2.9 KiB
id, aliases, tags
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Alternating Current
Alternating current (AC) is electric current that reverses direction periodically. The voltage and current in an AC circuit oscillate in a sinusoidal manner. The frequency of the oscillation is the number of complete cycles per second measured in hertz (Hz). The frequency of the AC power grid in the United States is 60 Hz.
- Ungrounded conductor - "Hot"
- Grounded conductor - "Neutral"
3-Phase Power
The conductors between a voltage source and a load are called lines, and the voltage between any two lines is called line voltage. 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
[!info] Phase Abbreviations
- PH
- Φ (capital phi)
- Ø (latin O with stroke)
208Y/120V 480Y/277V
Voltage Systems
120/240V 1-Phase 3-Wire:
- 120V 1-Phase 2-Wire # Line to Neutral
- 240V 1-Phase 2-Wire # Line to Line
120/208V 3-Phase 4-Wire:
- 120V 1-Phase 2-Wire # Line to Neutral
- 208V 1-Phase 2-Wire # Line to Line
- 208V 3-Phase 3-Wire # Line to Lines
277/480V 3-Phase 4-Wire:
- 277V 1-Phase 2-Wire # Line to Neutral
- 480V 1-Phase 2-Wire # Line to Line
- 480V 3-Phase 3-Wire # Line to Lines
wiring-configurations:
- 1-Phase 2-Wire # Line to Neutral or Line to Line
- 1-Phase 3-Wire # Line to Line and Line to Neutral
- 3-Phase 3-Wire # Line to Lines
- 3-Phase 4-Wire # Line to Lines and Line to Neutral
Active and Reactive Power
As a consequence of the periodic nature of AC, and the electromagnetic "inertia" of inductance and capacitance, inherent of all matter, the power in an AC circuit is divided into two components:
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Active Power (abbreviated
P, measured in watts) also known as real power, is power that does work. -
Reactive Power (abbreviated
Q, measured in volt-amperes reactive (VAR)) transfers no net energy to the load.
derived from these components are others:
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Complex Power (abbreviated
S, measured in volt-amperes (VA)) is the vector sum of the active and reactive components. It is "complex" because it exists on the real and imaginary axes of active and reactive power respectively. -
Apparent Power (abbreviated
|S|, measured in volt-amperes (VA)) is the magnitude of the complex power vector. -
Power Factor (abbreviated
\text{PF}, unitless) is the ratio of active power to apparent power.
P = S \times \text{PF}, \quad S = \frac{P}{\text{PF}}, \quad PF = \frac{P}{\text{S}}
Power Factor Correction
Capacitance and inductance can both be measured in VAR, but their effects cancel each other out rather than add.
Motors
1hp = 746 watts
full-load current (FLC) / full-load amperes (FLA)
minimum circuit ampacity (MCA)
\text{MCA} = 1.25 \times \text{FLC}