a pure high-frequency current signal for analysis. It filters the signal output by the DC isolation amplifier module and outputs it to the next-level high-gain amplifier module. Capacitors C9, C10, C11 and resistors R15, RC16, and R18 jointly determine the inflection point frequency. This is also determined by setting the inflection point frequency to 1 kHz and obtaining the corresponding value from the coefficient table of the corresponding Chebyshev filter.

[0034] The high-gain common-mode amplifier P5 is located on the high-frequency current small-range channel. In order to measure subtle high-frequency current signals, it is necessary to amplify and output the signal for easy analysis. The high-gain amplifier module amplifies the tiny voltage signal after filtering by the third-order filter, and the amplification result is directly output. Wherein: (1+R19 / R17) is the amplification factor. In this embodiment, the amplification factor is set to 20 times. C12 is a high-frequency noise suppression capacitor. The C12 capacitor suppresses the disturbance of ultra-high frequency interference signals, such as high-frequency ripple of the power supply, to obtain a relatively small noise output. This capacitor smoothes the output waveform.

[0035] Figure 2 The amplifiers shown in the figure are powered by positive and negative 5V voltages.

[0036] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A transmission line current sensor, characterized in that: include Rogowski coil module: The output signal is a differential voltage signal of the measured current; the Rogowski coil module is a high-frequency Rogowski coil module with a bandwidth of at least 2 MHz; Integrator module: converts the differential voltage signal into the voltage signal of the measured current; DC isolation amplifier module: filters out DC from the voltage signal of the integrator module, then amplifies it and outputs power frequency signal and high-frequency current signal; High-pass filter module: filters out the power frequency and its harmonics in the high-frequency current signal and outputs a high-frequency current signal with large and small amplitudes; The high-pass filter module includes a fourth-order high-pass filter and a third-order high-pass filter. The fourth-order high-pass filter filters out the low-frequency signal and outputs a high-frequency current signal with a large amplitude. The third-order high-pass filter filters out the low-frequency signal and outputs a high-frequency current signal with a small amplitude. The above modules monitor and measure the power frequency current, high frequency lightning current and high frequency partial discharge current of the transmission and distribution lines in real time.

2. The power transmission line current sensor according to claim 1, characterized in that: The high-frequency current signal with a small amplitude output by the high-pass filtering module is output via the high-gain amplification module.

3. The power transmission line current sensor according to claim 1, wherein: The signal output by the integrator module passes through a DC isolation circuit composed of capacitors and resistors and reaches the non-inverting end of the non-inverting amplifier. The output signal of the DC isolation amplifier module is adjusted by an adjustable resistor to calibrate the output accuracy.

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