Alternating Current

Chapter 12

Generating AC (12-1)

Generating AC (12-1)

Armature

PositiveAlternation

NegativeAlternation

One Cycle

SineWave

AC Cycle - Alternation

• Cycle – The complete revolution of an AC generator.

• Alternation – One cycle of a AC generator is made up of two alternations.

• Positive Alternation• Negative Alternation

AC - Frequency

• Frequency – The number of cycles in a second.

• Hertz – The unit for frequency.

Household Current – 60Hz

60Hz – 60 Cycles/second

Degree of Rotation

Degree of Rotation

Degree of RotationDegree of Rotation

Amplitude

Peak

Peak

Time

Peak to Peak

Period t

AC ValuesAmplitude – The value of the wave from

zero. (- +)Peak – The maximum value of the

amplitude. (- +)Peak to Peak – The value measured

from one Peak (+) to the other Peak (-).Period – The time of one complete sine

wave. (seconds – s)Frequency – Number of cycles per

second. (hertz – Hz)

f = t1

AC Values

Peak =Peak to Peak =

Period =

Frequency =

500mV

1000mV

50ms

f = 0.05s120

Hz

Effective / RMS Values

• Effective value of AC is the amount of AC that produces the same heating effect as an equal amount  of  DC.

• The Effective value is determined by the mathematical process call the Root Mean Square method or RMS.

Vrms = 0.707 VPeak

AC Values

Effective Voltage =

Vrms = 0.707 VPeak

Vrms = 0.707 (500mV)

Vrms = 354 V

Non-Sinusoidal Wave Forms

Square Wave

Square Wave – Pulse Width

Pulse Width = ½ Period

Non-Sinusoidal Wave Forms

Non-Sinusoidal Wave Forms

Non-Sinusoidal Wave Forms

Fundamental Frequency

• The lowest frequency produced by any particular instrument is known as the fundamental frequency.

Harmonics• Harmonics are higher frequency sine

waves that are exact multiples of the fundamental frequency.

Volts

Time(ms)