14:332:221 Lecture 7: 5.5 Power In AC Circuits

• School: Rutgers University
• Department: Electrical and Computer Engineering
• Course: 14:332:221
• Professor: Professor Wilhelms

Document Summary

Current, voltage, and power for a resistive load. Average power is absorbed by resistances in ac circuits. Current, voltage, and power for an inductive load. Power surges into and out of the inductances in an ac circuit. The average power absorbed by inductances is zero. Current, voltage, and power for a capacitive load. Power surges into and out of capacitances in ac circuits. The average power absorbed by capacitances is zero. Thus, we say that reactive power is positive for an inductance and is negative for a capacitance. ifaloadcontainsbothinductanceandcapacitancewithre activepowers of equal magnitude, the reactive powers cancel. Theta sub v is the phase shift of the voltage. Theta sub i is the phase shift of the current. Power fa(cid:272)tor is the (cid:272)osine of the angle (cid:271)y whi(cid:272)h the current lags the voltage. (if the current leads the voltage, the angle is negative. ) Often, power factor is expressed as a percentage.