Step 1: Voltage level
Domestic type: determined based on the nominal system voltage and neutral grounding method.
Export type: one voltage level every 3kV, selected according to equipment insulation coordination requirements.
Step 2: Structural features
Gap free type: For regular use, there are corresponding gap free models for various purposes.
Gap type: only used in areas that require enhanced protection. (e.g. line protection)
Step 3: Protecting Objects
S-shaped Z-type is used for conventional electrical appliances. In terms of performance, Z-type is good, and those with high nominal current are good.
D-type protective motor. The nominal current of 5 is dedicated to generators, and its performance is much higher than that of 2.5.
R-type protective capacitors are selected based on their power and connection method to convert their current capacity.
There are two types of neutral point type motors and transformers, both of which are selected based on the neutral point grounding method
In other models, X. T-shaped is a conventional structure that only requires special design parameters and wiring methods; F. The L-type is not a conventional structure and cannot be replaced by a conventional structure lightning arrester.
Step 4: Place of Use
Conventional lightning arresters are commonly used both indoors and outdoors, and products with umbrella shaped designs that comply with regulations should be able to meet the anti fouling requirements of Class III and below.
If the pollution level exceeds Level III, anti fouling products need to be used and the climbing distance needs to be calculated.
If the altitude exceeds 2000m, it is necessary to calculate the proportion of reinforced insulation and use plateau type products.
Other selection matters.
The performance of a magnetic blowing valve type silicon carbide lightning arrester (FCD) is similar to that of a gap free metal oxide overvoltage protector, but slightly worse than that of a gap free metal oxide overvoltage protector. Other F-type lightning arresters (FZ The performance of FS is significantly worse.
Advantages and disadvantages of 2-ceramic sleeve lightning arrester.
Advantages: Durable, no major accidents. Theoretically, it can be used for 50 years.
Disadvantages: bulky and inconvenient for installation, prone to breakage during handling, and prone to explosion and injury to personnel and equipment during use.
Advantages and disadvantages of silicone rubber lightning arresters.
Advantages: High insulation, good heat dissipation, conducive to miniaturization and complete set use of electrical appliances.
Disadvantage: The jacket has a lifespan issue, and the rubber ages after a certain period of use.
Step 5: The most troublesome issues in the procurement of metal oxide overvoltage protectors
Lightning arrester is the basic equipment for insulation coordination in the entire power system. Simply put, the design unit must determine the withstand voltage capability of all high-voltage electrical equipment in the system based on the performance of the lightning arrester. So its performance selection is of great significance. Below is a brief explanation of the most troublesome structural, model, and parameter issues in the selection of metal oxide overvoltage protectors.
The question of 1 YH or HY.
First of all, you need to know that, What do Y and H mean. Y represents "metal oxide", which is commonly referred to as a metal oxide overvoltage protector; H represents "composite jacket", which is commonly referred to as silicone rubber lightning arrester. The meaning of connecting is: silicone rubber metal oxide overvoltage protector. So YH and HY are the same.
So why do two different writing styles appear? This is because the expression order of the sequential national standard is different, which leads to inconsistency in the alphabetical order of the sequential national standard products. After 2000, the industry has gradually unified the model description as YH. The HY type products still exist in the market, mainly due to the updating and replacement of old projects and outdated products, as well as the information blockage of some design units and production enterprises, which have not kept up with the development of the industry.
Performance issues with 2 W and C.
Step 6: Selection of important parameters for lightning arresters
There are three most important parameters for lightning arresters. One is the rated voltage, one is the nominal residual voltage, and one is the energy absorption capacity. Let's take YH5WS-17/50 as an example to illustrate.
1 Rated voltage
17 in the above models represents the rated voltage. The definition of rated voltage is quite complex. As a non professional manufacturer, it can be simply understood as the effective value of overvoltage reaching around 17kV, and the lightning arrester will start working. This parameter should not be too low, otherwise it may cause the lightning arrester to be overloaded and burn out. Although the old national standard defines the rated voltage as 12.7, the actual working value is still around 17, so there is a lot of controversy about the old national standard definition, which is no longer promoted.
So, whether the rated voltage is 17, 16.5, or 17.5 is actually the same performance level, and they all meet the definition of Class 17 products according to national standards. When purchasing, do not be too narrow-minded. As for why there are items like 17.5 and 16.5, it is because each manufacturer has slight differences in specific parameters, and the sales strategy of the unique model shown in the picture requires it.
2 nominal residual pressure
The 50 in the above models represents the nominal residual voltage of lightning, which can be simply understood as the surge arrester being able to limit the peak overvoltage below 50kV during the most severe lightning strike. This parameter is actually the most important parameter of the lightning arrester, because the foundation of the entire system insulation coordination is here. We keep saying that reducing residual voltage is good because it reduces the residual voltage of lightning arresters, which is equivalent to improving the safety margin of all high-voltage electrical appliances in the system.
However, reducing residual voltage is limited by the performance of zinc oxide resistors themselves, and there is a bottom line. Although products with gaps can further reduce residual pressure, they are not infinitely reduced and there is also a bottom line. If a small factory claims that its product residual pressure is lower than that of a regular large factory, it can basically be judged as tampering and not buying.
3 Energy absorption capacity
When the lightning arrester is working, due to the passage of a high current of kA level, it will generate significant heat and temperature rise. If it cannot withstand it, it will cause damage or even explosion. Therefore, the energy absorption capacity of lightning arresters is a very important parameter. Export oriented products, expressed in terms of how much kJ/kV this capability is; Domestic products are expressed in terms of square wave current capacity A. The higher this value, the greater the current that the lightning arrester can withstand without damage, and the better its performance.
Simply put, this ability is directly related to the diameter of the resistor. Just like when purchasing copper wire, the thicker the wire, the greater the current that can flow. When the formula is similar, the larger the resistor, the stronger the natural square wave current carrying capacity.
