30-04-2014, 02:37 PM
TRANSFORMER
TRANSFORMER.pptx (Size: 84.14 KB / Downloads: 20)
Some basic points on transformer
Static electrical device.
Considered as 4 terminal & 2 port network.
Coupled circuit.
Negative feedback device.
Singly excited device.
Electromagnetic energy conversion device.
Constant freq. and power device.
Phase shifting device.
Constant flux device
Static electrical device:
Transformer has no rotating part.
According to the Faraday’s law, when a conductor is placed in a time varying magnetic field, the emf induced in the conductor is called static induced emf which is satisfied in case of transformer.
But in case of machines(motors and generators),the emf induced is called dynamically induced emf as there the conductor is rotating and the field is stationary.
Four terminal and two port network:
Transformer has four variables such as V1, I1, V2,I2. So, it can be considered as a two port networt so that A,B,C,D parameters canbbe calculated for the simplification of calculations.
Singly excited and negative feedback circuit:
As only one supply is given to the transformer,it is said to be singly excited.But in case of motors and generators(except induction motor) two excitation is required.
The windings in the transformer shows inductive effect where the induced emf opposes the current to flow through it . So, it is said to be negative feedback circuit.
At no load:
At no load , there is no current flowing in the secondary. So, no flux in the secondary side. The only flux created at the primary will flow through the core.That’s why the flux remains constant .
At loading condition:
When the transformer is loaded current will flow through it and this extra current wil be drawn from the source. As a result flux will be generated at the secondary side which will be in opposition to the main flux. Also the extra amount of current drawn from the source will generate some flux in the direction of main flux. This flux will oppose the flux generated at the secondary side. So, at last the flux in the core remains constant.