Woodward easYgen-3000XT Series, Руководство пользователя, Страница: 461 / 1205

Calculation
Fig. 189: Generator ground fault - calculation
1 No ground fault
2 Ground fault (with vectorial calculation)
3 Ground fault (I
S
= ground fault current)
The ground current I
S
is calculated geometrically/vectorially. The pointers for phase
currents IL1 and IL2 are parallel shifted and lined up as shown in ( ╚═▷ Fig. 189 /1).
The pointer between the neutral point and the point of the shifted pointer I
L2
' results is
the sum current I
S
as shown in ( ╚═▷ Fig. 189 /2).
In order to be able to add the pointers vectorially, these must be divided into their X- and
Y-coordinates (IL2X, IL2Y, IL3X and IL3Y).
The ground fault current may be calculated using the following formula:
• (I
L1rated
+ I
L2rated
+ I
L3rated
) - (I
L1measured
+ I
L2measured
+ I
L3measured
) / 1.73 = I
S
•
• (7 A + 7 A + 7 A) – (7A + 6.5 A + 6 A) / 1.73 = 0.866 A •
Results of a calculation example:
• Phase current I
L1
= I
Rated
= 7 A •
• Phase current I
L2
= 6.5 A •
• Phase current I
L3
= 6 A •
Measured ground fault
Ground fault current is actively measured when the mains current input is configured to
monitor for ground current. The ground fault threshold is configured as a percentage of
the value entered for parameter "Generator rated current" (parameter
╚═▷ 1754 ).
The ground fault protection zone is determined by the physical installation location of the
generator current transformer.
461 easYgen-3000XT Series B37574
4 Configuration
4.5.1.6.2.1 Generator Ground Fault (Level 1 & 2)
Released