What are the basic steps and distance measurement methods for power cable fault testing? Wuhan UHV specializes in producing cable fault testers with a wide range of product options. When looking for a cable fault tester, choose Wuhan UHV.   

The search for power cable faults generally involves two steps: fault nature diagnosis and fault testing. The process of fault nature diagnosis is the initial understanding and analysis of the fault situation of the cable. Then classify the nature of the fault based on the size of the insulation resistance. Select different ranging methods based on the nature of the fault and determine the rough fault distance. Distance measurement method for power cable faults

1. Bridge method

This mainly includes several methods such as traditional DC bridge method, voltage drop comparison method, and DC resistance method.it is a method of measuring the ratio of cable faults to the voltage drop across the entire length, and then multiplying it with the entire field to calculate the fault distance. Generally used to test the distance of cable faults with insulation resistance within a few hundred kiloohms at the fault point.

2. Low voltage pulse method

Also known as radar method, it is a method of inputting low-voltage pulse signals into a cable through an instrument at one end. When a fault point with mismatched wave impedance is encountered, the pulse signal will be reflected and returned to the measuring instrument. The fault distance can be measured by detecting the time difference between the reflected signal and the transmitted signal. This method has the advantages of simple operation and high testing accuracy. It is mainly used for testing wire breakage and low resistance faults (insulation resistance below a few hundred ohms), but cannot test high resistance faults and flashover faults later. High resistance faults are more common in high-voltage cables.

3. Pulse voltage method

This method applies a DC high voltage signal to the faulty cable through a high voltage signal generator, causing the fault to click through discharge. After the fault clicks through discharge, a voltage traveling wave signal is generated, which propagates back and forth between the measuring end and the fault point. At the high voltage end of the DC high voltage generator, the device receives and measures the time it takes for the voltage traveling wave signal to travel back and forth once, and multiplies it with the propagation speed of the pulse signal to calculate the fault distance. This method can detect both high and low resistance faults, but when using this method for testing, there may be safety hazards due to the direct electrical connection between the distance measuring instrument and the high-voltage part.

4. Pulse current method

This method, like the pulse voltage method, is also a method of calculating the fault distance by applying a high voltage current signal to the faulty cable, causing the fault to click discharge, and then receiving and measuring the pulse current traveling wave signal generated by the discharge at the fault point through an instrument to travel back and forth once between the fault point and the measuring end. The difference is that this method involves attaching a current coupler to the grounding wire of the DC high-voltage generator to collect the current traveling wave signal generated by the discharge at the fault point in the line. This signal is easier to understand and interpret, and the current coupler has no direct electrical connection with the high-voltage part, making it safer.  

5. Secondary pulse method

This is a relatively advanced testing method that has emerged in recent years. It is a new ranging method developed based on the easy analysis and high testing accuracy of low-voltage pulse waveforms. The basic principle is to apply high-voltage pulses to cables with high resistance or flashover faults through a high-voltage generator, causing arc discharge at the fault point. Due to the small arc resistance, high resistance or flashover faults during the arc ignition period become low resistance short circuit faults. At this point, injecting a low-voltage pulse signal into the faulty cable through a coupling device and recording the low-voltage pulse reflection waveform (known as the charged arc waveform), the low impedance reflection pulse at the fault point can be clearly observed; After the fault arc is extinguished, inject a low-voltage pulse signal into the fault cable and record the low-voltage pulse reflection waveform at this time (called the arc free waveform). At this time, due to the fault resistance returning to high resistance, the low-voltage pulse signal does not reflect or reflects very little at the fault point. Comparing the charged arc waveform and the non arc waveform, the two waveforms will be significantly different at the corresponding fault points, and the distance between the obvious divergence point of the waveform and the testing end is the fault distance.  

To test the distance of cable faults using this method, the following conditions must be met: firstly, arc discharge can occur at the fault point under the action of high voltage; The second is that the distance measuring instrument can emit and receive low-voltage pulse reflection signals during arc discharge time. In practical work, it is generally necessary to extend the arc discharge time at the fault point by inserting a low-voltage capacitor with a large capacitance at the moment of discharge, or to accurately detect the start of the arc and inject low-voltage pulse signals to ensure that the low-voltage pulse reflection waveform during the arc discharge at the fault point can be obtained.  

This method is mainly used to test the fault distance of high resistance and flashover faults, which can generally generate arc discharge, while low resistance faults themselves can be tested using low-voltage pulse method.  

The waveform measured by this method is easier to analyze and understand than the waveform obtained by pulse current or pulse voltage methods, can achieve automatic calculation, and has higher measurement accuracy.  

According to different pulse counting methods, it can also be referred to as the three pulse method or the multiple pulse method.