It is applicable to all kinds of cables with metal conductors (pairs, protective layer, shielding layer) and metal conductors (wire pairs, protective layer, shielding layer), and the dead ground faults that cannot be located by the high-voltage cable discharge acoustic test, railway signal lines, low-voltage power and lighting buried cables and the earth form a loop. Its main function is to detect the cable routing and the depth of cable burying in addition to the location test of the poor insulation point to the ground.
This instrument uses a quartz crystal oscillator, medium and large-scale integrated circuits. It is characterized by high receiving sensitivity, low static drift, strong anti-interference ability, stable work and high accuracy. Because the instrument is powered by a small nickel-cadmium battery, the instrument has the advantages of small size, light weight, low power consumption, and easy portability, and is especially suitable for field operations.
Section 2 Main Technical Performance
1. The distance between the detection route and the fixed point of the fault: the low-voltage cable is ≥3km, and the high-voltage direct-buried cable is ≤10Km.
2. Accurately fixed-point fault insulation resistance: 0～5MΩ.
3. Accuracy of positioning test: ≤±10cm.
4. Detection cable depth: ≤3m.
Section 3 The working principle of the instrument
1. How probe routing works
When an alternating current passes through a linear conductor, a coaxial alternating electromagnetic field is generated around the conductor. Placing a coil in this magnetic field will induce an alternating voltage with the same frequency in the coil. The magnitude of the induced voltage is determined by the position of the coil in the magnetic field. When the direction of the magnetic line of force is parallel to the axis of the coil, the voltage induced by the coil will be the largest (as shown in Figure 1); when the axis of the coil is perpendicular to the direction of the magnetic line of force, the voltage induced by the coil will be the smallest (as shown in Figure 2). From this, the routing of the cable can be judged. The 45° method of the receiving coil can also be used to measure the buried depth of the underground cable.
2. Working principle of fault detection:
Send the DC pulse generated by the transmitter to the cable under test, and into the ground through the poor insulation point. A point electric field is formed at the entrance point, and the electric field formed by the point electric field on the ground surface is shown in Figure 2 below. The DC amplifier in the receiver obtains the potential difference before and after the fault point (along the cable route) through the potential difference probe. Since the potential difference before and after the fault point has the opposite sign, when the front and back sequence of the potential difference detection frame remains the same, the DC amplifier The head of the value meter will swing in different directions, and the head of the median meter will change in direction before the fault point and when it crosses the fault point. Through the change of the swing direction of the meter head, the fault point of the poor insulation of the cable to the ground can be determined. According to the principle of electric field, the closer the potential difference probe of the receiver is to the fault point, the greater the potential difference obtained under equidistant conditions; the greater the swing of the median gauge needle; the same, when the probe frame just leaves the fault point, the median gauge needle The swing amplitude is also the largest (but it is opposite to the swing direction of the failure point). If the middle of the probe happens to be the fault point, since the potential difference is zero, the swing amplitude of the median meter head is also zero.
Signal generator
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