Mod_1_Transformers1.ppt

Transformer -Types &
Applications
Module 1

What are transformers?
• Transformers are electrical devices used
to convert or "transform" AC voltage from
one level to another. (high to low or low to
high)
• Input and output are AC
• They do this by the principle of
electromagnetic induction

Parts of a Transformer
A transformer consists of 3 basic components
• Primary Coil or Primary Winding : It is an
electrical wire wrapped around the core on the
input side
• Secondary Coil or Secondary Winding: It is an
electrical wire wrapped around the core on the
output side
• Core : A ferromagnetic material that can conduct
a magnetic field through it. Example: Iron

Transformer Operation
• An electrical transformer normally consists
of a ferromagnetic core and two coils
called "windings".
• A transformer uses the principle of mutual
inductance to create an AC voltage in the
secondary coil from the alternating electric
current flowing through the primary coil.
• The voltage induced in the secondary can
be used to drive a load.

What is Mutual Inductance?
• The principle of mutual inductance says
that when two electrical coils are placed
near to each other, AC electrical current
flowing in one coil induces an AC voltage
in the other coil.
• This is because current in the first coil
creates a magnetic field around the first
coil which in turn induces a voltage in
second coil

• The transformer improves the efficiency of
the transfer of energy from one coil to
another by using a core to concentrate the
magnetic field.
• The primary coil creates a magnetic field
that is concentrated by the core and
induces a voltage in the secondary coil

Turns Ratio
• The voltage at the secondary coil can be
different from the voltage at the primary.
This happens when the number of turns of
the coil in primary and secondary are not
the same
• The Turns Ratio (TR) is the ratio of the
number of turns in the primary coil to the
number of turns in the secondary coil

Formulas
•TR= Vp / Vs
•Also TR= Np /Ns
•So we can say
Vp / Vs = Np /Ns
Also Vp/Vs=Is /Ip

Transformer Voltages &
Currents

Problems
1. A transformer has a primary voltage of
230v and turns ratio of 5:1. Calculate the
secondary voltage
2. A transformer has 200 turns in the
primary, 50 turns in the secondary, and
120 volts applied to the primary (Vp).
What is the voltage across the secondary
(V s)?

More Problems….
1. There are 400 turns of wire in an iron-
core coil. If this coil is to be used as the
primary of a transformer, how many turns
must be wound on the coil to form the
secondary winding of the transformer to
have a secondary voltage of one volt if
the primary voltage is five volts?
2. A 12 volts transformer has 20 turns in the
primary, 5 turns in the secondary. What is
the voltage across the primary side (VP)?

Lab Activity 2
•Complete Pages 19 -22
of Module 1

Input Power and Output Power
of a Transformer
• Under ideal conditions input power and output
power should be the same. But there is power
loss between the primary and secondary and so
practically they are not exactly equal.
• So, Pin = Pout + Ploss

Transformer Efficiency
• The power loss is converted to heat . The
heat produced can be found by calculating
the transformer efficiency.

Transformer Types
•Isolation Transformer
•Autotransformer

Isolation Transformer
• In isolation transformer, the primary and
secondary are physically isolated (no
electrical connection)

Advantages of Isolation
Transformer
• Voltage spikes that might occur on the
primary are greatly reduced or eliminated
in the secondary
• If the primary is shorted somehow, any
load connected to the secondary is not
damaged
• Example: In TV monitors to protect the
picture tube from voltage spikes in main
power lines

Autotransformers
• An autotransformer uses only one coil for the
primary and secondary.
• It uses taps on the coil to produce the different
ratios and voltages.

The Control Transformer
• A control transformer is used
to reduce voltage from the
main power line to a lower
voltage that operates a
machine’s electrical control
system.

The Control Transformer
• The most common type of control transformer
has two primary coils (H1H2 and H3H4) and one
secondary coil (X1X2). Note that the primary
windings are crossed

To get 120V at the secondary from
240 V at the primary using a control
transformer

It is actually a parallel
connection of the primary coils

To get 120V at the secondary
from 480 V at the primary using
a control transformer

This is actually a series
connection of the primary coils

Problem 1
• Connect the primary coils in parallel and
calculate the secondary voltage if the primary
voltage is 48 Volts and the number of turns in
each primary is 50 turns and the secondary has
25 turns.

Problem 2
• Connect the primary coils in series and calculate
the secondary voltage if the primary voltage is
48 Volts and the number of turns in each primary
is 50 turns and the secondary has 25 turns.

Problem 3:Make connections in the transformer coils to
produce a turns ratio of 1:1. Use both primary and
secondary coils.

Problem 4:Make connections in the transformer coils to
produce a turns ratio of 2:1. Use both primary and
secondary coils.

Problem 5:What is the turns
ratio in the circuit?

Problem 6:What is the turns
ratio in this circuit?

Mod_1_Transformers1.ppt

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