BEX 100 – Basic Electricity Alternating Current (AC) Unit 15

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 Unit Objectives:

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

INTRODUCTION xTRANSMISSION VOLTAGES RUN 69KV TO 345KV. WHY???? xAC VOLTAGE CANNOT BE STORED: SO CAN’T BE USED IN AUTOS x1940 WORLD’S FAIR: EDISON LOW VOLTAGE DC: $1 PER LAMP xWESTINGHOUSE: 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

“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

“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 x1. WHAT DOES AC STAND FOR? x2. WHAT IS THE MOST COMMON AC WAVE FORM? x3. NAME A BIG ADVANTAGE OF AC CURRENT. x4. WHY RUN HIGH VOLTAGES? x5. WHY ISN’’T AC USED IN AUTOS? x6. WHAT TERM DESCRIBES STEPPING VOLTAGE UP OR DOWN? x7. DEFINE THE TERM HERTZ. x8. 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