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: • V S = secondary voltage or output voltage (Volt) • V P = primary voltage or input voltage (Volt) • N S = number of turns on secondary coil • N P = 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 (V P < V S ) -
secondary voltage is larger
than the primary voltage (V P < V S ) -
number of turn
on secondary coil is
larger
than on primary coil (N P < N S ) -
Output current is smaller
than
input current
(I P > I S ) Step-down transformer used
to decrease
the AC voltage (V P > V S ) -
secondary voltage is smaller
than the primary voltage (V P > V S ) -
number of turn
on secondary coil is
smaller
than on primary coil (N P > N S ) -
Output current is the larger
than
input current
(I P < I S )
• 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: P P = P S V P .I
P = V S .I
S P P = Power in primary coil or power input (Watt) P S = Power in secondary coil or power output (Watt) I P = Current in primary coil or current input (Ampere) I S = 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