Harmonic testing is the detection and analysis of harmonic components in power systems or electronic equipment. Harmonic refers to the frequency component in the signal, which is an integral multiple of the fundamental frequency, and usually affects the power quality, equipment performance and system stability. Therefore, the testing and analysis of harmonics is very important in the design, operation and maintenance of power systems and electronic equipment。

     In practical application, there are two main ways of harmonic measurement: direct measurement method and computational analysis method. These two methods identify and quantify harmonics by different means.

1. Direct measurement method
    Direct measurement method is to directly measure the frequency components of harmonic current, voltage and other signals in power system by using instruments. This method is simple, intuitive, and usually applied to the actual field test.
    Common direct measuring instruments include:
    Harmonic Analyzer (Power Quality Analyzer)
    Oscilloscope
    Main steps:
    Access to a test instrument: Connect an instrument such as a harmonic analyzer to a test point, usually the load side or power side of the power system, to measure the current or voltage waveform.
    Data acquisition: The instrument will continuously record the voltage or current signal and capture the waveform change of the signal.
    Harmonic spectrum analysis: The instrument automatically performs a fast Fourier transform (FFT) to convert the acquired signal into frequency domain data, thereby identifying the individual harmonic components.
    Result display and analysis: The analyzer will display the total harmonic distortion rate (THD) of the harmonics, as well as the amplitude, frequency and other parameters of each harmonic component (such as 2nd harmonic, 3rd harmonic, etc.).
    Application scenario:
    Power system: Used to detect harmonic pollution in the power system, check all kinds of equipment (such as transformers, motors, frequency converters, etc.) on the generation of harmonics.
    Electrical equipment: Used to detect the harmonic characteristics of electronic equipment (such as UPS, power adapters, etc.).
    Advantages:
    Field test: can directly obtain the real field test data.
    High degree: The use of high-precision instruments, can measure low or high order harmonics.
    Strong real-time: it can observe the harmonic waveform changes in real time and find problems in time.
    Cons:
    Interference in the test environment: During field testing, environmental factors (such as noise generated by other devices) may affect the test results.
    High cost: The test instrument costs more and requires personnel to operate.

2. Computational analysis
    Computational analysis does not rely on field testing, but predicts and evaluates harmonics through theoretical calculation and modeling analysis. It is usually applied in the design stage or the system simulation stage, and can also be used for harmonic evaluation under the condition of known parameters.
    Main ways:
    Fourier transform (FFT) based analysis: Through the fast Fourier transform of the signal, the time domain signal is converted to the frequency domain, and the harmonic component is identified. FFT is a common tool for harmonic analysis and is widely used in signal processing.
    Harmonic analysis based on system modeling: use the mathematical model of the power system (such as load model, transmission model, etc.) to model the harmonic source and propagation path, and then use simulation software (such as MATLAB/Simulink, PSCAD, ETAP, etc.) to calculate. The simulation results can provide spectrum data of harmonic current and voltage.
    Harmonic load model method: According to the characteristics of the load (such as nonlinear load, electronic equipment, etc.), estimate the harmonic current generated, combined with the parameters of the power system for harmonic analysis.
    Current harmonic source modeling and analysis: Through the modeling of various electrical equipment (such as rectifiers, frequency converters, welding machines, etc.), calculate the harmonics they may produce and the transmission characteristics of harmonics.
    Main steps:
    Model building: Build a mathematical model according to the system architecture or the working principle of the electrical equipment.
    Signal analysis: Through theoretical calculation or simulation analysis of the voltage and current waveform in the system to identify the harmonic components.
    Results: The amplitude, frequency and other parameters of harmonic components are calculated, and the harmonic pollution of the system is evaluated by further analysis.
    Application scenario:
    System design: In the design stage of power system or equipment, through computational analysis to predict the possible harmonic pollution, and then optimize the design.
    Harmonic source analysis: calculation and analysis of known harmonic sources to determine their impact on the entire power grid.
    Advantages:
    Low cost: there is no need for expensive test instruments, and the cost of computational analysis is low.
    Flexibility: It can be evaluated at the design stage or in a simulation environment.
    Predictability: It is possible to predict the harmonic performance of different designs or equipment configurations without an actual system.
    Cons:
    Limited accuracy: The accuracy of the computational analysis method depends on the accuracy of the model and the assumptions.
    No actual test data: Lack of actual measurement data, there may be errors.

Sum up
    Direct measurement method: Through the field test, real-time acquisition of harmonic data in the power system or equipment, suitable for the system or equipment that has been running, can provide accurate and direct test results. The disadvantage is that it is more expensive, requires equipment, and may be subject to environmental interference.
    Computational analysis: Harmonic analysis through theoretical models or simulation software, suitable for the system design stage or the need to predict harmonic effects. The advantages are low cost and flexibility, but accuracy may be limited by models and assumptions.