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API-SIEE Exam - Topic 10 Question 3 Discussion
Topic #: 10
The cosine of the difference in phase angle between voltage and current is:
The correct answer isA, power factor. In AC electrical systems, the phase relationship betweenvoltageandcurrentis an important indicator of how effectively electrical power is being used. Thecosine of the phase angle differencebetween voltage and current is called thepower factor. Mathematically, power factor expresses the ratio ofreal power, which performs useful work, toapparent power, which is the total power supplied to the circuit. When voltage and current are in phase, the cosine value is 1 and the power factor is unity. When they are out of phase due to inductive or capacitive effects, the power factor becomes less than 1.
From a source inspection and quality surveillance standpoint, understanding power factor is important when reviewing electrical test data, motor performance, transformer loading characteristics, and system efficiency information.Real poweris measured in watts,apparent powerin volt-amperes, andmhois a unit of conductance, so none of those terms define the cosine of the phase angle itself. Therefore, the correct technical term for this cosine relationship ispower factor.
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