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Electromagnetic
Principles
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Definition
Electromagnetic is made up of two words.
1. Electro, which has something to do
with electricity and
2. magnetic, which has something do
with magnetism.
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Definition
So, electromagnetic principles deal
with the relationship between
electricity and magnetism, as well as
the relationship between magnetism
and electricity.
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There are two electromagnetic
principles that we are going to
review.
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The first principle that we want to review
states that electrons will flow in a
conductor when the conductor MOVES
or PASSES through a magnetic field.
Principle # 1
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If it were not for this principle, we would
not have ‘electricity’ today. Let’s take a
closer look at this principle.
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© 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2
Magnet
Conductor
SOUTH
NORTH
Magnet
Passing a conductor between two magnets and the magnetic field causes electrons to flow in the wire.
This produces electrical current in the wire.
Generating Current
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© 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2
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0º 90º 180º 270º 360º
Positive
Negative
One cycle
Magnet
SOUTH
NORTH
Magnet
Conductor
Alternating Current
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Effective voltage
• Alternating current starts at 0, reaches a peak, then returns to 0
• Peak voltage at 90° (electrical degrees)• Effective voltage is .707 times peak voltage
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© 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2
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0º 90º 180º
Effective Voltage
Peak Voltage 170 v
120 v
0 v
Effective voltage = .707 x Peak voltage
.707 x 170 = 120 v
Note: Meters measure effective voltage
Effective Voltage
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© 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2
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0º 90º 180º
Effective Voltage
Peak Voltage 340 v
240 v
0 v
Effective voltage = .707 x Peak voltage
.707 x 340 = 240 v
Note: Meters measure effective voltage
Effective Voltage
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The ‘effective voltage’ is also
known as the RMS (Root Mean
Square) value or the DC (Direct
Current) equivalent.
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Many years ago, there was only
Direct Current. AC was not
invented yet. But when it was,
what do you think the reference
current would be?
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If you said DC, you would be
correct. So, 120v AC will do the
same ‘work’ that 120 DC will do.
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In other words, if you plug a 100w
incandescent light bulb into 120v
AC, it will glow just as bright as if
you plugged it into 120v DC, thus
the DC equivalent.
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For another example, if you wired
a 240v AC electric hot water tank
to 240v DC, it will heat the water
just as quickly. Thus, the DC
equivalent.
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© 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2
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Generating Alternating Current (AC)
• Passing a conductor through a magnetic field• A generator uses many conductors and a large
magnetic field to produce electrical current
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Expressing AC with a Sine Wave
• A sine wave shows how alternating current flows in one direction, then reverses to flow in the opposite direction.
• A sine wave is a mathematical derivation of the trigonometric function – sine. You do not need to know trig. in order to understand AC though.
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© 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2
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0º 90º 180º 270º 360º
Positive
Negative
One cycle
Magnet
SOUTH
NORTH
Magnet
Conductor
Sine Wave of Alternating Current
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Cycles and Frequency• Cycle:
– One complete electrical alternation• Frequency
– Number of cycles in a second• Measurement of frequency:
– Hertz (Hz)– Cycles
• U.S. frequency is 60 hertz, or 60 cycles
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The second principle that we want to
review states that a magnetic field will be
produced when electrons flow in a
conductor.
Principle # 2
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If it were not for this principle, we would
not have motors, relays, contactors,
solenoids, timers, etc. Let’s take a
closer look at this principle.
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For the first example, let’s take a look at
how electricity produces a magnetic field
and is used on a device known as a
‘solenoid valve.’
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Solenoid Valve
Magnetic coil energized
Plunger pulled up
Fluid flowsFluid stops
Power off
Plunger drops
Plunger
Seat
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For the second example, let’s take a look
at how electricity produces a magnetic
field and is used on a device known as a
‘contactor.’
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© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
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Side View
L1 L2
T1 T2
LINE
LOAD
CONTROL CIRCUIT
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© 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2
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L1 L2
T1 T2
LINE
LOAD
Power to Contactor
Power to Load
CONTROL CIRCUIT
Contacts pulled in
Magnetic Coil energized
Side View
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For the third example, let’s take a look at
how electricity produces a magnetic field
and is used on a device known as a
‘motor.’
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© 2005 Refrigeration Training Services - E2#1 Fan Motors v1.2
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Two-pole stator motor
NN S
_+
SN S
Stator (Stationary)
When stator is energized the rotor will make a half turnwith each half of current cycle
Rotor(Rotates)
Polarity reverses (N to S) on stator
Stator repels & attracts rotor into motion
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Second half of cycle
NS
+ _
N S
The alternating current now
changes direction
NSPolarity reverses (N to S) on stator
Stator continues motion by repelling and attracting
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In conclusion, if it were not for
electromagnetic principles, we would be
living in the dark ages.
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T h eE n d