Electrical Transformers

Electrical transformers  changed the way of handling the voltage of electrical power lines. At every street end we see electrical transformers used for providing consistent voltage supply.  It is an engineering marvel that shaped the electrical distribution network.

It is a electromagnetic machine, converts A.C electrical energy from higher voltage to lower voltage and vice verse or even equal voltage with corresponding increase or decrease in current without any change in frequency.

Working Principle:

Metal usually iron made into a C shape structure, each sheet is laminated to each other forming the square block called as core.  Copper wire is coiled to one of the sides of the core and similarly to it opposite side. Power supply is provided to the one of the coiling ends (primary) and to the other (secondary) load is connected.
 
Voltage supplied to the winded primary coil due to this an alternating flux is generated in metal core. If N1 and N2 are number of individual windings of primary and secondary coil respectively. E1 and E2 are the e.m.f of each coils then
E2/E1 =N2/N1


When the secondary is open circuit, its terminal voltage is the same as induced e.m.f. The primary current is then very small, so that the applied voltage V1, is equal and opposite to the e.m.f induced in primary coil.
V2/V1 = N2/N1 = K

where K is known as transformation ratio.
(1) if K>1 , the transformer is known as step up transformer.
(2) if K< 1, the transformer is known as step down transformer.

The size of fuse wires to be used on the HV side of various sizes of transformers.

Capacity of transformers KVA H.T.Voltage rating , KV Size of T.C fuse wire S.W.G Horn gap length in inches
3000 66 21 20
2500 66 21 20
2000 66 21 20
1750 '' 22 20
1500 '' 22 20
1250 '' 23 20
1000 '' 26 20
750 '' 28 20
500 22 32 20
250 22 23 10
500 11 20 8
250 11 23 8
Note: Above values are approximate may change as per the region and manufacturer.
Electric transformer design sketch