Noise and high-order harmonics case of capacitive voltage divider

作者： GOZ Electric 时间：2024-05-16 09:25:19 阅读：13

    At present, coupling capacitors are widely used in power systems and communication systems, and the application range of capacitive voltage transformers (cvt) has also covered various voltage levels of 35 kV and above, becoming an important equipment for energy measurement and relay protection in power systems. In terms of structural composition, the capacitive voltage transformer is composed of a capacitive voltage divider and an electromagnetic unit. The capacitive voltage divider and the coupling capacitor are composed of a capacitor core and a shell. However, operating experience has found that: the capacitance points of the coupling capacitor and the CVT are In some operating modes, the voltage regulator will emit abnormal sounds due to the presence of high-order harmonics. This article provides two cases to analyze the causes of noise and introduce the processing results. It also provides some experience for operators to identify and suppress the noise of coupling capacitors and CVT capacitor dividers.

Harmonics and internal noise generation mechanism of capacitor unit

    Capacitive voltage dividers and coupling capacitors are both composed of capacitor units. From a theoretical analysis, the noise inside the capacitor element is due to the action of the electric field, which causes internal vibration and generates noise. When AC voltage is applied to the capacitor, an electrostatic force will be generated between the electrodes of the capacitor element, causing the components inside the capacitor to vibrate. The vibration of this component is transmitted to the shell, causing the wall of the box to vibrate and form noise, which is then radiated from the shell. go out.

The relationship between line harmonics and noise of CVT and coupling capacitors

    When the 220 kV × The hearing threshold of the 1100 Hz to 100 Hz sound generated by harmonics is nearly ten orders of magnitude smaller than the hearing threshold of the sound generated by the fundamental wave. In this way, the high-frequency sounds generated by harmonics are easier for operators to perceive. Electrical tests and equipment disassembly analysis show that the noise during equipment operation does not indicate abnormality of the equipment. The current flowing through the coupling capacitor in the harmonic test: fundamental wave 0.21 A, 11th harmonic 20 mA, 13th harmonic 30 mA does not exceed the regulatory requirement of 1 A. This case is characterized as follows: there is a harmonic source in the first section of the 220kV no-load line, and harmonic amplification occurs at the end; the louder sound of the coupling capacitor and CVT capacitor divider at the end of the no-load line is caused by the 11th and 13th harmonics; the current The test results did not exceed the limit and there were no internal defects in the equipment.

    It has been experimentally demonstrated (the demonstration process is temporarily omitted) that when the coupling capacitor and the capacitive voltage divider of the CVT are operating, due to the existence of the 11th, 13th or higher harmonics, a sound that is easier to perceive than the fundamental wave will be emitted. From two engineering cases, it can be seen that the high-frequency sound generated by high-order harmonics is easier for operators to perceive, but the abnormal sound of coupling capacitors and CVT capacitor dividers does not indicate that the equipment itself is defective. When analyzing the abnormal operation of such equipment, you should first pay attention to whether the operating conditions are abnormal.