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  • Topic: Power factor, Electric power, Three-phase electric power
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  • Published : March 10, 2013
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TUTORIAL 1
Fundamentals

1.An inductive load consisting of R and X in series feeding from a 2400-Vrms supply absorbs 288 kW at a lagging power factor of 0.8. Determine R and X.

2.An inductive load consisting of R and X in parallel feeding from a 2400-Vrms supply absorbs 288 kW at a lagging power factor of 0.8. Determine R and X.

3.Two loads connected in parallel are supplied from a single-phase 240-Vrms source. The two loads draw a total real power of 400 kW at a power factor of 0.8 lagging. One of the loads draws 120 kW at a power factor of 0.96 leading. Find the complex power of the other load.

4.The load shown in figure 1 consists of resistance R in parallel with a capacitor of reactance X. The load is fed from a single-phase supply through a line of impedance 8.4 + j11.2 . The rms voltage at the load terminal is 12000o Vrms, and the load is taking 30 kVA at 0.8 power factor leading.

a.Find the values of R and X

b.Determine the supply voltage V

Figure 1

5.Two impedances, Z1 = 0.8 + j5.6 and Z2 = 8 - j16, and a single-phase motor are connected in parallel across a 200-Vrms, 60-Hz supply as shown in figure T2. The motor draws 5 kVA at 0.8 power factor lagging.

Figure T2

a.Find the complex powers S1, S2, for the two impedances and S3for the motor.

b.Determine the total power taken from the supply, the supply current, and the overall power factor.

c.A capacitor is connected in parallel with the loads. Find the kvar and the capacitance in F to improve the overall power factor to unity. What is the new line current?

6.A 4157- Vrms, three-phase supply is applied to a balanced Y-connected three-phase load consisting of three identical impedances of 4836.870. Taking the phase to neutral voltage Van as reference, calculate:

a.The phasor currents in each line

b.The total active and reactive power supplied to the load

7.Repeat problem 6 with the same three-phase impedances arranged in a...
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