Alternating Current Fundamentals Flashcards

Alternating Current Fundamentals

• Polarity of an AC power source changes periodically.
• Three requirements for inducing a voltage include a conductor, a magnetic field, and relative motion.
• Maximum voltage is induced when a conductor is cutting through the maximum number of magnetic flux lines.
• In a sine wave representation, voltage below the horizontal line is considered negative.
• Frequency measures the number of cycles completed each second, quantified in hertz.
• Effective AC values are expressed using the letters RMS (Root Mean Square).
• Inductance is the property in AC circuits that opposes a change in current flow.
• Inductive reactance measures the opposition to current flow due to inductance.
• An increasing current through a conductor results in a building magnetic field around it.
• Contrary to increasing current, CEMF (counter-electromotive force) opposes the applied voltage, limiting current.
• To enhance inductive reactance in AC circuits: coil the conductor and insert a metal core inside the coiled conductor.
• In a purely inductive circuit, the only current-limiting factor is inductive reactance.
• When voltage and current variations occur at different times, they are described as being out of phase.
• Capacitance is a property that opposes changes in voltage in AC circuits.
• Capacitive reactance measures opposition to current due to capacitance and is quantified in ohms.
• A capacitor's dielectric prevents electron flow between its plates.
• A capacitor must be charged before it can store energy.
• When fully charged, the source voltage equals the voltage across the capacitor in magnitude but opposite in polarity.
• Capacitance creates a phase difference between current and voltage.
• True power is the actual power used to perform work.
• Positive power refers to power supplied to a load from a power source.
• Reactive power does not perform useful work.
• Voltage and current sine waves for reactive power are always out of phase.
• Apparent power results from multiplying voltage times current in any circuit.
• The combined effect of resistance, inductance, and capacitance on current flow in an AC circuit is termed impedance.
• True power in AC circuits is often calculated using the power factor relevant to the circuit.
• A transformer changes a two-wire single-phase system into a three-wire single-phase system.
• In a three-wire single-phase system, the middle line on the secondary side is referred to as the neutral line.
• The current flowing through the coils or resistors in a three-phase system is called phase current.
• In a delta-connected system, phase voltage equals line voltage, but phase current does not equal line current.
• To calculate the line voltage in a wye-connected three-phase system, multiply the phase voltage by 1.73.
• Phase current and line current are equal in a wye-connected three-phase system.