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Laboratory 9: Problems: AC Power Calculations

201025

Laboratory #9:

Problems: AC Power Calculations

Objectives:

Review power in AC circuits, including power factors.

In Lab: Work the following problems

1. What is the real power with a current and voltage as follows:

I(t) = 2 cos(ωt + π/6) A

V(t) = 8 cos(ωt) V

2. An unknown impedance Z is connected across a 380 V, 60 Hz source. This causes a current

of 5A to flow and 1500 W is consumed.

Determine the following:

a. Real Power (kW)

b. Reactive Power (kvar)

c. Apparent Power (kVA)

d. Power Factor

e. The impedance Z in polar and rectangular form

3. An industrial load consists of the following:

• A 200 hp motor loaded to 100-hp: efficiency = 0.82, pf = 0.6 lagging

• A 350 hp motor drawing 80 kW: pf = 0.8 lagging

• A 500 hp motor drawing 47 kW: pf = 0.7 leading

• A 70 kW lighting load

Determine for the overall load:

a. Real Power (kW)

b. Reactive Power (kvar)

c. Apparent Power (kVA)

d. Power Factor

4. Three heaters and a three-phase y-connected motor are connected to a y-connected source of

208 v line-to-line. Each heater draws 10A at unity power factor (pf = 1), and each phase of

the motor draws 2 A at 0.85 power factor.

a. Find the total line current.

b. Find the total power consumed.

c. Determine the motor’s inductive reactance per phase if the motor’s R and X are consid-

ered to be in series.

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BK Precision 4011A Instrucciones de operaciones Pagina 37