[0037] Example 1:
[0038] Such as figure 1 As shown, a method for suppressing the overvoltage at the head of a transmission line during lightning strikes includes the following steps:
[0039] 1) Set the coaxial overhead cable 1 according to the wave impedance value of the overhead lightning protection line, and design the coaxial overhead cable 1 with a smaller wave impedance;
[0040] 2) Design low impedance coaxial cable down conductor 2;
[0041] 3) Connect and install the coaxial overhead cable 1, the coaxial cable down conductor 2 and the ground lightning arrester 3 on the iron tower in turn. The ground lightning arrester 3 is connected to the grounding grid 4, of which the coaxial overhead cable 1 is erected on the iron tower At the top, one end of the coaxial cable down conductor 2 is connected to the coaxial overhead cable line 1, the other end of the coaxial cable down conductor 2 is connected to the ground lightning arrester 3, and the coaxial cable down conductor 2 is set against the tower body , The ground lightning arrester 3 is arranged at the bottom of the iron tower, the grounding net 4 is arranged under the ground at the bottom of the iron tower, and the ground lightning arrester 3 is electrically connected to the grounding net 4;
[0042] 4) When lightning strikes the coaxial overhead cable 1, the lightning current sequentially passes through the coaxial overhead cable 1, the coaxial cable down conductor 2, the ground arrester 3 and the grounding grid 4, and finally flows into the ground. The connection will greatly reduce the tower head discharge and insulator discharge flashover failure, thereby reducing the trip rate of the line lightning strike and improving the reliability of the power supply.
[0043] Step 1) According to the calculation formula of wave impedance value To design overhead lightning protection lines with low wave impedance, where L is inductance and c is capacitance. From this formula, it can be known that when the capacitance increases, the wave impedance value is decreasing, so a coaxial overhead cable 1 with a lower wave impedance value can be designed.
[0044] A device designed according to the above method for suppressing the overvoltage at the tower head of a transmission line during lightning strikes, comprising a coaxial overhead cable 1, a coaxial cable down conductor 2, and a ground lightning arrester 3 installed at the bottom of the tower And the grounding network 4 set underground at the bottom of the tower, one end of the coaxial cable down conductor 2 is connected to the coaxial overhead cable line 1, and the other end of the coaxial cable down conductor is connected to the ground lightning arrester 3, the ground lightning arrester 3 It is electrically connected to the grounding grid 4, one end of the coaxial cable down conductor 2 is connected to the coaxial overhead cable line 1, the other end of the coaxial cable down conductor is connected to the ground lightning arrester 3, and the ground lightning arrester 3 is connected to the ground grid 4 Electrical connection, when lightning strikes the coaxial overhead cable 1, the lightning current passes through the coaxial overhead cable 1, the coaxial cable down conductor 2, the ground arrester 3 and the grounding grid 4, and finally flows into the ground.
[0045] Such as figure 2 As shown, the coaxial overhead cable 1 includes an inner core conductor 1-1, an insulating layer 1-2, and an outer conductor 1-3 arranged in order from the inside out. This design makes the coaxial overhead cable 1 suffer from When a lightning strikes, the lightning current can pass through quickly, and present a downward pilot effect on the outer layer of the overhead ground wire, that is, connect the equipotential value with the earth, and form an obvious potential difference with the phase conductor, prompting the lightning current to take the lead in the overhead The outer conductor 1-3 of the ground wire discharges, so as to prevent lightning from being struck by the live phase line; the inner core conductor 1-1 is made of steel wire, and the outer conductor 1-3 is made of aluminum foil. Low cost, and can play an effective conductive role.
[0046] Such as image 3 As shown, the coaxial cable down conductor 2 includes a polyvinyl chloride filling core 5, an inner conductor layer 6, a cross-linked polyvinyl chloride layer 7, an outer conductor layer 8 and a polyvinyl chloride shell 9 arranged in sequence from the inside out. The structural design has formed the low-wave impedance characteristics of the down conductor. When lightning strikes the line tower, the powerful lightning energy must be quickly transmitted to the underground grounding grid 4 to safely eliminate lightning. The coaxial cable down conductor 2 is designed like this It can withstand the high voltage and high current carried by lightning to ensure that no side flash discharge is generated to nearby objects.
[0047] Such as Figure 4 As shown, the ground arrester 3 is a zinc oxide arrester. When the lightning voltage intruding wave exceeds the breakdown strength of the protective gap, the gap is broken down, limiting the amplitude of the overvoltage that invades the electrical equipment. After the intruding wave passes, the gap insulation strength Self-recovery, so that electrical equipment can continue to run, zinc oxide arrester has a stronger ability to restore the insulation strength than ordinary gaps.
