transformer Flashcards
what is tranformer
A transformer consists of two coils of insulated wire wound onto a laminated soft-iron frame. The two coils may be wound on top of one another or on opposite side of the frame. The one which carries the varying current is called primary coil and the other is called the secondary coil.
Any of the two coils can act as a primary coil and secondary coil
principle
Principle: It works on the principle of electro magnetic induction.
working
An alternating current is passed through the primary coil and this sets up a varying magnetic field which cuts the secondary coil. By electromagnetic induction an EMF is set up in the secondary coil
Types of transformer
Transformers used in radio and TV are broadly classified as 1. Power transformer 2. Audio Frequency transformer 3. Radio Frequency transformer 4. Auto transformer.
The power transformers are meant to supply various voltages required in radio receivers and other electronic equipment’s.
Audio frequency transformer meant to operate on audio frequencies of 20 – 20000htz. The construction is similar to power transformer with two windings wound on a silicon laminated core. The two windings are layer wound, with the secondary on the outside. These transformers are used in coupling, for coupling microphone to amplifiers and for coupling amplifiers to speakers.
Radio frequency transformer: These are meant for operation at very high frequency compared to AF transformer.
Auto transformer: In auto transformer the same coil is used for the primary and the secondary windings, The whole coil is used as primary and a part of the coil as a secondary. It becomes the step down transformer and vice versa is step up transformer.
Functions of transformer
To alter the voltage of an alternating current by changing the number of turns in the coil
ratio transformer
- If both primary and secondary have the same number of turns, then the voltage in each will be the same. This is an example for even ratio transformer
step up and step down
- If the no of turns in the secondary is more than that of primary, then EMF set up in the secondary is more than that primary. Then we have step up transformer
- Reverse case is for step down transformer
unit of power
watt
watt = volts*amphere
to render a current earth free
Mains electricity is produced by a dynamo and the consumer is supplied with a wire at high potential called live wire, and a wire at zero potential connected to earth called neutral wire.
If an accidental connection is made between the live wire and the earth, current will flow along it. If this connection were made with a person, then they would receive the electric shock as the current flowed through them. This danger is not so in case of static transformer
static transformer
In static transformer, this danger is reduced by using electromagnetic induction to transfer the electrical energy into the secondary coil where earth plays no part in the circuit. The effect on the secondary coil of the magnetic field around the primary is to cause the electron to move around the secondary circuit, but not to leave it. Earth plays no part in the secondary circuit, because even if an earth connection is made with it, electrons will not leave but continue to flow around it. This is an important safety factor, and all the currents applied to patients are rendered earth free by using static transformer.
variable transformer
This consists of a primary and secondary coil, but is constructed so that one of them can be altered in length.
The primary coil has a number of tappings taken from it and a movable contact can be placed on any one of these by turning a knob.
Auto Transformer
This consists of single coil of wire with four contact points coming from it.
When used as step up transformer, CD is used as primary coil and AB as secondary.
Disadvantage:
1. Allows small step up voltage
2. Does not render current earth free
Uses:
1. It is found in the starter circuit of Ultraviolet lamps to strike an electric arc.
