Medium and large-sized facilities commonly use switchboards to safely distribute power to transformers, panelboards, control equipment, and, ultimately, to system loads.
Substations and switchgear in an electrical system perform the functions of voltage transformation, system protection, power factor correction metering, and circuit switching. Electrical power apparatus, such as transformers, regulators, air switches, circuit breakers, capacitors, and lightning arresters comprise the components necessary to perform these functions.
Basic Components
- Frame – The frame of the switchboard houses and supports the other components.
- Bus – Metal bars mounted inside the switchboard to conduct power to the switchboard’s devices. Phase arrangement per NEMA is ABC left to right, and top to bottom.
- Instrumentation – This instrumentation often includes one or more meters designed to accept signals from sensors and other equipment and display representative values for power monitoring and management.
- Overcurrent Protective Devices – This includes overcurrent protective devices, such as circuit breakers and disconnect switches. These devices are mounted to the bus bars using straps connected to the line side of the devices. Draw-out breakers are designed to mount on extension rails and are equipped with racking mechanisms for easy interchangeability.
- Service Section – Also referred to as the main section, and one or more distribution sections. The service section can be fed directly from the utility transformer. In addition to the main disconnect, the service section usually contains utility or customer metering provisions.
- Distribution Section – The distribution section receives power from the service section and distributes it to various downstream loads.
Basic Maintenance
- General Visual and Mechanical Inspection of Switchgear
- Moisture and Corona Inspections
- Wiring and Bolted Connections
- General Wiring Checks
- Moving Parts and Interlocks
- Lubrication
- Insulating Barriers
- Electrical Tests: Insulation resistance/overpotential, Connection Resistance
- Ground Resistance
- Circuit Breakers and Instrumentation
