2.1 Name the instrument that is used to measure electrical energy - NSC Electrical Technology Power Systems - Question 2 - 2016 - Paper 1

1. Three-phase systems can be operated in star or delta configurations, allowing for flexibility in design and application.

2. Three-phase systems can supply both three-phase and single-phase installations, making them more versatile for various loads.

The sketch should represent three sine waves, each 120 degrees apart. Label the voltages as V₁, V₂, and V₃, showing their maximum and minimum values as well as the phases' displacement.

To calculate the line voltage, use the formula:

V_L = rac{S}{rac{√3}{I_L}}

Substituting the given values:

V_L = rac{20000}{rac{√3}{25}}

Calculating yields:

$V_L = 461.88 ext{ V}$

The phase voltage can be calculated using the formula:

V_{ph} = rac{V_L}{√3}

Using the previously calculated line voltage:

V_{ph} = rac{461.88}{√3} \\ = 267.67 ext{ V}

To calculate the total input power, sum the power readings from the two meters:

$P_T = P_1 + P_2 = 8 ext{ kW} + 4 ext{ kW} = 12 ext{ kW}$

The line input current can be calculated using the formula:

I_L = rac{P}{√3 V_L ext{ Cos } φ}

Using the values:

I_L = rac{12000}{√3 * 380 * 0.8}

Calculating yields:

$I_L ≈ 22.79 ext{ A}$