Transformer
- Static device
Principle: electromagnetic induction
Used for: Step up or step down voltage
Types: single phase &three phase
Core type & shell type
Construction:
In this, it has two types of winding primary and secondary winding. Windings are placed on iron core which has low reluctance for magnetic flux.
Working :
Primary winding gets input voltage and produces flux in iron core ,then this settled flux get linked with secondary winding, .
Because of ac supply flux will change its direction and magnitude …...so secondary coil will get inducement of voltage.
Induced voltage=-N(dphi/dt)
Where N is number of turns in secondary windings and dphi/dt is rate of change of flux.”-”ve sign describes Lenz's law.
As rate of change of flux is same for both,
E1/N1=E2/N2
E1/E2=N1/N2………**
Transformer changes the voltage levels without affecting power .
Power remains same for both sides.
P1=P2
E1I1=E2I2
E1/E2=I2/I1
N1/N2=I2/I1(from…**).
As it is static device ,losses are too small .
Efficiency :96℅ to 98℅
There are many types of transformers based on their level of usage
- Power Transformers
- Distribution Transformers
- Instrument Transformers
- Power Transformers:
- Distribution transformers:
These Transformers are used in distribution side to further decrease the voltage level for supplying the load .Generally delta-star transformers are used in distribution side because the loads we use are 1 phase (1 phase and 1 neutral wire) To split the 3 phase power into 3 -single phases we need star connection. These transformers are supplying power through out the day whether load is on or off. Turning on transformers even on no load results in increased core losses ,so the distribution transformers use amorphous alloy core whereas power transformers use silicon steel core .
- Instrument Transformers:
In substations the voltage and current levels are to be monitored at every instant and as these voltages and currents are of very high values ,the meters used for these purpose should be of very large rating which increases the size and cost of the meters. To avoid this, Instrument transformers are used to step down the voltage and current values to required level. Again there are two types of instrument transformers.
a) Current Transformer: To decrease the current level ,an ammeter is connected in parallel to the secondary of current transformer.
b)Potential Transformer :to decrease the voltage level
Types based on Phase
- Single phase transformer
- Three phase transformer
- Single phase transformer contains two coils, one on the primary side, and another one on the secondary side, while three phase transformer contains six coils, three for primary side, and another three coils for the secondary side.
- Single phase transformer has four terminals, two on the input (phase & neutral), and two on the output (phase & neutral), no delta or star connections are available here, but three phase transformer has twelve terminals with different connection for them for star or delta connections.
- Single phase transformers are most used in the household devices applications, such as TV, Microwave Oven, Phone Charger, etc., while three phase transformers are most used as a power or distribution transformers, with high rated KVA.
- In most cases, no cooling system is required for single phase transformer, on the other side, three phase transformers have many cooling systems depending on the transformer rated power, may be by oil, forced oil, air, forced air or by forced water.
- The magnetic core for each type is different, and it's always bigger in the three phase transformers than the single phase ones.
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