Emulations of Overvoltage and Overcurrent Relays In Transmission Lines

An “Over Voltage Relay” is one of the protective relays which operates when the voltage exceeds a preset value. In a typical application the over voltage relay is used for over voltage protection, which is connected to a potential transformer, and calibrated to operate at or above a specific voltage level. An “Under Voltage Relay” and an “Over Current Relay” are also protective relays which operate when the voltage is reduced, or the current is increased below or above a preset value. In a typical application these relays are connected to potential transformers, and calibrated to operate at, above or below a specific voltage or current levels. The emulator used in paper simulated experiments of all three types of relays mentioned above. The transmission line emulator used in this paper is an HVAC transmission line of length of 180 km. The transmission line of the emulator can be used as a 3-phase transmission line of 180 km length or as a single-phase transmission line of 540 km long. This transmission line in the emulator is divided into 6 $\pi$ sections and each $\pi$ section is 30 km long. The line inductance of the transmission line of the emulator is examined for every 30 km and the line capacitance is examined for every 15 km. The line parameters of the emulator (RLC) for the 400kV transmission line are: 0. 02978$\Omega$/km, 1.06 mH/km and 0.0146 $\mu$F/km, respectively.