106 lines
2.9 KiB
Markdown
106 lines
2.9 KiB
Markdown
---
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id:
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aliases: []
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tags:
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- destiny/fleeting
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- topic/electrical
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- type/encyclopedia
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title: Alternating Current
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---
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# Alternating Current
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[Alternating current (AC)](https://en.wikipedia.org/wiki/AC_power)
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is electric current that reverses direction periodically.
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The voltage and current in an AC circuit oscillate in a sinusoidal manner.
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The frequency of the oscillation is the number of complete cycles per second measured in hertz (Hz).
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The frequency of the AC power grid in the United States is 60 Hz.
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* Ungrounded conductor - "Hot"
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* Grounded conductor - "Neutral"
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## 3-Phase Power
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The conductors between a voltage source and a load are called lines,
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and the voltage between any two lines is called line voltage.
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The voltage measured between any line and neutral is called phase voltage.
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* Poles vs Phases vs Wires
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* 3Ø = 3PH 3W
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* 3ØY = 3PH 4W
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> [!info] Phase Abbreviations
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> * PH
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> * Φ (capital phi)
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> * Ø (latin O with stroke)
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208Y/120V
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480Y/277V
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In a 3-phase wye connected system,
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ignoring the difference in voltage,
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is voltage drop calculated differently
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between a line to line load and a line to neutral load
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### Voltage Systems
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120/240V 1-Phase 3-Wire:
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* 120V 1-Phase 2-Wire # Line to Neutral
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* 240V 1-Phase 2-Wire # Line to Line
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120/208V 3-Phase 4-Wire:
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* 120V 1-Phase 2-Wire # Line to Neutral
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* 208V 1-Phase 2-Wire # Line to Line
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* 208V 3-Phase 3-Wire # Line to Lines
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277/480V 3-Phase 4-Wire:
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* 277V 1-Phase 2-Wire # Line to Neutral
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* 480V 1-Phase 2-Wire # Line to Line
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* 480V 3-Phase 3-Wire # Line to Lines
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wiring-configurations:
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* 1-Phase 2-Wire # Line to Neutral or Line to Line
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* 1-Phase 3-Wire # Line to Line and Line to Neutral
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* 3-Phase 3-Wire # Line to Lines
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* 3-Phase 4-Wire # Line to Lines and Line to Neutral
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## Active and Reactive Power
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As a consequence of the periodic nature of AC,
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and the electromagnetic "inertia" of inductance and capacitance,
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inherent of all matter,
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the power in an AC circuit is divided into two components:
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* **Active Power**
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(abbreviated $P$, measured in watts)
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also known as real power, is power that _does work_.
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* **Reactive Power**
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(abbreviated $Q$, measured in volt-amperes reactive (VAR))
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transfers no net energy to the load.
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derived from these components are others:
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* **Complex Power**
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(abbreviated $S$, measured in volt-amperes (VA))
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is the vector sum of the active and reactive components.
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It is "complex" because it exists on the real and imaginary axes
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of active and reactive power respectively.
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* **Apparent Power**
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(abbreviated $|S|$, measured in volt-amperes (VA))
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is the magnitude of the complex power vector.
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* **Power Factor**
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(abbreviated $\text{PF}$, unitless)
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is the ratio of active power to apparent power.
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$$
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P = S \times \text{PF}, \quad S = \frac{P}{\text{PF}}, \quad PF = \frac{P}{\text{S}}
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$$
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### Power Factor Correction
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Capacitance and inductance can both be measured in VAR,
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but their effects cancel each other out rather than add.
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