Power System Glossary

on 23 November 2024. Posted in Power System Engineering

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AC Input Currtent - The flow of electricity pulled under the highest DC load.
AC Input Frequency - Most AC power is generated at either 50 or 60 Hz. Switching power supplies typically accept any frequency between 47-63 Hz (nominal).
AC Input Voltage - The nominal AC input voltage that a power supply will accept during normal operation. Safety agencies require a power supply to operate an extended 10% of the stated input range on the product label.
AC Inrush Current - The instantaneous current drawn when the power supply is turned on cold. Smaller power supplies generally incorporate a thermistor to limit this amount. It is most important in considering an AC switch rating.
Alternating Current - An electric current that periodically reverses direction, typically at a rate of 50 or 60 cycles per second (Hz). This reversal of direction produces a sinusoidal waveform that can be used to transmit electrical power over long distances.
Altitude - The maximum altitude at which a supply can be operated without derating. Supplies must often be de-rated due to the thinner air which is required to cool the power supply.
Ampere's Law - A basic principle in electromagnetism that stated the magnetic field at a point along a closed loop is directly proportional to the total current passing through the loop and inversely proportional to the distance from the point to the wire.
Available Transfer Capability (ATC) - The amount of electric power that can be transferred over the interconnected transmission systems in a reliable manner under base case conditions.
Average Demand - The energy demand in a given geographical area over a period of time.

B

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Balance of Plant - The remainder of a power plant's infrastructure that supports major components such as boilers, turbines and generatore.
Baseline Forcast - A prediction of future energy needs which does not take into account the likely effects of new conservation programs that have not yet been started.
Base Load Plant - A plant that is normally operated to take all or part of the minimum load of a system, which consequently produces electricity at an essentially constant rate and runs constinuously.
Black Out - A condition when all electrical power is disrupted to your area.
Boost Converter - A boost converter (step-up converter) is a power converter with an output DC voltage greater than its input DC voltage.
Bottleneck Facility - A point on the system, such as a transmission line, through which all electricity must pass to get to its intended buyers. If there is limited capacity at this point, some priorities must be developed to decide whose power gets through. It also must be decided if the owner of the bottleneck may, or must, build additional facilities to relieve the constraint.
Breakdown Voltage - The voltage at which an insulator or dielectric ruptures, or at which ionization and conduction take place in a gas or vapor.
Bridge Converter - A switching supply topology that employs four switching elements (full bridge) or two switching elements (half bridge). Bridge converters provide high output power and low ripple, but are significantly more complex than other types of supply topologies.
Brownout - When the system voltage drops below acceptable levels causing lights to dim and potentially causing other electrical equipment to function improperly or to be damaged.
Buck - The AVR function of a UPS which reduces voltage when the utility power approaches the high voltage threshold.
Bulk Power Market - Wholesale purchases and sales of electricity.
Bus - An electrical conductor that serves as a common connection for two or more electrical circuits.
Bypass Diode - A diode connected across one or more solar cells in a photovoltaic module such that the diode will conduct if the cell(s) become reverse biased. Alternatively, diode connected anti-parallel across a part of the solar cells of a Photovoltaic module. It protects these solar cells from thermal destruction in case of total or partial shading of individual solar cells while other cells are exposed to full light.

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Cable Sheath - A conductive protective covering applied to cables. A cable sheath may consist of multiple layers of which one or more is conductive.
Capacitor - A passive electronic component that stores electrical energy in an electric field. It consists of two conductive plates separated by a non-conductive insulating material called a dielectric.
Capacity Benefit Margin (CBM) - The amount of inter-utility transmission transfer capability held in reserve to help ensure that there is a reliable source of power even if the utility experiences problems with its internal generation.
Cased - Enclosed in a metal or perforated metal cover assembly. Often referred to as Enclosed or Covered. Typically, a cased power supply is covered on all 6 surfaces for finger safe operation.
Cell junction - The area of immediate contact between two layers (positive and negative) of a photovoltaic cell. The junction lies at the center of the cell barrier or depletion zone.
Centralized Power System - These systems generate electricity in large power plants and distribute it over long distances to consumers. The key features are high generation capacity, centralized control, long transmission lines.
Charge Carrier - A free and mobile conduction electron or hole in a semiconductor.
Circuit - A conductor or system of conductors through which an electric current is intended to flow.
Circuit Breaker - A switch that opens an electric circuit when a short occurs.
Cogeneration - The process in which fuel is used to produce heat for a boiler-steam turbine or gas for a turbine. The turbine drives a generator that produces electricity, with the excess heat used for process steam.
Conduits - Conduits are hollow tubes running from manhole to manhole in an underground transmission or distribution system.
Connector Discontinuity - An ohmic change in contact resistance.
Connector Insert - For connectors with metal shells, the insert holds contacts in proper arrangement while electrically insulating them from each other and from the shell.
Connector Shell - The case that encloses the connector insert and contact assembly. Shells of mating connectors can protect projecting contacts and provide proper alignment.
Contact Plating - Plated-on metal applied to the base contact metal to provide the required contact resistance and/or wear resistance.
Contact Resistance - The resistance between metallic contacts and the semiconductor.
Continuous Load - A load where the maximum current is expected to continue for three hours or more. Rating of the branch circuit protection device shall not be less tan 125% of the continuous load.
Coolant - The liquid or gas used to transfer heat from the reactor core to the steam generators or directly to the turbines.
Critical Mass - The smallest mass of fissile material that will support a self-sustaining chain reaction under specified conditions.
Current - The flow of electric charge in a circuit or a conductor. The current flow is caused by the movement of electrons, which are negatively charged particles, through a conductor such as a wire. The rate of flow of electric charge (current) is typically determined by the voltage (potential difference) applied across the conductor and the resistance of the conductor.
Cycle Life - Number of discharge-charge cycles that a battery can tolerate under specified conditions before it fails to meet specified criteria as to performance (e.g., capacity decreases to 80-percent of the nominal capacity).

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Decentralized (Distributed) Power System - These systems generate electricity closer to the point of consumption, often with smaller, modular power plants. The key features are local generation, reduced transmission losses, improved reliability.
Demand Factor - For an electrical system or feeder circuit, this is a ratio of the amount of connected load that will be operating at the same time to the total amount of connected load on the circuit. An 80% demand factor, for instance, indicates that only 80% of the connected load on a circuit will ever be operating at the same time. Conductor capacity can be based on that amount of load.
Dielectric Constant - That property of a dielectric that determines the electrostatic energy stored per unit volume for a unit potential gradient. Permittivity is the preferred term.
Dielectric Strength - The maximum voltage that a dielectric material can withstand, under specified conditions, without rupturing. It is usually expressed as volts/unit thickness. Also called Disruptive Gradient or Electric Strength.
Dielectric Withstanding Voltage - Maximum potential gradient that a dielectric material can withstand without failure.
Direct Current - An electrical current that flows in one direction through a conductor. Unlike alternating current (AC), which periodically reverses direction, DC flows consistently in one direction.
Distributed power - Generic term for any power supply located near the point where the power is used. Opposite of central power.
Distributed systems - Systems that are installed at or near the location where the electricity is used, as opposed to central systems that supply electricity to grids. A residential photovoltaic system is a distributed system.
Distribution Bus - A distribution bus is a steel structure array of witches used to route power out of a substation.
Distribution Substation - These are located near to the end-users. Distribution substation transformers change the subtransmission voltage to lower levels for use by end-users.
Distribution Transformers - Distribution transformers reduce the voltage of the primary circuit to the voltage required by customers.
Dustproof - Constructed or protected so that dust will not interfere with its successful operation.
Dusttight - Constructed so that dust will not enter the enclosing case under specified test conditions.

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Energy Consumption - The amount of energy consumed in the form in which it is acquired by the user. The term excludes electrical generation and distribution losses.
Energy Isolating Device - A physical device that prevents the transmission or release of energy, including, but not limited to, the following: a manually operated electric circuit breaker, a disconnect switch, a manually operated switch, a slide gate, a slip blind, a line valve, blocks, and any similar device with a visible indication of the position of the device. (Push buttons, selector switches, and ther control-circuit-type devices are not energy isolating devices.)
Energy Levels - The energy represented by an electron in the band model of a substance.
Equipotential Zone - A zone of equal potential used to protect workers from hazardous step and touch potentials.
Explosion Proof - Designed and constructed to withstand and internal explosion without creating an external explosion or fire.

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Feeder - A circuit, such as conductors in conduit or a busway run, which carries a large block of power from the service equipment to a sub-feeder panel or a branch circuit panel or to some point at which the block power is broken into smaller circuits.
Float Charge - Float charge is the voltage required to counteract the self discharge of the battery at a certain temperature.
Float Life - Number of years that a battery can keep its stated capacity when it is kept at float charge.
Frequency - The context of electrical and wave phenomena, refers to the number of occurrences of a repeating event or cycle within a specified unit of time.
Fuel Cell - A device that converts the energy of a fuel directly to electricity and heat, without combustion. Because there is no combustion, fuel cells give off few emissions; because there are no moving parts, fuel cells are quiet.
Fuse - A protective device for electric circuits containing a wire designed to melt and open the circuit under abnormally high electric loads.

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Gassing Current - Portion of charge current that goes into electrolytic production of hydrogen and oxygen from the electrolytic liquid. This current increases with increasing voltage and temperature.
General Use Switch - A switch intended for use in general distribution and branch circuits. It is rated in amperes and is capable of interrupting its rated voltage.
Gigawatt (GW) - One billion watts. One million kilowatts. One thousand megawatts.
Grid System - An arrangement of power lines connecting power plants and consumers over a large area.
Ground - An electrical system connection that serves as a conduit between the circuit and earth.
Grounded Conductor - A system or circuit conductor that is intentionally grounded, usually gray or white in color.
Grounding Conductor - Used to connect metal equipment enclosures and/or the system grounded conductor to a grounding electrode, such as the ground wire run to the water pipe at a service; also may be a bare or insulated conductor used to ground motor frames, panel boxes, and other metal equipment enclosures used throughout electrical systems. In most conduit systems, the conduit is used as the ground conductor.
Grounding Electrode - The conductor used to connect the grounding electrode to the equipment grounding conductor, to the grounded conductor, or to both, of the circuit at the service equipment or at the source of a separately derived system.
Grounding Resistors - Designed to provide added safety to industrial distribution systems by limiting ground fault current to reasonable levels.
Grounding Transformers - A grounding transformer intended primarily to provide a neutral point for grounding purposes.
Ground Fault Circuit Interrupter - A device intended for the protection of personal that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds some predetermined value that is less than required to operate the overcurrent protection device of the supply circuit.

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Hardwired - High amperage devices that require installation by a qualified electrician to be directly wired-in instead of simply being plugged in to an outlet.
Hybrid System - A photovoltaic system that includes other sources of electricity generation, such as wind or diesel generators.
Hybrid Power System - These systems combine multiple sources of power generation, often integrating renewable and non-renewable energy. The key features are increased reliability, optimized energy use, reduced dependence on fossil fuels.

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Impedance - The total opposition that a circuit offers to the flow of alternating current or any other varying current at a particular frequency.
Indium Oxide - A wide band gap semiconductor that can be heavily doped with tin to make a highly conductive, transparent thin film. Often used as a front contact or one component of a heterojunction solar cell.
Insulation - A material that offers high electric resistance making it suitable for covering components, terminals and wires to prevent the possible future contact of adjacent conductors resulting in a short circuit.
Insulation - Materials that prevent or slow down the movement of heat.
Interconnect - A conductor within a module or other means of connection which provides an electrical interconnection between the solar cells.
Interconnection - The physical plant and equipment, usually at transmission-level voltage, that transfers electric energy between two or more entities. It can consist of a substation and an associated transmission line and communications facilities, or a simple electric power line or switching station.
Isolating Switch - A switch intended for isolating an electrical circuit from the source of power. It has no interrupting rating and is intended to be operated only after the circuit has been opened by some other means.

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Jacket - Outermost layer of insulating material of a cable or wire.

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Knife Switch - A switch in which the circuit is closed by a moving blade engaging contact clips.

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Load - Anything in an electrical circuit that, when the circuit is turned on, draws power from that circuit.
Load Factor - The ratio of the average load supplied to the peak or maximum load during a designated period.

N

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Off-grid Power System - These systems operate independently of the main power grid, typically in remote areas. The key features are self-sufficient, often use renewable energy, suitable for remote locations.
Off-peak - Off-peak is a period of time when consumers typically use less electricity - normally on weekends, holidays or times of the day when many businesses are not operating.
On-peak - A period of time when consumers typically use more electricity, normally on weekdays, when many businesses are operating.
Operating Day - The daily 24 hour period beginning at midnight EPT for which transactions on the PJM (Pennsylvania-New Jersey-Maryland) Interchange Energy Market are scheduled.
Overcurrent - Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit or ground fault.
Overload - Load greater than the load for which the system or mechanism was intended. A fault, such as a short circuit or ground fault, is not an overload.
Overhead Transmission Lines - Overhead AC transmission lines share one characteristic; they carry 3-phase current. The voltages vary according to the particular grid system they belong to.
Over Voltage - Occurs when incoming voltage is higher than normal but not high enough to be classified as a surge or a spike.

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Peak Demand - The highest electric requirement occurring in a given period of time. In PJM there are hourly, daily, monthly, seasonal and yearly peaks.
Peak Load - The amount of electric power required by a consumer or a system during peak demand.
PJM - The PJM (Pennsylvania-New Jersey-Maryland Interchange Energy Market) Energy Market procures electricity to meet consumers' demands both in real time and in the near term. It includes the sale or purchase of energy in PJM's Real-Time Energy Market (five minutes) and Day-Ahead Market (one day forward).
Power Surge - A sustained over voltage that generally subsides after a few seconds.
Power System Dynamic Performance - The behavior of an electrical power system in response to disturbances or changes in operating conditions over short periods, typically ranging from milliseconds to a few minutes. The dynamic performance of a power system is used for ensuring the stability, reliability, and efficiency of electricity supply.
Power System Operations - The planning, control, and management of electrical power systems to ensure a reliable and efficient supply of electricity. Overall, power system operations are essential to ensuring that electricity is delivered to consumers safely, reliably, and economically.
Power System Typical Components -

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Rated Voltage - The maximum voltage at which an electric component can operate for extended periods without undue degradation or safety hazard.
Renewable Energy System - Systems that generate electricity from renewable sources. The key features are environmentally friendly, sustainable, often decentralized.
Resistance - A measure of how much an object or substance opposes the flow of electric current through it. In order to overcome the resistance and get the current to flow a higher voltage will be required.
Resistive Voltage Drop - The voltage developed across a cell by the current flow through the resistance of the cell.
Repository - A permanent disposal place for radioactive wastes.

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Safe-fail Protection - This feature cuts power to connected equipment when the surge protector cannot provide protection anymore.
Semiconductor - Any material that has a limited capacity for conducting an electric current. Certain semiconductors, including silicon, gallium arsenide, copper indium diselenide, and cadmium telluride, are uniquely suited to the photovoltaic conversion process.
Service Drop - Run of cables from the power company's aerial power lines to the point of connection to a customer's premises.
Short-circuit Current - The current flowing freely from a photovoltaic cell through an external circuit that has no load or resistance, the maximum current possible.
Shunt Reactors - These are used in an extra high-voltage substation to neutralize inductive reactance in long EHV transmission lines.
Shunt Regulator - Type of a battery charge regulator where the charging current is controlled by a switch connected in parallel with the Photovoltaic generator. Overcharging of the battery is prevented by shorting the photovoltaic generator.
Smart Grid - An advanced power system that uses digital communication technology to monitor and manage electricity flows. The key features are real-time monitoring, efficient energy distribution, integration of renewable energy, demand-side management.
Solar Energy - Energy from the sun. The heat that builds up in your car when it is parked in the sun is an example of solar energy.
Spinning Reserve - Utility generating capacity on-line and running at low power in excess of actual load.
Step Potential - The voltage between the feet of a person standing near an energized grounded object. It is equal to the difference in voltage, given by the voltage distribution curve, between two points at different distances from the electrode. A person could be at risk of injury during a fault simply by standing near the grounding point.
Step-down Transmission Substation - These substations are located at switching points in an electrical grid. They connect different parts of a grid and are a source for subtransmission lines.
Step-up Transmission Substation - Receives electric power from a nearby generating facility and uses a large power transformer to increase the voltage for transmission to distant locations.
Substations - A high-voltage electric system facility. It is used to switch generators, equipment, and circuits or lines in and out of a system. It also is used to change AC voltages from one level to another, and/or change alternating current to direct current or direct current to alternating current.
Subtransmission Lines - These lines carry voltages reduced from the major transmission line system, usually 69 kv.
Superconductivity - The pairing of electrons in certain materials when cooled below a critical temperature, causing the material to lose all resistance to electricity flow. Superconductors can carry electric current without any energy losses.
Supervisory Control - Supervisory control refers to equipment that allows for remote control of a substation's functions from a system control center or other point of control.
Surge Protection - Diverts excess voltage away from sensitive electronic equipment during an AC power surge or power spike to prevent damage.
Surge Suppressor - An electronic device that protects electric equipment from short-term, high-voltage flows of electricity such as lightning strikes.
Switchboard - A large single panel, frame, or assembly of panels having switches, overcurrent, and other protective devices, buses, and usually instruments mounted on the face or back or both. Switchboards are generally accessible from the rear and from the front and are not intended to be installed in cabinets.
Switch-leg - That part of a circuit run from a lighting outlet box where a luminaire or lampholder is installed down to an outlet box that contains the wall switch that turns the light or other load on or off. It is a control leg of the branch circuit.

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Thermal Mass - Materials that store heat within a sunspace or solar collector.
Thermal Shock - The effect of heat or cold applied at such a rate that non-uniform thermal expansion or contraction occur within a given material or combination of materials. In connectors, the effect can cause inserts and other insulation materials to pull away from metal parts.
Transformer - Converts the generator's low-voltage electricity to higher voltage levels for transmission to the load center, such as a city or factory.
Transformer Vault - A transformer vault is an underground structure or room in which power transformers, network protectors, voltage regulators, circuit breakers, meters, etc. are housed.
Transmission Bus - Transmission buses are steel structure arrays of switches used to route power in a substation.
Transmission Lines - Transmit high-voltage electricity from the generation source or substation to another substation in the electric distribution system.

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Underground Distribution Substation - These are also located near to the end-users. Distribution substation transformers change the subtransmission voltage to lower levels for use by end-users.
Underground Transformer - It is the same as an aboveground transformer, but is constructed for the particular needs of underground installation.
Under Voltage - Occurs when voltage is lower than normal for an extended period of time without recovering, but not so low that the electronic device will not function. Two types of undervoltages are brownouts and sags.

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Voltage - The measure of the electric potential energy per unit charge that is required to move a charge from one point to another in an electric field. A unit of electrical pressure. One volt is the amount of pressure that will cause one ampere of current in one ohm of resistance.
Voltage Drop - The loss of voltage between the input to a device and the output from a device due to the internal impedance or resistance of the device. In all electrical systems, the conductors should be sized so that the voltage drop never exceeds 3% for power, heating, and lighting loads or combinations of these. Furthermore, the maximum total voltage drop for conductors for feeders and branch circuits combined should never exceed 5%.
Voltage Regulator - A device or component that normalizes voltage to a certain standard when it is fluctuating.

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Wafer - A thin sheet of semiconductor material made by mechanically sawing it from a single-crystal or multi-crystal ingot or casting.
Waveform - The shape of the curve graphically representing the change in the ac signal voltage and current amplitude, with respect to time.

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