IEEE 946:2020 pdf free download – IEEE Recommended Practice for the Design of DC Power Systems for Stationary Applications
4. Organization of this recommended practice
Stationary dc power systems appear in many applications and industries.All have certain commonalities, whilesome have some unique requirements. It should be noted that these commonalities or unique requirements arederived from variance in environmental conditions, reliability expectations, and importance of application.That translates to specific feature requirements or technology differences (thyristor versus high-frequencyswitched mode chargers, or lead-acid versus Ni-Cd batteries) that can provide an engineering approach to theselection/design of dc power systems. For example, a substation charger can be used in a telecom applicationand vice versa as long as it can meet the requirements.
Describing every application is beyond the scope of this document, therefore the three dominant applicationsare generation, substations, and telecommunications. Large telecommunication carriers may have their owninternal dc power system standards that examine dc power systems and their requirements in detail.This isalso beyond the scope of this document, but is worthy of a mention.In this recommended practice, each sectionincludes subparagraphs reserved for these three applications when there are unique requirements. For otherindustrial applications, one can use the recommendations—-in part or as a whole— of one of the three dominantapplications. For example, substation application recommendations may be used, where applicable, for thedesign of an industrial process control dc power system. It is not the intent of this recommended practiceto exclude other industrial applications. Lead-acid and nickel-cadmium batteries are the types of batteriesprimarily used in these applications. Some other battery technologies may be used but are not fully addressedin this document.
5. Description and operation
DC power systems provide reliable power to critical loads.Examples of critical loads include auxiliarymotors, 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 oneor more distribution panels. If a battery isolation/protective device is used, refer to the battery protectionguidelines of IEEE Std 1375.Refer to simplified typical connection in Figure 1 for the line of demarcation thatlimits the application ofIEEE 946 versus IEEE1375.
The designer should consider a single system or multiplesystems based on the voltage, current, and redundancyrequirements of the components. For example, if a communication system requires 48 v dc input and the dcbus is 125 V dc, then consider whether the communication equipment would be either supplied by its ownbattery and charger or by a dc-dc converter fed from the main 125 V dc system.
A recommended practice is to create a diagram at the start of the design process showing the battery orbatteries, charger(s), dc panel(s), and all connected loads.Consideration should also be given for future growth.Redundant dc power systems may also be considered.Redundancy may provide flexibility for maintenance,testing, or replacement in the event of equipment failure or the need to upgrade in the future.The ability toconnect other dc power systems may also aid in maintenance activities.
Although not recommended,center-tapped battery designs have been utilized in special applications. In mostcascs, a center-tapped battery design should be considered as the least advantageous design, as it may resultin issues such as a more complicated ground fault detection, battery state of charge imbalance, cell voltageimbalance,load imbalance，improper autonomy,etc. Designing separate systems for different voltages isrecommended in licu of center tapped battery. See informative Annex H for more details on center tapped battery.When special loads such as inverters and dc-dce converters are connected to a dc power system, considerationsshould be made to understand their potential effect on the dc bus in terms of charger regulation, current andvoltage ripple, transient behavior, or other disruptive interactions.