03 Q3. An engineer is given a sample transformer for testing. The sample transformer carries the label with 240 V at the primary winding, 12 V at the secondary winding and rated apparent power of 15 VA. The DC resistance measured at the primary and secondary windings are 240 02 and 1 2, respectively. (a) The primary winding of the sample transformer is connected to a 50 Hz 240 V AC source while the secondary winding is left open. The current measured at the primary side is 5.1 mA with power factor of 0.2. Determine the magnetizing current and the iron loss of the sample transformer. State your assumptions and justify them. (b) (8 marks) The secondary winding of the sample transformer is then shorted. The primary winding of the sample transformer is connected to an auto-transformer with operating frequency of 50 Hz. The output voltage of the auto-transformer is slowly raised, until the output current measured at the secondary winding of the sample transformer reaches the rated current of the sample transformer. The power factor measured at the input of the primary winding is 0.98. (i) Determine the impedance of the sample transformer viewed from the primary winding. Write your answer in complex number. (6 marks) (ii) Determine the copper loss of the sample transformer. (3 marks) (iii) Determine the magnitude of the output voltage of the auto-transformer. (2 marks) State your assumptions and justify them. (c) The primary winding of the transformer is connected to a 50 Hz 240 V AC source. The secondary winding of the transformer is connected to a load which draws the current equals to the rated current of the transformer. The power factor measured at the primary side of the transformer is unity. Determine the impedance of the load. Write your answer in the form of compl d state whether the load is resistive, inductive or capacitive. 8/10 [2