D.C.directional relay

例句：

1. 1.The directional relay is used to control the flow of electrical current.
   方向继电器用于控制电流的流动。
2. 2. The directional relay was designed to improve the accuracy of the system.
   方向继电器被设计用来提高系统的准确性。
3. 3.The directional relay is essential for maintaining the stability of the power grid.
   方向继电器对于保持电网的稳定性至关重要。