The transformer is an electromagnetic static device, which is used to transfer the electrical energy from one level to another level without changing the frequency. It can increase or decrease the voltage with the corresponding decrease and increase in current keeping the power of transformation as same. A transformer can change high voltage to low voltage and low voltage to high voltage but in both the cases the frequency remains unchanged.
Step up transformer: If a transformer changes low voltage to high voltage, it is known as the step up transformer .
Step down transformer: The transformer which changes the high voltage into low voltage is known as the step down transformer:
The energy transformation in the transformer is magnetically. Truly speaking there is no electrical and mechanical connections (in a two winding transformer) between the circuit energised by the supply and the circuit to which load is connected, but magnetically these are connected. The winding where supply is connected is known as primary winding. This winding may be H.V. winding, having more number of turns or L. V. winding having less number of turns. The winding to which load is connected is known as secondary winding and that too can be H.V. or L. V. depending upon the number of turns.
Write down the different causes of popularity of a transformer?
These are the following reasons for the popularity of the transformer:
- The transformer is a static device, there is no moving part in it, so it requires less maintenance.
- It can be designed and can be made of any size and power and can be installed anywhere, even at the poles in open area.
- Being stationary unit the losses are considerably less than the rotating machines, hence the efficiency is very good, say 97-98%.
- It is a self regulating device. The primary winding draws current automatically if the load is increased on secondary winding.
- Being stationary and self regulating, no attendant is required.
- The voltage can be stepped up or stepped down whenever needed according to the requirement and nature of load.
- The construction is easily.
- Less possibility of faults.
Transformer Working Principle
A transformer works on the principle of Faradays Laws of Electromagnetic Induction. As the transformer is a static device and no rotating part, so the type of induction is also the static induction that too the mutual induction. “Whenever a conductor links the changing flux an e.m.f. is induced in that conductor”. This induced e.m.f. is proportional to the rate of change of flux and the number of turns.
Consider there are two coils and ‘B’ wound on the iron cores as shown in Fig. 18.1 (a). Coil A, is connected across the supply i.e. it is the primary winding and coil B, where load is connected is known as secondary winding. If the coil ‘A’ is energised by a.c. mains the magnetic flux of alternating nature will be produced. This changing flux is also realised by the iron cores. The coil ‘B’ which is wound on the cores will also link this changing flux, through iron cores which is a path of low reluctance. A result the e.m.f. is induced in coil ‘B’.
Fig. 18.1 (a) Windings (b) Windings and cores
This phenomenon is known as mutual induction, the basic principle of transformer. Both windings are shown in Fig. 18. I(b), the winding which is fed and the winding in which e.m.f. is induced.
Construction of a Transformer
The transformer has the following parts:
(a) Cores, (b) windings, (c) terminals and bushings, (d) tank (e) transformer oil, (f) conservator, and (g) breather.
Transformer Cooling System and Methods
Whenever the current is flowing through the winding inherently some heat is produced; which should be dissipated; otherwise the heat may spoil the windings and insulation etc. There are a number of methods used for this purpose. Natural air cooling, oil-immersed forced air, water and oil cooling and the air blast cooling.
Define the efficiency of the transformer? State the conditions for maximum efficiency.
The efficiency is the ratio of output to input generally in percentage. The efficiency depends upon the load and load power factor. the efficiency is maximum when variable losses are equal to the constant losses. It decreases with the decreasing of the load and power factor. In other words, the iron losses are equal to copper losses so the efficiency will be maximum.
Define the all-day efficiency of the transformer. What is the necessity Of this efficiency?
The transformers are connected to line to give service around the clock irrespective of the load, whether these are fully loaded or even without load. The primary winding is always connected across the line and draws some current from the mains. Under these circumstances the ordinary efficiency, the ratio of output to input, does not give any correct picture of the performance of the transformer. So it leads to find out some other efficiency taking time into consideration, generally the time is 24 hrs.
The copper and iron losses are inherent when the transformer is supplying. The iron losses remains constant where the copper losses depends upon the load Current. The coplrr losses vary as the square of current. The all day efficiency is defined as the ratio of output in kWh over a state a period to the intake power in kWh over the same period. This duration is usually 24 hrs.
So all day efficiency = kWh output in stated period/kWh input in same period