Amplification Effect of High-order Harmonics in Power Cables of New Energy Grid-connected Systems

To investigate the amplification effect of high-order harmonics in power cables of the new energy grid-connected system, a cable distributed parameter model is developed, and the cable harmonic amplification formula is deduced. For specific examples, an analysis has been conducted on the quantitative relationship between the harmonic amplification multiple at each point on the cable and the cable length, as well as the load carried during the transmission of high-order harmonic voltages and harmonic currents of different frequencies in the cable. The research results indicate that when high-order harmonics traverse power cables, harmonic amplification phenomena will occur on the cables. The degree of harmonic amplification exhibits a periodic distribution at various positions along the power cables. The value of the maximum amplification factor and its occurrence position are jointly affected by the cable structure parameters, total length, end load, and harmonic frequency. Under non-resonant conditions, the amplification factors for both harmonic voltage and harmonic current typically remain below 15, which is consistent with the actual measurement results in engineering. However, when the end of the cable precisely reaches the resonant length, the amplification factors of harmonic voltage and harmonic current can attain 50 to 300. When the length of the cable is constant, the size and type of the load carried by the cable have a significant impact on the amplification effect at various positions of the power cable. When the load borne by the cable remains unchanged, as the cable length increases, the harmonic frequencies that lead to amplification gradually decline.