2.1 Determine the value of the phase voltage in a delta-connected system if the line voltage is 380 V - NSC Electrical Technology Power Systems - Question 2 - 2016 - Paper 1

A well-labelled phasor diagram should be drawn representing the three phases. The phases ($V_L1$, $V_L2$, and $V_L3$) should be at 120-degree intervals, and each should be represented by a vector starting from a common point. The diagram should clearly indicate each phase's direction and angle.

To calculate the current delivered at full load, we use the formula:

$I_{L} = \frac{S}{\sqrt{3} V_L}$

Substituting the values: $I_{L} = \frac{20 \times 10^3}{\sqrt{3} \times 380}$

This gives: $I_{L} \approx 30,39 A$

The power rating can be calculated using:

$P = \sqrt{3} imes V_L imes I_L imes \cos(\theta)$

Where (\cos(\theta)) is the power factor. Substituting the known values:

$P = \sqrt{3} \times 380 \times 30,39 \times 0,87$

This results in: $P \approx 17,4 kW$

The function of a kilowatt-hour (kWh) meter is to measure the amount of energy consumed by a load over a given period of time. It records energy consumption in kilowatt-hours.

1. Adding power-factor correcting capacitors in parallel with the load.
2. Using synchronous motors to improve power factor.

The total power consumed by the load can be found by:

$P_n = P_1 + P_2$

Substituting the given values:

$P_n = 120 + 50 = 170 W$

1. Only two watt meters are required instead of three, simplifying the measurement apparatus.
2. The method allows for the power of balanced and unbalanced loads to be accurately measured.