Step-up?transformer (increases the voltage of the power source) where?Ns > Np
Step-down?transformer (decreases the voltage of the power source) where?Np > Ns
For an ideal transformer, there is no electrical energy lost and it is 100% efficient
This means the power in the primary coil equals the power in the second coil;
Where:
Ip?= current in the primary coil (A)
Is?= output current from the secondary coil (A)
Worked Example
A step-down transformer turns a primary voltage of 0.5 kV into a secondary voltage of 100 V. Calculate the number of turns needed in the secondary coil if the primary coil contains 3000 turns of wire.
Step 1: List the known quantities
Primary voltage,?εp?= 0.5 kV = 0.5 × 103?V
Secondary voltage,?εs?= 100?V
Number of turns in the primary coil,?Np?= 3000 turns