A 735-kV line is used to carry energy over long distances since the higher the voltage on a line, the more electricity it can carry. Such high-voltage lines run all the way down from the Baie-James region.

**Voltage transformers** lower the voltage so protection and control units can measure it. Voltage is the difference in electrical level (or potential) between two points. It's expressed in volts (V). A 735-kV line is thus at a very high voltage—many thousands of volts. Potential transformers are generally located where lines enter and exit the substation.

Like potential transformers, **current transformers** lower the amount of current so that protection and control units can measure it. Current is comparable to flow. It is alternating or direct and expressed in amperes or amps (A).