McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Electricity Principles & Applications Seventh Edition Chapter 8 Alternating Current and Voltage (student version) Richard J. Fowler McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. INTRODUCTION Types of Waveforms Induced Voltage Generating a Sine Wave Ac Terminology Three-Phase Ac

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Dear Student: This presentation is arranged in segments. Each segment is preceded by a Concept Preview slide and is followed by a Concept Review slide. When you reach a Concept Review slide, you can return to the beginning of that segment by clicking on the Repeat Segment button. This will allow you to view that segment again, if you want to.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Preview Direct currents never change direction. Direct voltages never change polarity. Alternating current periodically changes direction. Rapidity of an ac waveform can be specified by its frequency or its period. Amplitude can be given in peak, peak- to-peak, average, or rms(effective) values.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Electrical Waveforms Alternating current or voltage Pulsating direct current or voltage Fluctuating direct current or voltage

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Common Alternating Current Waveforms Sinusoidal Wave Triangular Wave Square Wave

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Ac Waveform Terminology 0.2 s s 0.6 s Time Voltage or Current 1 st cycle2 nd cycle3 rd cycle T = period =time to complete 1 cycle =0.2 s f = frequency = 1 / T = 1 / 0.2 s =5 Hz Peak amplitude can be either negative or positive. Peak-to-peak amplitude includes both the - and + peaks. peak to + peak - peak

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. rms = peak av = peak peak = (1 / 0.707) rms = rms peak = (1 / 0.637) av = 1.57 av peak = peak-to-peak / 2 Specifying Sine-Wave Amplitude Examples: 20 V p-p / 2 =10 V p and10 V p x =7.07 V 8 A av x 1.57 =12.56 A p peak-to-peak peak

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Wave-Form Quiz The ____ dc waveform never reaches or crosses the zero reference line. The part of the waveform that includes its complete negative and positive excursions is called a ____. The ____ is the time required to complete one cycle. The base unit of frequency is the ____. For a sine wave, 30 V P = ____ V. For a sine wave, 10 A P-P = ____ A. For a sine wave, 25 V = ____ V P. fluctuating cycle period hertz

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Repeat Segment Concept Review Direct currents never change direction. Direct voltages never change polarity. Alternating current periodically changes direction. Rapidity of an ac waveform can be specified by its frequency or its period. Amplitude can be given in peak, peak- to-peak, average, or rms(effective) values.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Preview Producing a sine wave requires circular motion, constant speed, and uniform flux. Cutting flux at a 90  angle produces V peak. Cutting flux at 45  produces V peak. A two-pole generator produces one cycle for each revolution of the rotating coil.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Induced Voltage in a Constant-speed Conductor N S N S N S N S If motion is parallel to the flux, no flux is cut; thus no voltage is induced. When motion is at an angle, some flux is cut; and some voltage is induced. When motion is perpendicular to the flux, maximum voltage is induced. Reversing the direction of motion, reverses the polarity of the induced voltage.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Generating A Sine Wave N S Motion is parallel to the flux.No voltage is induced.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. x Generating A Sine Wave N S Motion is 45  to flux. Induced voltage is of maximum.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. x Generating A Sine Wave N S Motion is perpendicular to flux.Induced voltage is maximum.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. x Generating A Sine Wave Motion is 45  to flux. N S Induced voltage is of maximum.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Generating A Sine Wave N S Motion is parallel to flux.No voltage is induced.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. x Generating A Sine Wave Motion is 45  to flux. N S Notice current in the conductor has reversed. Induced voltage is of maximum.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Generating A Sine Wave N S x Motion is perpendicular to flux.Induced voltage is maximum.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Generating A Sine Wave N S x Motion is 45  to flux. Induced voltage is of maximum.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Generating A Sine Wave Motion is parallel to flux. N S No voltage is induced. Ready to produce another cycle.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Ac Generation Quiz Maximum voltage is produced when a conductor is moving ____ to the flux. No voltage is produced when a conductor is moving ____ to the flux. When a conductor is moving at 45° to the flux, the voltage is ____ of maximum value. For a two-pole generator, one cycle of ac is produced during ____ revolution(s). To produce a sine wave the flux field must be ____. perpendicular parallel one uniform

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Repeat Segment Concept Review Producing a sine wave requires circular motion, constant speed, and uniform flux. Cutting flux at a 90  angle produces V peak. Cutting flux at 45  produces V peak. A two-pole generator produces one cycle for each revolution of the rotating coil.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Preview Adjacent waveforms in a three-phase system are separated by 120 . The algebraic sum of the instantaneous voltages in a three-phase system is zero. Three-phases devices can be connected in either a wye or a delta configuration. A three-phase system can use both wye- and delta-connected devices.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Phase 1Phase 2Phase 3 Three-Phase Waveform 120  Phase 2 lags phase 1 by 120  120  Phase 2 leads phase 3 by 120  Phase 3 lags phase 1 by 240  240  Phase 1 lags phase 3 by 120 

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Phase 1Phase 2Phase 3 Generation Of Three-Phase Ac Phase 1 is ready to go positive. Phase 2 is going more negative. Phase 3 is going less positive. The algebraic sum of the instantaneous voltages of the three phases equals zero. N xx S

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Delta Connections Phase 3 Phase 2 Phase 1 Line 1 Line 2 Line 3 Delta-Connected Source The sum of the instantaneous phase voltages equals zero. Delta-Connected Load Each load resistor will be connected to one of the phases. For the delta-to-delta connection, V line = V phase = V load. For the delta-to-delta connection, I line = I phase = I load.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Wye Connections Line 3 Line 2 Line 1 Wye-Connected SourceWye-Connected Load I line = I phase = I load. V line = V phase = V load. For the wye-to-wye connection with a balanced load: Phase 3 Phase 1 Phase 2 There is no voltage between the source and load star-points.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Three-Phase Ac Quiz In a three-phase system, the phases are separated by ____ electrical degrees. In a three-phase system, the phase coils are separated by ____ mechanical degrees. The algebraic sum of the instantaneous phase voltages equals ____. The phase coils in a ____ connected source are connected in series. Phase and line currents are equal in a ____ connected system with balanced loads. In a delta-connected system, the line current equals ____ times the phase current. 120 zero delta- wye

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Repeat Segment Concept Review Adjacent waveforms in a three-phase system are separated by 120 . The algebraic sum of the instantaneous voltages in a three-phase system is zero. Three-phases devices can be connected in either a wye or a delta configuration. A three-phase system can use both wye- and delta-connected devices.

McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. REVIEW Types of Waveforms Induced Voltage Generating a Sine Wave Ac Terminology Three-Phase Ac