University:
Kentucky State University
Course:
PHY 212 | General Physics II
Academic year:

2024
Views:

432

Pages:

26
Author:

Lily Callahan

(8 marks) Q(1): Three loads are connected in parallel across 250V (rms) as shown in Fig. 1. Load 1 absorbs 16kW and 28 kVA. Load 2 absorbs 10kVA at 0.6 leading PF. Load 3 absorbs 8kW at unity PF. 1. Find the Impedance that is equivalent to the three parallel loads. 2. Find the power factor of the total load. 3. If the source operates at 50 Hz, find the value of the capacitor to be connected in order to improve the power factor to 0.96. (4 marks) Q(2): Fig.2 shows the instantaneous power p(t) consumed by the load terminals, where the terminal voltage is given by v(t) = Vm cos(ωt), then find the followings: 1. P 2. The reactive power Q 3. The Complex power S v(t) = Vm cos(ωt + θ), θ = 0 i(t) = Im cos(ωt + φ) p(t) = vi = VmIm cos(ωt) cos(ωt + φ) ⇒ P = VmIm / 2 cos(θ - φ) = 600 W Q = VmIm / 2 sin(θ - φ) ⇒ 600 = 1200 cos(θ - φ) ⇒ θ - φ = 0 ⇒ θ = φ = 60° Q = 1200 sin(60°) = 1039.23 VAR S = (600 + j1039.23) VA S = 1200 ∠60° VA Internal Connection CKTNetwork Passive sign convention: P: +ve quantity → absorbs P: -ve quantity → delivers (there will be no reading because it's an upscale) (We reverse the order of Pc to have a reading.) Ex: Determine the wattmeter reading & whether or not the potential coil had to be reversed in order to obtain an upscale reading, & identify the device (s) absorbing or generating this power. The true terminals of the wattmeter is connected to: a) x, b) y, c) z.