explain the role of both types of transformers in getting electric energy from an electric power plant (coal-fired, natural gas or nuclear) to our homes.
A step UP transformer is used to boost the VOLTAGE, as by doing so the CURRENT is reduced by the same factor, e.g. boost voltage by 100 x, reduces current to 1/100th. By reducing current, power losses due to the transmission line RESISTANCE is very significantly reduced, especially in long run distances between consumers and the generating plant. The formula I^2*R is power, and the square of (say) 100A is 10,000, whereas if the current were reduced by 100 fold as above, the current becomes 1A., so you can see the difference! 1^2 1, versus 100^2 10,000. But the voltage is too high for consumer use, So a step DOWN transformer is used to change the voltage down to the required domestic voltage. The ratio of this transformer can easily be adjusted to allow for the minute power lost in the high voltage lines. The overall effect is very much less power lost in heating the connecting wires in the transmission lines, so much more power available to consumers.
The voltage is transformed up to thousands of volts and low current for minimum heat loss in the wires. Then down to low voltage at high current to the neighbor hood.
