Transcript BEX100 - Basic Electricity

BEX 100 – Basic Electricity
Alternating Current (AC)
Unit 15
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
Introduction
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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
INTRODUCTION
TRANSMISSION VOLTAGES RUN 69KV
TO 345KV. WHY????
AC VOLTAGE CANNOT BE STORED: SO
CAN’T BE USED IN AUTOS
1940 WORLD’S FAIR: EDISON LOW
VOLTAGE DC: $1 PER LAMP
WESTINGHOUSE: HIGHER VOLTAGE AC:
$.25 PER LAMP: SET PRECEDENT
AC Wave Forms
AC current flow “reverses direction” at
periodic intervals
AC Wave Forms
• “Triangle / Linear Waves”
• Voltage rises/falls at a constant (linear) rate
per time cycle
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”
AC Wave Forms
The “Sine Wave”
Alternating Current
Sine Wave Values
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
Sine Wave Values
Sine Wave Values
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“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
Sine Wave Values
Resistive Loads
 Loads that contain “pure
resistance” such as:
• A Heating element
• Incandescent lights
 Current “copies” voltage
 Current is in “phase” with
the voltage
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 ISN’’T 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 ?
Elizabethtown Technical College
Basic Electricity BEXS100/101
Text: Delmar’s Standard Textbook of Electricity
Unit 15 – Alternating Currents