Power Cable Fault Tester, What is the Principle of Cable Fault Tester?

Huali Tongda Electric Power ** Power Cable Fault Tester. The cable fault intelligent tester adopts a variety of fault detection methods, applies the most advanced electronic technology achievements and devices in contemporary times, adopts computer technology and special electronic technology, and combines the company's long-term successful experience in developing cable testers to launch high-tech, intelligent and full-function new products. HLGZ Cable Fault Intelligent Tester is a comprehensive set of cable fault detection instruments.

It can test the high-resistance flashover fault, high-low-resistance grounding, short circuit and cable disconnection, poor contact and other faults, and can accurately determine the precise location of the fault point if equipped with an acoustic pointing instrument. It is especially suitable for testing power cables and communication cables of various types and different levels of voltage.

Often installed on the 10kv line, when the short circuit, ground fault, will send a red indication, or red light indication, cup size, some called fault display, some called fault addresser, I hope it will be useful to you.

How a cable fault tester works.

The method is to first measure the reflected waveform of the low-voltage pulse without breaking down the fault point of the cable under test, and then use the high-voltage pulse to impact the fault point of the cable to generate an arc, and when the arc voltage drops to a certain value, the medium-voltage pulse is triggered to stabilize and prolong the arc time, and then the low-voltage pulse is sent out, so as to obtain the reflected waveform of the fault point, and the divergence point can also be found to be the corresponding position of the fault point after the two waveforms are superimposed. Since the medium-voltage pulse is used to stabilize and extend the arc time, it is easier to obtain the fault point waveform than the secondary pulse method. Compared with the secondary pulse method, the synchronization time of the arc is not selected for the three-pulse method, and the operation is also simple.

The three-pulse method uses a double impact method to extend the arcing time and stabilize the arc, which can easily locate high-resistance faults and flashover faults. The three-pulse method has advanced technology, simple operation, clear waveform, fast and accurate positioning, and has become the mainstream positioning method for high-impedance faults and flashover faults. The triple pulse method is an upgrade of the quadratic pulse method.

The full length and the approximate location of the cable fault point from the test end. The cable fault pointer is the cable fault tester host to determine the precise location of the cable fault point on the basis of determining the approximate location of the cable fault point. For buried cables with unknown directions, the working principle of the power cable fault tester The power cable fault tester is composed of three main parts: the power cable fault tester host, the cable fault locator and the cable path meter.

The cable fault tester is used to measure the fault nature of the cable fault. A path meter is used to determine the underground course of the cable. The basic method of testing power cable fault is to apply a high-voltage pulse to the faulty power cable, and the breakdown occurs at the cable fault point, and the electromagnetic wave is generated and the sound is emitted at the same time as the cable fault breakdown point is discharged.

Let the high-resistance fault point of the cable break down and arc. At the same time, the test end adds a low-voltage pulse for measurement, and when the measurement pulse reaches the high-resistance fault point of the cable, it encounters an arc, and the surface of the arc is reflected. Due to the fact that the high-resistance fault becomes an instantaneous short-circuit fault during arcing, the impedance characteristics of the low-voltage measurement pulse will change significantly, so that the waveform of the flashover measurement becomes the short-circuit waveform of the low-voltage pulse, making the waveform discrimination particularly simple and clear.

This is known as the two-pulse method, in which a low-voltage pulse is received, and the reflected waveform is equivalent to a waveform in which the core is completely shorted to ground. The waveform of the low-voltage pulse obtained when the high-voltage pulse is released and the high-voltage pulse is not released are superimposed, and the two waveforms will have a divergence point, which is the reflected waveform point of the fault point. This method combines the low-voltage pulse method with the high-voltage flashover technique, making it easier for the tester to determine the location of the fault point.

Compared with the traditional test method, the working principle of the application of the arc reflectometry (quadratic pulse method) in cable fault location is that a high-voltage pulse of a certain voltage level and a certain energy is first applied to the faulty cable at the test end of the cable. The advanced point of the secondary pulse method is that the complex waveform in the impact high-voltage flashover method is simplified to the simplest low-voltage pulse short-circuit fault waveform, so the interpretation is extremely simple, and the fault distance can be accurately calibrated.

According to the principle of fault detection, when the instrument is in the flashover trigger mode, the flashover echo formed by the instantaneous breakdown discharge at the fault point is a random single transient waveform, so the test instrument should have the function of storing an oscilloscope, which can capture and display a single transient waveform. The cable fault tester adopts digital storage technology, uses high-speed AD converter sampling, converts the input transient analog signal into a digital signal in real time, stores it in the high-speed memory, and sends it to the LCD display control circuit after being processed by the CPU microprocessor, which becomes the timing dot matrix information, so the waveform parameters of the current sampling are displayed on the LCD screen.

When the instrument is in pulse trigger mode, the instrument sends out a probe pulse to join the tested cable and input circuit at a certain period, and immediately starts the work of AD, and its sampling, storage, processing and display are the same as the above process. There should be a reflected echo on the LCD display.

How a cable fault tester works.

1. Tracing principle (maximum signal method).

We know that when an alternating current flows through a conductor, an alternating magnetic field is generated around the conductor, and the magnetic field lines of the magnetic field are all coaxial with the conductor. In this case, if an electromagnetic coil is placed into the magnetic field, an induced voltage is generated at both ends of the coil. When the direction of the coil is the same as the direction of the magnetic field line, the induced voltage generated at both ends of the coil is maximum.

When the direction of the coil is perpendicular to the direction of the conductor, the induced voltage is maximum, as shown in Figure 1; When the direction of the coil is parallel to the direction of the conductor, the induced voltage is minimal, as shown in Figure 2. Therefore, the "maximum signal method" is obtained to explore the trajectory of the buried cable, and the buried depth of the underground cable can be measured by using the 45° rule of the receiving coil.

2. Positioning principle.

Differential potentiometric method.

If a buried cable has a ground fault, use the potential difference method to find the fault point. The method is to add a test voltage between the test point and the ground of the faulty cable, so that a concentric distributed electric field will be formed around the entry point of the cable. There is no potential difference between any points with the same radius in the electric field, but there is a potential difference between any two points with different radii, as shown in Figure 3, points A and B, and when the distance between the two points is fixed, the closer the two points are to the center, the stronger the potential difference.

Taking advantage of this feature, the two points A and B are gradually approaching the center point. When the fault point is exactly between points A and B, the potential difference becomes zero. If you continue to move past the fault point, the potential difference polarity will be inverted, so that the ground point can be accurately determined by moving back and forth.

Vibration detection method.

When the cable presents a high-impedance fault and the fault must be detected by the shock flashover method, the discharge of the fault point to the ground will produce a slight vibration to the ground, and the fault point can be found by using the method of earpiece detection epicenter.

The cable fault tester is an instrument that controls the process of signal transmission, reception and digitization of signals with a microprocessor as the core.

The microprocessor of the cable fault tester completes the process tasks of converting the signal into a digital signal: the acquisition, storage, digital filtering, cursor movement, distance calculation, waveform comparison, expansion of the waveform ratio, until it is sent to the LCD display screen. There can also be communication port and PC communication for working feedback detection signal process results.

The pulse generator in the cable fault tester is an accessory instrument that automatically converts the encoded signal transmitted by the microprocessor into a certain width of logic pulses. The pulse generator converts the transmit circuit into a high-emission emission pulse that is transmitted to the cable under test.

The high-speed AD generator in the cable fault tester converts the test result signal returned from the faulty cable under test to the high-speed AD sampling circuit through the input circuit and converts it into a digital signal. It is transferred to a microprocessor for analysis and processing.

The keyboard is a window for human-computer interactive dialogue, and the operator can input the commands required for the test through the keyboard, transmit them to the computer, and finally the computer controls the cable fault tester for detection.

To sum up, the detailed composition of the cable fault detector and its work process. Correctly grasp the origin, composition and working status of the instrument, and use the instrument more conveniently; It plays the role of accurate detection position, protection and mode in the use of the instrument; This makes the repair of faults more quickly guaranteed.

Respondent: Huatian Power.

Measure the distance of the breakpoint, measure the line.

After the occurrence of cable fault, we must first use simple tools to effectively judge the type and phase of the fault, and the correct judgment of the nature of the cable fault can improve the work efficiency of 80% for the rapid treatment of cable fault, which shows that it is of great significance to accurately judge the fault cable.

Method for determining the nature of cable faults.

The method of judging the nature of the cable fault can be carried out by using a multimeter or an insulation resistance tester, and the resistance value between the three opposite ground and the phase is measured with a 500V or 1000V insulation resistance meter respectively, and the specific steps are as follows:

01) Use an insulation resistance tester to measure the resistance value of each phase, if one of the insulation resistance values is measured to be zero or low, then use a multimeter to retest, the purpose of the retest is to determine whether it is a high-resistance fault or a low-resistance fault.

02) Measure the insulation resistance between the two items, if the measurement insulation resistance is zero or low, it indicates that one of the phases has an insulation fault, and then combined with the multimeter to eliminate the fault phase and the fault type of the faulty cable, it is convenient to take a targeted search method.

03) Short circuit the end of the cable, measure the DC resistance of the wire core, and determine which phase has an open circuit fault by the size of the DC resistance.

Through the above three methods, it is completely possible to determine the fault phase and the type of fault, and it is also possible to judge whether the conductor of the fault phase is complete.

1. It can test the low-resistance, short-circuit, open-circuit, high-resistance leakage and high-resistance flashover faults of various power cables below 35kV.

2. It can test the open circuit and short circuit fault of communication cable, control cable, signal cable, street lamp cable and local telephone cable.

3. The length of various cables can be tested and calibrated.

4. It can test the propagation speed of radio waves in the cable.

Test Method: 1. Pulse method (test the full length of cable open circuit, short circuit, low resistance, and open circuit fault distance);

2. Flashover method (test cable high-resistance leakage fault, high-resistance flashover fault);