UIM UIM-90, Руководство пользователя

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UIM-90 (221)
UIM-90 (221/В)
UIM-90 (221/Р)
UIM-90 (221/ВР)
25
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,

u
;
– coefficient of variation, V.
4.5.1 Mean breakdown value Ubrk. is calculated by the formula:



N
1 i
U[i]
N
1
U
brk. , (1)
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

u
of mean breakdown value is calcu-
lated by the formula:
 
 
1 N N
U U[i]
σ
N
1 i
2
u
brk.





. (2)
4.5.3 Value of breakdown voltage must correspond with standardized value
of variation coefficient V, calculated by the formula:
brk.
U
100 σ
V
u


. (3)
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.