•
A
Transformer consists of two or more windings linked by a magnetic circuit.
•
The
Magnetic circuit is usually in form of a laminated iron core, and in most
transformers,
there is no metallic connection between the windings. Though
Autotransformers have both Primary and Secondary windings connected in series.
•
The
Electrical circuit consist of the copper
windings on the laminated cores.
•
The
winding connected to the source of power
is called the Primary, and the winding supplying power to the load is called
the Secondary.
•
The
Voltage across the secondary winding will vary directly with the voltage across
the primary winding as the ratio of the number of turns in the secondary (Ns)
to the number of turns in the primary (Np). This is called the turns ratio of
the transformer.
•
Turns
ratio = (Ns)̸(Np)
•
With
the secondary winding open circuited, the current drawn by the primary winding
will be almost 90% out of phase with the voltage across it and lagging. This is
called the ‘exciting current’.
•
If a
load is connected across the secondary, current will flow in it producing a
magnetic flux which by Lenz’s Law will oppose the main magnetic flux. With the
secondary supplying a load, the secondary voltage will be lower than it was at
no load because of the voltage drop to resistance and leakage reactance of the
windings. This reduction in voltage under load is called ‘The Regulation’.
•
Core
losses will generate heat in the transformer.
•
I2R
(Copper) losses will be present when the transformer is on load.
•
The
Current flowing in the primary and secondary windings vary inversely as the
•
number of turns in the windings =
Ip ̸Is
= Primary ampere turns = Secondary ampere turns
The Voltage in the primary and secondary windings varies directly as the
number of turns.
Esec = Nsec = Ipri
Epri Npri
Isec
Isec x Esec = Ipri x Epri = VA =
VA = KVA = KVA =
MVA
1000 1000
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