The arrester is one of the main lightning protection devices in the power system. Only when the arrester is correctly selected can it play its proper lightning protection.

   

1. Selection of gapless metal oxide arresters
 

The general requirements for selection are as follows:
 

(1) The environmental conditions of the arrester should be determined according to the temperature, altitude, wind speed, pollution and earthquake conditions in the area of ​​use, and the system's nominal voltage, system maximum voltage, rated frequency, neutral point grounding method, short-circuit current value and Conditions such as the duration of the ground fault determine the operating conditions of the arrester.

(2) Determine the type of arrester according to the protected object.

(3) Determine the continuous operating voltage of the arrester according to the highest voltage applied to the arrester for a long time.

(4) Select the rated voltage of the arrester according to the temporary overvoltage amplitude and duration of the arrester installation location.

(5) Estimate the magnitude of the discharge current through the arrester and select the nominal discharge current of the arrester.

(6) According to the rated lightning impulse withstand voltage and rated operational impulse withstand voltage of the protected equipment, determine the lightning overvoltage protection level and the operating overvoltage protection level of the arrester according to the requirements of insulation coordination.

(7) Estimate the surge current and energy through the arrester, select the test current amplitude of the arrester, the line discharge withstand test level and the energy absorption capacity.

(8) Select the pressure release level of the arrester according to the maximum fault current at the lightning arrester installation.

(9) According to the environmental pollution degree of the arrester installation site, select the leakage ratio of the arrester porcelain sleeve.

(10) Select the mechanical strength of the lightning arrester based on the tension, wind speed and earthquake conditions.

(11) When the arrester does not meet the requirements for insulation coordination, remedial measures such as appropriately lowering its rated voltage or nominal discharge current level or increasing the insulation level of the protected equipment may be taken.
 

2. main characteristic parameter selection
 

(1) Continuous operation voltage Uc. A relatively gap-free metal oxide arrester for a neutral point direct earthing system, the Uc of which can be selected not lower than the highest phase voltage of the system ( ). In the non-direct grounding system at the neutral point, if the single-phase ground fault can be cut within 10s, the Uc can still be selected below, but because most of the neutral point indirectly grounded systems in China are allowed to operate with ground fault for more than 2h. Therefore, Uc can be selected according to the following principles: 10s and less, 2h and above, 3~10kVUc~1.1UL, 35~66kV Uc≥UL, 10s~2h, can be selected for more than 2h, or refer to the arrester The power frequency voltage withstand characteristic curve is selected.

(2) Rated voltage Ur. Ur is the effective value of the maximum allowable power frequency voltage between the two ends of the arrester. It can withstand the rated voltage Ur10s after injecting the specified energy at 60 °C.

Then, under Uc, withstand for 30 min, it can maintain heat stability.

(3) Temporary overvoltage UT. The temporary overvoltage UT is the basis for determining the rated voltage of the arrester. When selecting the UT, the power frequency voltage caused by the single-phase grounding, the load shedding and the long-line capacitance effect is mainly considered, and the amplitude can be selected according to the following conditions.

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FATECH ELECTRONIC LTD.

Feb.18, 2019