What kind of measurements do distance relays utilize to perform their function?

Distance relays are designed to protect transmission lines by estimating the distance to a fault based on electrical measurements. They utilize both voltage and current measurements to perform this function.

When a fault occurs on a transmission line, the relay assesses the voltage and current flowing through the line. By analyzing these two parameters, the relay can determine the impedance of the line, which is directly related to the distance to the fault. The impedance is calculated using Ohm’s Law, where voltage divided by current gives the impedance value. This value can then be compared to pre-defined settings to establish whether the relay should trip the circuit to isolate the fault.

The integration of both voltage and current measurements allows distance relays to provide precise fault location information, improving the speed and accuracy of the protection system. Additionally, this capability enables them to distinguish between faults inside the protected zone and normal load conditions, enhancing their effectiveness in the overall power system stability and reliability.