BPA Definitions - D

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daily load shaping

See load shaping.

dam

A structure built to provide flood control, irrigation, and/or power generation. Some have storage reservoirs. Also see reservoir.

multipurpose dam

A dam that serves more than one purpose, such as Grand Coulee Dam. Purposes can be flood control, navigation, irrigation, power generation, recreation, and fish and wildlife.

run-of-river dam

A dam with limited storage capacity, such as Bonneville Dam. Hydroelectric generating plants at these dams (run-of-river plants) operate based only on available streamflow and some short-term storage (hourly, daily, or weekly).

storage dam

A dam with a reservoir that serves to store water from runoff for later, controlled release, such as Libby Dam.

dam passage

The percentage of fish that get from one side of a dam to the other alive.

data switch

A device to connect a computer terminal to different computer systems through a single physical connection.

daylighting

The use of natural sunlight as a replacement for some or all of the indoor electric lighting in buildings.

dB

See decibel.

DC

See direct current.

dead-end tower

See tower.

dead storage

See storage

debt service

1) The principal and interest on outstanding bonds. 2) The retirement of bonds according to schedules in each bond issue, plus any reserve and contingency requirements reduced by investment income on various reserve accounts. 3) Sometimes used to refer to principal and interest on unpaid appropriations.

debt service coverage

1) In general, a ratio that measures the adequacy of a business’s cash flow to cover debt service costs, both principal and interest. Used to assess the ability to generate sufficient cash flow to make payments due on outstanding debt. 2) At BPA, sometimes used to measure the level of assurance BPA has that it can meet in particular the planned payments to the U.S. Treasury for Federal investment in regional hydroelectric projects or can meet third party financial obligations.

decibel (dB)

1) A unit used to describe the strength or intensity of wave-propagated phenomena such as sound or transmitted signals. Technically, a logarithmic scale so used. 2) One dB equals the least sound level detectable by the human ear, while 70 dB is equivalent to busy traffic and 150 dB is equal to a nearby jet taking off.

declining block rates

A rate structure that prices successive blocks of kilowatthour use or kilowatt demand at decreasing per-unit prices; reverse of inverted rates.

decommission

In terms of a resource, to remove from service permanently.

decremental cost

See cost.

dedicated circuit

See circuit.

dedicated resource

A generating resource owned by a BPA customer and used to serve its firm load; these resources are declared for a rolling seven-year period in utility power sales contracts with BPA.

deeming utility

A utility that has elected to exercise its right under section 10 of the Residential Purchase and Sale Agreement that sets its average system cost equal to the priority firm (PF) exchange rate when its average system cost would otherwise fall below the PF exchange rate; a utility thereby avoids making exchange program payments to BPA.

deenergized

Dead. Refers to current-carrying parts that can be energized but are at present free from any electrical voltage. Said of a transmission line or piece of equipment when disconnecting switches are open and the line or equipment is isolated from the system.

deferrable resource

See discretionary resource.

deferral

1) The non-payment of Federal interest in the year it is due. 2) In BPA financial planning, refers to BPA not meeting annual U.S. Treasury payments in full.

deferred borrowing capability

The amount of capital expenditures that BPA has financed from revenues, which borrowing authority has been received and BPA can issue revenue bonds to the U.S. Treasury.

deficit utility

A utility that has fewer resources than it needs to meet its loads.

degree day

The number of degrees that the average outdoor temperature falls below or exceeds a base value (usually 18 degrees C, or 65 degrees F) in a given period of time. Considered a reasonably good index of heating and cooling requirements of buildings. One F degree day equals 0.556 C degree day.

cooling degree day (CDD)

Each degree the mean daily temperature is above the base value.

heating degree day (HDD)

Each degree the mean daily temperature is below the basic value.

delegated State

A State (or other governmental entity) that has applied for and received authority to administer, within its territory, its State regulatory program as the Federal program requires under a particular Federal statute.

delta connection

A connection of the windings of a three-phase transformer or three single-phase transformers making up a three-phase bank that are in series to form a closed path. Delta connections may also be used for three-phase shunt reactor banks, shunt capacitor banks, or generator windings.

demand

1) In a consumer context, the amount of electricity used. 2) In a public utility context, the rate at which electric energy is delivered to or by a system over any designated period. Expressed in kilowatts or megawatts, or in kilovoltamperes or megavoltamperes. 3) At BPA, the amount of electric energy, in kilowatts or megawatts, needed at any given time to meet a BPA customer’s or total BPA system load.

coincidental demand

Any demand that occurs simultaneously with any other demand. Also the sum of any set of coincident demands.

coincidental peak demand

The moment of system peak load, occurring when the sum of all meters is the highest, although some meters may be below their eventual peak.

integrated demand

The amount of energy delivered or used in one hour. The technical unit for integrated demand is kWh/h, often simplified to kW. See demand and maximum demand.

maximum demand

The greatest demand of a load occurring during a specified time period.

non-coincidental demand

The sum of the individual maximum demands regardless of time of occurrence within a specified period.

peak demand

The highest demand for power during a stated period of time.

demand factor

The ratio of the maximum demand of a system, or part of a system, to the total connected load of the system or part of the system under consideration.

demand forecast

See forecast.

demand meter

See meter.

demand-side management (DSM)

The strategies that focus on influencing when and how customers use electricity, with an emphasis on reducing or leveling load peaks, such as conservation measures and rate incentives for shifting peak loads, and energy storage schemes for reducing, redistributing, shifting, or shaping electrical loads.

demand-side resource

An energy resource such as conservation that is based on how electricity is used, not produced.

Department of Energy

See U.S. Department of Energy.

depreciation

1) In accounting and many ratemaking applications, a systematic means of recognizing or allocating the non-cash expense of a long-lived asset to a particular year. 2) In land acquisition usage, a loss of value of real estate caused by deterioration, obsolescence, or both and can affect personal or real property.

Detailed Fisheries Operating Plan

A Columbia River hydroelectric system operation manual prepared by fish and wildlife agencies and Indian tribes for fish passage related to the mainstem Columbia River.

dewater

1) In environmental usage, to remove water from a solution or suspension containing wastes in order to concentrate the wastes and dispose of them. 2) In engineering, to divert or remove water from a stream or river channel in order to construct or rebuild dams and related hydroelectric facilities; or the process of removing water from the scroll case of a hydro turbine so the generator can be used as a synchronous condenser to control system voltage.

dielectric

Insulating material, such as air or glass, that has a high resistance to the conductance of electric current; a non-conductor.

dielectric strength

The potential (voltage) gradient at which electric failure or breakdown occurs. The dielectric strength of a material is an indication of how good an insulator a material or gas is.

differential relay

See relay.

digital fault recorder

A device installed in a substation that records the waveform resulting from a fault on a transmission line, such as a fault caused by a break in the line.

digital-to-analog converter (D/A)

A device that converts digital data, in one of many digital formats, to analog.

dioxin

Any of a family of compounds known chemically as dibenzo-p-dioxins, created in breakdown of some chlorinated hydrocarbons. Tests on laboratory animals indicate that dioxins are some of the more toxic man-made chemicals known.

direct costs

See costs.

direct current (DC)

An electric current that flows in a single direction and whose magnitude does not vary, or varies only slowly.

direct-current pole

Ether the positive or negative conductors of a direct-current transmission system.

directional relay

See relay.

directly served customers

Direct-service industries and also Federal agencies that buy electricity directly from BPA for their own use.

direct-service industrial, or 7(c), rates

See rates.

direct-service industrial customers (DSIs)

Industrial customers, primarily aluminum smelters, that buy power directly from BPA at relatively high voltages.

disaggregation

A method for extracting individual utility loads from a regional forecast.

disclosure

Accurate and complete information, as provided in an official statement which is material to a securities transaction, must be made available to purchasers or prospective purchasers. This includes any information which a potential investor would be likely to consider important in making investment decisions.

disconnecting switch

A power system switch, manually or motor operated, used for changing connections in a circuit (open or close) or for isolating a circuit or piece of equipment from the source of power. Also called a disconnect switch.

discount rate

An interest rate that reflects the value of money over time. In comparing alternatives for a decision, a discount rate is applied to make different monetary stream flows equivalent, in terms of a present value or a levelized value.

nominal discount rate

An interest rate that includes inflation.

real discount rate

An interest rate adjusted to remove the effect of inflation.

discretionary costs

See costs.

discretionary resource

Deferrable resource. A resource whose acquisition can be deferred without cost or availability penalties.

dispatch center

A room located in a system control center (for transmission or distribution) that contains the display and control devices used by dispatchers to monitor and control the power system.

dispatcher

1) Individual at a control center who monitor and control a power system. 2) At BPA, dispatcher responsibilities include: operating the automatic generation control equipment to regulate the loading of the generators in the Federal power plants to help maintain scheduled system frequency and the scheduled power interchange with other utilities; issuing electrical clearances on the BPA system for safe maintenance and repair of equipment; isolating system trouble and dispatching of maintenance forces to repair facilities and restore service; maintaining transmission voltage schedules.

displace

To substitute one generating resource for another, such as to shut down a coal plant for a time and supply the load instead with nonfirm hydroelectric energy.

displacement

1) The shutdown of a high-cost generating facility when low-cost energy is available. 2) The substitution of less expensive energy (usually hydroelectric energy transmitted from the Pacific Northwest or Canada) for more expensive thermal energy produced in California. Such substitution means that thermal plants may reduce or shut down their production, saving money and often reducing air pollution.

disposal

Final placement or destruction of hazardous materials — toxic, radioactive, or other wastes; pesticides or other chemicals; and polluted soils —at Federally approved sites.

dissolved gas concentrations

Amount of chemicals normally occurring as gases, such as nitrogen and oxygen, that are held in solution in water, expressed in units such as milligrams of the gas per liter of liquid. Dissolved oxygen is vital to fish and other aquatic life.

distance relay

See relay.

distribution

The transport of electricity to ultimate use points, such as homes and businesses, from a source of generation or from one or more substations.

distribution costs

Costs faced by a utility for transporting power from a transmission substation to consumers.

District offices

BPA administrative centers, more numerous and more local in focus than Area offices. Field offices for BPA maintenance crews are also called District offices.

disturbance

Any occurrence that adversely affects normal power flow in a system, including a fault or loss of an interconnection carrying a large block of power.

disturbance monitor

An instrument used to produce a record of the time-varying components of the power system.

diversion dam

A dam built to turn water aside from its usual course, such as for irrigation. See dam.

diversity

1) In resource planning, refers to having a variety or mix of resources. 2) The differences among individual electric loads resulting from the fact that the maximum demands of consumers do not all occur at the same time (load diversity). See seasonal diversity.

DOE

See U.S. Department of Energy.

double circuit

See circuit.

double-circuit tower

See tower configurations.

double-string yoke

A triangular plate installed in a suspension or dead-end assembly to distribute the load to two strings of insulators.

downstream benefits

In a hydro system, the additional amount of power that can be generated at dams downstream from, and due to the construction of, a storage dam.

downstream migrant survival

The survival of a juvenile salmon or steelhead from the time it enters the mainstem Snake or Columbia River, until it gets below Bonneville Dam.

draft

The release of water from a storage reservoir, usually measured in feet of reservoir elevation.

draft tube

A device that carries the water away from the turbine runner to the tailrace in a hydropower system.

drawdown

The distance that the water surface of a reservoir is lowered from a given elevation as water is released for power generation, flood control, irrigation, or other use. Also refers to the act of lowering reservoir levels.

dry scrubber

See scrubber.

DSI

Direct-service industry. See direct-service industrial customers.

DSM

See demand-side management.

ducts

1) Tubes through which heated or cooled air flows. 2) Enclosures through which cabling in a substation passes.

dynamic braking resistor (resistance brake)

See resistor.

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