BEX 100

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BEX 100 Basic Electricity

• Alternating Current (AC)
• Unit 15

2
Unit Objectives

• To understand the differences between (DC) direct
  current (AC) alternating current
• To be able to identify different types of AC
  current wave forms
• To understand the different values associated
  with AC current
• Understanding skin effects of AC current

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Introduction

• Most of the electrical power produced in the
  world is AC / Alternating Current
• AC current is bi-directional
• AC current can be transformed by means of
• A Step up transformer
• Step down transformer

4
INTRODUCTION

• TRANSMISSION VOLTAGES RUN 69KV TO 345KV. WHY????
• AC VOLTAGE CANNOT BE STORED SO CANT BE USED IN
  AUTOS
• 1940 WORLDS FAIR EDISON LOW VOLTAGE DC 1 PER
  LAMP
• WESTINGHOUSE HIGHER VOLTAGE AC .25 PER LAMP
  SET PRECEDENT

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AC Wave Forms

• AC current flow reverses direction at periodic
  intervals

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AC Wave Forms

• Triangle / Linear Waves
• Voltage rises/falls at a constant (linear) rate
  per time cycle

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AC Wave Forms

• The Sine Wave
• The most common
• Produced by rotating machines
• Has a total of 360 degrees in each cycle
• Frequency the number of cycles per second
• Frequency is measured in Hertz

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AC Wave Forms

• The Sine Wave

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Alternating Current

• Sine Wave Values

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Sine Wave Values

• Peak to Peak value
• Maximum positive to negative voltage
• Peak value
• Measured from zero to either the maximum positive
  or negative voltage

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Sine Wave Values
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Sine Wave Values

• Average values
• Actually a Direct Current (DC) value
• Used when AC voltage is rectified to DC voltage
• The amount of voltage indicated by a DC voltmeter
  measured across the load

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Sine Wave Values
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Resistive Loads

• Loads that contain pure resistance such as
• A Heating element
• Incandescent lights
• Current copies voltage
• Current is in phase with the voltage

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REVIEW

• 1. WHAT DOES AC STAND FOR?
• 2. WHAT IS THE MOST COMMON AC WAVE FORM?
• 3. NAME A BIG ADVANTAGE OF AC CURRENT.
• 4. WHY RUN HIGH VOLTAGES?

• 5. WHY ISNT AC USED IN AUTOS?
• 6. WHAT TERM DESCRIBES STEPPING VOLTAGE UP OR
  DOWN?
• 7. DEFINE THE TERM HERTZ.
• 8. WHAT DOES PEAK TO PEAK STAND FOR ?

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Elizabethtown Technical CollegeBasic Electricity
BEXS100/101Text Delmars Standard Textbook of
ElectricityUnit 15 Alternating Currents