2.1 State THREE advantages of a three-phase distribution system over a single-phase distribution system - NSC Electrical Technology Power Systems - Question 2 - 2017 - Paper 1
Question 2
2.1 State THREE advantages of a three-phase distribution system over a single-phase distribution system.
2.2 Draw a fully labelled representation diagram of a three... show full transcript
Worked Solution & Example Answer:2.1 State THREE advantages of a three-phase distribution system over a single-phase distribution system - NSC Electrical Technology Power Systems - Question 2 - 2017 - Paper 1
Step 1
State THREE advantages of a three-phase distribution system over a single-phase distribution system.
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Answer
Load Distribution: A three-phase system allows for more balanced load distribution across phases, reducing the risk of overload on any one phase.
More Power: Three-phase systems can deliver more power compared to single-phase systems, which makes them more efficient for industrial applications.
Reduction in Conductor Size: For the same amount of power, three-phase systems require less conductor material than single-phase systems, leading to cost savings.
Step 2
Draw a fully labelled representation diagram of a three-phase generated voltage waveform in a three-phase system.
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Answer
The diagram should include three sine waves representing the phase voltages, each separated by 120 degrees, with appropriate labels for each phase (R, Y, B) and the voltage levels.
Step 3
State ONE disadvantage of using the two-wattmeter method to measure power in a three-phase system.
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The two-wattmeter method can be less accurate when measuring power in systems with non-linear loads, as it may not account for harmonics and other power factor issues effectively.
Step 4
Calculate the Line voltage
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Answer
To calculate the line voltage (
V_L ext{)}:
V_L = rac{S}{ rac{ ext{√3}}{3} imes I_L}
Inserting the values:
= 379.84 ext{ V}$$
Step 5
Calculate the Phase voltage
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To calculate the phase voltage (
V_{PH} ext{)}:
V_{PH} = rac{V_L}{ ext{√3}}
Using the calculated line voltage:
= 219.31 ext{ V}$$
Step 6
Calculate the Impedance per phase
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To find the impedance per phase (
Z_{PH} ext{)}:
Z_{PH} = rac{V_{PH}}{I_{PH}}
Where
I_{PH} = I_L = 38 A. Substituting the values:
= 5.77 ext{ Ω}$$
Step 7
Describe how Eskom could benefit if consumers improved the power factor of their systems.
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Answer
An improved power factor leads to less wasted energy, which allows for more power to be made available to consumers. Additionally, utilizing power more efficiently reduces generation costs, ultimately benefiting both Eskom and its consumers.
