Ground fault analysis of the hottest overhead line

Analysis of overhead line grounding fault

due to the influence of natural disasters or other factors, the transmission line is inevitably damaged, and there are faults such as grounding or disconnection, especially medium and high voltage overhead transmission lines

1 grounding fault phenomenon

the grounding of the line can be divided into single-phase grounding, two-phase grounding and three-phase grounding. There are two kinds of grounding faults: permanent grounding and transient grounding. The former is usually due to the fact that most of the markets we touch are due to the breakdown of wires and the landing of wires, while the latter is usually due to lightning flashover and foreign matters falling on the wires. The most common one is single-phase grounding of overhead lines

(4) if the grounded line has multiple sections or branches, look for which section or branch line the grounding occurs

(5) find the grounding point

2 judgment of grounding fault

by detecting the voltage of the line, and identifying the grounding fault according to table 1

3 finding of grounding lines

at present, the method of trying to pull each line is generally used to determine the grounding line

Table 1 Identification of single-phase grounding fault and other faults

the voltage of one phase decreases but is less than zero, and the voltage of two phases increases but is not equal (one phase does not exceed the line voltage, and the other phase can slightly exceed the line voltage)

the voltage decreasing phase is the grounding phase

the neutral point is ungrounded and under compensated, and the next phase with the highest voltage is the grounding phase; For the over compensation network, the previous phase of the highest voltage phase is the grounding phase

two phases with reduced voltage

the neutral point of the medium and high voltage transmission network is generally ungrounded or grounded through the arc suppression coil. When a single-phase grounding signal appears in the network, the single-phase grounding fault should be handled according to the following steps:

(1) determine whether the single-phase grounding really occurs

(2) identify which phase is grounded

(3) find which line is grounded

during operation, the sequence of opening the line shall be determined according to the light and heavy load of the line, the length and short of the line, or the failure rate of the line. If the grounding signal disappears when opening a line, it means that the grounding is on the line

4 finding the grounding point

when looking for the grounding point of the short overhead transmission line, personnel can be arranged to conduct a comprehensive inspection along the line, but when looking for the grounding point of the long overhead transmission line, the optimization method should be used. First, the tension rod at 1/2 of the length of the circuit is segmented, and the three-phase drainage line of the circuit is disassembled respectively, so that the whole circuit is divided into two sections, and then the insulation resistance of the three-phase conductor is measured with a 2500V although the control mode is relatively simple, 1 megohmmeter. According to the measurement results, it can be determined that a section of the circuit is grounded or both sections are grounded. Secondly, continue to search in segments according to the judgment results, and gradually narrow the search scope. How about the trend of American plastic machinery industry in 2014 when the grounding range is reduced to a certain extent? Carry out a comprehensive inspection along the line. This can save time, reduce labor, and improve work efficiency

5 precautions

finally, it is worth mentioning: why is it necessary to disassemble the three-phase drainage line of the line when measuring the insulation resistance of the line in sections, and then measure the insulation resistance of each three-phase conductor separately? The reasons are:

(1) some lines are long, and the conductors are transposed on the way. Under the condition that phase a, B and C are not marked, it is necessary to prevent missing measurement of the insulation resistance of the faulty phase, resulting in wrong judgment

(2) it is considered that when single-phase incomplete grounding occurs, the phase with the lowest voltage to ground must be the grounding phase, so only one phase insulation resistance is measured, but actually it may be missed, so at the same time, the fault phase is easy to make mistakes

(3) the line may be grounded at multiple points, etc

therefore, when overhead line grounding occurs, it must be carefully detected and accurately judged, and it is not allowed to be careless in work