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Arrester is one of the main lightning protection devices in power system

Time:2018/5/6Author:adminClick: 2529
The lightning arrester is one of the main lightning protection devices in the power system. Only properly selecting the lightning arrester can exert its proper lightning protection.
   
1 Selection of gapless metal oxide surge arresters
The general requirements for selection are as follows:
(1) The environmental conditions of the arrester should be determined according to the conditions of temperature, altitude, wind speed, pollution, and earthquake in the area of use, and the nominal voltage of the system, the maximum voltage of the system, the rated frequency, the neutral point grounding method, the value of the short-circuit current and Grounding fault duration and other conditions determine the system operating conditions of the arrester.
(2) Determine the type of lightning arrester according to the object to be protected.
(3) Determine the continuous operating voltage of the arrester according to the longest voltage applied to the arrester.
(4) Select the rated voltage of the lightning arrester according to the temporary overvoltage amplitude and duration of the lightning arrester installation site.
(5) Estimate the discharge current amplitude of the arrester and select the nominal discharge current of the arrester.
(6) According to the rated lightning impulse withstand voltage and the rated operating impulse withstand voltage of the equipment to be protected, the lightning surge protection level and the operating overvoltage protection level of the arrester shall be determined according to the requirements of the insulation coordination.
(7) Estimate the inrush current and energy through the arrester, select the amplitude of the test current of the arrester, the line discharge withstand test level and the energy absorption capability.
(8) According to the maximum fault current of the arrester installation, select the surge relief level of the arrester.
(9) According to the degree of environmental pollution at the arrester installation location, select the leakage distance of the arrester porcelain sleeve.
(10) Select the mechanical strength of the lightning arrester according to the conditions of lead wire tension, wind speed, and earthquake.
(11) When the arrester does not meet the requirements for insulation coordination, remedial measures such as reducing its rated voltage or rated discharge current level or increasing the insulation level of the protected equipment may be taken.
2 main characteristic parameter choice
(1) Continuous operating voltage Uc. The relatively gapless metal oxide arrester of a neutral point directly earthed system can have a Uc that is not less than the highest phase voltage () of the system. In the neutral point non-directly earthed system, if the single-phase earth fault can be cut off within 10s, the Uc can still be selected not less than, but because most of neutral point in our country is not allowed to run with earth fault in the non-directly earthed system for more than 2h. Therefore, Uc can be selected according to the following principles: 10s and within the removal of failure 2h and above the removal of the fault 3 ~ 10kVUc ~ 1.1UL, 35 ~ 66kV Uc ≥ UL to between 10s ~ 2h, can be selected by more than 2h, can also refer to the arrester Selection of power frequency withstand characteristics curve.
(2) Rated voltage Ur. Ur is the effective value of the maximum allowable power frequency between the two ends of the arrester. It is the rated voltage Ur10s can withstand after injecting the specified energy at a temperature of 60°C.
, and then under Uc, tolerate 30min, can maintain thermal stability.
(3) Temporary overvoltage UT. Temporary overvoltage UT is the basis for determining the arrester's rated voltage. When selecting the UT, the main consideration is single-phase grounding, load shedding and long-line capacitance effects caused by the increase of the power frequency voltage, the amplitude can be selected according to the following conditions.

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