Factors affecting the selection of rated voltage of gapless metal oxide arresters
The rated voltage of the arrester manufacturer is the maximum allowable effective power frequency voltage applied between the arrester terminals. The arrester designed according to this voltage can work correctly under the temporary overvoltage determined in the specified operating load test. According to the International Electrotechnical Commission (IEC99-4) and GB11032-2000 regulations for gapless metal oxide arresters, the arrester must be able to withstand a temporary overvoltage equivalent to the rated voltage value for at least 10s at a temperature of 60°C without thermal collapse after injecting the energy specified in the standard.
After the arrester manufacturer preheats to 60°C and is subjected to large current or line discharge level energy loads, the data of the duration of power frequency voltage allowed to be applied to the arrester and the corresponding power frequency voltage value without damage or thermal collapse is called the power frequency voltage withstand time characteristics of the arrester. The arrester can withstand the rated voltage and the temporary overvoltage duration is l0s. If the temporary overvoltage duration is shorter than l0s, the amplitude of the temporary overvoltage can be increased, and conversely it can be reduced. The amplitude of the temporary overvoltage is higher or lower than the rated voltage of the arrester, and its action time can be shorter or longer than l0s. Then when selecting the rated voltage of the arrester, the power frequency voltage withstand time characteristic curve of the arrester can be used to check according to different system operation modes.
In the arrester product manufacturing standard "AC gapless metal oxide arrester" GB11032-1989, which has been used for many years, Article 5.11 regarding the power frequency voltage withstand time characteristics of the arrester stipulates that "power station arresters and distribution arresters with a rated voltage of 3.8-12.7kV used in neutral point non-effective grounding systems should withstand 2h at 1.3 times the rated voltage and 24h at the rated voltage." According to this clause, taking the medium-voltage 10kV neutral point non-effectively grounded system as an example, the arrester should withstand a power frequency voltage of 13kV for 2 hours. According to the time characteristics of the gapless metal oxide arrester withstanding power frequency voltage, generally 10s is 15%-25% higher than the 2h power frequency voltage resistance. Then according to the definition, the rated voltage of the arrester should be 1.3 times of 13kV, which is 17kV. This result is consistent with the IEC definition of the rated voltage of gapless metal oxide arresters. But at the same time, we noticed that the premise of this clause is for power station arresters with a rated voltage of 3.8-12.7kV for neutral point non-effectively grounded systems, which obviously contradicts our calculation result of 17kV. This is probably the reason why this clause no longer appears in the "AC Gapless Metal Oxide Surge Arrester" GB11032-2000/IEC60099-4:1991 (hereinafter referred to as the "New Standard") that was implemented on August 1, 2000. In Article 6.13 of the "New Standard", it is pointed out that the power frequency voltage withstand time characteristics of the arrester are necessary for selecting the rated voltage of the arrester, but it fails to mention the temporary overvoltage amplitude and duration requirements in detail. The power frequency voltage withstand time characteristics of lightning arresters given by various manufacturers are different, which causes difficulty in selection. In this way, designers must take the grounding method and operation method of the medium voltage system into consideration when selecting arresters. For different medium-voltage system grounding methods, the neutral point is effectively grounded (directly grounded or grounded through low resistance) or the non-effectively grounded system (neutral point insulation is grounded through an arc suppression coil or high resistance), the rated voltage of the metal oxide arrester is different. The reason is: For the neutral point of the medium-voltage system with non-effectively grounded system, when a ground fault occurs on one phase, it does not trip immediately. The ground voltage of the other two healthy phases rises to the line voltage. The ground fault lasts for a period of time (may exceed 2h, cold shrink cable terminal). According to the gapless metal oxide arrester withstands power frequency electricity Voltage time characteristics, generally 10s is 15%-25% higher than the 2h power frequency voltage tolerance, so the rated voltage of the gapless metal oxide arrester of the neutral point non-effective grounding system of the medium voltage system is 1.3 times the rated voltage of the gapless metal oxide arrester of the neutral point effective grounding system of the medium voltage system.
It can be seen from the above that the power frequency voltage withstand time characteristics of the arrester itself and the grounding method of the power system will affect the selection of the rated voltage of the arrester.
Yichang Hengyuan Technology Co., Ltd. specializes in the production of European-style cable joints, plug-and-pull heads, cable branch boxes, American-style elbow joints, high-voltage vacuum circuit breakers, high-voltage load switches, arresters, zinc oxide arresters, tank arresters, over-voltage protectors, counters, monitors, heat-shrinkable cable accessories, Manufacturer of cold shrink cable accessories, T-heads, wall bushings, European cable accessories, American cable joints, transformer neutral point protection devices, fuses, isolating switches, PT cable heads, elbow cable joints, 10kV outdoor terminals, switch cabinets, cable intermediate joints, cable accessories and other products
