A switchgear is used to manage an electrical power-supply system. Specifically, the switchgear disables circuit breakers and other working components to make an electrical system safe for a technician to manually analyze. The switchgear isn't a single component, but a collection of switches that control a fusebox.
A technician cannot merely disconnect an electrical system that uses a lot of power. The switchgear makes the system safe for handling by de-energizing the system and allowing excess energy to go to the ground. The collection of power-switching devices available are also used to regulate and control the system without turning it off.