What device allows for the manual closing of a circuit breaker between two control areas?

The device that allows for the manual closing of a circuit breaker between two control areas is a synchroscope. A synchroscope is specifically designed to monitor the phase relationship between two or more alternating current (AC) systems. It provides visual indicators that show whether the systems are in sync regarding voltage, frequency, and phase angle.

When operators are preparing to connect two systems, they need to ensure that they are synchronized; this means that the phases of the voltages must align closely. The synchroscope assists operators in determining the right moment to close the circuit breaker, thereby minimizing the risk of damaging equipment or causing disturbances in the grid. This capability is crucial for maintaining system stability and reliability when interconnecting different electrical networks.

In contrast, the other devices mentioned do not perform this function. For example, a power meter measures the electrical power in a system but does not assist in synchronizing or manually closing breakers. A frequency relay protects equipment by trip signals based on frequency deviations, while a voltage regulator ensures voltage levels remain stable but does not involve manual operations for breakers.