TRIGONOMETRIC FUNCTION CALCULATING CIRCUIT

摘要

PROBLEM TO BE SOLVED: To drastically improve the calculation speed at the time of determining grounding direction in a directional ground relay and to judge the grounding direction at real time. SOLUTION: The directional ground relay 1 previously calculates relation between a phase valueθand tan (I/R) and stores the value of tanθ(the value of a division value (I/R)) corresponding to each phase valueθin an address indicated by an address value expressed by each phase valueθstored in a table 11. In the case of calculating the valueθof tan<-1> (I/R), the value of tanθstored in the table 11 is retrieved and the tanθcoincident with a specified value or most close to the specified value is found out and an address value corresponding to the tanθis set up as the phase valueθof the tan<-1> (I/R).