Questions regarding an open circuit transofrmer test:

1-What causes the primary current to be non zero when thesecondary winding is open circuied?

2-What is the main type of power loss being measured in an opencircuit test?

3-The back-EMF equation tells us that the peak flux density isproportional to the AC supply voltage. Now knowing that the currentwhich flows in the transformer under open-circuit conditions is thecurrent (or mmf) which produces the magnetic flux density, explainwhy the peak open-circuit current increases nonlinearly whereas theapplied voltage increases linearly.

4-Calculate the rated primary current of the followingtransformer ratings and express it as a percentage of the ratedprimary current.

A single-phase transformer (240/120V, 1kVA). Note: thistransformer actually has two identical secondary windings, eachrated at 1kVA resulting in a total transformer rating of 2kVA.However we are only considering one winding in the experiment andso the effective transformer is only 1kVA.

•AC mains supply (240V, 50Hz)

•An autotransformer (240V, 8A, 50Hz)•A 50? (5A) resistor with anunknown inductance (available on dc switchboard)

•A voltmeter (1000V) and an ammeter (5A), both available on theac switchboard•Voltage and current transducers (available on the dcside of the main switchboard, but can be used to measure theinstantaneous values)