Design for Sampling Plan for Life Test of ZnO Non-Linear Resistors

Presently the MOV life evaluation test plan under voltage/temperature stress is based on the “Failure rate sampling plans and procedures”(Refer to MIL-STD-690D/GJB-2649), which can only be used in the case that the life follows an exponential distribution, that is, only in the case that the failure rate λ(\pmbt) is constant throughout the life. However, the failure rate λ(\pmbt) of MOV is not constant in the whole lifetime and varies with the life time. The market demand for ZnO non-linear resistors with established service life is increasing year by year. The IEC-SC37B has created a project team to prepare a standard document for such products. The sampling plan for the life test of ZnO non-linear resistors under voltage-temperature stresses will be an important part of the standard document, and we believe, it will also be a part of the standard for metal-oxide arrestors, such as IEC 60099-4. There are two sampling plans applicable to the life test on the products whose life distribution is Weibull function. One sampling plan is based on the reliability index of life time t0.9 at reliability R=0.9, and the other is based on the reliability index of the failure rate at the time \pmbt0.9, denoted as
^''
λ(\pmbt0.9)
^''
or
^''
λ(B10)
^''
. The former sampling plan is used herein. This contribution gave three tables of the sampling plan, which are applicable respectively to the permitted failure number \pmbc=0, \pmbc=1, and \pmbc=2. The principles and methods for developing the tables are presented in this paper, so that some new sampling plans can be developed if necessary.