Views:239 Author:Site Editor Publish Time: 2021-04-15 Origin:Site
In railway power lines, due to the large number, many branches and complex operation modes of lines, and with the rapid development of railways, the power supply of railways is increasing, and the failure of power lines occurs frequently. How to quickly and accurately find and judge the nature and location of the fault, shorten the troubleshooting time, and improve the reliability of power supply is particularly important.
1) Single-phase Grounding Fault
The single-phase grounding fault is a relatively common fault, which usually occurs in wet and rainy weather. The single-phase grounding fault not only affects the user's normal power supply, but also may produce overvoltage, burn out equipment, and even cause a phase-to-phase short circuit to aggravate the accident. When a phase is grounded, the voltage of the faulty phase drops to zero, and the voltage of the non-faulty phase rises.
2) Short Circuit Fault
Two points of different potentials in the line are short-connected by a conductor, or the insulation between them is broken down, causing the line to fail to work normally, such as single-phase short circuit and multi-phase short circuit.
3) Open Circuit Fault
The most basic manifestation of open circuit faults is that the circuit is not open. In a three-phase circuit, if one-phase open circuit failure occurs, it may cause the motor to be burned out due to phase loss. It also will make the three-phase circuit asymmetrical, and the voltage of each phase will change, which will increase the phase voltage, causing accident.
1) Open Circuit Fault
A cable has one or several core conductors open or the metal sheath (steel armor) is broken. Simple open circuit faults are not common, and are generally accompanied by resistance grounding.
2) Low Resistance Fault or Short Circuit Fault
A fault in which the insulation resistance of one or several cores of the cable to the ground or the insulation resistance between the core and the core is lower than a few hundred ohms. Generally, there are single-phase low resistance grounding, two-phase short circuit grounding, and three-phase short circuit grounding.
3) High Resistance Fault
A fault in which the insulation resistance of one core or several cores to the ground or the insulation resistance between the core and the core is lower than the normal value but higher than a few hundred ohms.
4) Flashover Fault
The insulation resistance between one core or several cores of the cable or the insulation resistance between the cores is very high, but when the DC withstand voltage test is performed on the cable, the voltage is increased to a certain value, and the insulation breakdown phenomenon suddenly appears. This type of faults is not common and usually occurs during preventive tests.
When the power line fails, it is necessary to find the fault location as soon as possible to eliminate the fault. At present, the manual inspection method is still one of the main methods to find faults. People patrol along the line to find fault points. When encountering bad weather or bad terrain conditions, it will bring great difficulties to find faults. This way of finding faults not only consumes a lot of money and manpower, and it is easy to cause the line outage for a long time.
In order to find cable fault points faster and more accurately, fault indicators can be installed on power equipment and power lines. However, if using ordinary fault circuit indicators without communication function, after the line fails, line inspectors still need to search along the line to determine the fault zone and find the fault point with the help of the alarm of the cable fault indicator.
The ground fault indicator with communication function, especially the line fault indicator based on wireless communication, can change the backward practice of manual inspection to find the fault in the past. It can be combined with the fault location system in the dispatch center within a few minutes after the fault occurs. The indication information of the fault location and the time of the fault is given to help the maintenance personnel to rush to the scene quickly to eliminate the fault and restore the normal power supply, which greatly improves the reliability and work efficiency of the power supply.
The installation of fault current indicators should follow the principle of "combining sufficient and saving". Insufficient power line fault indicators are not conducive to finding fault points, and excessive fault indicators will cause economic waste. Generally we can follow the next principles.
Install a set of fault path indicators at the exit of the substation to find out whether the fault occurs inside or outside the substation. For trunk lines without branches, consider the installation interval according to comprehensive conditions such as terrain conditions and surrounding environment, a set of earth fault passage indicators can be installed every 20 to 40 poles. If there are branch lines, install a set of fault indicators on the load side of each branch line and the main line "T" contact. If the branch line is longer, you can install a set of fault indicators at the branch line 1/2. A set of fault indicators should be installed at each connection of the cable and the overhead line. In order to realize the communication function of the fault indicator, it is necessary to install a local communication terminal, which is generally installed at the branch point of the line, and the relationship with the fault indicator is one to many groups. The communication function of the fault indicator and the communication terminal can be completed by wireless signal (overhead system) and optical signal (cable system).
At the same time, it should be considered that due to complex outdoor electromagnetic interference, such as corona discharge and lightning flashover in nearby ultra-high voltage lines, it will often cause the overhead fault indicator to malfunction or refuse to operate, and the communication is affected. Therefore, when installing the line fault indicator, it should be combined with the surrounding environment and avoid places with magnetic field interference.
Therefore, in order to find and determine the nature and location of the fault more quickly and accurately, and shorten the time for troubleshooting, it is recommended to promote the installation of fault indicators based on automation technology and communication technology.