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Transformers What? • Power stations produce high voltage electricity about 25kV • A transformer will ‘step up’ this voltage to about 400kV before the electricity is put through over head cables Why? • When a current passes through a wire, friction causes the wire to get hot. The more current passing through the wire the hotter it gets. • A transformer that has ‘stepped up’ the voltage will also have ‘stepped down’ the current. How? • Example. Drax power station produces a given amount of energy. Lets estimate that every second Drax is pumping out 4000,000,000J of energy • Energy can not be created or destroyed • All the energy that goes into a transformer should come out (less any losses) V P = 450 000 000W V = 25 000V Using P = IV I = P/V I = 450000000 250000 I = 1800A Transformers What is a transformer? A device used to increase or decrease voltage Where are transformers used? On the National Grid, household appliances What do we call a transformer that increases voltage? STEP-UP Transformer What do we call a transformer that decreases voltage? STEP-DOWN Transformer How electricity gets to your home…. Power station Step-up transformer National Grid Step-down transformer Homes, businesses and factories etc Why bother with transformers? riction in When electrical current flows you get f_____ eat the conductor. With friction you always get h___. nergy You get more wasted This heat is wasted e____. oltages than high voltages. So the energy at low v______ electricity is increased in voltage before it is ational G__. rid In this way less transferred to the N_____ energy is lost. Then, when it gets to your home, a own school or a factory, the voltage is stepped d___. Step-down More/less turns on the primary coil than the secondary coil. Primary Secondary Step-up More/less turns on the primary coil than the secondary coil. Primary Secondary Transformer calculations The size of the output voltage depends upon the ratio of the turns on the primary and secondary coils. Guess what? There’s a formula (it is Physics after all!) - V – voltage V1 = N1 V2 = N2 N - number of turns Transformer Question 1 A transformer has 200 turns on its primary coil and 50 turns on its secondary coil. The input voltage is 920V. a) Is is a step-up or step-down transformer? Step-down a) What is the output voltage? 230V Transformer Question 2 A transformer has 100 turns on its primary coil. It has an input voltage of 35V and an output voltage of 175V. a) Is is a step-up or step-down transformer? Step-up a) How many turns are on the secondary coil? 500 turns