Understanding Surge Impedance Loading (SIL) in Power Systems

Electric power, the rate at which work is done or energy is transformed in an electrical circuit, is represented by Watts. Various formulas and units are used to measure electric power; Joules per second is the SI unit of power. The fundamental formula for electric power is:

P VI, where:

P is Power V is the Potential Difference in the circuit I is the Electric Current VI Q/t, where Q is the Electric Charge in coulombs and t is Time in seconds

In a power system, Surge Impedance Loading (SIL) refers to the loading in megawatts at which the voltage drop in the transmission line is compensated by the voltage rise due to the Ferranti effect, ensuring the remote end has the same voltage as the local busbar.

What is Power?

Power is defined as the rate of doing work, which is quantified by the following equation:

Power Work Done / Time, With the SI unit of power being Watts (W). No matter the nature of the power, the SI unit remains the same, and for DC electrical power, the formula is:

DC Power Current x Voltage

Components of Electric Power

In an AC electrical circuit, the components of power are:

Apparent Power (S) is measured in Volt-Amps (VA) Reactive Power (Q) is measured in Volt-Amps Reactive (VAr) Active or Real Power (P) is measured in Watts

SI Units and Electric Power

SI does not have a unit specifically for electric power; power is measured in Watts. Some entities may incorrectly state power as joules per second (J/s), which is equivalent to 1 watt. Similarly, megajoules per hour (MJ/h) is close to 277.7 Watts, though the correct unit remains watts.

The SI unit for electric power is Watt (W).

Therefore, the formula for electric power in its simplest form is:

Electric Power P VI, with the SI unit being Watt (W).