Glossary N-Z

Link to entries A-M


n-1 (n minus one) is the operating standard to which European transmission system operators are obliged to work. It refers to a system that can maintain normal operations despite the loss of any single component. In the case of a power network, a component may be a transmission line, a generating unit of a power station, etc.

Network control: Network control systems monitor and control the electricity network to keep power flowing and to preserve the balance between power generation and consumption.

Network management: A system that uses network control and asset management to oversee all aspects (operational and maintenance) of a network.
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Ohm: Unit of electrical resistance. If a 1 volt source is connected to a wire with a resistance of 1 ohm, then 1 ampere of electric current will flow.

Oil sands: Naturally occurring mixture of bitumen (a heavy, viscous form of crude oil), water, sand and clay. Using hydroprocessing technology, bitumen can be refined to yield synthetic crude oil.

Optimization: The process of making a system as near to perfect or as effective as possible.

Original Equipment Manufacturer (OEM): Manufacturers who produce an end product such as automobiles, machines or switchboards, incorporating components from sub-suppliers, such as ABB.
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Parallel: Electrical components that are connected in such a way that the flow of electricity can take multiple, or parallel, paths through the circuit are said to be connected “in parallel” or “in shunt,” as opposed to “in series.” If one of the components in a parallel circuit was to fail, the electricity would continue to flow through an alternative path. (See also Series.)

Phase angle monitoring (PAM): A device that monitors power-network stresses caused by heavily loaded lines. This is part of the Wide-Area Monitoring System, which relies on a number of phasor measurement units (PMUs) to collect data from strategic positions in the grid. (See also Wide-Area Monitoring System and Phasor Measurement Units.)

Phase-shifting transformer (also known as a quadratic booster): A specialized type of transformer used on 3-phase power grids (AC) to balance the active (real) and reactive power in the system (see Reactive power, Power factor correction and Three-phase power), preventing the loss of lines through physical overloading.

Phasor Measurement Units (PMUs): Monitoring devices that are installed at critical nodes in a power network where they collect data on power flow. (See also Wide-Area Monitoring System, Line thermal monitoring.) Signals sent from the units via satellite to a central control room, enabling operators to identify and counteract any instabilities before they spread through the grid.

Photovotaic cells (PV): Device that converts the sun's radiation directly into DC electricity. PV cells are made of semiconductor materials such as silicon, cadmium telluride and gallium arsenide. The semiconductor material can be structured in different ways including crystalline, multi-crystalline and amorphous form. Cells are assembled together using interconnections, terminals and protective devices and form a module. The module shields the assembly from environmental conditions.

Photovoltaic plants: Photovoltaic plants convert the sun's radiation into electricity through the photovoltaic process. A photovoltaic plant is composed of many elements including PV modules, solar inverters, DC and AC low voltage components and monitoring equipment.

Pig: A cleaning device placed that is used to scrape residues from the inner wall of oil pipelines. A pig is pushed through the pipeline by the pressure of the oil flowing past. Pipelines can be equipped with pig launch sites and pig traps. These are points at which pigs can be introduced or removed from the pipeline.

Polyethylene: Also known as polythene, this plastic material has excellent properties of electrical insulation.

Power factor: Power factor is a measure of an electrical circuit's effectiveness in doing useful work on a scale of zero (lowest) to 1 (highest). It reflects how much the waveforms of voltage and current are in phase, usually measured at the customer's load. When the voltage and current are significantly out of phase, as is common in industrial environments with many electric motors, the current will be high even at relatively low power levels. The economic result of this low power factor is expensive electrical losses on the circuit and underutilization of the circuit's power transfer capability. In these cases the customer or the electric utility may deploy additional capacitor banks near the customer load, restoring the power factor to or near unity and improving system utilization. (See also Power factor correction.)

Power factor correction (reactive power compensation): Depending on the type of equipment a consumer connects to the electricity supply (whether there is a net consumption or generation of reactive power), power factor varies. Unless this variation is corrected, higher currents are drawn from the grid, leading to grid instability, higher costs and reduced transmission capacity. Most utilities impose penalties on consumers who fail to correct errant power factors. (See also Power factor.)

Power losses: This term generally refers to electrical energy that is lost to inefficiencies in transmission, distribution, or in the use of electricity. As electricity flows through a conductor, individual electrons collide with the atoms of the conductor and transfer energy to them, causing them to heat up. This heat is lost to the atmosphere in the form of thermal radiation. Some power is also lost to electromagnetic radiation.
Losses in an electricity distribution system depend on the length of the cable (the longer the cable, the greater the losses); the conductivity of the material (higher resistance means greater losses); the square of the current (at twice the current, there will be four-times the losses); and the cross-sectional area of the cable. Therefore, to minimize losses, power should be transmitted at the highest practical voltage. This reduces the current and therefore the amount of power lost in transmission. Most electrical transmission systems are alternating current at voltages between 110 and 800 kV. (See also HVDC.)

Process Industry: an industry in which raw materials are treated and converted into products by means of a series of stages (or processes). Process industries include oil and gas refining, pharmaceutical and chemical production, water and sewerage treatment etc.

Process Analytical Technology (PAT): as defined by the United States Food and Drug Administration, PAT is a mechanism to design, analyze, and control pharmaceutical manufacturing processes through the measurement of critical process parameters, which affect critical quality attributes. The concept actually gains a clearer understanding of processes by defining and monitoring their critical process parameters, in order to improve productivity by enhancing consistency and minimizing rejects.

Process automation: The term process automation is used to refer to an automation system, the principal purpose of which is to automate or support the operator of a manufacturing process. Such a process can be the manufacturing or treatment of any goods made in a continuous or quasi-continuous manner such as fuel, paper, cement, steel, chemicals, food.

Process historian: A process historian is a mechanism for storing data relating to a particular process.
The data stored by modern historians typically include time-stamped information from a variety of traceable sources. The data are used for modeling, optimization and auditing purposes.

Power capacity: In terms of generation, the capacity of a power plant is the maximum power that installation is capable of producing. It does not account for periods of inactivity due to maintenance work, for example. Nuclear power stations have low maintenance requirements and few shutdowns (as do all “base-oad” power plants), which enable them to achieve about 90 percent productivity. Gas-fired power stations, which are more expensive to run, often operate well below capacity, ramping up to full productivity only during periods of high demand. This means that their productivity may be only 20 - 30 percent of the plant’s actual capacity. The relationship between capacity and output is known as the “capacity factor,” where 100 percent is the theoretical maximum.
As an example, the hydropower station on the Itaipu dam in Brazil has a total generating capacity of 14,000 megawatts and could therefore theoretically produce 122,640,000 megawatt-hours of electricity per year (14,000 MW x 8,760 hours = 122.6 million MWh). The Itaipu dam actually produced 91,651,808 MWh of electricity in 2009. The actual production divided by the theoretical maximum production gives Itaipu a capacity factor of 74.7 percent. (See also Base-load power plant.)

Programmable logic controller (PLC, or programmable controller): These are electronic devices used to control equipment, especially in automation. They are small, programmable units that can receive information from output devices, such as sensors in a control system, and transmit signals to input devices, such as actuators, that can effect changes in the control system.

Pumped storage: see Electricity storage.
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Reactive power: It is a concept that describes the loss of power in a system resulting from the production of electric and magnetic fields in it. Reactive loads in a power system drop voltage and draw current, which creates the impression that they are using up power, when they are not. This “imaginary power” or “phantom power” is called reactive power, and is measured in Volt-Amps-Reactive (VAR). Reactive power is significant because it must be provided and maintained to ensure continuous, steady voltage on transmission networks. Reactive power is produced for maintenance of the system, and not for end-use consumption. If elements of the power grid cannot get the reactive power they need from nearby sources, they will pull it across transmission lines and destabilize the grid. In this way, poor management of reactive power can cause major blackouts.

Real time: In business, a system is described as real-time if it will operate in a deterministic manner, ie, it will respond to an input within a defined time limit. For example, safety-relevant systems must always respond within pre-determined time limits. Many automation applications are also real-time, as unpredictable response times and reaction delays would effectively destabilize the process. To ensure a system is real-time, it must fulfill stringent demands with both hardware and software design.

Some applications are described as near real-time. Such systems are sufficiently fast that it can be assumed that critical time limits will not be exceeded. An example would be the communications between an automation system and a business system designed to provide management level information, which must be fast enough for accurate decisions, but not instantaneous.

Recloser: A circuit breaker designed to interrupt short-circuit current and reconnect the circuit after interruption.

Rectifier: An electrical device used to convert alternating current (AC) into direct current (DC). (See also Inverter.)

Regenerative braking: A braking method that is used to recoup some of the energy lost as vehicles slow down or brake against an incline (downhill). It exploits the ability of electric motors to work as generators during breaking. This enables the mechanical energy from the load to be converted into electric energy and returned to the electricity supply systems for use either by other vehicles, or by the braking vehicle at a later time if onboard energy storage systems such as batteries or super-capacitors are available. The method can be used to improve the energy efficiency of cranes and elevator systems, trains and hybrid cars.

Relays: 1. A switch that can be operated remotely.
2. Control and protection relays are switches used to signal and control the operation of electrical equipment and systems. They include electronic and electromechanical relays and components; high-voltage protection, substation control and communications; automated substation components; and distribution relays.

Remote Terminal Unit (RTU): Remote terminal units collect data from points around a power transmission and distribution network and transmit the information to a central location. They are typically used to control and monitor power networks, and are components of supervisory control and data acquisition (SCADA) systems.

Resistance: Cables and electrical devices resist the movement of electrons that constitute the current passing through them. This is known as electrical resistance and is measured in Ohms. If an electric circuit is likened to water flowing through a system of pipes, the resistance in a wire is analogous to the restriction of the water flow imposed by the diameter of the water pipe, or any obstacles within the pipe.

Resistor: A resistor is any electrical component that resists the flow of electrical current. Resistors can be used to control current and therefore protect a circuit from overload. Resistors are also an important component in instrumentation and are used together with capacitors in power filters to eliminate unwanted harmonics.

Ringgeared mill drives (RMD): a system used to drive (rotate) a mill. The RMD itself is comprised of motor(s) (synchronous or asynchronous), a frequency converter, transformers and control equipment. As opposed to gearless mill drives, the motor in RMD is mechanically connected to the mill via a coupling, pinion(s) and ringgear.

Ringmotor: also called wrap-around motor, a ringmotor is a very large synchronous motor. The poles of the motor are directly flanged on the driven equipment. (See also Machine).

Robot, industrial: An industrial robot is defined by ISO 8373 as an automatically controlled, reprogrammable, multipurpose, manipulator, programmable in three or more axes, which may be either fixed in place or mobile for use in industrial automation applications. Typical robot applications include welding, painting, assembly,
pick and place, packaging and palletizing, product inspection, and testing, all accomplished with high end-urance, speed, and precision. ABB developed the first commercially available electric robot almost 40 years ago.
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SCADA (supervisory control and data acquisition): A SCADA system is a computer system that gathers and analyses data across distributed industrial and enterprise-wide equipment, processes and infrastructure. SCADA systems can be deployed in a wide variety of application areas, such as oil and gas gathering, gas and liquids transport pipelines, oil and gas distribution networks, water treatment facilities, electrical networks, and many other areas. SCADA systems may also be used as the platform for higher level applications such as facilities and asset management, load balancing, production management, leak detection, supply contracts management and a host of other applications.

Semiconductor: A semiconductor is a material whose electrical properties can be significantly influenced by physical factors (mostly electrical conditions, but also pressure, temperature, light, etc). This means that a semiconductor will behave either as an insulator or a conductor of electricity, depending on the conditions to which it is exposed. They are a fundamental component of electronic devices. Because of their ability to respond to external conditions, semiconductors are commonly used in sensor systems.

Series: Electrical components that are connected in an unbranched line are said to be “in series,” as opposed to “in parallel” or “in shunt.” If any one of the components in a series circuit was to fail, the circuit would be broken and no electricity would flow. (See also Parallel.)

Series capacitor: See FACTS.

Ship-to-shore connection: see HVSC

Short circuit: An electric contact between parts of an electric circuit, which causes a very high current, increases in temperature and potentially fire, if the circuit is not properly protected. This can occur if two live wires come into contact with each other, perhaps because of worn insulation. The term is also used when defining the safe operating conditions for electrical devices. If a device is said to have a short-circuit resilience of 400 amps (A), that means that it can be subjected to up to 400 A before it will shut itself down.

Shunt: see Parallel.

Shunt reactors: Shunt reactors are used in AC high voltage energy transmission systems to stabilize the system voltage during load variations. The shunt reactor can be regarded electrically as a large coil connected between the line and ground to absorb reactive power in the system. This function is especially important at high voltages, typically over 130 kilovolts (kV), and long transmission lines. Cable systems require even more compensation of reactive power, also at lower system voltage due to the high capacitance of the cable. Besides stabilizing the system voltage, the shunt reactor increases the active or the useful power transmitted in the system.

SIL (Safety integrity level): The safety integration level (SIL rating) of a system indicates the level of risk associated with it. It is a measure of its ability to perform safely and, in the event of failure, to fail safely. There are four SIL levels, with level 4 indicating the highest performance.

Smart grid: Smart grids are modern power transmission and distribution systems, capable of accepting power of any quality from any source and delivering it to consumers of all kinds via a bidirectional supply system. They are an evolutionary development of traditional grids, which are based mainly on centralized generating plants, supplying power via long-established, unidirectional transmission and distribution systems whenever consumers request it. Smart grids are being developed in response to rising demand for power and the increasing need to incorporate renewable or distributed, less predictable generation into the grid. ABB’s smart grid concept is of an observable and controllable system, based on industry-wide standards, providing a stable, secure, efficient and environmentally sustainable network. The system will cross national and international borders. It must be able to detect and react automatically to disturbances and changes in supply and demand, re-establishing balance and maintaining the stability demanded by both end-users and government legislation. This is achieved by an automation and information technologies infrastructure integrating the whole supply chain from production to consumption, based on an infrastructure of enabling smart grid components. Thus smart grids also accommodate customer response management systems that allow utilities to optimize the performance of the grid and to integrate consumption into balancing load and generation. Many of the technologies and standards needed to establish smart grids on a large scale have been the subject of research and development at ABB for some years and many are already in use.

Solar inverters or Photovoltaic (PV) inverters convert the variable DC output of PV modules into AC power that can be fed into the electrical grid. Solar inverters are categorized into off-grid and grid-tie inverters. Grid-tie inverters are categorized into central inverters (used in utility and commercial scale PV plants), string inverters (used in commercial and residential scale PV plants) and micro-inverters (used as module scale inverters).

Solar power (thermal or concentrating solar power): Solar power is electricity generated using sunlight as its primary energy source. In the case of thermal solar power, the sun’s heat is used to heat water, either directly or via a heat-conducting fuid, and generate steam. The steam is then used to generate electricity in the same way as it is used in conventional thermal power stations.
Thermal solar power is suitable for large-scale generating plants (eg, Desertec) and can be used in combination with conventional generation (eg, gas-fired).
Static var (volt amperes reactive) compensator (SVC): A device that provides fast-acting reactive power compensation (see Power factor and Power factor correction) in high-voltage electricity networks. Cheaper to build and maintain than rotating compensation devices, such as synchronous compensators (see also FACTS), SVC has no rotating parts (it is static). It compensates for fluctuations in the voltage and current of an electric grid, thereby allowing more power to flow through the network while maintaining safety margins, increasing network stability.

Solar trackers: A solar tracker is a structure that orients one of its surfaces to follow the path of the sun in order to maximize incident solar radiation on this surface. One axis trackers follow the sun's path from east to west, two axes trackers orient the surface towards the sun throughout the day.

Storage: see Electricity storage.

String test: In a string test, a complete drive train, comprising a frequency converter, a motor and an application, such as a pump or a compressor, are tested in a factory situation that simulates site conditions. String tests are performed prior to delivery to verify the performance and functionality of the equipment and to ensure that the units comply with specifications under the working conditions of the destination plant. String tests are time consuming and expensive but often reduce time spent on erection and commissioning on the customer’s premises.
Substation automation: The various technologies, methods and equipment used for the automatic operation of substations. This includes control and protection functions.

Submetering: Metering of individual units in multi-unit properties.

Substation: Substations are key installations in the power grid. They house equipment for the protection and control of electrical power transmission and distribution, including power transformers, switchgear and measuring equipment. (See also Reactive power, Power factor correction, Circuit breaker and Switchgear.)

Supercritical (SC) and ultra-supercritical (USC) coal-fired power plants: Conventional coal-fired power plants, which burn fuel to boil water that generates steam to activate a turbine, have an efficiency of about 31 percent. Supercritical and ultra-supercritical power plants operate at temperatures and pressures above the critical point of water. The critical point of water – above 374°C and 22.064 MPa - represents the temperature and pressure at which liquid and gas phases coexist in equilibrium, where there is no difference between water gas and liquid water. In a power plant, this results in higher efficiencies above 45 percent, compared to turbines driven by steam at a lower, subcritical temperature. Supercritical and ultra-supercritical power plants require less coal per megawatt-hour, leading to higher efficiency, lower costs and lower emissions, including carbon dioxide and mercury. Operating under such conditions requires the use of extremely robust equipment. The specifications for products used in supercritical and ultra-supercritical plants are higher than those used in subcritical plants.

Supergrid: Trademarked by Airtricity in 2006, the term Supergrid refers to a pan-European subsea power grid. The term is widely used in the context of renewable energy. The Desertec project, for example would rely on a supergrid for the transmission of offshore wind power from European coastlines, solar power from northern Africa and southern Europe, together with hydro power from northern Europe.

Surge protector: Also known as a surge arrester, this is a device used to protect equipment from damage caused by high-voltage power surges. These can occur when substations are hit by lightning or as a result of switching operations in high-voltage transmission.

Switchgear: Equipment used to control, protect, and regulate the flow of electrical power in a transmission or distribution network. It is often located in substations, but can be associated with any electrical equipment that might need to be isolated for fault correction (eg, if a voltage drop occurred in one part of the grid, it might be necessary to shut off the affected section to prevent the fault spreading), or for maintenance purposes. The main components of switchgear are circuit beakers, which interrupt high-voltage current to protect electrical equipment from excessive current. The terms gas- and air-insulated switchgear (GIS and AIS) refer to switchgear equipped with gas- and air-insulated circuit breakers. The gas-insulated variety is more costly than the air, but it takes up less space and is therefore the preferred option when installing switchgear in urban environments (the substations can be one fifth the size of a conventional AIS substation).

Synchronous machines: See Machines

System 800xA: An Industrial IT-compatible control system that provides a means of achieving measurable productivity and profitability improvements. The full name is Extended Automation System 800xA, and it is used in many industry sectors to oversee and control a wide range of processes. It extends the scope of traditional control systems to include all automation functions within a single operations and engineering environment. This enables plants to perform in a more intelligent and cost-effective way, and to improve productivity.
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Three-phase power: A form of electricity used to supply heavy loads (power-hungry electrical equipment) such as industrial air conditioning units, grinding machines etc. Almost all power is generated as three-phase and, with the exception of HVDC, most transmission lines are three-phase. Three-phase is a more efficient way of delivering heavy loads and the three-phase motors it supplies are more efficient, smaller and cheaper to build than their single-phase counterparts. Wiring is simplified because no neutral return path is provided. Residential premises, however, are supplied with single-phase power.

Thyristor: A thyristor is a semiconductor device used in electrical systems, such as HVDC installations, as a high-speed, high-power switch, capable of turning power supplies of many megawatts on within a split second. Thyristors are a component used in inverters and rectifiers. (See also Inverter and Rectifier).

Thyristor-controlled series capacitor: see Capacitor

Traction motor: A traction motor is typically used to power the driving wheels of a railroad locomotive, a tram or an electric train, like a subway or light rail vehicle. There is usually one traction motor on each driven axle. Traction motors differ from other motors in the scale of their design. They must be extremely compact, because of the limited space available on the locomotives, and highly reliable as there is no room for any backup systems. (See also Traction transformer.)

Traction substation: A substation used to feed power into railway electrification systems.

Traction transformer: This is a fundamental component of a rail locomotive’s traction chain. It adapts the catenary (overhead) voltage to the various low voltage levels needed by the train, mainly for traction, but also for lighting, heating and ventilation, passenger information and safety systems such as door blocking, brakes, signaling and communication. The traction transformer is the unique energy transfer point between high voltage (HV) and low voltage (LV) and therefore must achieve the highest availability and reliability levels to guarantee uninterrupted train service.

Transformer: A transformer is a device used to transfer energy from one AC circuit to another and to increase (step up) or reduce (step down) voltage as required. Transformers are an essential component in an electrical grid. Electricity generated in a power station must be stepped up to the appropriate voltage for transmission (between 100 and 800 kV) and then stepped down again to the distribution voltage (110 - 230 V), which is delivered to homes. Note that the voltage of DC cannot be transformed in the same way as it can for AC. (See Alternating current.)

Transmission and distribution (T&D): The term refers to the transport of electricity from the power station to the end user. Transmission is the movement of power at high voltage (above ca. 50 kV), usually over long distances. Raising the voltage allows power to be transmitted more efficiently (ie, with fewer losses - at lower voltages, more electrical power is converted to heat and lost to the atmosphere) over a wide area. Distribution is the transport of electricity at medium voltage (between ca. 1 and 50 kV) over shorter distances to industrial, commercial and residential areas. Transformers are generally, though not always, housed in substations.
Turbine: A propeller-like device that is turned by a stream of hot gas (steam in a conventional thermal power station), water (in a hydro plant), gas (in a gas power plant: here the gas burns in the turbine and exhaust gases cause it to rotate); or wind (as in a wind farm). The rotation of the turbine drives the generator that converts the mechanical rotation into electrical power. (See also Generator.)

Turbocharger: An air compressor that is used to boost the oxygen intake of a motor. In an internal combustion engine, a mixture of fuel and air is pumped into the confined space of a piston cylinder and ignited by a spark. When it ignites, the fuel burns, using the oxygen in the air, and the remaining gasses expand almost instantly, releasing a huge amount of energy. This expansion pushes the piston out, turning the crankshaft that drives the engine. The amount of fuel that can be ignited in the cylinder, and therefore the power generated, is limited by the amount of oxygen present. If there is too little oxygen, not all the fuel will burn. By compressing the air that is fed into the cylinder, more oxygen is made available for the combustion process, allowing more fuel to be burned, more completely, leading to more power obtained at higher efficiency and “cleaner” exhaust-emissions.

Turbogenerator: a collective term referring to a turbine and the generator to which it is connected.

Turnkey project: A turnkey project is one in which the contractor will design, engineer, deliver and commission an installation, taking responsibility for all aspects of the work. A lump-sum turnkey project is one in which the contractor undertakes a turnkey project for a set fee, agreed by the contractor and the customer before the work has begun.
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Ultrahigh voltage (UHV): This term refers to voltages in excess of 800 kilovolts (kV). UHV transmission using alternating current (AC) has been possible for several decades, and it is now also possible to transmit power this way using direct current (DC). DC transmission has lower losses and requires fewer overhead lines than AC transmission. Ultrahigh-voltage DC links will make it viable to produce electricity in remote regions and transmit it to centers of demand via energy “superhighways.” The efficient transmission of electricity at 800 kV DC power transmission is now feasible over distances as far as 3,000 km. UHVDC systems are cheaper, smaller and more efficient than comparable AC transmission systems.

Upstream: The oil industry term “upstream” refers to oil and natural gas exploration and extraction activities. See also Downstream.
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Vacuum interrupter: A vacuum interrupter is a device that uses a vacuum to extinguish the arc formed when a circuit breaker is opened. It also insulates the contacts after the arc has been interrupted. Vacuum interruption is seen as the ideal switching technology for medium-voltage applications. Excellent switching capabilities, combined with high reliability and a compact design, provide economical switching solutions with virtually no maintenance requirements. Vacuum interruption offers the lowest environmental impact of all medium-voltage switching technologies over the entire product life cycle. Vacuum interrupters are comprised of materials that are environmentally benign and safe to handle during periodic out-of-service maintenance and at end-of-life disposal. The devices perform well in all medium-voltage switching applications required in modern power systems. They have exceptionally long life and are virtually maintenance free.

Variable Shunt Reactors: A traditional shunt reactor has a fixed rating. Recently Variable Shunt Reactors (VSRs) have been developed and introduced on the market. The rating of a VSR can be changed in steps. The maximum regulation range typically is a factor of two, eg, from 100-200 MVAr (see Megavar). The regulation speed is normally in the order seconds per step and around a minute from max to min rating. VSRs are today available for voltages up to 550 kilovolts (kV). The largest VSRs in operation today have a rating of 120-200 MVAr at 420 kV.
The variability brings several benefits compared to a traditional fixed shunt reactor. The VSR can continuously compensate reactive power as the load varies and thereby secure voltage stability. Other important benefits are:
    • reduced voltage jumps resulting from switching in and out of traditional fixed reactors
    • flexibility for future (unknown) load and generation patterns
    • improved interaction with other transmission equipment and/or systems such as coarse tuning of static var compensator (SVC) equipment
    • limiting the foot print of a substation if parallel fixed shunt reactors can be replaced with one VSR
    • a VSR can be used as a flexible spare unit and be moved to other locations in the power grid if needed.

Variable-speed drive: see Drive.

Volt: standard unit of electrical “pressure” in a circuit. (See also Voltage.)

Voltage (potential difference): The voltage between two points in an electrical circuit is a measure of the potential difference, or the force, that is pushing electrons between these two points. It is analogous to water pressure in a water system. Voltage is measured in volts, and is directly proportional to the current and resistance of a circuit: V=IR, where V = potential difference in volts, I = current in amperes (amps) and R = resistance in ohms. This is Ohm’s law.

Voltage drop: A voltage drop is a reduction in the force that “pushes” current through a circuit. Under these conditions, resistive loads, such as light bulbs, will give suboptimal performance- lights will flicker or become dimmer because less current is flowing. Inductive loads, such as motors, respond to voltage drops by working harder to obtain the same power, which can cause overheating, increased operating costs and the risk of equipment failure. Devices such as computers often have sensors that warn of suboptimal voltage or excess heating and will shut down automatically in response to a voltage drop.

Voltage rating: The maximum voltage that can be applied to an electronic device.
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Waste-to-energy plant: A waste-to-energy plant produces energy, either heat or electricity using waste as a fuel. Their furnaces cannot easily be ramped up or down and so the plants are not used for peak-load generation. Due to the highly variable composition of the plants’ fuel, stringent environmental standards are imposed and waste-to-energy plants use sophisticated flue-gas cleaning devices and monitoring devices to ensure emission control.

Watt (W): Standard unit of electrical power (1 watt = 1 amp at 1 volt). The watt is also a general unit of power. One watt = 1 joule per second.
Watt hour (Wh): 1 watt hour is the amount of electrical energy consumed by a 1 watt load over a period of one hour. For example, a 100 watt light bulb (a 100 watt load) uses 100 watt-hours of energy every hour. Rather confusingly, watt-hours are sometimes used to describe “power.” This is incorrect. Watt-hours are a measure of energy transferred, ie, the product of power (kW) x time (hours). Confusion can also arise when describing electricity generation. For example, a wind farm described as “150 MW” has a peak power output of 150 MW. If the farm was 100 percent efficient, it would transfer 150 MW x 24 hours = 3600 MWh to the electricity grid every day. Because of various inefficiencies and the fact that wind blows erratically, wind turbines are actually only about 30 percent efficient. This means that 150 MW (theoretical maximum) x 24 h (number of hours in a day) x 30 percent (efficiency) = 1080 MWh will be produced each day.
Cables can also be described as, for example, 350 MW. This is the capacity of the cable, ie, the maximum amount of power it can carry. In an hour, a 350 MW cable could (theoretically) deliver 350 MWh of electricity.

Web inspection system (WIS): Web inspection systems are used by the pulp and paper industry to inspect the surface of the paper as it is being produced. The systems can detect and report many types of defects, including holes, spots and streaks.

Wide-area monitoring system (WAMS): WAMS is an advanced early-warning technology for power grids that helps operators prevent system instabilities and overloads, as well as cascade tripping that leads to power blackouts. It comprises a series of phasor measurement units, set up in strategic positions around the grid. These monitor stresses (loads and temperatures) on the power lines and send data back to a central control station via a GPS satellite link. This allows operators to identify problems at an early stage and prevent widespread disruption of the grid (ultimately rolling blackouts). WAMS is used in conjunction with phase shifting transformers to protect and stabilize power grids.
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Last edited 2015-07-21
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