July 2, 2011

Electrical Engineering Terms - D

  • DA Bolt - A Double Arming Bolt.
  • Data Encryption Standard - See "DES".
  • Day ahead market - The forward market for the supply of electrical power at least 24 hours before delivery.
  • dB - See "decibel".
  • dBi - Decibels compared to an isotropic antenna. The higher the dBi, the stronger the antenna.
  • dBm - Decibels compared to one milliwatt. The higher the dBm, the higher the devices transmit or receive power.
  • DC - See "Direct Current".
  • DCF77 - A LF transmitter located at Mainflingen, Germany, broadcasting a time signal on a 77.5 kHz frequency.
  • De-energized - Free from any electrical connection to a source of potential difference and from electrical charge. A circuit is not truly de-energized until protective grounds have been installed.
  • De-ionization Time - The time required for dispersion of ionized air after a fault is cleared so that the arc will not re-strike on re-energization.
  • Dead Front - Generally refers to equipment that is connected without exposed conductor. Dead front equipment is normally connected with elbows.
  • Dead Time - The time between the fault arc being extinguished and the circuit breaker contacts re-mating.
  • decibel - A logarithmic mathematical ratio that indicates a devices electric or acoustic signal to that of another
  • Deep Discharge (Battery) - Withdrawal of 50% or more of the rated capacity of a cell or battery.
  • Delivery Traffic Indication Message - See "DTIM".
  • Delta - A three phase connection where each phase is connected in series with the next, separated by a phase rotation of 120 degrees.
  • Delta-Wye - Refers to a transformer that is connected Delta on the primary side and Wye on the secondary.
  • Dependent Time Measuring Relay - A measuring relay for which times depend, in a specified manner, on the value of the characteristic quantity.
  • Depth of Discharge - The portion of the nominal capacity from a cell or battery taken out during each discharge cycle, expressed in percent. Shallow Depth of Discharge is considered as 10% or less. Deep Discharge is considered 50% or more.
  • Derating - Calculations that reduce standard tabulated ratings based, generally based on ambient temperature or proximity to a heat source.
  • DES - Data Encryption Standard. DES is an encryption, method that uses an algorithm for private key encryption, in which the sender uses the same private key as the recipient uses to decode it.
  • Design Load - The actual, expected load or loads that a device or structure will support in service.
  • Design Test - Tests done to equipment to verify the design meets certain established charactistics or standards.
  • Device Control Point - Local keypad on device level to control the switchgear often combined with local or remote switch.
  • DFT - Discrete Fourier Transform.
  • DHCP - Domain Host Control Protocol. DHCP is a protocol used for dynamically assigning IP addresses to networked computers.
  • Dielectric - 1) Any electrical insulating medium between two conductors. 2) The medium used to provide electrical isolation or separation.
  • Dielectric Constant - A number that describes the dielectric strength of a material relative to a vacuum, which has a dielectric constant of one.
  • Dielectric Grease - A silicone based chemical compound used to seal and lubricate connections between medium voltage connectors such as cable termination elbows.
  • Dielectric Strength - The maximum voltage an insulation system can withstand before breakdown, expressed in volts per mil of insulation thickness.
  • Dielectric Test - A test that is used to verify an insulation system. A voltage is applied of a specific magnitude for a specific period of time.
  • Dielectric Withstand - The ability of insulating materials and spacing's to withstand specified overvoltage's for a specified time (one minute unless otherwise stated) without flashover or puncture.
  • Dielectric Withstand Voltage Test - The test to determine Dielectric Withstand.
  • Digital Signal Processing - A technique for the processing of digital signals by various filter algorithms to obtain some desired output.
  • Digital Signal Processor - A microprocessor optimized in hardware design and software instruction set for the processing of analog signals digitally. This is achieved by DFT and similar techniques.
  • Digital Subscriber Line - See "DSL".
  • Dip Tolerance (Lighting) - With regard to outdoor lighting, the percentage of instantaneous voltage variation from normal that is required to extinguish a light source.
  • Dipole Antenna - A type of antenna commonly used in wireless networking devices. It has a signal range of 360 degrees horizontally and 75 degrees vertically.
  • Direct Current - Electric current in which electrons flow in one direction only. Opposite of alternating current.
  • Direct Sequence Spread Spectrum - See "DSSS".
  • Direct-on-Line - A method of motor starting, which full line voltage is applied to a stationary motor.
  • Directional Relay - A protection relay in which the tripping decision is dependent in part upon the direction in which the measured quantity is flowing.
  • Discharge (Battery) - The conversion of the chemical energy of a cell or battery into electrical energy and withdrawal of the electrical energy into a load.
  • Discharge Current - The surge current that is dissipated through a surge arrester.
  • Discharge Rate (Battery) - The rate of current flow from a cell or battery.
  • Disconnect Switch - A simple switch that is used to disconnect an electrical circuit. It may or may not have the ability open while the circut is loaded.
  • Discrimination - The ability of a power protection system to differentiate between the conditions it was intended to operate and those it was not intended for.
  • Distortion Factor - The ratio between the r.m.s. value of the harmonic content and the r.m.s. value of the non-sinusoidal quantity.
  • Distribution Automation - A system consisting of line equipment, communications infrastructure, and information technology that is used to gather intelligence about a distribution system. It provides analysis and control in order to optimize operating efficiency and reliability.
  • Distribution System - A term used to describe that part of an electric power system that distributes the electricity to consumers from a bulk power location such as a substation. It includes all lines and equipment beyond the substation fence.
  • Distribution Transformer - A transformer that reduces voltage from the supply lines to a lower voltage needed for direct connection to operate consumer devices.
  • Distribution Voltage - A nominal operating voltage of up tp 38kV.
  • Disturbed Network Protocol - A proprietary communication protocol used on secondary networks between HMI, substation computers or bay computers and protective devices.
  • DMZ - Demilitarized Zone. Networking has corrupted the term and used it to refer to an unprotected subnet connected to a local network, but outside the protection of a firewall.
  • DNS - Domain Name System. The DNS is an international network of Internet domain name servers, names, and addresses that enables locating computers on the internet.
  • Dolly - See "Stringing Block".
  • Domain Host Control Protocol - See "DHCP".
  • Domain Name System - See "DNS".
  • Door - The fuse tube of a fused cutout.
  • Double Arming Bolt - A special long bolt used to assemble two cross arms, one on each side of the pole.
  • Draw-Lead - A cable or solid conductor that has one end connected to the transformer or a reactor winding and the other end drawn through the bushing hollow tube and connected to the top terminal of the bushing.
  • Drawing - The process of reducing a cylindrical rod or wire to a desired diameter by pulling the wire through dies.
  • Drop-Out - A relay drops out when it moves from the energized position to the un-energized position.
  • Dry Charge (Battery) - The process by which the electrodes are formed and assembled in a charged state. The cell or battery is activated when electrolyte is added.
  • Dry-Type Transformers - Transformers that use only dry-type materials for insulation. These have no oils or cooling fluids and rely on the circulation of air about the coils to provide necessary cooling. Such units are usually limited in size to a few hundred kVA because of prob
  • DSL - Digital Subscriber Line. A method to Lines carry data at high speeds over standard telephone lines.
  • DSSS - Direct Sequence Spread Spectrum. Used in radion transmission, DSSS alters, or modulates, the signal by spreading it over a wider frequency, generating what seems like signal noise to anything except the device that is designed to reassemble the signal in
  • DTIM - Delivery Traffic Indication Message. A DTIM is a signal sent as part of a beacon by an access point to a client device in sleep mode, alerting it that a packet of data awaits delivery.
  • Dual Voltage Switch - A switch used to select primary windings of a transformer.
  • Dual Voltage Transformer - A transformer that has switched windings allowing its use on two different primary voltages.
  • Duct - A channel for holding and protecting conductors and cables, made of metal or an insulating material, usually circular in cross section like a pipe. Also referred to as Conduit.
  • Duct Bank - Two or more ducts or conduits used as part of a system.
  • Dynamic DNS - This is a system by which Internet Service Providers temporarily assign IP addresses. This allows the reassignment of the address when no longer in use.




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