Processing Of Test Results - UIM -90 User Manual

4.5 Processing of test results

After the test, if the parameter "Number of break. N =" is set greater than
one, the following values are calculated:
– mean breakdown value, Ubrk.;
– standard error value,
– coefficient of variation, V.
4.5.1 Mean breakdown value Ubrk. is calculated by the formula:
where U[i] – is value of breakdown voltage, obtained at a given number of N
series breakdowns, kV.
4.5.2 The value of the standard error
lated by the formula:
4.5.3 Value of breakdown voltage must correspond with standardized value
of variation coefficient V, calculated by the formula:
If coefficient of variation V exceeds 20 %, six more breakdowns are addi-
tionally carried out, and for calculation according to formulas (1) and (2) N is
taken equal to 12. If the coefficient of variation V repeatedly exceeds 20 %, the
liquid dielectric quality is considered unsatisfactory.

;
u
N
1

U

brk.
N
i 1


u
N


U[i]

i 1
σ 

u

N N
σ 100

u
V

U
brk.
25
U[i]
,
of mean breakdown value is calcu-
2

U
brk.
.

1

.
UIM-90 (221)
UIM-90 (221/В)
UIM-90 (221/Р)
UIM-90 (221/ВР)
(1)
(2)
(3)