What is the nature of power factor if surge impedance loading is less than load?

Surge Impedance Loading (SIL):

• It is the loading on the line whenever the load impedance is exactly matching to surge impedance of the transmission line.
• It is also known as characteristic impedance loading or ideal loading or ideal power transfer capability.
• So, at SIL the load impedance is equal to characteristic impedance (ZL = ZC).

Surge impedance loading \(SIL = \frac{V^2}{Z_C}\)

Where, ZC = Characteristic impedance = √(z/y)

Case 1: If loading is equal to SIL

• Load impedance is equal to characteristic impedance.
• The transmission line will act as neither sink nor source of reactive power.
• Receiving end voltage is equal to sending end voltage.
• Sending end current is equal to receiving end current.
• Both sending end and receiving end power factors are unity

Case 2: If loading is greater than SIL

• Load impedance is less than the characteristic equation.
• The transmission line will act as a sink of reactive power.
• Receiving end voltage is less than the sending end voltage
• Receiving current is more than sending end current.
• Receiving end power factor is unity but sending end power factor is lagging.

Case 3: If loading is less than SIL

• Load impedance is greater than the characteristic equation.
• The transmission line will act as a source of reactive power.
• Receiving end voltage is greater than the sending end voltage
• Receiving current is less than sending end current.
• Receiving end power factor is unity but sending end power factor is leading.