Glossary of Electric Utility Industry Terms
DC – See Direct Current
Delta – There are two related meanings for delta. One meaning is a method of connecting transformers in which the windings form a complete loop. The second meaning is a distribution system in which single-phase transformers are connected phase-to-phase. An example of a delta-connected transformer would be a transformer connected to A phase and B phase. (EUSO-photo, EDS, CAEDS, IESO-photo)
Delta Bank – Three transformers connected such that the transformers’ windings form a complete loop. . (EUSO-photo, EDS, CAEDS, IESO-photo)
Demand – Power being consumed by a customer. Demand can be measured in watts or in kiloVolt Amperes. (EUSO)
Demand Charge – A financial charge based on the average power consumed in a period of time. The most commonly used period of time is 15 minutes. The next most common is 30 minutes. (EUSO,IESO)
Diode – A solid state device used to change alternating current to direct current. (EUSO, CAEDS, IESO)
Direct Current – Electrons flow in one direction without ever changing directions. It is the most efficient method for the transmission and distribution of power because it has no inductive losses. It is not used, except for very long transmission lines, due to the inability to change voltages. (EUSO-photo, EDS, CAEDS, IESO, System Operator classes)
Disconnect – An abbreviated term for a disconnect switch.
Disconnect Switch – A device that is used to disconnect a device, or to disconnect two systems. Some disconnect switches are designed to break up to full load current. These are called load-break switches. Other switches are designed to break no current; these are called no-load-break switches.
Distributed Generation – Generating plants that are located at or near the customers being served. These plants do require the use of a transmission line.
Doble ®Test – An insulation test named after the company, Doble Corporation, that lead the research in test-equipment development and in interpreting the findings. It is a really a power-factor test that uses the displacement of the current sine wave from the voltage sine wave in determining the quality of insulation. With a power factor test, the lower the reading, the better the quality of insulation. (EDS)
Duct – Tubular or rectangular enclosures that carry rigid conductor called bus. The bus is supported on insulators so that the bus does not touch the duct. It is a shorter version of the term bus duct. (EUSO, IESO)
Duct Work - Tubular or rectangular enclosures that carry rigid conductor called bus. The bus is supported on insulators so that the bus does not touch the duct. (EUSO, IESO)