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1 2009

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Ocena odporności warystorów tlenkowych na narażenia udarowe

Jaroszewski M., Pospieszna J., Pietrusewicz M.

Pomiary Automatyka Kontrola

2009

R. 55, nr 2

101-103

Warystory ograniczników przepięć ulegają w trakcie eksploatacji procesom starzeniowym. Czynnikami narażenia są: napięcie robocze przemienne lub stałe, przepięcia, wyładowania niezupełne. Proces degradacji prowadzi do zwiększenia wydzielanej energii i tym samym do podwyższenia temperatury warystorów i wzrostu prądu przewodzenia. W pracy przedstawiono wyniki badań zmian degradacyjnych warystorów narażonych na oddziaływania udarowe. Warystory poddawane były oddziaływaniu serii impulsów, o liczbie zwiększanej w kolejnych etapach starzenia.

The paper presents the effect of multiple impulse voltages on electrical properties of a zinc oxide (ZnO) varistor. The multiple impulse sequences were generated by a combination wave generator delivering a standard impulse voltage wave of 10/800 žs and, at the short-circuited output, a standard impulse current wave of 8/40 žs. Varistors were exposed to a series of impulses, repeated every 5 seconds, with a peak voltage value equal to five times value of the reference voltage. Changes in the voltage-current characteristics were measured at DC voltage supply. The measurements of these characteristics were taken immediately after the ageing process and then after 15 and 30 minutes since the end of pulse ageing. The durability of the observed ageing changes was studied using the additional measurement of the voltage-current characteristics after 65 hours since the completion of ageing. The test results show that the increase in the number of impulses in the series causes the visible reduction in the reference voltage U1mA. These changes are not of lasting nature - the reference voltage value grows with the time since the end of the aging and after a significant length of time (Fig. 2) reaches the value similar to that characterizing a new varistor (Fig. 1). The greater number of impulses in the series, the smaller reference voltage in the steady state, that is after ceasing the degradation process, as shown in Fig. 3. In this case, a longer time is needed to achieve the initial reference voltage U1mA. This means that the phenomenon of return is slower. The observed degradation and partial return to the initial varistor characteristics can be related to the processes of absorption and desorption of oxygen ions on grain boundaries [3, 4]. These ions are least connected with the varistor structure. In state of degradation and partial or total return to the initial state they are transported along the borders of ZnO grains and the intergranular phase.