Selection of metal oxide surge arresters
Lightning arrester is one of the main lightning protection devices in the power system. Only by selecting the lightning arrester correctly can it play its due role in lightning protection.
Personal recommendation of lightning arrester brand; Minrong Electric
1. The general requirements for selecting gapless metal oxide arresters are as follows:
(1) The environmental conditions for the use of arresters should be determined according to the temperature, altitude, wind speed, pollution, earthquake and other conditions in the area of use, and the system operating conditions of the arrester should be determined according to the system's nominal voltage, system voltage, rated frequency, neutral point grounding method, short-circuit current value and ground fault duration.
(2) Determine the type of arrester according to the object to be protected.
(3) Determine the continuous operating voltage of the arrester based on the voltage acting on 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 amplitude of the discharge current passing through the arrester and select the nominal discharge current of the arrester.
(6) Determine the lightning overvoltage protection level and operating overvoltage protection level of the arrester based on the rated lightning impulse withstand voltage and rated operating impulse withstand voltage of the protected equipment and the insulation coordination requirements.
(7) Estimate the impulse current and energy passing through the arrester, select the test current amplitude of the arrester, the line discharge withstand test level and the energy absorption capacity.
(8) According to the fault current installed on the arrester, select the pressure release level of the arrester.
(9) According to the degree of environmental pollution at the place where the arrester is installed, select the leakage ratio of the porcelain sleeve of the arrester.
(10) Select the mechanical strength of the arrester according to the lead tension, wind speed, earthquake and other conditions for the arrester installation.
(11) When the arrester does not meet the insulation coordination requirements, remedial measures such as appropriately reducing its rated voltage or nominal discharge current level or improving the insulation level of the protected equipment can be taken.
2. Main feature parameter selection
(1), continuous operating voltage Uc.
For phase-to-ground gapless metal oxide surge arresters in systems with a neutral point directly grounded, the Uc can be selected not less than the system phase voltage.
In a neutral point non-directly grounded system, if a single-phase ground fault can be removed within 10 seconds, its Uc can still be selected not less than 10 seconds. However, since most of the neutral point non-directly grounded systems in my country are allowed to operate with a ground fault for more than 2 hours, Uc can be selected according to the following principles:
Remove the fault U within 10 seconds or less. Remove the fault 2h or more after 2U1 3~10kV 1.0~1.1U, 35~66kV Uc≥UL and between 10s~2h, it can be selected based on 2h or more, or you can refer to the power frequency voltage withstand characteristic curve of the arrester.
(2) The rated voltage UrUr refers to the effective value of the allowable power frequency voltage between the two ends of the arrester. It can withstand the rated voltage Ur10s after injecting specified energy at a temperature of 60"C, and then withstand 30min under Uc and maintain thermal stability.
(3) Temporary overvoltage Ur temporary overvoltage UT is the basis for determining the rated voltage of the arrester. When selecting U, the main consideration is the increase in power frequency voltage caused by single-phase grounding, load shedding and long-term capacitance effects. The amplitude can be selected according to the following conditions.
Neutral point non-directly grounded system:
3~10kV U=1. 1Um35~ 66kV, U_=Um neutral point directly grounded system:
110~220kV U] =14U1 rear line side U,=1.4U15 (4), the rated voltage of the phase-to-ground arrester, the rated voltage of the phase-to-ground arrester can be determined according to Table 1.
(5) Power frequency voltage withstand time characteristics The power frequency voltage withstand time characteristics of an arrester is its ability to withstand temporary overvoltage after absorbing the specified overvoltage energy. The arrester used in a system with a directly grounded neutral point or a system with an automatic ground fault removal device can withstand a temporary overvoltage equal to its rated voltage for 10 seconds. If the temporary overvoltage acts for a long time, the amplitude of its tolerance will be low, and vice versa. Therefore, if a temporary overvoltage occurs
If the time is shorter than or greater than 10s or its amplitude is lower than or higher than the rated voltage of the arrester, the power frequency withstand time characteristic curve of the arrester can be used for verification.
(6) The nominal discharge current of the arrester is the nominal discharge current IB specified in the national standard GB11032 "Technical Specifications for Metal Oxide Arresters".
(7) Protection level and insulation coordination coefficient The lightning overvoltage protection level is the higher of the following two items:
Residual voltage at nominal discharge current.
The residual voltage under steep slope impulse current is divided by 1. 15 (referring to oil-immersed insulated electrical appliances, other electrical equipment may have different coefficients).
The protection level of operating overvoltage is the residual voltage under operating surge current.
When performing insulation coordination according to the usual method, the ratio between the insulation level of the equipment and the protection level of the arrester is the coordination coefficient.
1. Lightning overvoltage coordination coefficient:
When the arrester is close to the protected equipment > 1.25 When the arrester is not close to the protected equipment > 1.42, the operating overvoltage coordination coefficient is > 1. 15
