The importance of the protection level of the surge arrester Up!

May 18, 2022

The important parameters of the power supply (power line) lightning arrester are generally Un—rated working voltage, Uc—maximum continuous working voltage; In—nominal flux, Imax—maximum flux; Up—protection level, or the residual voltage value. Here, we only explain the parameter Up, why is it the main parameter of the electric surge arrester?

According to 3.15 of GB18802.1 "protector performance requirements and test methods for low-voltage power distribution systems": Up is the full name of voltage protection level, which characterizes the performance parameters between the SPD limit terminals.


There are many factors that determine the size of the Up value, but it can be simply understood as: the larger the Uc value of the SPD, the larger the Up value; the larger the In value, the larger the Up value. For example, Uc=385V, In=20kA, Up is generally about 1.8kV for the pressure-sensitive lightning arrester. As the continuous operating voltage and flux increase, the residual pressure value also increases accordingly. For example, UC: 385V, In: 40kA, Up is 2.1kV.

The main function of using T1-level power lightning arrester in outdoor power transmission and transformation systems is to discharge a large amount of lightning current and assess its flow; the main function of indoor use of T2-level power lightning protection device is to limit the high voltage in the line to the protected Within the range that the equipment can bear, examine its pressure limiting capability (Up). Moreover, the indoor electronic and electrical equipment has a withstand voltage limit, such as: household appliances are usually 2.5kV, electronic equipment is 1.5kV, industrial appliances are 4kV, and industrial appliances are 6kV. The more sophisticated the electrical and electronic equipment, the smaller the rated value of its impulse withstand voltage. In terms of protection effect, the Up value of the SPD is naturally as small as possible, and the protection ability of the equipment is also stronger. Therefore, when we choose a power surge arrester, it is not the bigger the parameter, the better, but the right one.

Therefore, when we choose the flow rate and Uc of the lightning arrester in the project, we should consider the Uw value of the protective equipment, that is, the rated value of the insulation impulse voltage (kV) of the equipment, as shown in the following figure:


Insulation impulse withstand voltage rating of equipment in 220V,
380V power distribution systems in buildings
Device location Equipment at the power source Equipment for distribution lines and last branch lines Electrical equipment Equipment requiring special protection
Impulse voltage category IV type III type II type I type
Impulse voltage rating UW (kV) 6 4 2.5 1.5


If the impulse withstand voltage of the equipment is less than 1.5kV, the front end should be equipped with a power surge arrester with Up of 1.2kV and Imax 20kA, because its Up value is lower than that of a 40kA power surge protector, and its residual voltage is lower than that of the insulation. Under the impulse voltage rating, the effect is naturally better. But in fact, in the case of the same Uc, in addition to the higher cost, the surge arrester with large gate flow has no other disadvantages. For example, the AM40 40kA and AM20 20kA surge arresters, which are also Uc275V, are impacted by 10kA. Below 1.2kV. It is only a 40kA lightning arrester. Generally, the In is marked with 20kA, and the Up is obtained under the In, so it seems that the Up is larger than the AM20 series.