Transformers

Construction Transformers are based on the mutual induction principle A basic transformer consists of 2 laminated windings based around a steel core

Transformer Construction

Transformer Calculation To calculate the size of transformers and number of turns required to achieve the output, we can use the following formula:

Transformer Calculation To calculate the size of transformers and number of turns required to achieve the output, we can use the following formula: N = Number of turns V = Voltage I = Current P = Primary S = Secondary

Example Calculation A single phase step down transformer has 796 turns on its primary side and 365 turns on the secondary winding. If the primary voltage is 240v calculate the secondary voltage If the primary current is 10A, calculate the secondary current

Solution

Types of transformer Double Wound Most common type Usually wrapped around silicon steel to reduce losses

Types of transformer Auto Transformer Used in national grid transmission because of only using one winding A short circuit will destroy whole of transformer

Types of transformer Current Transformer Same principle as double wound Used to measure high currents

Current Transformer Example A current of 300A flowing through a 300mm2 supply cable needs to be measured. The ammeter to be fitted in the control panel has a rating of 0.5A How many turns on the secondary of a current transformer would be required to measure the primary current where the NP = 1, IP = 300A and IS = 0.5A (rating of the instrument)?

Losses A transformer is approximately 90% efficient Losses can be made through: Copper losses (I2R) Eddy current losses Hysteresis losses