10 things about transformer
1. Transformer is a static device which is generally used to change the voltage level of power system without changing its power and frequency. The main purpose of using transformer is to either increase or decrease the voltage level. The input side of transformer is called primary side and output side of transformer is called secondary side.
2. Transformer works only on AC supply and never works on DC. If DC supply is given to transformer its output voltage is zero and primary winding may burn out. Therefore its not desirable to connect a transformer to the dc supply.
3. Transformer works on the principle of mutual induction. Which means that the changing flux produce by primary winding links with the secondary winding. According to Faraday law of electromagnetic induction, when a changing magnetic field links with secondary winding, an emf is induce in secondary winding. That is it.
4. Primary and secondary winding of transformer are magnetically coupled. There is no electrical connection between primary and secondary winding of transformer. The transfer of energy from primary side to secondary side is done by the magnetic flux.
5. Transformer is rated in kVA ot MVA, not in kW or MW. There are two main losses in transformer, copper losses and iron losses. Copper losses depends on current flow through winding and iron losses depends on voltage. In means, total losses of transformer depends on both current and voltage. Therefore the transformer are rated in kVA, not in kW.
6. The Iron losses (hysteresis losses + eddy current losses) are constant at all load and copper losses varies with load. Actually the iron losses depends on voltage and voltage is almost constant for all the load, therefore these losses are constant at all load. On the other hand, copper losses depends on current and current varies with load. Hence copper losses varies with load.
7. Power transformer are designed to have maximum efficiency near full load and distribution transformer are designed to have maximum efficiency near half load. Because, the power transformer runs mostly on full load throughout the day and the distribution transformer runs near half load throughout the day. That is by the they are design to have maximum efficiency at full loaf (power transformer) and at half load (distribution transformer).
8. In a transformer, the voltage per turn in primary and secondary winding remains always same. For example, a transformer having 400 turns in primary winding and 800 turns in secondary winding. If voltage per turn in primary is 0.5 V then voltage per turn in secondary will also 0.5. Hence transformer will step up the total voltage.
9. From no load to full load on a transformer, the flux linkage with the core is almost constant. The flux linkage to the transformer depends on the voltage and the voltage is almost constant at all load. Therefore, the flux linkage to the transformer is almost constant.
10. The efficiency of transformer will be maximum when copper losses are equal to its iron losses. As we discussed that iron losses are constant and depends on voltage. On the other hand copper losses are variable losses and depends on load current. As iron losses are fixed and copper losses varies from zero load to full load. There is a load current at which copper losses becomes equal to iron losses. At this condition, transformer is said to have maximum efficiency.
- In a tap changing transformer, the taps are usually provided on the high voltage side.