Multiple measurements of power quality

Weshine's independently developed power quality analyzer is a portable product that detects and analyzes the operational quality of the power grid. It can provide harmonic analysis and power quality analysis in power operation, and is equipped with large capacity memory for long-term data collection and detection of power grid operation. At the same time, it is equipped with PC application software to upload the collected data to the computer for various analyses.

For most engineers, the concept of power quality is related to the characteristics of the AC lines that feed grid energy into the facilities. But the variation of the term "power quality" can now refer not only to AC lines, but also to the properties of devices connected to AC power sources. Therefore, reviewing the basic knowledge of power quality and some newer explanations may be helpful.

Firstly, consider an "ideal" three-phase power system. Here, the current is in phase with each phase voltage, and the phase voltage and current are exactly 120 ° apart and equal to each other. The voltage and current sine waves are not distorted, and the source impedance is zero. Therefore, the event at the load does not affect the source voltage, and the actual frequency is equal to the nominal frequency.

Of course, there is no ideal power system in the real world. There is an acceptable range of deviation.

The reactance present in the communication system causes voltage and current sine waves to be out of phase with each other. Voltage is used to induce leading current, while current is used to capacitive lead voltage. Low power factor often occurs in industrial facilities containing a large number of motors or other inductive loads. For low power factor loads, power companies typically charge higher fees to large industrial and commercial customers.

When single-phase loads (lighting, office equipment, etc.) absorb unequal amounts of current on each phase, the three-phase power system will experience imbalance. This load will cause greater pressure on the neutral line. In an ideal situation, the load is balanced, which means that the voltage and current phases are exactly 120 ° different from each other, although the current may be different from the voltage phase. The current on the neutral line of a balanced three-phase four wire Y-shaped system is zero. The current on the neutral line in an unbalanced system increases with imbalance, which may lead to overheating and fire risks.

A motor driven by unbalanced voltage will produce a phenomenon called reverse torque, where the smaller motor torque is opposite to the direction of motor rotation. Therefore, the partial energy transmitted to the motor will have adverse effects on itself.

Harmonic is a waveform distortion that occurs in circuits containing nonlinear loads, mainly characterized by switching power supplies. These nonlinear loads may apply higher frequency sine waves to the AC input, resulting in power loss in the form of waste heat. The excess heat generated by harmonics may be harmful to the power system. Transformers are particularly susceptible to damage caused by harmonic eddy currents, which circulate in the iron core and generate excessive heat.

Harmonics are multiples of the main frequency, which is 60 Hz in the United States. For example, in a 60 Hz system, the third harmonic is 180 Hz, and the fifth harmonic is 300 Hz. The power quality meter can display the magnitude of each harmonic frequency. They can also read total harmonic distortion (THD) and total demand distortion (TDD) to provide individual harmonic distortion measurements, rather than the entire spectrum.

Weshine Electric Manufacturing Co., Ltd.