IEEE Std 3001.2-2017 pdf download – IEEE Recommended Practice for Evaluating the Electrical Service Requirements of Industrial and Commercial Power Systems.
4.3 Service availability 4.3.1 Service voltage The service voltage selected and its characteristics for primary or secondary service are based on the utility’s distribution standards and the voltage grids in the specific area of the facility. The utility should be contacted to determine the available voltages based on the load to be served and, in some cases, the geographic location of the load. The designer may become aware of service voltages provided to customers in the service area that are no longer available. Such services continue to be offered only to existing facilities and are not typically offered to new facilities. Service is usually available at the utilization voltages, such as 240 V delta (3-phase/3-wire), 120/240 V high- leg delta (3-phase/4-wire), 208Y/120 V, 480Y/277 V, or 600Y/347 V. Utilities may have kilowatt demand limitations for each specific voltage. When the facility’s load becomes too large to be supplied at the utilization voltage, due to excessive cost or excessive voltage drop, the facility should be supplied at a distribution voltage, typically, but not limited to, 4.16 kV, 12.47 kV, 13.2 kV, 13.8 kV, 26 kV, or 34.5 kV. In the case of large facilities, it may also be economically feasible to connect to the utility transmission line system. A primary substation is used to step the voltage down from transmission line levels to medium-voltage levels. Refer to 8.6 and Clause 11.
4.3.3.3 Utility system design The reliability of utility service depends on generating facilities, the exposure of the transmission system from the generating plant, and more importantly on the design of the utility’s distribution system. The reliability of the electric service also depends on the other loads on the same distribution system. For instance, a facility supplied at the same voltage level and on the same lines as a rock-crushing operation may incur power quality and reliability issues compared to a facility supplied from lines supplying a shopping mall or office building. Utility tariffs usually have requirements to limit the impact of customers with special loads on other customers. Distributed generation connected to the distribution system may increase reliability through the voltage support it provides. However, these sources cannot be counted upon to support adjacent loads in the event of a complete utility outage.