Multifunctional cable fault locator manufacturer

Author: Noyafa–Noyafa Cable Tester

The test method and test principle of the multi-function cable fault locator manufacturer's cable tester are briefly introduced. The test method and test principle of the multi-function cable fault detector manufacturer are briefly introduced. The ultimate purpose of any kind of cable fault test is to find the fault. Brief introduction to the test method and test principle of the cable tester manufacturer of the cable fault locator As far as its testing process is concerned, it is generally divided into three steps: one is the rough measurement of the fault distance; the second is the rough measurement of the fault distance to find the faulty cable laying path; the third is to accurately locate the fault point. Of course, in the actual test, these three steps are used flexibly according to the on-site situation. 1.

Overview and development history of cable fault rough detection methods 1. Pulse reflection method: In the 1970s and 1980s, the flash test method was widely used in cable fault testing, and its principle was the pulse reflection method (also known as the radar method). The instruments used are mainly electronic tubes and transistor circuits, which are very large.

The displays used successively include oscilloscope tube flash tester and storage oscilloscope tube flash tester. After the 1990s, with the wide application of computer technology, the intelligent cable fault flashover tester (flashover tester) began to be used, and its test principle was still the pulse reflection method. From the picture tube display to the liquid crystal display, the flash tester is generally controlled by a single chip, which improves the rough detection of cable faults to a new level.

At that time, resistor bridges, capacitor bridges, low-voltage bridges and high-voltage bridges were used. Using the bridge principle to test the cable fault distance was a common method in the 1960s and 1970s. After 2000, the instrument for testing the cable fault distance using the bridge principle is still in use and has some development. After the use of computer technology, more intelligent bridge testers (such as high voltage digital bridges) appeared.

The pulse reflection method (also known as the pulse flash method) is the most widely used and largest cable fault detection instrument on the market. For example, in the Beijing power supply system, due to the long use time of buried cables, the large amount of cable laying, and the long application history of cable fault detectors, there are more than 50 cable fault detectors controlled by single-chip microcomputers. In the past 10 years, domestic and foreign purchases The early products of DTC series detectors and TC series large-screen LCD monitors are used by almost all power supply departments. And in some power supply departments, the use of this type of cable fault tester is regarded as a skill that must be mastered in the examination of advanced cable testers.

Due to the long use time of this type of instrument, there are various training materials and monographs on the knowledge and experience of this type of flash tester, which will help users to master the use of the instrument in time. The test principle of the pulse reflection method flash tester is as follows: When measuring the fault of the cable, the cable can be regarded as a uniformly distributed transmission line. According to the transmission line (long line) theory, a pulse voltage is applied to one end of the cable, and the pulse will be transmitted along the line at a certain speed (determined by the dielectric constant and permeability of the cable medium).

Reflections occur when a pulse encounters a faulty point (or a point of impedance non-uniformity). If the flash tester records the transmission time Δt between the transmitted pulse and the reflected pulse, the distance LX of the fault point can be calculated from the known transmission speed V, LX=V·△t/2 If the total length is measured, the terminal reflected pulse: l=V·T/2 If the total length of the cable is known, the pulse transmission speed can be measured: V=2L/T The pulse method is divided into a low-voltage pulse method and a high-voltage pulse method. The principle of the pulse method is the same, but the pulse generation method is different. The fault distance calculation of the intelligent tester is automatically completed by the instrument.

(3). Secondary pulse method: The basic principle of the secondary pulse method or the pulse reflection method is a new method for rough detection of cable faults that is relatively advanced in recent years. Its technical characteristics are: the high-resistance fault presents the waveform characteristics of the low-voltage pulse short-circuit fault, which is easy to identify.

That is to say, the moment when the high-voltage pulse breaks down the high-resistance fault, the low-voltage pulse signal is sent to the faulty cable, and the high-resistance fault of the cable is tested with the low-voltage pulse short-circuit fault waveform. Compared with the traditional test method, the advantage of the secondary pulse method is that the complex waveform of the impulse high-voltage flashover method is simplified to a simple low-voltage pulse short-circuit fault waveform. The key to the second pulse method is to add a high frequency and high voltage data processor to the flash tester.

From the test principle, the principle of the double pulse method has its advanced nature, but the test instrument is relatively complicated, and the instrument is also more complicated than the ordinary flash tester. 2. Introduction of cable path detection method: The use of electromagnetic waves for path detection is a very mature method, and the practical application effect is also very good.

The difference lies in the different cable lengths, probing depths and signal frequencies. A large number of path detection instruments on the market are mostly used to detect power failure cables. The length of the detection cable is greater than 10KM, the depth of the detection cable is greater than 2m, and the electromagnetic wave frequency is 1KHZ-20KHZ. For example, the electromagnetic wave frequency of the DTC series cable path detector is 16KHz. The peak power of the signal source is greater than 100W, even if the cable is buried 2m deep, the signal received by the path detector is still very large. Figure 2. Schematic diagram of the magnetic field distribution around the cable and the principle of path detection. The path signal is received from the magnetic signal of the fixed-point instrument to find the cable path.

According to the minimum characteristics of the electromagnetic signal received by the ground directly above the cable, the buried position of the cable can be accurately found. The magnetic field distribution around the cable and the principle of path detection are shown in Figure 2: 3. Overview of cable fault precise point method: There are several methods for cable fault precise point: (1).

Acoustic measurement methods: Acoustic measurement methods have been widely used from the past to the present. This is the most efficient way. But the instruments used have developed from simple acousto-electric amplifiers to commonly used acoustic-electric synchronous fixed-point instruments.

Suitable for high voltage cables, low voltage cables, direct buried cables, cable trench cables, etc. The fixed point of the acoustic wave measurement method is that the high-voltage pulse generator discharges the faulty cable, and the fault point generates an arc, which produces a discharge sound. In the case of direct burial of cables, seismic waves will be generated.

The acoustic probe (acoustic sensor) of the fixed-point instrument receives the seismic wave signal and amplifies it, and then outputs it through the earphone or meter. Through a large number of field experiments, after the seismic wave is transmitted from the fault point of the cable to the ground, it quickly attenuates to a minimum value beyond the radius of 2 meters. Therefore, when monitoring seismic waves with fixed-point instruments, monitoring is usually performed at 4 meters.

When the supervisor hears the seismic waves, it indicates that the fault point is within 2m. As long as the loudest point is carefully searched, the fault point can be accurately found. (3) Electromagnetic method and audio frequency method: The use of electromagnetic wave fixed point or audio frequency legal point is to use the change of electromagnetic wave signal or audio signal before and after the cable fault point to determine the fault point, which is feasible in principle. But there is no reliable and practical fixed-point instrument at present.

In other words, the fixed-point instrument using electromagnetic waves is still being developed by various scientific research institutions, and it needs to be further verified and improved in practice to reach the level of practical application. When using the sonic method for point measurement, the sonic meter of the fixed-point instrument indicates the seismic waves received by the sonic probe, and the earphones also reflect the seismic waves received by the sonic probe. Just above the fault point, the acoustic signal is the largest, and after leaving the fault point, the acoustic signal decreases, or there is no acoustic signal.

When using the acoustic-magnetic synchronization method, the acoustic wave meter reflects the seismic wave received by the acoustic wave probe, and the magnetometer and the earphone simultaneously indicate the electromagnetic wave received by the antenna when the fault point is discharged. When the acoustic probe is placed over the fault point, the two gauge indicators of the pointing device are synchronized with the headphone sound. When the acoustic signal is not received, using the acousto-magnetic synchronous electromagnetic wave receiving function, the discharge rhythm of the ball gap can be grasped in time, which is beneficial to identify the weak acoustic signal of the fault point in the noise environment.

In addition, the acousto-magnetic synchronous locator can also detect the fault point and the cable path synchronously, which greatly improves the efficiency of fault locating. It is the most widely used cable fault spotting instrument. The audio signal is shorted by the arc at the cable fault point and no longer propagates to the cable termination.

A special receiver is used to receive the audio electromagnetic wave signal radiated by the cable. By comparing the change of the amplitude value of the audio electromagnetic wave before and after the fault point, the position of the receiver before and after the fault point is judged, so as to achieve the purpose of quickly pre-determining the fault point. The cable fault magnetic field predetermined point technology is a relatively new fault location method.

The concept was developed for a relatively short period of time, and the time for instrument development and use was also relatively short. After the predetermined point of the fault, we also need to carry out the precise point excavation of the fault point. Shenzhen Noyafa Electronic Technology Co., Ltd.