What is the polarity of the flashover voltage of a lightning strike tower

When it should be a lightning strike, the lightning current can be shunted through the tower grounding resistance and the ground wire, but the wire can only propagate in the form of waves to both sides, and the overvoltage generated by the lightning current of the same amplitude at both ends of the insulator string is much greater than the overvoltage when counterattacking, that is, as long as the small lightning current can make the insulator string flashover. Therefore, the lightning resistance level during winding is much lower than the lightning resistance level of the lightning strike tower.

1. Poor contact, increased calorific value, light wire burning, heavy cause fire.

2. Cause the motor to lose phase and burn out the motor.

3. Cause interference to other sensitive electronic devices.

The only way to deal with this is to immediately (if the current is high) and reconnect the power failure, and clean up the scorched and oxidized places in the original interface, if it is not possible to clean up and reconnect with another terminal.

Any fault where the insulation resistance of the cable fault point drops to the characteristic impedance of the cable, or even the DC resistance is zero, is called a low-resistance fault or a short-circuit fault (Note: This definition is from the perspective of using the pulse reflection method, taking into account the influence of different wave impedances on the polarity change of the reflected pulse. For the bridge method, the definition of a low-impedance fault is not limited by the concept of characteristic impedance.

Power cable faults are caused by damage to the insulation of cables, and the types of general faults are roughly divided into two categories: low-resistance short-circuit, open-circuit and open-circuit faults; High-impedance leakage faults and flashover faults.

Answer]: B In the occurrence of induced lightning overvoltage, there is this overvoltage between the three-phase wires, there is almost no potential difference between the phases, and the hazard is often bright only to the ground flashover; When the two or three phases are both flashed to the ground, the line may have an interphase flashover accident. The grounding resistance of the tower is generally very small, so that the amplitude of the lightning current generated by the induced lightning overvoltage will be large.

The insulation level of 35kV line is lower than that of 110kV line, so it is more likely to cause flashover accidents, that is, the harm is greater. So item b is correct, and cd is two wrong. Item A, when lightning strikes the tower, because of the rapid change of the electromagnetic field generated by the lightning channel, the overvoltage opposite to the polarity of the lightning current will be induced on the wire, and the relevant regulations suggest that for the general high roll degree (about 40m below) no lightning protection wire, the maximum value of the induced lightning overvoltage is calculated as follows:

ug·d＝αhd。where is the induced overvoltage coefficient (kv m), whose value is equal to the average steepness of the lightning current in terms of kas , i.e. il. When there is a lightning cable, considering its shielding effect, the induced lightning overvoltage on the wire can be written as: