In high voltage testlng. impulse flashover voltage of xtemal insulation
that has the ability of self-restoring s estimated by up-and-down
method (UDM) or nterpolation method (IM), supposing that flashover
oltage follows a normal distribution with mean M nd standard deviation
S. Trans l.E.E of Japan
UDM is suited for estimating M. On the other hand, IM is suited
for estimating S if sampling points are appropriately selected.
Therefore, by combining UDM and IM, we can deslgn the testing method
where estimators M and S have more adequate errors than those by
UDM or IM alone Especially, when it is important to estimate the
voltage corresponding to low probability of flas_hover (for example
probability = 0.001, 0.01) , combined method (CM) is also suf~ciently
eff ective. This paper explains two research results as follows.
( I ) To show the way to gain the estimators M and ~ and their errors
(with the data obtained by CM) by maximum likelihood method. ( 2
) To decide the parameters of UDM and IM of CM for doing efflcient
test and getting reliable estimators and small errors. and to estimate
the voltage corresponding to low flashover probabil-ity. To achieve
these object, it is desirable to test CM by the following method.
At first, getting Ml and S1 by UDM where T1 (the number of repeti-tion
test times) is 30-50 and d/s (d : up-and-down voltage distance)
is about l. Next, with M1 and S1, test T2 times ( T2 is greater
than 20) at two sampling points (M1-1. 5S1, Ml+1 5S1) by IM. Then,
CM is a good method to estimate M,S and the voltage corresponding
to low flashover proba-bility also with high reliability.
The paper written in English is available