What type of relay operates based on a specific ratio of potential transformer to current transformer measurements?

The correct choice is a Distance Relay. A Distance Relay is specifically designed to measure the impedance, which is derived from the ratio of voltage (potential transformer measurements) to current (current transformer measurements). This relay operates under the principle of calculating the distance to a fault along a transmission line by monitoring these two parameters. When the relay measures a ratio of voltage to current that falls below a predefined setting, it indicates the presence of a fault within its protection zone.

Distance Relays are commonly used in high-voltage transmission systems for protection against faults because they can indicate the location of a fault based on the impedance calculated from the voltage and current inputs. This is crucial for effective management of the power system and ensures that the fault can be isolated quickly to maintain system integrity.

In contrast, other types of relays listed, such as Overcurrent Relays, Voltage Relays, and Synchronization Relays, serve different operational purposes. Overcurrent Relays operate based on absolute current levels rather than a ratio. Voltage Relays focus on voltage levels and may not involve current measurement ratios. Synchronization Relays are used for ensuring the proper timing and phase alignment of voltages in interconnected systems before closure to a circuit, rather than measuring impedance or fault distances.