Differences between step-up and step-down transformer:-

Step-down transformer converts high voltage level to low voltage level. VP > VS 

While

Step-up transformer converts low voltage level to high voltage level.
VP < VS

In step-down transformer, number of turns in primary winding is greater than the number of turns in secondary winding. NP > NS

While

In step-up transformer, number of turns in secondary winding is greater than the number of turns in primary winding.NP < NS


In step-down transformer, current flowing in the primary winding is less than the current flowing in the secondary winding.IP < IS 

While

In step-up transformer, current flowing in the secondary winding is less than the current flowing in the primary winding.IP > IS


Applications:-

Transformers used in rural and urban distribution lines are step-down transformers. 

While

Step-up transformers are used at power generation stations to boost up the voltage level.

Step-down

Step-up