A three -phase voltage harmonic synchronous detection method

Abstract

The invention provides a method for synchronous detection of three-phase voltage harmonics of a high-voltage transmission line, which includes the following steps: respectively bringing three detection devices close to or in contact with the high-voltage transmission line, and connecting the first and second stray capacitances formed with the voltage-dividing capacitance in series ; Send the ASK-modulated 50Hz square wave signal to the three signal processing units through the remote handheld device to make them open synchronously, and each signal processing unit starts to collect the voltage at both ends of the voltage dividing capacitor after receiving the square wave signal, and After calculating the harmonic content of the transmission line voltage based on this voltage, the calculation result is sent to the handheld device. The invention utilizes the electric field coupling to realize the direct synchronous detection of the harmonic content of the three-phase high-voltage transmission line, the detection is simple and convenient, the precision is high, the voltage level of the voltage transmission line is not limited, and the application range is wide.

Description

technical field [0001] The invention relates to the field of harmonic detection, in particular to a method for synchronous detection of three-phase voltage harmonics of a high-voltage transmission line. Background technique [0002] The traditional harmonic detection method for high-voltage transmission lines adopts a wired method, that is, the harmonic detector is connected to the secondary side of the PT / CVT in the substation, and the voltage on the bus is detected by detecting the small voltage signal at the secondary end of the PT / CVT. Obtain the harmonic content in transmission lines. According to statistics, almost all voltage transformers with a voltage level above 72.5kV in foreign countries use capacitive voltage transformers (CVT). In China, CVTs are also widely used in voltage transformers with voltage levels above 110kV. However, due to the inherent influence of CVT transmission characteristics, this method is not suitable for harmonic analysis. The national sta...

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Problems solved by technology

However, due to the inherent influence of CVT transmission characteristics, this method is not suitable for harmonic analysis. The national standard GB / T14549 "Power Quality Harmonics of Public Grid" and IEC related standards clearly stipulate that CVT cannot be used for harmonic measurement.

The reason is that by measuring the harmonic content of the secondary voltage signal of the CVT, and then converting the harmonic content of the line according to the ratio, this measurement method will attenuate the harmonics of different frequencies in different proportions due to the capacitance characteristics of the CVT itself, and the attenuation ratio does not vary. The non-linear proportional relationship leads to a large deviation in the measurement results, and the maximum deviation can reach 36.70%. Therefore, the harmonic voltage test results measured from the CVT will cause false phenomena that the power supply voltage of many public connection points is unqualified.

Therefore, the traditional CVT detection of high-voltage line harmonics is not accurate enough, and the traditional detection method can only measure the internal lines of the substation. For the high-voltage lines outside the substation, the harmonics cannot be measured because there is no CVT cabinet installed.

At the same time, for the 10kV high-voltage line, since the neutral point of the primary side of the CVT is grounded with a harmonic elimination resistor in series, it may affect the measurement results of the harmonic voltage that reflects the zero-sequence characteristics (such as the third harmonic), and finally affect the harmonic voltage. The test result of the total distortion rate

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