4.1 Name the processes at A, B and C - NSC Electrical Technology Power Systems - Question 4 - 2021 - Paper 1
Question 4
4.1 Name the processes at A, B and C.
4.1.2 Draw the voltage waveforms generated at A.
4.1.3 Explain why Transformer 1 is a step-up transformer.
4.1.4 Determine t... show full transcript
Worked Solution & Example Answer:4.1 Name the processes at A, B and C - NSC Electrical Technology Power Systems - Question 4 - 2021 - Paper 1
Step 1
Name the processes at A, B and C.
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Answer
A - Generation
B - Transmission
C - Distribution
Step 2
Draw the voltage waveforms generated at A.
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Answer
The voltage waveforms can be represented as follows:
+V +V +V
| | |
-V -V -V
| | |
-----------
R Y B
The three waveforms are 120 degrees apart.
Step 3
Explain why Transformer 1 is a step-up transformer.
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Answer
Transformer 1 is a step-up transformer because it increases the voltage from the generation process to reduce the current in the transmission lines. This reduction in current leads to lower copper losses (I²R losses) in transmission, making it more efficient.
Step 4
Determine the type of connection used on the secondary windings of Transformer 3 and motivate your answer.
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Answer
The type of connection used on the secondary windings of Transformer 3 is a star connection. This configuration allows for both three-phase and single-phase equipment to be powered efficiently, which is essential for compatibility with various load types. Additionally, it facilitates the use of neutral for single-phase equipment.
Step 5
Calculate the phase current.
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Answer
To find the phase current (
I_{PH}
), we use the formula:
IPH=3IL=315≈8.66A
Step 6
Calculate the apparent power.
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The apparent power (S) can be calculated using the formula:
S=3×VL×IL=3×380×15≈9.87kVA
Step 7
Calculate the phase angle.
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The phase angle (
θ
) can be calculated using the power factor:
θ=cos−1(0.9)≈25.84°
Step 8
Calculate the reactive power.
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The reactive power (Q) can be calculated using the formula:
Q=3×VL×IL×sinθ=3×380×15×sin(25.84°)≈4.3kVAR
Step 9
State TWO advantages of power factor correction to the consumer.
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Reduced current drawn from the supply, leading to a lower electricity bill.
Improved efficiency and longevity of equipment, as reduced heat generation results in less wear and tear.
Step 10
Does the reading show a leading or lagging power factor?
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The meter reading indicates a lagging power factor.
Step 11
State the cause of this type of reading.
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The lagging power factor is caused by predominantly inductive loads connected to the system.
Step 12
State how the meter reading could be brought closer to unity.
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The reading can be brought closer to unity by connecting capacitors in parallel with the load or using synchronous motors.
Step 13
Calculate the total power of the load.
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The total power (P_T) is calculated by summing the individual powers:
PT=P1+P2=250+460=710W
Step 14
State TWO quantities, other than power, that can be determined by using the two-wattmeter method.
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Reactive power (Q)
Phase angle (θ)
Step 15
Explain why the two-wattmeter method is preferred over the three-wattmeter method.
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The two-wattmeter method is preferred as it can be easily connected to the lines without requiring additional equipment, making it more economical for load measurement.
