The advantages and disadvantages of zinc oxide varistors

Zinc based varistors have increasingly come into people's sight, and their presence can be seen in the fields of communication, power supply, and intelligent product design. So, what are the advantages of this varistor in the application process? What other issues do engineers need to pay special attention to? Today, the editor will take a detailed inventory for everyone!

Based on the current application and manufacturing process of zinc oxide varistors, this new type of varistor can be divided into two categories in terms of formula and performance that cannot be replaced by each other, namely high-voltage varistors and high-energy varistors. Next, we will conduct a detailed inventory and introduction of its advantages and disadvantages.

Firstly, let's take a look at high-voltage varistors. The biggest advantage of this type of varistor is that its voltage gradient is very high, usually reaching 100-250V/mm. Therefore, its high current characteristics are good, with V10kA/V1mA ≤ 1.4. However, this type of zinc oxide varistor also has a drawback, which is that it only has ideal protection against overvoltage and surges with a narrow pulse width (2 ≤ ms), and has a lower energy density.

Next, let's take a look at the advantages and disadvantages of high-energy varistors. The outstanding advantage of this zinc oxide varistor is its high energy density, which can reach 300J/cm3~750J/cm3 in practical applications, and has strong ability to withstand long pulse width surges. But it also has a major flaw, which is that its voltage gradient is relatively low, with a gradient range of only 20V/mm~500V/mm, and poor high current characteristics.

From the above introduction, we can also see that the performance differences between these two types of zinc oxide varistors in their formulations have caused many blind spots in their applications. Based on the current usage of collectible elements, vacuum switches are widely used in 10kV voltage transmission and distribution systems. Due to their fast operation speed and small arc pulling, they can cause extremely high overvoltage and surge energy during operation. If high-voltage varistors are used for protection, although they have high voltage gradients and low costs, their energy capacity is small and they are prone to damage. If a high-energy varistor is selected, although it has a large energy capacity and a long lifespan, the voltage gradient is low and the cost is too high, which is 5-13 times that of the former. In medium and small power variable frequency power supplies, due to the target of system overvoltage protection being power semiconductor devices, it has strict requirements for the high current characteristics and energy capacity of varistors, and at the same time, it needs to achieve miniaturization of components, which puts forward strict screening standards for the selection of varistors. High energy varistors can meet the requirements in terms of energy capacity, but their high current performance is not ideal, and the residual voltage of small diameter components is relatively high, often failing to meet the voltage limit requirements; High voltage varistors have good high current characteristics and are easy to miniaturize, but their energy capacity is insufficient and cannot meet the energy absorption requirements. Therefore, the application of small and medium-sized variable frequency power supplies in this field of varistors is almost blank.