Answera step up transformer steps up the voltage and a step down transformer steps down the voltage.... simple
THE DIFFERENCE IS ONLY IN THE APPLICATION. YOU CAN USE AS STEP-DOWN OR STEP-UP AS YOU WISH AS LONG AS YOU APPLY THE RIGHT INPUT VOLTAGE IN EITHER SIDE.
A step up transformer gives a output greater than the input and step down trnsformer does the opposite!!
Hope this helped..Thank u
Power Transformers are used to step up or step - down a.c. voltages and to transfer electrical power from one voltage level to another. Tap changers are used for voltage control.