In high voltage testlng. impulse flashover voltage of xtemal insulation
that has the ability of selfrestoring s estimated by upanddown
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 probability. 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 repetition
test times) is 3050 and d/s (d : upanddown voltage distance)
is about l. Next, with M1 and S1, test T2 times ( T2 is greater
than 20) at two sampling points (M11. 5S1, Ml+1 5S1) by IM. Then,
CM is a good method to estimate M,S and the voltage corresponding
to low flashover probability also with high reliability.
The paper written in English is available
upon request.
