Electrical properties and AC degradation characteristics of low voltage ZnO varistors doped with Nd2O3

Percolation effects in the capacitive properties of metal-oxide varistors in the range of high voltage

“…3,4 This effect is one of the main methods for determining parameters of metal-oxide varistors (in particular, the height of the intercrystallite potential barrier and concentration of donors) in studying the influence of admixtures (additives) or appearance of defects in the structure of the ceramics caused by some or other peculiarities of manufacturing technologies or by the process of degrading. [5][6][7][8][9] Interpretation of the effect of negative capacitance is being discussed until now. In particular, there are known ideas of fast growth of conductivity in the area of breakdown, which stipulates bridging and fast fall of capacitance, 1 of appearance of an inversion layer in the reversely shifted area of the spatial charge of the intercrystallite barrier in case of strong bends of energetic zones, 10,11 of tunnel generation, stimulated by absorption of phonons, 3 of generation of \hot" electrons overcoming the intercrystallite boundary that are capable of impact ionization and creation of holes in its depleted part, further recombination of which leads to appearance of inductance properties.…”

Degradation assessment of metal oxide varistors using a statistical experimental design

“…However, it is worth noting that both these tests consist of various aspects of the V ‐ I characteristic test . This test provides an accurate description of key parameters (reference voltage, leakage current, coefficient of nonlinearity) of MOV arresters and therefore gives a good indication of the health or performance of these devices . For the purpose of this study, several levels of DC current were injected through the MOV samples before and after degradation tests.…”

“…As a result of the configuration of the MOV microstructure, a junction diode (Zener type) effect is created between several adjacent ZnO grains with a double‐barrier potential constituted across the intergranular boundaries. This junction potential is commonly referred to as the double Schottcky barrier (DSB) height and is responsible for the high capacitance across varistors as a result of the presence of trapped charges in this region. The DBS, such as that formed across intergranular regions, could be perceived as some form of microstructural switch or regulator, which plays an important role in the performance as well as the degradation or breakdown mechanism of varistor devices.…”

A Review of Leakage Current-based Condition Monitoring Techniques of Metal Oxide Surge Arresters

“…The leakage current in MOSA-based surge protection units consists of two fundamental current components: the capacitive component which consists of 95% of the leakage current and the resistive component which forms 2% -5% content of the leakage current [12]. The applied voltage stress and the environmental temperature in which MOSA components operate consist of major contributing ageing or degradation factors in this popular family of SPD's [13,14]. Therefore, the dependence of the resistive current on the supply voltage and temperature [15,16], makes this current component to be regarded as key indicator of the health status or ageing diagnosis of metal oxide arresters.…”