The flashover mechanism of power cable fault point
as is known to all, China is accelerating the process of socialist modernization construction, the city's growing electricity demand. Therefore, the power cable as connection circuit and the tool, widely application. In today's situation, power cable fault is a vital aspect of power failures. So, know the cause of the power cable fault, type, thus the real-time and accurate detection method is applied to deal with the power cable fault.
power cable fault point in a variety of forms, fault point resistance is protean, very complicated. Flashover mechanism of the cable fault point is a fundamental theoretical basis of pulse reflection method. If the flashover failure point not breakdown, the fault waveform is impossible to produce.
cable fault, besides metallicity grounding fault not discharge, the rest of the cases, due to the insulating medium. The dielectric strength drops, in different pressure mode ( Dc voltage or impulse voltage) , as long as the applied voltage at or above the electric strength of insulating medium, the point of failure will occur the flashover of puncture, its mechanism is briefly as follows.
in high voltage field, solid conductor due to cold or hot launch some electron, the electronic side outside under the action of electric field are accelerated to obtain kinetic energy and interaction between side and lattice and stimulate the lattice vibration, the electric field energy transfer to the lattice, as the two process under certain conditions ( Electric field intensity and temperature) Balance, the solid medium with stable conductivity; When the energy of the electrons from the electric field is greater than the loss to the lattice vibration energy, with the assistance of electronic energy will be more and more big, when the electronic energy increases to a certain value, the electron interaction with crystal lattice led medium impact ionization, resulting in a new electronic, and these new electronic repeat the same process. This allows the rapid increase of the number of free electrons in medium or form 'avalanche'. So the conductance of the dielectric breaks the original steady state and a sharp increase in the breakdown began to occur, the point of failure is powerful electron flow instantaneous short circuit.
medium avalanche breakdown, need a certain amount of time, this phenomenon is called delayed effect. Cable fault point in the process of flashover breakdown, but because of the current and loss, and with the role of heating effect, leading to the failure point insulation condition worsens, fault resistance decrease, thus accelerating the breakdown process of fault point.