1.
1. What is armoured cable? Cable with steel barriers wound over for protection from
mechanical damage.
2. Name three types of armours – steel wire braid, steel wire (SWA), steel tape (STA).
3. State Ohm’s law. V=IR, R=V/I.
4. Example of Ohm’s law. Light bulb.
5. What purpose Transformer is used for? Converting high voltage to low voltage (and vice
versa).

2.
6. Name some parts of Transformer. Isolator, Fuse, Lightning Arrestor, Oil Circuit Breaker (OCB) etc.
7. How is Transformer rating calculated? Based on load voltage and load current. For load voltage 120V 1Ph
and load current 50A, rating is 120 x 50 / 1000 (for single phase) which is 6KVA and for load voltage 240V
3Ph and load current 60A, 240 x 60 x √3 / 1000 (for three phase) which is 24.94 rounded up 25KVA. For
final sizing, a 20% extra is considered in calculation.

3.
8. What are standard sizes of Transformers?
-Standard KVA sizes for singe-phase transformers:
1, 1.5, 2, 3, 5, 7.5, 10, 15, 25, 37.5, 50, 75, 100, 167, 200, 250 and 333 (KVA)
-Standard sizes for three-phase transformers:
3, 6, 9, 15, 30, 45, 75, 112.5, 150, 225, 300, 500, 750 and 1,000 (KVA)