2.1 Name the instrument that is used to measure electrical energy - NSC Electrical Technology Power Systems - Question 2 - 2016 - Paper 1
Question 2
2.1 Name the instrument that is used to measure electrical energy.
2.2 State TWO advantages of three-phase systems over single-phase systems.
2.3 Draw a neatly lab... show full transcript
Worked Solution & Example Answer:2.1 Name the instrument that is used to measure electrical energy - NSC Electrical Technology Power Systems - Question 2 - 2016 - Paper 1
Step 1
Name the instrument that is used to measure electrical energy.
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Answer
The instrument used to measure electrical energy is a Kilo-watt hour meter.
Step 2
State TWO advantages of three-phase systems over single-phase systems.
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Answer
Three-phase systems can be operated in star or delta configurations, allowing for versatile system designs.
Three-phase systems can supply both three-phase and single-phase loads, offering greater flexibility in applications.
Step 3
Draw a neatly labelled sketch representing the voltage waveforms of a three-phase AC generation system.
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Answer
A labelled sketch should depict three sine waveforms offset by 120 degrees each, demonstrating the amplitude and the displacement of the waveforms across the phases (Ph1, Ph2, and Ph3).
Step 4
Calculate the Line voltage.
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Answer
To find the line voltage (VL), we use the formula:
S = rac{ ext{√3} imes I_L imes V_L}{S}
Substituting the known values:
V_L = rac{S}{ ext{√3} imes I_L} = rac{20000}{ ext{√3} imes 25} = 461.88 ext{ V}
Step 5
Calculate the Phase voltage.
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To calculate the phase voltage (Vp), we use:
V_p = rac{V_L}{ ext{√3}} = rac{461.88}{ ext{√3}} = 267.67 ext{ V}
Step 6
Calculate the Total input power.
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Answer
Total input power (PT) is calculated as:
PT=P1+P2=8extkW+4extkW=12extkW
Step 7
Calculate the Line current.
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Answer
Using the formula for line current (IL):
P=ext√3imesVLimesILimesextCosφ
Rearranging gives:
I_L = rac{P}{ ext{√3} imes V_L imes ext{Cos φ}} = rac{12000}{ ext{√3} imes 380 imes 0.8} = 22.79 A
