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 Losses: Refer to FIGURE 4.1 and answer t

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

Question 4

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 dow... show full transcript

Worked Solution & Example Answer: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.

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Answer

The typical line voltage value of a three-phase supply for the end user ranges from 380 V to 415 V.

Step 2

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

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Answer

The standard international colour code for the phases is:

L1: Red
L2: Yellow / White
L3: Blue

Step 3

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

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Answer

In the phasor diagram, three vectors representing L1, L2, and L3 are drawn at 120° intervals. L1 is represented on the horizontal axis, L2 is rotated 120° counterclockwise, and L3 is rotated 240° counterclockwise.

Step 4

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

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Answer

The three network stages of the national power grid are:

Generation
Transmission
Distribution

Step 5

4.3.1 Line voltage

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Answer

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

Step 6

4.3.2 Phase voltage

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Answer

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

Step 7

4.4 Explain reactive power in an AC system.

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Answer

Reactive power is the power that oscillates between the supply and the reactance (inductor or capacitor) in an AC system, thus performing no real work but is necessary to maintain voltage levels.

Step 8

4.5.1 The line voltage.

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Answer

The line voltage (V_L) is calculated using the formula:

oot{3}{V_{ph}}$$ Substituting the values: $$V_L = oot{3}{230 V} = 398.37 V$$

Step 9

4.5.2 Apparent power.

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The apparent power (S) is calculated using the formula:

oot{3}{V_L imes I_L}$$ Substituting the values: $$S = oot{3}{398.37 imes 35} = 24149.90 VA$$, or approximately 24.15 kVA.

Step 10

4.5.3 Reactive power.

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Answer

Reactive power (Q) is calculated using the formula:

oot{3}{V_L imes I_L imes ext{Sin} heta}$$ Substituting the values: $$Q = oot{3}{398.37 imes 35 imes ext{Sin} 18^{ ext{°}}} = 7462.73 VAr$$, or approximately 7.46 kVAr.

Step 11

4.5.4 True power.

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True power (P) is calculated using the formula:

oot{3}{V_L imes I_L imes ext{Cos} heta}$$ Substituting the values: $$P = oot{3}{398.37 imes 35 imes ext{Cos} 18^{ ext{°}}} = 22967.91 W$$, or approximately 22.97 kW.

Step 12

4.6.1 Identify the following coils.

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(a) Coil 1 of W1 is the current coil. (b) Coil 2 of W2 is the voltage coil.

Step 13

4.6.2 Name TWO advantages of using this wattmeter method.

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Answer

Two advantages of using the two-wattmeter method are:

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

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: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.

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