1) Voltage ratio: The voltages in primary and secondary winding is proportional to number of turns in primary and secondary respectively. So, the voltage ratio is same as transformation ratio.
V2/V1 = N2/N1 = K
If the number of turns of secondary winding (i.e. N2) is more than number of turns of primary winding (i.e. N1) then voltage on secondary winding (i.e. V2) will be more than the voltage on primary winding (i.e. V1) and if the voltage on secondary side is more than primary side then the transformer is known as step up transformer.
If the number of turns of secondary winding (i.e. N2) is less than number of turns of primary winding (i.e. N1) then voltage on secondary winding (i.e. V2) will be less than the voltage on primary winding (i.e. V1) and if the voltage on secondary side is less than primary side then the transformer is known as step down transformer.
If the number of turns of secondary winding (i.e. N2) is equal to number of turns of primary winding (i.e. N1) then voltage on secondary winding (i.e. V2) will be equal to the voltage on primary winding (i.e. V1) and if the voltage on secondary side is equal to primary side then the transformer is known as isolation transformer.
2) Current ratio
The ratio of current on primary winding of transformer (i.e. I1) to current on secondary winding of transformer (i.e. I2) is called as current ratio of transformer.
V2/V1 = I1/I2 = K
3) Transformation ratio of transformer:
The ratio of number of turns of secondary (i.e. N2) to number of turns of primary (i.e. N1) is called as transformation ratio of transformer. It is denoted by K.
K = N2/N1