A generating station can have direct-current equipment in addition to the systems used to produce and distribute alternating-current power. Batteries and charging equipment are part of the direct-current arrangements documented for some facilities. The details depend on the station and its equipment.
An example from Carters Dam
The U.S. Army Corps of Engineers' pertinent-data document for Carters Dam and Reregulation Dam describes a powerhouse with generating units and pump-turbine units. In its direct-current system section, the document lists a station battery and two static chargers for that battery. It separately lists a switchyard battery and a charger for the switchyard battery.
That distinction is useful when reading facility records: the station and switchyard entries refer to separately identified equipment in this document. The listing does not by itself show their connections, the loads supplied by each battery or how the equipment operates during a particular outage. It should not be used as a wiring diagram or as evidence of the present configuration.
Battery and charging equipment in context
A battery stores electrical energy, while a charger supplies charging power to a battery. The Carters document identifies the battery and charger equipment for its station and switchyard, but does not describe a complete charging or transfer sequence. Other installations need their own design and equipment documentation to establish those details.
The same Carters document separately describes a station service system with normal and emergency supplies. Its station-service listing and its direct-current battery listing are different sections. The document does not establish the connections between every item in those sections.
Why direct-current supplies matter to protection equipment
Protective devices can depend on an auxiliary supply. For example, the Siemens 7SR242 transformer protection relay manual describes an auxiliary supply for that model and an indication when its DC supply is absent. This is an example of a specific device, not evidence that the relay is installed at Carters Dam or that all station loads use the same supply.
A station's drawings, equipment manuals and operating documentation are needed to identify its actual DC loads and arrangements. The Carters example illustrates one documented set of equipment; it does not prescribe battery capacity, charger settings or a standard arrangement for other generating stations.
Sources
The facility example comes from the Carters Dam and Reregulation Dam pertinent-data document, especially PDF pages 4–8. The device example comes from the Siemens 7SR242 technical manual, PDF pages 27 and 32.