MAIN ELECTRIC SUPPLY STATION/SUBSTATION.

The main electric supply station/substation is the installation/utility interface point where further

transmission, distribution and utilization of electrical power, the monitoring and control of such

power or equipment and the protection of electrical equipment or systems becomes the sole responsibility

of the Government. Electrical power will be supplied by the same utility over one or more

incoming power lines that are metered by the use of items of equipment provided and maintained by

the utility. The design of new stations, or modifications to existing stations, must be coordinated

with the supplying utility and with any other suppliers or users of power supplied through the station. Such coordination should be accomplished by the responsible field operating agency, or a designer employed to accomplish the coordination and design of new electrical facilities. Complete coordination should be performed to ensure proper protection for electrical equipment and systems, to obtain the required degree of availability, reliability and maintainability, and to achieve the most cost effective billing, construction, operation and

maintenance costs during a station life of 25 years or less.

a.     Billing.

Since electric utility rates and rate structures vary from state to state and with the user’s energy and demand requirements, the serving utility will be contacted at an early point in the planning process to assist in determining probable electric rates and charges. In dealing with a large user, the serving utility often has

flexibility to negotiate a special rate. Where the new installation will be large, this aspect of utility charges will be vigorously pursued. A typical facility monthly electric bill will contain the following types of charges:

(1)   Energy charge based upon kilowatt-hours (kWH) used. The energy charge may be based on time-of-day usage (the “on-peak” rate often being higher during the 12 daytime hours of the normal five day work week than during the “off-peak” remaining time). Additionally, many utilities charge more for energy used during the “peakseason” summer months than for energy used during the “off-peak-season” fall, winter, and spring months.

(2)   Demand charge based upon the maximum kilowatts (kW) used. This charge is based on the maximum rate at which energy is used (kW demand) for a period of 15, 30, or 60 consecutive minutes (depending on the utility) during “onpeak” hours. Alternately, demand charges may be based partially on “on-peak” demand and partially on “off-peak” demand.

(3)   Power factor charge.

This charge may be based upon the facility power factor recorded during the maximum demand period   or upon total kWH and total kilovar-hours (kVARH). Often the power factor adjustment is a  multiplication factor

applied to the kWH and/or the kW demand. Some utilities will charge a penalty for low power factor     (below the 0.85 to 0.90 range) and offer a credit for a high power factor.

(4)   Fuel adjustment charge. This charge is a surcharge or a credit to the energy charge and is based upon the price paid by the utility for fuel for its generating stations.

(5) Facility charge. This is a fixed monthly charge which is based upon the sophistication of

the utility’s revenue metering equipment, ownership (utility or user) of the main supply station(s), and number of points metered.

b.     Revenue metering

A utility provides a totalizing watthour meter equipped with a demand register that is supplied by highly accurate instrument transformers. A demand type of varhour meter will be provided by the utility when the rate schedule includes a power factor charge. Utility meters cannot be used for any other purpose without prior approval by the utility. Revenue metering equipment will be provided by the Government only when required by the utility, and will comply with the utility requirements.

c.      Energy conservation requirements.

Reduction in energy usage is a national goal. Several programs have been implemented to effect energy

reduction, including utility monitoring and control systems (UMCS). Provide for future UMCS monitoring by installing the following equipment during substation construction: potential and current transformers, watt and VAR transducers, circuit breakers with auxiliary contacts, and watt-hour meters with pulse initiators for interface to UMCS equipment. See TM 5-815-2 for additional information.

d.     Power factor correction.

 Provisions for future installation of shunt capacitor equipment will not be initially provided in the main electric supply station. Power factor correction capacitors should be provided at or near the terminals of inductive devices to minimize energy losses in the electrical supply systems.

e.     Protection.

 The ratings and settings of overcurrent protective devices will be selected to afford optimum protection of the electrical equipment and systems. Utilities will have additional requirements when any electric power generating units on the site are to be paralleled with the utility. The utility may also have special requirements for

protection and coordination of its system on a nonparalleled installation. Some utilities have carrier relaying schemes, and may require the Government to provide line relays, or companion type relays, power supplies and housing for carrier relaying equipment. Auxiliary equipment such as batteries and chargers, annunciator panels, and supervisory or telemetering equipment may need to be provided or housed or supplied. Written utility requirements and approval of the system proposed will be obtained in the criteria development or early design stages of a project.

f.       Short-circuit capacity.

The available shortcircuit capacity of the electrical power sources influences the design of circuit-controlling and protective devices located in the station, and those provided in the distribution system. The serving

utility’s future planned short-circuit current should be considered in the design as well as the short-circuit current available at the time of design.

g.     Coordination study.

 A short-circuit study and a protective devices coordination study will be performed for each new or modified station or substation. The studies will be performed at a date early enough to ensure that proper equipment can

be specified and proper protection provided. Refer to IEEE Std 242 and TM 5-811-14 for guidance regarding coordinated power system protection. A short-circuit and protective devices coordination study will be prepared to be used as a basis for equipment ratings and protective devices settings, and, for large projects, will include settings for 20, 40, 60, 80, and 100 percent load using typical devices.