ELECTRICAL INSTALLATION. TEST 1 LEVELIII

ELECTRICAL INSTALLATION

LEVEL III

INSTRUCTION:

·         Attemp all questions.

·         Test duration 2HRS

·         Scientific calculator allowed.

1.       a) Define the term transformer.

b) A transformer with a 4:1 voltage ratio has a secondary voltage of 1440v. A 144Ω load is connected across the secondary. Calculate the secondary and primary currents.

2.       a) Distinguish between core type and shell-type transformer.

b) A 50KVA single phase transformer has a turns ratio of 2200/200. The primary winding is connected to a 2200v, 50HZ supply. Calculate: (i) The secondary voltage (ii) The primary and secondary current.

3.       (a) State the differences between an autotransformer and double wound transformer.

(b) The ideal autotransformer is used to step down 600v to 480v. The 480V output is to supply a 24KW resistive load. Determine:

                                                        I.            The load current.

                                                      II.            The input current

                                                    III.            The current between terminal 1 and 2

                                                    IV.            the current between terminal 3 and 2.

4.       a) State Ohm’s law in word and by symbol.

b) Three resistors having resistance of 4.8Ω, 8Ω and 12Ω all connected in parallel, are supplied from a 48V supply. Calculate the current through each resistor and the current taken from supply.

5.       Draw power circuit and control circuit of DOL