Glossary of electric industry, energy & cooperative terms

D

Damper
A movable plate for regulating the draft in a fireplace. Should be closed except when the fireplace is being sued.

Deciduous Trees
Trees that shed at a particular season or stage of growth.

Degree Day
A unit measuring the extent to which the average daily temperature varies from a standard reverence temperature. The difference in degrees between the reference temperature and the average temperature (high plus low divided by two) for a particular day gives the number of degree days experienced. If a day’s average temperature exceeds the reference temperature, the deviation is expressed in units of cooling degree days; if its average temperature is lass than the reference temperature, the deviation is expressed in units known as heating degree days.

Demand
The amount of electricity a customer or class requires from the system at a certain point in time. Demand is often measured in kilowatts.

Demand Bid
A bid into the power exchange indicating a quantity of energy or an ancillary service that an eligible customer is willing to purchase and, if relevant, the maximum price that the customer is willing to pay.

Demand Interval
Any period of time during which the flow of electricity is averaged in order to determine average demand.

Demand Meter
A meter for electricity that also measures and records the maximum demand over a specified periods of time.

Demand Rate
Charge based on a consumer’s maximum kilowatt use; combines a charge for the peak demand placed on the system plus the charge for electricity used during the billing period.

Demand-Side Management
The planning, implementation, and monitoring of utility activities designed to encourage consumers to modify patterns of electricity usage, including the timing and level of electricity demand. It refers only to energy and load-shape modifying activities that are undertaken in response to utility-administered programs. It does not refer to energy and load-shape changes arising from the normal operation of the marketplace or from government-mandated energy-efficiency standards. Demand-Side Management (DSM) covers the complete range of load-shape objectives, including strategic conservation and load management, as well as strategic load growth.

Depreciation
An accounting mechanism in which the cost of a fixed asset (such as a building or apiece of machinery) is allocated to the periods of the asset’s useful life, or the periods in which services are received from it. Depreciation is a recognized cost of doing business and is recorded as an operating expense on the utility’s income statement. A utility’s physical assets do not last indefinitely. Although there are some exceptions, such as land or natural gas or coal reserves, most assets deteriorate over time. Equipment can physically break down from normal use; it also can become damaged, obsolete or inadequate to perform its functions. Depreciation, in a sense, represents this decline in value.

Deregulation
The elimination of regulation from a previously regulated industry or sector of an industry.

DHTML
Dynamic HTML. A technology designed to add richness, interactivity, and graphical interest to Web pages by providing those pages with the ability to change and update themselves dynamically, in response to user actions.

Direct Access
The ability of a retail customer to purchase commodity electricity directly from the wholesale market rather than through a local distribution utility.

Direct Current (DC)
Electric current that flows in a single direction. Direct current voltage stays at a uniform magnitude. The properties of direct current (DC) contrast with those of alternating current (AC) in the AC changes its direction at regular intervals and flows and pulses with voltage magnitude, reach a peak and subsiding before the next pulse. DC electricity is more effective than AC for high voltage, long-distance transmission. This is because it suffers only minor transmission losses and uses transmission lines that cost less than those used for AC transmission. However, the process of converting DC to AC, so that voltage can be transformed up or down, is expensive and energy-consuming. Therefore, DC voltage is primarily used for transmitting electricity over very long distances. The use of DC for long-distance transmission only became feasible with development of solid state electronics and, in turn, high-power rectifiers in the late 1950’s. These devices allow for effective conversion between DC and AC.

Dispatching
The operating control of an electric utility’s system. Dispatching involves monitoring and controlling the moment-to-moment changes in the electric generation and transmission system. Dispatchers also assign generator outputs as needed for economy and reliability, control maintenance and switching operations, and schedule energy transactions with other utilities.

Distillate Fuel Oil
A general classification for one of the petroleum fractions produced in conventional distillation operations. It is used primarily for space heating, on-and-off-highway diesel engine fuel (including railroad engine fuel and fuel for agriculture machinery), and electric power generation. Included are Fuel Oils No. 1, No. 2, and No. 4; and Diesel Fuels No. 1, No. 2, and No. 4.

Distribution
The delivery of electricity to retail customers (including homes, businesses, etc.).

Distribution System
The substations, poles, transformers and lines that convey, or deliver, electricity from high-power transmission lines to the ultimate consumers.

Diversification
Expansion of a company’s business activities. For utilities, expansion could be either into regulated or non-regulated areas. Diversification can serve a number of goals. Utilities, for example, might expand the scope of their business activities into a non-regulated area to supplement the earnings of the regulated portion of the business. They could also diversify to provide adequate fuel resources, increase financial strength and improve cash flow. A 1984 Edison Electric Institute publication, Business Diversification Activities of Investor-Owned Electric Utilities, showed that 86 of 120 companies polled had diversified to some degree either into regulated or non-regulated activities.

Divestiture
The stripping off of one utility function from the others by selling (spinning-off) or in some other way changing the ownership of the assets related to that function. Stripping off is most commonly associated with spinning-off generation assets so they are no longer owned by the shareholders that own the transmission and distribution assets.

Domain Name
The text name corresponding to the IP address of a computer on the Internet. For example, www.secoenergy.com is a domain name.

Dormer
An opening in a sloping roof, the framing of which projects out to form a vertical wall suitable for windows or other openings.

Downspout
A pipe, usually of metal for carrying rainwater from roof gutters.

Dry Wall
Interior covering material, such as gypsum board or plywood, which is applied in large sheets or panels.

Duct
A tubular passage through which heated or cooled air flows.

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Page last updated: Friday, March 5, 2010