Highly stable nonlinear behavior against impulse current of ZnO-Pr6O11-CoO-Cr2O3-Y2O3 varistors

The nonlinear electrical behavior against the impulse stress (400-1200 A) in the ZnO-Pr₆O₁₁-CoO-Cr₂O₃-Y₂O₃ varistors has been investigated with sintering time. The sintering time did have a significant effect on the clamp ratio, which exhibits a surge protection capability. The varistors sintered for 1 h exhibited the best clamp characteristics, in which the clamp voltage ratio was in the range of K = 1.61-1.92 at a lower impulse current region (5-50 A) and was in the range of K = 2.06-2.55 at a higher single impulse current region (400-1200 A). The best electrical stability against the multi-impulse aging stress of 1200 A was also obtained from the varistors sintered for 2 h, where %ΔE_{1 mA} =−1.6%, %Δα =1.3%, and %ΔJ_L =−4.9%.