Lightning arresters are divided into two types: gapped and gapless. The basic components of a gapped arrester are a spark gap and a zinc oxide nonlinear resistor. These components of the high-voltage surge arrester are stacked in series within a sealed outer jacket of insulating material. The basic component of the gapless arrester is only the valve plate, and its material is mainly zinc oxide and other metal oxides.
The following is a combination of the series of metal oxide arresters produced in my country and classified according to their different technical objectives.
Classified by voltage level
Metal oxide arresters are classified according to the additional voltage value and can be divided into high voltage category, which refers to metal oxide arrester series products above 66kV; medium voltage category, which refers to metal oxide arrester series products from 3kV to 66kV (excluding 66kV series products); low voltage category, which refers to metal oxide arrester series products below 3kV (excluding 3kV series products).
Classified by nominal discharge current
Metal oxide arresters can be divided into five categories based on nominal discharge current: 20, 10, 5, 2.5, and 1.5kA.
Classified by use
Metal oxide surge arresters can be divided into seven categories according to their uses: system line type, system power station type, system distribution type, parallel compensation capacitor bank protection type, electrified railway type, motor and motor neutral point type, and transformer neutral point type.
Classification by outerwear material
Metal oxide arresters can be divided into porcelain coated type and composite coated type according to their structure.
Classified by structure and function
Metal oxide arresters can be divided into three categories according to their structure and function: no gap (W), with series gap (C), and with parallel gap (B).
Gapless arresters mainly have the following characteristics:
a)Simple structure
b) The protection function is good. The resistor has excellent nonlinear volt-ampere characteristics. The current passing through the arrester under normal operating voltage is small, and there is no need for a series gap. The impact caused by changes in gap breakdown characteristics is eliminated. The protection characteristics are only determined by the residual voltage.
c) The protection effect is good. As long as the overvoltage exceeds the rated voltage of the arrester, the protection effect will begin. This will reduce the overvoltage that frequently acts on the protected equipment, reduce extreme insulation breakdown, and have a positive effect on extending the life of the equipment.
d) Operation and testing are convenient, and changes in arrester characteristics can be detected through live experiments.
e) Large energy absorption. Nonlinear metal oxide resistors absorb 5 to 10 times more energy per unit volume than silicon carbide nonlinear resistors. At the same time, resistors or arresters can be used in parallel, doubling the absorption capacity.
f) Since there is no series gap, the resistor chip not only has to withstand lightning and operating overvoltage, but also normal operating voltage and temporary overvoltage, so there are problems with degradation and thermal fluctuations under the action of these voltages.
Gap arresters mainly have the following characteristics:
a) Compared with the gapless arrester, the arrester with a series gap increases the series gap to isolate the resistor from the live conductor, which can prevent the temporary overvoltage caused by the single-phase grounding of the system and the indirect effect of arc grounding or resonant overvoltage on the resistor. However, after using a series gap, the advantages of a gapless arrester are no longer available.
b) Lightning arrester with a parallel gap: A gap is connected in parallel on a part of the resistor sheet. When the lightning current reaches a certain amplitude, the residual voltage on this part of the resistor sheet causes the gap to discharge and short-circuit. When the lightning current amplitude is equal to the nominal discharge current, the residual voltage value of the arrester can be lower than the residual voltage of the gapless arrester. It has certain effectiveness in protecting equipment with low lightning impact insulation, such as generators, etc., but the structure is complex.
c) Compared with ordinary silicon carbide valve-type arresters, with similar protection characteristics, the arrester may have no freewheeling or very little freewheeling. If the guaranteed continuous current is similar, the residual voltage value can be lower than that of silicon carbide valve arrester. In the neutral point non-indirect grounding system, the residual voltage value can also be lower than that of gapless arrester.
d) There is a series gap arrester: Since the discharge voltage is similar to the residual voltage of the resistor, it brings certain difficulties to the power frequency discharge voltage experiment, and the discharge voltage is difficult to detect.
e) Gap arresters are generally used for protection in lines or 3kV ~ 66kV neutral point non-indirect grounding systems.
Since gapped products have inherent defects, such as the dispersion of discharge and the discharge voltage being affected by internal air pressure and external contamination, gapped products are currently mainly used in power distribution systems of 66kV and below. In comparison, gapless arresters have the advantages of wide protection range, strong energy absorption capability, fast response characteristics and good steep wave characteristics, so they have been widely used in power systems.
Cable connector
