NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
Language
NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
Author: Noyafa–CCTV Tester
The working principle of the high-voltage flashover measurement method: As far as the nature of most faults is concerned, they basically belong to the damage of insulators. High resistance faults are caused by a decrease in the dielectric strength of the insulating medium. Because the resistance value of the fault point is high and the measurement current is small, the working principle of the flashover measurement method with sufficient high voltage: In essence, most faults are basically damage to the insulator.
High-resistance faults are caused by a decrease in the electrical strength of the insulating medium. Because the resistance at the fault point is high and the measurement current is small, it is difficult to measure even with a sufficiently sensitive instrument. For the pulse method, since the equivalent impedance of the fault point is almost equal to the characteristic impedance of the cable, the reflection coefficient is almost equal to zero, which cannot be measured because the reflected pulse cannot be obtained.
However, starting from the electrical breakdown phenomenon of the medium, as long as a sufficiently high voltage is applied to the cable (of course lower than the maximum test voltage), the breakdown phenomenon will occur at the fault point. At the moment of breakdown, the fault point is short-circuited by the discharge arc, so a voltage jump occurs before and after the discharge of the fault point. Due to dielectric breakdown, the ionization process takes a certain amount of time, and arc discharge generally lasts from hundreds of microseconds to several milliseconds, so the jump voltage goes back and forth between the fault point and the cable end in the form of waves during the discharge. reflection.
If at the end of the cable (beginning or terminal), the instantaneous jump voltage and the waveform reflected back and forth can be recorded, and the time of the back and forth reflection of the radio wave can be measured; then according to the propagation speed of the radio wave in the cable, the fault point can be calculated. distance to the end. Based on this physical mechanism, the flashover test method was developed.
Copyright © 2022 SHENZHEN NOYAFA ELECTRONIC CO.,LIMITED - www.noyafa.net All Rights Reserved.