2.1 Determine the value of the phase voltage in a delta-connected system if the line voltage is 380 V - NSC Electrical Technology Power Systems - Question 2 - 2016 - Paper 1
Question 2
2.1 Determine the value of the phase voltage in a delta-connected system if the line voltage is 380 V.
2.2 Draw a neat, labelled voltage phasor diagram that represe... show full transcript
Worked Solution & Example Answer:2.1 Determine the value of the phase voltage in a delta-connected system if the line voltage is 380 V - NSC Electrical Technology Power Systems - Question 2 - 2016 - Paper 1
Step 1
Determine the value of the phase voltage in a delta-connected system if the line voltage is 380 V.
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Answer
In a delta-connected system, the phase voltage (
V_{ph}) is equal to the line voltage (
V_L).
Therefore, the phase voltage is:
Vph=VL=380extV
Step 2
Draw a neat, labelled voltage phasor diagram that represents a three-phase delta-connected system.
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Answer
The voltage phasor diagram for a delta-connected system consists of three vectors (
V_L1, V_L2, V_L3) separated by 120°.
It can be represented as follows:
Vector V_L1 is at 0°.
Vector V_L2 is at 120°.
Vector V_L3 is at 240°.
Each vector has a magnitude of 380 V.
Step 3
Current delivered by the alternator at full load
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Answer
To calculate the current delivered by the alternator, use the formula:
I_L = rac{S}{ ext{sqrt}(3) imes V_L}
Substituting the values:
S=20imes103extVA,VL=380extV
Thus,
I_L = 30.39 ext{ A} $$
Step 4
Power rating of the alternator
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Answer
The power delivered can be calculated using:
P=extsqrt(3)imesVLimesILimesextCOS(θ)
Given the power factor (p.f.) is 0.87, we can substitute:
P = 17.4 ext{ kW} $$
Step 5
State the function of a kilowatt-hour meter.
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Answer
The function of a kilowatt-hour meter is to measure the amount of energy consumed by a consumer over a period of time.
Alternatively, it measures the energy usage of electrical systems.
Step 6
State TWO methods used to improve the power factor of a resistive inductive load.
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Answer
Adding power factor correcting capacitors in parallel with the load.
Using synchronous motors to improve the overall power factor.
Step 7
Calculate the power consumed by the load.
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Answer
To find the power consumed by the load, use the formula:
Pn=P1+P2
Substituting the given values:
Pn=120+50=170extW
Step 8
TWO advantages of using the two-wattmeter method when measuring power of a balanced load.
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Only two watt meters are required instead of three for balanced loads.
The power of a balanced and unbalanced load can be measured accurately.
