Question 5 [15 marks]
A 230V, 50Hz single phase supply feeds an industrial plant with the following loads: (a) incandescent lamps drawing a current of 8A at unity power factor; (b) fluorescent lamps drawing a current of 5A at 0.8 leading power factor; (c) a motor drawing a current of 7A at 0.75 lagging power factor.
No solutions are given, so I have no idea whether my methods are right or wrong, could someone please provide answers or explanations for these questions.
Is this correct for 5.1?
Consider each load to be a parallel branch,
then work out Z for each branch using E = IZ; Z = E/I
Power factor = P/S = (I^2*R)/(I^2*Z)
In each branch the currents are the same, so power factor = R / Z.
Therefore we can now work out R, and subsequently P, Q, S for each branch.
5.2
I thought of doing this two ways, adding up the true powers for each branch (can you do this, eg (Ia ^ 2) * Ra + (Ib ^ 2) * Rb) and then the same for the reactive powers, and then finding apparent power from these.
Also thought of finding overall impedance and finding the apparent power first, but then I don't know what to do from there.
5.3 is easy if I could work out the powers.
5.4 is not too bad applying methods
SOURCE: UCT EEE2038W June 2009 Exam
A 230V, 50Hz single phase supply feeds an industrial plant with the following loads: (a) incandescent lamps drawing a current of 8A at unity power factor; (b) fluorescent lamps drawing a current of 5A at 0.8 leading power factor; (c) a motor drawing a current of 7A at 0.75 lagging power factor.
- Find the real and reactive power drawn by loads (a), (b) & (c).
- Find the total real, reactive and apparent power that the plant draws from the s upply.
- Draw a power triangle for the plant and show its operating power factor angle.
- Find the value of capacitance required to correct the plant power factor to unity.
No solutions are given, so I have no idea whether my methods are right or wrong, could someone please provide answers or explanations for these questions.
Is this correct for 5.1?
Consider each load to be a parallel branch,
then work out Z for each branch using E = IZ; Z = E/I
Power factor = P/S = (I^2*R)/(I^2*Z)
In each branch the currents are the same, so power factor = R / Z.
Therefore we can now work out R, and subsequently P, Q, S for each branch.
5.2
I thought of doing this two ways, adding up the true powers for each branch (can you do this, eg (Ia ^ 2) * Ra + (Ib ^ 2) * Rb) and then the same for the reactive powers, and then finding apparent power from these.
Also thought of finding overall impedance and finding the apparent power first, but then I don't know what to do from there.
5.3 is easy if I could work out the powers.
5.4 is not too bad applying methods
SOURCE: UCT EEE2038W June 2009 Exam