computer Cable Djfp2vp2 executive standard
Common faults of cable lines include mechanical damage, insulation damage, insulation damp, insulation aging and deterioration, overvoltage, cable overheating, etc. When the above fault occurs to the line, the fault cable shall be cut off Power Supply Find the fault point, check and analyze the fault, and then repair and test. The power supply can be restored after the fault is eliminated. Executive standard of computer cable djfp2vp2
The direct cause of the cable fault zui is the breakdown of the insulation
Mainly:
a. Overload operation. Long term overload operation will cause cable temperature rise and insulation aging, resulting in insulation breakdown and lower construction quality
b. The electrical aspects include: the construction process of the cable head fails to meet the requirements, the sealing of the cable head is poor, moisture invades the cable interior, and the cable insulation performance drops; The protective layer is damaged and insulation is reduced due to failure to take protective measures when laying cables Executive standard of computer cable djfp2vp2
c. In terms of civil engineering, the drainage of the pipe trench of the construction well is not smooth, and the cable is soaked in water for a long time, which damages the insulation strength; The working shaft is too small, the bending radius of the cable is not enough, and it is damaged by the external force of extrusion for a long time. It is mainly due to the mechanical barbaric construction in the municipal construction, which damages and breaks the cable
d. Corrosion. The protective layer is subject to chemical corrosion or cable corrosion for a long time, resulting in the failure of the protective layer and the reduction of insulation
e. The quality of cable itself or cable head accessories is poor, and the sealing of cable head is poor, Insulating adhesive Dissolution and cracking lead to the resonance phenomenon of the station, which is that the inter phase capacitance and ground capacitance of the line are connected with the power distribution due to the line break fault transformer The excitation inductance forms a resonance circuit, which excites ferromagnetic resonance
Hazards of resonance caused by broken wire fault
In serious cases, the superposition of high frequency and fundamental frequency resonance can make the overvoltage amplitude reach 2.5 times of the phase voltage [P], which may lead to the displacement of the system neutral point, overvoltage of windings and conductors, and in serious cases, insulation flashover, lightning arrester explosion, and electrical equipment damage. In some cases, the phase sequence of the load transformer may reverse, and the overvoltage may also be transferred to the low-voltage side of the transformer, Cause harm
Measures to prevent line break resonance overvoltage
The main measures to prevent line break resonance overvoltage include:
(1) No fuse is used to avoid open phase operation
(2) Strengthen line patrol and maintenance to prevent wire breakage
(3) Do not hang the no-load transformer on the line for a long time
(4) Loop network or dual power supply is adopted
(5) Add interphase capacitance at the distribution transformer side,
The principle is that capacitance is used as an energy absorbing element to absorb the energy in the transient process, so as to reduce the intensity of impact disturbance to ease the occurrence of resonance. s - (o 3C,,) 1C, The interphase capacitance △ C is added at the distribution transformer side to increase the 8 - [Co3 (CUA0)/Ca, so that the capacitance required to increase the equivalent capacitance C and the equivalent electromotive force Eo can be calculated according to the method in literature [6] (6) The use of transformers with better excitation characteristics helps to reduce the probability of broken line overvoltage
