EC-12.1 AC Power and Three-Phase Systems
You can separate real, reactive and apparent power, work with power factor and say why it is billed for, analyse a balanced three-phase load in either connection, and explain what three phases buy that one does not.
Before:EC-2. Electromagnetics and Transmission LinesEC-6. Semiconductor Devices and Device Models
Circuit analysis already covers the sinusoidal steady state, and stops exactly where power engineering begins. This topic is the bridge: the same phasors, now used to ask how much energy actually moves and how much merely sloshes back and forth. Three-phase then follows, and it is the arrangement almost all generated and industrial power actually uses.
Work through these
Instantaneous power, and why an average is needed
The product of a sinusoidal voltage and current varies at twice the supply frequency and is negative for part of each cycle. Only its average over a cycle represents energy actually delivered.
NPTEL: Basic Electrical Technology (IIT Kharagpur) · CourseReal, reactive and apparent power
Real power does work, reactive power moves energy back and forth without doing any, and apparent power is the product of the measured voltage and current. The three form a right-angled relationship.
NPTEL: Basic Electrical Technology (IIT Kharagpur) · CoursePower factor, and why a supplier cares about it
Power factor is the ratio of real to apparent power. A poor one means conductors and transformers carry current that does no work, so the supplier sizes equipment for it and charges accordingly.
NPTEL: Basic Electrical Technology (IIT Kharagpur) · CourseCorrecting power factor with a capacitor
Most industrial load is inductive, and a capacitor supplies the reactive part locally instead of drawing it from the supply. Sizing it is a calculation on the reactive power alone.
NPTEL: Basic Electrical Technology (IIT Kharagpur) · CourseThree phases, and what they buy
Three supplies a third of a cycle apart deliver constant total power rather than pulsating power, need less conductor for the same energy, and produce a rotating field a motor can follow.
NPTEL: Electrical Machines (IIT Delhi) · CourseStar and delta, and the two ratios worth remembering
In a star connection the line voltage exceeds the phase voltage by the square root of three; in a delta connection the line current exceeds the phase current by the same factor. Balanced problems reduce to one phase.
NPTEL: Electrical Machines (IIT Delhi) · Course
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