Hi All, My name is Martin Cole and i'm new to all this... I've decided to start studying Electrical Engineering, and my topic touches on Series AC Circuits. I have been set some homework questions, and was needing a little help... Any help will be appreciated... Its pretty hectic i think... Martin QUESTION 1 A coil with an unknown resistance and inductance is connected in series with a resistor of 15 Ω and a capacitor of 150,5 μF. The circuit is connected across a 240-V, 50-Hz supply. The power factor of the load is 0.7771 lagging. A voltage drop of 142,5 V is measured across the resistor. Calculate the voltage drops across the capacitor and the coil. Calculate the resistance and inductance of the coil. Calculate the power dissipated in the circuit. Calculate the value of a capacitor to be connected in parallel with the circuit to raise the overall power factor to 0,9563 lagging. QUESTION 2 A voltage, represented by ν(t) = 339,411 sin (315t + (pi)/6 ) volt, supplies three parallel connected loads. The loads draw current from the supply as follow: Load a : 17,2 A at a power factor of 0,5878 lagging Load b : 9,5 A at unity power factor Load c : 18,8 A at a power factor of 0,7071 lagging Calculate the following: The total current The active and reactive components of the current The value of the components in each load The total impedance The total active power dissipated in the circuit The overall power factor of the circuit The value of a capacitor to be connected in parallel to the circuit to cause resonance to the parallel circuit The total current and the overall power factor, should these loads be connected in series The value of a capacitor to be connected in series to the circuit to cause resonance to the series circuit QUESTION 3 A circuit consists of a coil in series with a 9,6Ω resistor. When a direct current of 6,5 A is passed through the coil, the voltage measured across the coil is 117V. With an alternating current of 6,5 A at 60 Hz, the voltage across the coil is 273 V. When the coil is connected to a 240 V/50 Hz supply, calculate the following and also draw the power triangle: The voltage across the coil The value of a capacitor to be connected in parallel with the coil to improve the power factor to 0,866 lagging
Some hints: Zc = 1 / (2 * Pi * f * C) Zl= 2 * Pi * f * L Being: Zc and Zl, the impedance, or resistance at a frequency f of respectively, a capacitor and an inductor, C the capacitance, L the inductance and f the frequency. I won't solve the exercise. I'll be more helpful by doing this.
u must really try this one on your own as these are quite elementary problems after solving them u'll learn a lot; like mr cumesoftware i'll try to help u by providing some clue; to avoid confusion of symbols; z---is used for impedance; Xc-capacitive reactane ;XL--inductive reactance; i recommend u to have a look at volume 2 of the site. r--resistance the formula to calculate Xc,XL is in the above reply; in general; Z= sqrt(R^2 + (XL-Xc)^2) i would like to give the most detailed answer to above question; plz try and post your difficulties.
Thank you both for the assistance. I will attempt today and post my solutions for you to see if i'm doing anything wrong... Cheers, Martin
additionally u will find this helpful for z impedance voltage across it is given by V= i*z power factor of load z is cos(phi)= r/z ; where Z= sqrt(R^2 + (XL-Xc)^2) for v= Vsin(wt + epoch) frequency of above voltage is w/2pi; while epoch is initial lead/lag angle of the quantity with respect to some reference.