IEEE 946-2020 pdf free download – IEEE Recommended Practce for the Design of DC Power Systems for Statonary Applicatons.
4. Organization of this recommended practice
Stationary dc power systems appear in many applications and industries. All have certain commonalities, while some have some unique requirements. It should be noted that these commonalities or unique requirements are derived from variance in environmental conditions, reliability expectations, and importance of application. That translates to specific feature requirements or technology differences (thyristor versus high-frequency switched mode chargers, or lead-acid versus Ni-Cd batteries) that can provide an engineering approach to the selection/design of dc power systems.
For example, a substation charger can be used in a telecom application and vice versa as long as it can meet the requirements. Describing every application is beyond the scope of this document, therefore the three dominant applications are generation, substations, and telecommunications. Large telecommunication carriers may have their own internal dc power system standards that examine dc power systems and their requirements in detail. This is also beyond the scope of this document, but is worthy of a mention. In this recommended practice, each section includes subparagraphs reserved for these three applications when there are unique requirements. For other industrial applications, one can use the recommendations—in part or as a whole—of one of the three dominant applications. For example, substation application recommendations may be used, where applicable, for the design of an industrial process control dc power system. It is not the intent of this recommended practice to exclude other industrial applications. Lead-acid and nickel-cadmium batteries are the types of batteries primarily used in these applications. Some other battery technologies may be used but are not fully addressed in this document.
5. Description and operation DC power systems provide reliable power to critical loads. Examples of critical loads include auxiliary motors, circuit breakers and switchgear, relays, solenoids, SCADA, telecommunications equipment, inverters, emergency lighting equipment, fire suppression equipment, etc.
5.1 General A dc system normally consists of one or more battery strings, one or more battery chargers/rectifiers and one or more distribution panels. If a battery isolation/protective device is used, refer to the battery protection guidelines of IEEE Std 1375. Refer to simplified typical connection in Figure 1 for the line of demarcation that limits the application of IEEE 946 versus IEEE 1375.
In normal operation, the battery and battery charging system are both connected to the loads through a common bus or via a dc distribution panel. Therefore, they operate as parallel sources. The battery charging system applies voltage and supplies current to the battery in order to maintain a full state of charge in the battery. The charger also generally supplies the continuous load and/or other loads as specifed. If the load exceeds the maximum current rating of the battery charging system, the battery charging system output voltage will drop, causing all current in excess of the battery charging system rating to be supplied by the battery. In the event of a failure of the ac power supply to the battery charger (in case the charging system consists of only one charger), a battery charger failure, or the battery charger being removed from service, the battery should supply all the power required by the load(s) for some specifed periods of time. This is commonly referred to as the “duty cycle.”
5.1.1 Power generation
Specific design guidance for dc power systems for nuclear generating plants are discussed fully in numerous design standards listed in Annex A.
5.1.2 Substation
For additional guidance refer to IEEE Std 1818. 5.1.3 Telecommunications Telecommunication installations require dc power for almost all equipment, as only a small percentage of telecommunications equipment is ac-powered. Therefore, dc power systems are required for normal and backup powering of most telecommunications installations. Refer to Annex F for the specific considerations in telecommunication applications. Telecommunication loads in substations commonly used for telemetry and telecontrol generally operate at lower voltage (e.g., −48 V dc) than the main substation dc power system voltage (e.g., 125 V dc). A dedicated dc power system might be needed to feed such loads. In cases when the power consumption is relatively low, they can be fed by the substation dc power system through dc-dc converters (e.g., 125 V dc to 48 V dc converters).
5.2 System design considerations In addition to the load’s requirements, the design should accommodate any regulatory agency requirements, safety, or other requirements. The design should also address factors such as reliability, design philosophy, maintenance, testing, ventilation, floor and wall loading, and space limitations, etc.IEEE 946 pdf download.