4.1 Refer to FIGURE 4.1 and answer the questions that follow. 4.1.1 Write down the typical line voltage value of a three-phase supply for the end user. 4.1.2 Write down the standard international colour code for L1, L2, and L3. 4.1.3 Draw a phasor diagram for the waveforms in FIGURE 4.1. 4.2 Name the THREE network stages of the national power grid in the CORRECT order. 4.3 State how the following is measured in a star-connected system. 4.3.1 Line voltage 4.3.2 Phase voltage 4.4 Explain reactive power in an AC system. 4.5 A three-phase generator delivers power to a star-connected load. The phase voltage of the load is 230 V with a line current of 35 amperes. The phase angle is 18°. Given: Vph = 230 V IL = 35 A θ = 18° Calculate the following: 4.5.1 The line voltage. 4.5.2 Apparent power. 4.5.3 Reactive power. 4.5.4 True power. 4.6 Refer to FIGURE 4.6 below and answer the questions that follow. The readings on the wattmeters are W1 = 960 W and W2 = 870 W. 4.6.1 Identify the following coils: (a) Coil 1 of W1 (b) Coil 2 of W2 4.6.2 Name TWO advantages of using this wattmeter method.

NSC Electrical Technology Power Systems Transformer Principles: 4.1 Refer to FIGURE 4.1 and answ

4.1 Refer to FIGURE 4.1 and answer the questions that follow - NSC Electrical Technology Power Systems - Question 4 - 2022 - Paper 1

Question 4

4.1 Refer to FIGURE 4.1 and answer the questions that follow. 4.1.1 Write down the typical line voltage value of a three-phase supply for the end user. 4.1.2 Write... show full transcript

Worked Solution & Example Answer:4.1 Refer to FIGURE 4.1 and answer the questions that follow - NSC Electrical Technology Power Systems - Question 4 - 2022 - Paper 1

Step 1

4.1.1 Write down the typical line voltage value of a three-phase supply for the end user.

96%

114 rated

Answer

The typical line voltage value for a three-phase supply for the end user is between 380 V and 415 V.

Step 2

4.1.2 Write down the standard international colour code for L1, L2, and L3.

99%

104 rated

Answer

The standard international colour code is as follows:

L1: red
L2: yellow/white
L3: blue

Step 3

4.1.3 Draw a phasor diagram for the waveforms in FIGURE 4.1.

96%

101 rated

Answer

A phasor diagram for three-phase waveforms can be represented with three vectors, each separated by 120 degrees, indicating the sine wave representations of L1, L2, and L3.

Step 4

4.2 Name the THREE network stages of the national power grid in the CORRECT order.

98%

120 rated

Answer

The three network stages of the national power grid in order are:

Generation
Transmission
Distribution

Step 5

4.3.1 Line voltage

97%

117 rated

Answer

Line voltage is measured between any two lines, typically represented as (L1 & L2, L2 & L3, or L1 & L3).

Step 6

4.3.2 Phase voltage

97%

121 rated

Answer

Phase voltage is measured between any line and the neutral, typically represented as (L1 & N, L2 & N, or L3 & N).

Step 7

4.4 Explain reactive power in an AC system.

96%

114 rated

Answer

Reactive power is the power that flows back and forth between the supply and reactive components like inductors and capacitors in an AC system. It is essential for establishing the magnetic fields needed for the operation of transformers and motors but does no net work.

Step 8

4.5.1 The line voltage.

99%

104 rated

Answer

The line voltage ( $V_L$ ) can be calculated using the formula: $V_L = rac{V_{ph}}{ rac{1}{ ext{sqrt}(3)}} = ext{sqrt}(3) imes 230 V \\ = 398.37 V$

Step 9

4.5.2 Apparent power.

96%

101 rated

Answer

The apparent power ( $S$ ) can be calculated as: $S = ext{sqrt}(3) imes V_{L} imes I_L \\ = ext{sqrt}(3) imes 398.37 V imes 35 A \\ = 24149.90 VA$

Step 10

4.5.3 Reactive power.

98%

120 rated

Answer

The reactive power ( $Q$ ) can be computed using: $Q = ext{sqrt}(3) imes V_{L} imes I_L imes ext{sin}( heta) \\ = ext{sqrt}(3) imes 398.37 V imes 35 A imes ext{sin}(18°) \\ = 7467.73 VAr$

Step 11

4.5.4 True power.

97%

117 rated

Answer

The true power ( $P$ ) is calculated as: $P = ext{sqrt}(3) imes V_{L} imes I_L imes ext{cos}( heta) \\ = ext{sqrt}(3) imes 398.37 V imes 35 A imes ext{cos}(18°) \\ = 22967.91 W$

Step 12

4.6.1 Identify the following coils:

97%

121 rated

Answer

(a) Coil 1 of W1 - current coil (b) Coil 2 of W2 - voltage coil

Step 13

4.6.2 Name TWO advantages of using this wattmeter method.

96%

114 rated

Answer

Two advantages of using the two-wattmeter method are:

It can measure both balanced and unbalanced loads.
The power factor can also be determined.

4.1 Refer to FIGURE 4.1 and answer the questions that follow - NSC Electrical Technology Power Systems - Question 4 - 2022 - Paper 1

Worked Solution & Example Answer:4.1 Refer to FIGURE 4.1 and answer the questions that follow - NSC Electrical Technology Power Systems - Question 4 - 2022 - Paper 1

4.1.1 Write down the typical line voltage value of a three-phase supply for the end user.

4.1.2 Write down the standard international colour code for L1, L2, and L3.

4.1.3 Draw a phasor diagram for the waveforms in FIGURE 4.1.

4.2 Name the THREE network stages of the national power grid in the CORRECT order.

4.3.1 Line voltage

4.3.2 Phase voltage

4.4 Explain reactive power in an AC system.

4.5.1 The line voltage.

4.5.2 Apparent power.

4.5.3 Reactive power.

4.5.4 True power.

4.6.1 Identify the following coils:

4.6.2 Name TWO advantages of using this wattmeter method.

Join the NSC students using SimpleStudy...