IEEE 946-2020 pdf download
IEEE 946-2020 pdf download.IEEE Recommended Practice for the Design of DC Power Systems for Stationary Applications.
Once the voltage limits and design parameters are established, the size of the battery (number of cells and capacity) can be established as outlined in applicable best practices or standards, e.g., IEEE Std 485 and IEEE Std 1115. It may be useful to size the battery such that the design duty cycle can be met with a reduced number of cells (N—i, N—2).
When determining system voltage in facilities with long cable runs, voltage drop should be considered. In order to evaluate the voltage drop across a cable, Ohm’s law shall be applied using the maximum current times the cable resistance provided by the manufacturer.
Legacy equipment or available equipment may constrain the choice of dc voltages.
Considerations should he taken for special operation conditions. For example, the capabilities of a black start or system restoration plan may require more than one attempt to restore the station ac service. This can be the case when the main electrical grid power is unavailable, and electrical power is provided by a backup generator.
5.2.2 Substation
Telecommunication loads in substations commonly used for telemetry and telecontrol generally operate at lower voltages (e.g., 24 V dc or —48 V dc) than the main substation dc system voltage (e.g., 125 V dc). A dedicated dc system might be needed to feed such loads. In cases where the power consumption is relatively low, it can be fed by the main substation’s dc system through dc-dc converters (e.g., 125 V dc to 24 V dc or —48 V converters). In such cases, considerations for additional needs, such as required incremental power, voltage regulation, and high-frequency noise should be made when designing the main substation’s dc system.
For additional guidance refer to IEEE Std 1818.
5.2.3 Telecommunication
Nominal system voltages for telecommunications dc power plants are most commonly 48 V dc, 24 V dc, and 12 V dc. Minimum and maximum telecommunication equipment operating voltage levels are defined in ANSI/ATIS-06003 15.2013 [B21 and ANSI/ATIS 06003 15.01.2015 [B3]. It is recommended that chargers be equipped with filtered outputs to the appropriate level as charted in NEMA PE 7 [B28].
6. Batteries
Stationary batteries are used to supply dc power to specified dc loads when the source of ac power to the battery charger has been disrupted or is insufficient to support the loads. Refer to appropriate IEEE standards or the battery manufacturer’s guidance for the proper selection of battery type to be used in the application. Correct battery selection is essential for reliability, useful life, cost, and maintenance planning. Factors such as operating temperature, duty cycle, battery life, and deep cycling should also be considered.
6.1 Number of battery strings
The number of battery strings in an independent dc power system should be considered at the design stage. More than one battery string for capacity or redundancy should be considered to help ensure compliance or reliability requirements.
6.1.1 Power generation
Some examples of how to improve the reliability and protection of critical loads include the following:
When loads are divided into two or more independent systems, each independent system should be provided with its own dc power system.
When maximum dc power requirements exceed the capacity of one battery string, the system designer should consider either of the following:
The use of parallel battery strings.
The use of two independent dc power systems, each with its own battery. In this case, selectivity and coordination of dc buses and protective devices should be implemented.
When modifications to the facility cause the dc power demand to exceed the existing dc power system’s capacity, the installation of a new independent system should be considered. Other alternatives include the following.
