Glossary of electric industry, energy & cooperative terms

T

Tap
An electric circuit with limited capacity extending from the main line feeder, usually supplying a small number of customers.

Thermostat
A device that automatically responds to temperature changes, and activates switches controlling heating and cooling equipment.

Three-phase Power
An electric circuit that consists of three separate currents delivered at one-third cycle intervals by means of a three-wire circuit; typically used to power large industrial motors that operate at 230 volts or higher.

Therm
100,000 Btu.

Time-Of-Use
A rate structure that prices electricity at different rates, reflecting the changes in the utility'’ cost of providing electricity at different times of the day or year. On any given day, the average, as well as the incremental, costs of generating electricity rise as the energy load increases. With time-of-use (TOU) rates, higher prices are charged during the time when the electric system experiences its peak demand and marginal (incremental) costs are highest. Typically, the peak demand occurs on the late afternoon or early evening.

TOU rates price electricity closer to the cost of providing service, sending "better" price signals to customers than non-TOU rates. These price signals encourage efficient consumption, conservation and shifting of load times of lower system demand. Since the need for additional utility generating capacity is driven by peak demand, and utilities must meet customers’ demand at all times, TOU rates become a form of load management. That is, they help to shift energy consumption from peak to off-peak periods, thus avoiding construction of additional generating facilities or purchase of power from other utilities.

To compensate for higher on-peak rates, lower off-peak rates are charged when utility system demand is the lowest. Off-peak hours are typically the very early hours of the morning. To further encourage shifting usage away from peak hours, partial-peak rates are sometimes created to reflect changes in costs between on-peak and off-peak periods.

TOU rates are not new; they have been used in Europe for decades. The peak-load and TOU tariffs of France and the United Kingdom were models for U.S. TOU rates. In France, the Green Tariff was established in 1958. It has five distinct periods: three during the winter and two during the summer. Different prices apply for both kilowatt-hours of energy and kilowatts of power throughout these time periods.

In the U.S., TOU rates began to gain considerable attention after the oil embargo of 1973. It created dramatic changes in the economy – particularly higher plant construction and fuel costs – and a heightened awareness of the need to conserve natural resources and produce and consume energy efficiently. In 1978, The Public Utility Regulatory Policies Act (PURPA) required state public utility commissions to consider TOU rates as a rate design alternative to traditional utility rates.

Ton (Air Conditioning)
A measure of the size or cooling capacity of an air conditioner. One ton is equal to 12,000 BTUs per hour and is the amount of cooling released from melting 1 ton of ice per day.

Transformer
An electromagnetic device that increases the voltage of electricity as it leaves the power plant so it can travel long distances or lowers the voltage of electricity for distribution. Not to be confused with line transformers that step-down voltage for delivery to individual customers.

Transmission
The process of transporting electric energy in bulk on a high-voltage power line from a source or sources of supply to a point of use within a utility system or to a point of interconnection with another utility system or power grid.

Transmission System (Electric)
An interconnected group of electric transmission lines and associated equipment for moving or transferring electric energy in bulk between points of supply and points at which it is transformed for delivery over the distribution system lines to consumers, or is delivered to other electric systems.

Transmitting Utility
This is a regulated entity which owns, and may construct and maintain, wires used to transmit wholesale power. It may or may not handle the power dispatch and coordination functions. It is regulated to provide non-discriminatory connections, comparable service, and cost recovery. According to EPACT, this includes any electric utility, qualifying cogeneration facility, qualifying small power production facility, or Federal power marketing agency which owns or operates electric power transmission facilities which are used for the sale of electric energy at wholesale.

Tread
The horizontal board in a stairway on which the foot is placed.

Trim
The finish materials in a building, such as moldings, applied around openings or at the floor and ceiling of rooms.

Truss
A frame or jointed structure designed to act as a beam of long span, while each member is usually subjected to longitudinal stress only, either tension or compression.

Turbine
A machine that converts the energy of a stream of water, compressed or hot gas, steam or wind into the mechanical energy of rotation. This energy is then used to turn an electric generator or other device. Water drives a hydraulic turbines; steam drives a steam turbine; highly compressed, very hot air drives a gas turbine and wind drives a wind turbine or windmill. Water and wind turbines have a simple design; a stream of air or water turns one set of turbine blades. Multiple sets of blades are used for other types of turbines, such as steam and compressed or hot gases. One set of blades remains fixed, funneling the steam or gas stream into other movable blades. The blades on both turbine types are connected to a shaft. As the blades turn, they cause the shaft to rotate. The shaft is then connected to a generator, which produces electricity, or to other devices to form mechanical energy for uses such as pumping water or compressing gas.

Turbine Wheel
A vent similar to a roof louver, but when the wind blows the turbine spins to draw hot air and moisture out of the attic.

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Page last updated: Monday, October 24, 2011