Dyness Knowledge | Total harmonic distortion rate

Introduction

The total harmonic distortion rate includes THDi (Total Harmonic Distortion, total current harmonic distortion) and THDu (Total Harmonic Distortion, total voltage harmonic distortion). THDi and THDu sum are two important parameters used to measure the quality of current and voltage in power systems. They represent the degree of distortion of the harmonic components contained in current and voltage, usually expressed as a percentage.

THDi（Current harmonic total distortion）

THDi represents a measure of the degree of distortion of the harmonic components in the current, and represents the ratio of the total distortion of the harmonic current introduced by the nonlinear load to the basic frequency current. A lower THDi value indicates that the harmonic distortion of the current is smaller and the system is more stable. The current waveform can be analyzed through sampling and digital signal processing to determine the frequency and amplitude of the harmonics. This usually involves using techniques such as the Fourier Transform or Fast Fourier Transform (FFT).

THDu（Voltage harmonic total distortion）

THDu represents a measure of the degree of distortion of the harmonic components in the voltage. THDu is calculated by analyzing the harmonic components in the voltage waveform and represents the ratio of the total distortion of the harmonic voltage in the voltage waveform to the fundamental frequency voltage.

The analysis method of voltage waveform is similar to that of current, requiring the use of techniques such as Fourier transform or FFT to determine the frequency and amplitude of voltage harmonics. A lower THDu value indicates that the harmonic distortion of the voltage is smaller and the voltage quality of the power system is higher.

The measurement of the fundamental current effective values THDi and THDu is usually performed in power quality monitoring systems. Through current and voltage sensors, the data is transmitted to the monitoring device, and THDi and THDu can be monitored and recorded in real time. By reducing the distortion of harmonic currents and voltages, the efficiency and stability of the power system can be improved. This may involve the use of filters, harmonic suppression devices and control strategies to reduce the effects of harmonics.

The main hazards caused by high harmonic distortion

• Equipment damage: High levels of harmonic currents and voltages can cause equipment damage. Transformers, motors, switchgear and electronic equipment can be affected by overheating, insulation damage and increased mechanical stress, leading to early failure and increased repair costs.
• Reduced energy efficiency: Harmonic current will cause additional power loss and reduce the energy conversion efficiency of the system. This means more electricity is needed to complete the same job, increasing your electricity bill.
• Electromagnetic interference: Harmonic currents and voltages may cause electromagnetic interference and adversely affect surrounding electronic equipment and communication systems. This can cause interference, data corruption and communication failures.
• System instability: Harmonic currents and voltages may also cause instability in the power system, affecting voltage waveforms and frequencies. This can cause voltage drops or frequency fluctuations in the system, causing harm to sensitive equipment and systems. For nonlinear loads, harmonic currents and voltages may cause instability in the load equipment, affecting equipment performance, unstable current waveforms, and possible failures.

THDi and THDu are crucial parameters in energy storage systems. They affect the performance, stability and interoperability of the energy storage system with the grid. International standards and specifications usually stipulate upper limit values for THDi and THDu to ensure the quality and stability of the power system. Dyness has been deeply involved in the energy storage industry for many years and is committed to the research and development and manufacturing of energy storage products. The THDi and THDu of Dyness industrial and commercial storage products are both less than 3%, ensuring the stability of the energy storage system.