Task 5

(1)

Scenario

A company manufacturing extra low voltage fluorescent fittings is looking at improving the

adaptability and efficiency of their product.

The circuit shown below is for a typical ELV fluorescent lamp fitting, which operates at

24V 50Hz. Assuming the fluorescent tube has an operating resistance of 300 and an ideal

transformer, determine:

a. the current supplied by the source

b. the impedance seen at the supply (HV side)

c. the power dissipated by the tube

d. the operating power factor of the fitting

(ii) If the capacitor is now removed from the above circuit and is placed in parallel with the

secondary of the transformer, recalculate a to d in question (i).

Using a scale phasor diagram prove your answer to part (ii) d. and evaluate each

technique for determining circuit power factor.

(iii) Write a brief report of your findings in parts (i) to (ii) which will be submitted to the

company director (200 words).

(iv) After reading the report in part (iv) the director asks why the fitting cannot simply be

connected to a dc supply and the choke replaced by a resistor. In a written reply to this,

explain the operating principle of the transformer in the above circuit and the operating

principle and purpose of the choke when used in conjunction with a starter switch in a

fluorescent switch start circuit, with particular reference to electro-magnetic induction and

induced emfs.