| 摘要 |
PROBLEM TO BE SOLVED: To resolve a problem of increase in cost without increasing a size of a mounting area for a protection relay, and to protect an apparatus with certainty without increasing the number of components.SOLUTION: A three-phase open-phase protection device comprises: a current detector for detecting currents of two phases of a three-phase AC power supply; an analog input unit to which the currents of the two phases of the three-phase AC power supply that are detected by the current detector are inputted; an analog digital conversion unit converting a signal from the analog input unit into a digital signal; a calculation processing unit calculating a current value of a remaining one phase of the three-phase AC power supply on the basis of an input current value and a phase angle of the two phases of the three-phase AC power supply that is a digital signal from the analog digital conversion unit, and determining open-phase of a three-phase balanced load on the basis of the calculated current value of the respective phases; and a control signal output unit giving an AC circuit breaker an opening command in a case where the open phase of the three-phase balanced load is detected by the calculation processing unit. |
