Self Test



1.      Complete the sentences:


The National _____ is a network of high voltage transmission lines that connect _________ _______ with substations around the country.  The electricity is generated at __________ V, 1/3-phase.  The electricity is stepped up using __________ transformers to _____ voltage.  This means that the ________ is lower, so less energy is wasted.


3 sets of cables hang from the transmission towers, also called ___________.  The currents and voltages are ___________, so that the current in the neutral wire is very small/big.  At the sub-station, the voltage is stepped up/down by a transformer.  Then _________ voltage cables connect the substation to factories and homes.


2.      Draw a circuit diagram to show the idea of a star connection.



3.      Draw a circuit diagram to show the idea of a delta connection.



4.      Sketch a graph and a phasor diagram to show the idea of 3-phase electricity.



5.      Explain why a 415 V 3-phase supply to a small factory unit shares the same cables as the homes around it.