Electrical Fundamentals II: AC Generators

A type of alternator commonly used in aircraft where the magnetic field rotates, while the armature remains stationary. This design eliminates the need for sliding contacts, improving reliability.

A generator that uses permanent magnets to create the magnetic field instead of electromagnets. PMGs are typically compact and require no external power to operate.

PMGs offer several advantages, including high efficiency, low maintenance, and the ability to operate in harsh environments. They're often used in gas turbine engines to power essential systems.

PMGs are frequently used in aircraft to power ignition exciters, FADEC (Full Authority Digital Engine Control) systems, and other accessories.

A type of alternator that uses permanent magnets for the magnetic field and electronically controlled excitation. It eliminates the need for brushes and slip rings, making it highly reliable.

The brushless alternator uses a series of windings and electronic control to generate the magnetic field. The exciter field is energized by a DC current, which in turn inducts voltage into the main output field.

Brushless alternators are often used in large jet aircraft due to their efficiency, reliability, and ability to operate in high-altitude environments where brush arcing is a concern.

The brushless alternator starts generating output thanks to the permanent magnets. The exciter field winding induces voltage into the main output winding, where the final output is rectified and sent to the generator control unit (GCU).

The GCU monitors and regulates the main generator's output, essentially controlling the amount of current flowing through the exciter field winding. It does this to adjust the alternator's output.

Part of the brushless alternator, the exciter is a small generator that creates current to energize the main generator's field winding. The GCU controls the exciter to adjust alternator output.

A symmetrical waveform that oscillates around a fixed level, representing varying voltage or current, most notably in alternating current systems.

The electromotive force (voltage) generated when a conductor moves through a magnetic field. The amount of EMF depends on the rate the conductor cuts through the magnetic field.

An electrical current that flows in one direction, then reverses and flows in the opposite direction. It continuously changes its magnitude and direction.

A type of winding configuration in electrical generators where the three phases are connected in a Y-shaped pattern. This configuration provides balanced output and is common in brushless alternators.

The core of a brushless alternator is often made from laminated steel sheets. These sheets are insulated from each other to reduce eddy currents and improve efficiency.

The vertical axis represents the magnitude and direction of either current or voltage.

The horizontal axis represents time or the angle of rotation in degrees.

When the sine wave crosses the time axis, it indicates a change in the direction of the current or voltage. Above the axis is positive, below is negative.

At 0 degrees, the induced voltage is zero. The conductor is moving parallel to the magnetic field, not cutting any lines of flux.

As the armature rotates, the conductors cut through more magnetic lines of flux. This causes the induced voltage to increase, reaching its maximum positive value at 90 degrees.

The armature continues to rotate, but now cuts through fewer lines of flux. This results in a decrease in induced voltage, reaching zero at 180 degrees.

The conductors cut through more lines of flux, but now in the opposite direction. This causes the induced voltage to increase in the negative direction, reaching its maximum negative value at 270 degrees.

A generator that produces a single, continuously alternating voltage. Its stator windings are connected in series, adding up to create a single-phase AC voltage.

A type of alternator that produces a single alternating current (AC) output. Commonly used in homes and shops for powering tools and appliances.

An alternator with two separate windings that produce two AC outputs, 90 degrees out of phase. Each winding generates a single-phase voltage, independent of the other.

A variation of a two-phase alternator where two of the windings' ends are connected internally. This creates a third output voltage (C) that's the sum of the other two (A and B), resulting in a three-wire system.

The third output voltage in a two-phase, three-wire alternator. This voltage is the sum of the instantaneous values of phase A and phase B, resulting in a larger voltage.

Two-phase alternators offer advantages like multiple outputs, which can be used to power different loads simultaneously. The output at C is higher than the individual phase voltages.

A type of alternator commonly used in aircraft electric systems. It produces three AC outputs, each 120 degrees out of phase, providing a stable and efficient power source.

A term referring to AC systems with multiple phases, like three-phase alternators. Polyphase systems are more efficient and offer better power delivery than single-phase systems.

Alternators specifically designed for aircraft electric systems, often using a three-phase configuration for reliable and efficient power generation.

Three separate windings spaced 120° apart in an AC generator, producing outputs 120° out of phase. These windings can be connected in either a star or delta configuration.

A three-phase winding configuration where the ends of the three windings are connected to a common point called the neutral (N), forming a star shape. Line voltage is √3 times the phase voltage, and line current is equal to phase current.

A three-phase winding configuration where the ends of the three windings are connected in a closed loop, forming a triangle or delta shape. Phase voltage is equal to line voltage, while line current is √3 times phase current.

Current flowing through the lines in a delta-connected three-phase system. It is equal to the square root of 3 (√3) times the phase current.

Power in a three-phase circuit is calculated by multiplying the product of line voltage, line current, and √3 by the power factor (Cos θ).

Apparent power rating of a three-phase generator, calculated by multiplying the product of line voltage, line current, and √3 by 1000.

Real power rating of a three-phase generator, calculated by multiplying the product of line voltage, line current, √3, and power factor by 1000.

The order in which the voltage reaches its peak value in each phase of a three-phase system. It can be ABC or ACB, and affects the direction of rotation in motors.

Three-phase connections offer various benefits, including higher power efficiency due to balanced currents, smoother power delivery compared to single-phase, and reduced conductor material compared to equivalent single-phase systems.

The frequency of the output voltage of an alternator is determined by the speed of rotation of the rotor and the number of poles in the stator.

The formula to calculate alternator frequency is f = (N x P) / 120, where f is frequency, N is speed in rpm, and P is the number of poles.

A system used to maintain a constant frequency output from an alternator despite variations in engine speed. It uses a hydraulic pump and motor to connect the engine to the generator.

A single unit that combines the Constant Speed Drive (CSD) and the AC Generator. This reduces space and complexity.

The CSD control system uses a governor to sense the generator's rotational speed and adjusts the hydraulic pump's displacement to maintain a constant output frequency.