4.1 Explain the following terms with reference to three-phase systems: 4.1.1 Efficiency 4.1.2 Power factor correction 4.2 Name TWO advantages of power factor correction to the supplier - NSC Electrical Technology Power Systems - Question 4 - 2023 - Paper 1

Power factor correction refers to the techniques used to reduce the phase difference between voltage and current in an AC system, thereby increasing the power factor closer to 1. This is often achieved through the use of capacitors.

1. Reduced current flow: Correcting the power factor reduces the current drawn from the supply. This helps in reducing the losses in the distribution system due to lower heat generation in conductors.

2. Improved voltage regulation: A higher power factor improves the voltage stability in the supply network, leading to better performance of electrical equipment and reducing the risk of outages.

Power transmission is the large-scale transfer of electricity from power plants to substations. It usually involves high voltage and long distances to minimize losses. In contrast, power distribution is the final stage of the electrical power supply chain, converting this high voltage electricity at substations to lower voltages for residential and commercial use.

To calculate the line current, we use the formula:

Calculating this gives:

The apparent power can be calculated using:

Substituting the values:

The reactive power (Q) can be calculated using:

Where, $heta = ext{cos}^{-1}( ext{pf})$
Substituting the values, we get:

The phasor diagram for a three-phase system shows the line voltages (V_BR, V_BY, V_YR) spaced 120 degrees apart. This diagram represents the instantaneous voltage in each phase:

          V_YR
            / 
           /   
          /     
    V_BR /       V_BY
           \     
            \   
             \ 

The angle between the line voltages is 120 degrees.