Causes of varistor degradation

The varistor is a voltage-limiting protection element that absorbs or releases the lightning induced overvoltage and the operating overvoltage present in the line. At the same time, as a component of the line system and equipment, it must also withstand the temporary over-voltage of the low-voltage power supply line and equipment. Voltage, therefore, the varistor must withstand the impact of lightning overvoltage, operating overvoltage and temporary power frequency overvoltage when applied in the line. Under such conditions, its performance and use will be a matter of great concern. This paper systematically discusses the performance, characteristics and applications of varistor and overvoltage protector for lightning protection.

The varistor is a polycrystalline semiconductor ceramic component made of zinc oxide as the main body, adding various metal oxides, and a classic electronic ceramic process. Due to its unique grain boundary structure, under certain electric field, the grain boundary conduction is transformed from thermal electron emission conduction to electron tunnel conduction, and its resistance value decreases sharply with the increase of voltage, which has excellent nonlinear volt-ampere characteristics. . Then, when there is an overvoltage, the grain boundary electron tunneling suppresses the peak value of the overvoltage and absorbs part of the overvoltage energy, thereby protecting the line or equipment. However, regardless of whether the varistor is applied to a power line or an electronic circuit, if various types of overvoltages occur frequently, the varistor will frequently operate to suppress the overvoltage amplitude and absorb and release surge energy, thereby protecting the electrical equipment. And components, which will inevitably lead to degradation or even failure of the performance of the varistor.

At present, the international popular overvoltage protector combines the varistor with the current limiting, overcurrent and degradation warning devices. In addition to the overvoltage protection function, it also has the function of preventing self-degradation and short circuit. Features.