Content:
- Work order
- Installations for burning and cable diagnostics
Work order
In principle, two types of damage are distinguished - a cable break or one of its cores and a short circuit. However, the closure is not so unambiguous; it can be low-resistance and high-resistance. In the first case, the usual dial tone will show a short circuit, in the second - no. To reduce the resistance of the damaged area, it is necessary to burn through the insulation until a low-resistance circuit is formed or a single-phase circuit is converted to a 2-3-phase one.
The initial stage of cable burning occurs at high voltage, but with low current. Under the influence of high voltage, insulation breakdown occurs and current begins to flow. The insulation breakdown voltage gradually decreases along with the resistance of the damaged area. As the current increases and the resistance decreases, the pierce voltage is lowered and the current increased. This is how they achieve a decrease in resistance from tens of kOhms to units-tens of Ohms. The voltage is reduced to limit the piercing power. This process is carried out both with direct and alternating current, the operating algorithms of the installation depend on the specific model.
Burning the cable allows you to localize the damaged area, both visually and by the smell of burning and other consequences of the process.
A breakdown in the coupling can be distinguished among typical situations. Then, the burnout is characterized by a decrease in resistance during the execution of work and a reverse increase after its completion. Another case is when the damaged area is under water and an almost constant current flows, and the resistance of the damaged area remains within 2-3 kOhm. After burning, a search for the damaged area is carried out using an acoustic or induction method.
When cables are burned under high voltage, breakdowns occur, and after 5-10 minutes of repeating the procedure, the breakdown voltage decreases, then the installation is transferred to another stage of burning.
If, in the process of burning the place of damage to the power cables, the breakdown voltage rises back, the installation is again transferred to higher voltage and so on, until they achieve stable low-resistance results and the formation of a reliable metal bridge between veins.
To destroy a metal connection resulting from a breakdown, pulsed electrodynamic effects, for example, by discharging the capacity of two serviceable cores into a third and screen. Or use the capacity of a battery of capacitors charged to a high voltage (about 5 kV) and capacities up to 200 μF. The discharge energy is directly proportional to the capacity.
During primary high-voltage burning, the currents are fractions and units of amperes, and with further voltage drops, the current increases to hundreds of amperes. This procedure is carried out by specialists from the electrical laboratory.
The picture shows one of the cable burnout schemes, where the lower core is damaged:
Installations for burning and cable diagnostics
Such installations weigh a lot, and the damaged cable has to be looked for anywhere: in the tunnel, and underground and in the cable assembly. Therefore, electrical laboratories are usually equipped with mobile installations based on cars or buses. In addition to installation, the car is equipped with a gasoline or diesel generator.
Installations for burning the place of damage to power cables are usually not universal, designed for a specific range of voltages, adjustable in steps or do not have adjustment steps. Here are some examples:
- Installation of APU 1-3M, produces voltage up to 24 kV, and current up to 30 A.
- Installation VUPK-03-25, voltage 25 kV, current - 55A.
- Installation IPK-1, combined, consists of VPU-60 and MPU-3 Phoenix, burns with voltage up to 60 kV, output currents up to 20A.
Low-voltage afterburner: UD-300 and VP-300, produces 250 Volts with a current of up to 300A. They have no adjustment steps.
The video below clearly shows how the UPI-10 cable burner installation works:
Useful on the topic:
- How to find a damaged cable
- Continuity of wires and cables
- How to use a megohmmeter
