| 摘要 |
PURPOSE:To surely stop the electric current of a power supply line in an islanding state by a method wherein a frequency abnormality, a frequency change-rate abnormality and a voltage abnormality are detected and a system- interconnection inverter is released from a system. CONSTITUTION:An electric current always at a definite power factor is output from an inverter 2 over the wide range of the frequency (at which a frequency relay 18 is actuated surely) of an AC power supply 8 by a PLL circuit 22. A slight change in a system is caught by a voltage abnormality relay 25, a frequency abnormality relay 26, a frequency change-rate abnormality relay 27 and the like, an abnormality is found out, the electric current of the inverter 2 fluctuates and becomes out of balance, it is detected that a frequency and a voltage fluctuate largely, and the inverter 2 is released from the system. Thereby, it is possible to surely stop the electric current of a power-supply line in an islanding operation. |
