Understand the transformer or transformer should have a side and the secondary side of the concept, traditionally also called strong and weak.

Equipment refers to equipment used for power generation and transmission of electricity directly, such as generators, transformers, circuit breakers, switch, these devices are in direct contact with high voltage electricity.

Secondary equipment refers to equipment monitoring, measurement, control and protection equipment, for example, voltage meter, Watt-hour meters, data acquisition and processing equipment, protection equipment, computers, and so on, the equipment and high-voltage electricity is isolated, isolated through sensors and other equipment