Author: Noyafa–Cable Length Tester
Generally speaking, power cable fault detection usually includes three steps of diagnosis, ranging and positioning. Fault location is based on a simple analysis of fault information to roughly determine the fault distance; fault location is based on fault location to accurately locate the fault point. In general, power cable fault detection usually includes three steps: diagnosis, ranging and location.
Fault location is based on a simple analysis of fault information to roughly determine the fault distance; fault location is based on fault location to accurately locate the fault point. Next, the pipeline detector manufacturer will show you how to find the fault point of the cable. 1. Low-voltage pulse method (pulse method for short) When a pulse wave is input to the line, the pulse is transmitted along the line at the speed V. When the line Lx distance encounters the fault point, it is reflected and folded back to the input end. The round-trip time is T, and V is The propagation speed of radio waves in the line is related to the primary parameters of the line. It is a fixed value for each line and can be obtained by calculation and actual measurement of the DFDL-S cable fault tester.
The transmitted pulse of the pulse source and the reflected wave of the line fault point are displayed on a display in real time, and the time T can be measured by the clock signal provided by the instrument. For low-resistance grounding and short-circuit faults and disconnection faults of cables, and the impulse method can easily measure the fault distance. However, for high-resistance faults, the reflected wave is not obvious or even non-reflected because it still presents a high impedance under the action of low-voltage pulses.
In this case, it is necessary to add a certain DC high voltage or shock high voltage to make it discharge, and use the flashover arc to form an instantaneous short circuit to generate electric wave reflection. 2. DC high voltage flashover method (referred to as direct flash method) When the fault resistance is extremely high and a stable resistance channel has not been formed, a gradually increasing DC voltage can be applied to the cable under test. After reaching a certain voltage value, the fault point is firstly broken down to form a flashover. The flashover arc is used to form a short-circuit reflection to the applied voltage, and the reflected echo is reflected by a high-resistance source at the input end to form an open-circuit reflection.
Pipeline detector manufacturers point out that this voltage will reflect multiple times between the input and the fault point until the energy is exhausted. 3. Impulse high voltage flashover method (referred to as impulse flashover method) When the fault resistance is reduced and a stable resistance channel is formed, due to the limitation of equipment capacity, the DC high voltage cannot be added, and the impulse voltage test should be used instead. The DC high voltage charges the cable through the ball gap until it breaks down, and the flashover arc formed by it still produces short-circuit reflection.
A measuring inductance L needs to be added at the cable input to read the echo. The electric wave is reflected by the short circuit at the fault point, and reflected by L at the input end, and multiple reflections will be formed in between. Due to the self-inductance phenomenon of the inductance L, the open-circuit reflection initially appears due to the blocking effect of L, and the short-circuit reflection appears after a certain period of time as the current increases.
And the whole circuit is composed of a capacitor C and an inductance L to form an L—The large process of C discharge. Therefore, the wave process presented at the line input is a near-decaying cosine curve superimposed with fast pulsed multiple reflections. The distance to the fault can be obtained from the interval of the reflected waves.
The above are some methods shared by pipeline detector manufacturers to find cable fault points. Have you understood it?
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