Transcript Document

Transformer
• Transformer is used to increase or decrease AC
Voltage (potential difference).
• Transformer is consisted of a soft iron core, a primary
coil, and a secondary coil.
• Primary coil is connected to AC supply, while the
secondary coil is connected to the electrical
component (lamp, computer, TV, etc)
Soft iron
Primary
coil
secondary
coil
Symbol of transformer
Principle of Transformers
• A transformer works only with alternating
current supply (AC supply).
• Mutual induction: When the primary coil is
connected to a source of AC voltage, the
changing current creates a changing magnetic
field, which is carried through the core to the
secondary coil. In the secondary coil the
changing field induces a varying voltage.
• The voltage induced in the secondary coil is
called the secondary voltage and voltage
induced in the primary coil is called the primary
voltage.
• In a transformer, the ratio of input
voltage to output voltage depends on
the ratio of the number of turn on the
primary coil and secondary coil, as
shown by formula:
•
•
•
•
VS= secondary voltage or output voltage (Volt)
VP= primary voltage or input voltage (Volt)
NS= number of turns on secondary coil
NP= number of turns on primary coil
• In the above photograph the school’s
transformer was used. 10.05V (rounded by
the meter to 10.1V) across the primary coil of
2,000 turns resulted in an output of 100.5V
across the secondary coil of 20,000 turns.
Step-up and step-down transformer
• Step-up transformer
-used to increase the AC voltage (VP < VS )
-secondary voltage is larger than the primary voltage (VP < VS )
-number of turn on secondary coil is larger than on primary coil (NP < NS )
-Output current is smaller than input current (IP > IS )
Step-down transformer
-used to decrease the AC voltage (VP > VS )
-secondary voltage is smaller than the primary voltage (VP > VS )
-number of turn on secondary coil is smaller than on primary coil (NP > NS)
-Output current is the larger than input current (IP < IS )
• In an ideal transformer (100% efficient),
the electric power delivered to the
secondary coil equals the power supplied
to the primary coil. It can be represented
by the following equations:
PP = PS
VP .IP = VS .IS
PP = Power in primary coil or power input (Watt)
PS = Power in secondary coil or power output (Watt)
IP = Current in primary coil or current input (Ampere)
IS = Current in secondary coil or current output (Ampere)
Energy Losses in a Transformer
are caused by:
1) Resistance of winding
The windings of copper wire – have some resistance heat is produced
2) Eddy Currents.
Iron core – changing magnetic field of the primary –
induced – current (eddy currents)- caused heating.
Reduced by laminating core made of sheets
3) Leakage of field lines
Field lines produced – primary may not cut the
secondary – has air gap or badly designed
Application of Eddy Currents:
Speedometer
Application of Eddy Currents:
Metal Detector
Diagram of Power Transmission
Power station
Houses
Offices
Hotels
Substation