Sales
The amount of kilowatthours sold in a given period of time; usually grouped by classes of service, such as residential, commercial, industrial, and other. Other sales include public street and highway lighting, other sales to public authorities and railways, and interdepartmental sales. 

Sales for Resale
Energy supplied to other electric utilities, cooperatives, municipalities, and Federal and State electric agencies for resale to ultimate consumers. 

Scheduled Outage
The shutdown of a generating unit, transmission line, or other facility, for inspection or maintenance, in accordance with an advance schedule. 

Short Ton: A unit of weight equal to 2,000 pounds.

Spinning Reserve
That reserve generating capacity running at a zero load and synchronized to the electric system. 

Spot Purchases
A single shipment of fuel or volumes of fuel, purchased for delivery within 1 year. Spot purchases are often made by a user to fulfill a certain portion of energy requirements, to meet unanticipated energy needs, or to take advantage of low-fuel prices. 

Stability
The property of a system or element by virtue of which its output will ultimately attain a steady state. The amount of power that can be transferred from one machine to another following a disturbance. The stability of a power system is its ability to develop restoring forces equal to or greater than the disturbing forces so as to maintain a state of equilibrium. 

Standby Facility
A facility that supports a utility system and is generally running under no-load. It is available to replace or supplement a facility normally in service. 

Standby Service
Support service that is available, as needed, to supplement a consumer, a utility system, or to another utility if a schedule or an agreement authorizes the transaction. The service is not regularly used. 

Steam-Electric Plant (Conventional)
A plant in which the prime mover is a steam turbine. The steam used to drive the turbine is produced in a boiler where fossil fuels are burned. 

Stocks
A supply of fuel accumulated for future use. This includes coal and fuel oil stocks at the plant site, in coal cars, tanks, or barges at the plant site, or at separate storage sites. 

Subbituminous Coal
Subbituminous coal, or black lignite, is dull black and generally contains 20 to 30 percent moisture. The heat content of subbituminous coal ranges from 16 to 24 million Btu per ton as received and averages about 18 million Btu per ton. Sub bituminous coal, mined in the western coal fields, is used for generating electricity and space heating. 

Substation
Facility equipment that switches, changes, or regulates electric voltage. 

Sulfur
One of the elements present in varying quantities in coal which contributes to environmental degradation when coal is burned. In terms of sulfur content by weight, coal is generally classified as low (less than or equal to 1 percent), medium (greater than 1 percent andless than or equal to 3 percent), and high (greater than 3 percent). Sulfur content is measured as a percent by weight of coal on an "as received" or a "dry" (moisture-free, usually part of a laboratory analysis) basis. 

Switching Station
Facility equipment used to tie together two or more electric circuits through switches. The switches are selectively arranged to permit a circuit to be disconnected, or to change the electric connection between the circuits. 

System (Electric)
Physically connected generation, transmission, and distribution facilities operated as an integrated unit under one central management, or operating supervision.