Power-system automation
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Power-system automation is the act of automatically controlling the power system via instrumentation and control devices. Substation automation refers to using data from
Intelligent electronic device In the electric power industry, an intelligent electronic device (IED) is an integrated microprocessor-based controller of power system equipment, such as circuit breakers, transformers and capacitor banks. Description IEDs receive data from sens ...
s (IED), control and automation capabilities within the substation, and control commands from remote users to control power-system devices. Since full substation automation relies on substation integration, the terms are often used interchangeably. Power-system automation includes processes associated with generation and delivery of power. Monitoring and control of power delivery systems in the substation and on the pole reduce the occurrence of outages and shorten the duration of outages that do occur. The IEDs, communications protocols, and communications methods, work together as a system to perform power-system automation. The term “power system” describes the collection of devices that make up the physical systems that generate, transmit, and distribute power. The term “instrumentation and control (I&C) system” refers to the collection of devices that monitor, control, and protect the power system. Many power-system automation are monitored by SCADA.


Automation tasks

Power-system automation is composed of several tasks. ;Data acquisition: Data acquisition refers to acquiring, or collecting, data. This data is collected in the form of measured analog current or voltage values or the open or closed status of contact points. Acquired data can be used locally within the device collecting it, sent to another device in a substation, or sent from the substation to one or several databases for use by operators, engineers, planners, and administration. ;Supervision: Computer processes and personnel supervise, or monitor, the conditions and status of the power system using this acquired data. Operators and engineers monitor the information remotely on computer displays and graphical wall displays or locally, at the device, on front-panel displays and laptop computers. ;Control: Control refers to sending command messages to a device to operate the I&C and power-system devices. Traditional supervisory control and data acquisition (SCADA) systems rely on operators to supervise the system and initiate commands from an operator console on the master computer. Field personnel can also control devices using front-panel push buttons or a laptop computer. In addition, another task is power-system integration, which is the act of communicating data to, from, or among IEDs in the I&C system and remote users. Substation integration refers to combining data from the IED's local to a substation so that there is a single point of contact in the substation for all of the I&C data. Power-system automation processes rely on data acquisition; power-system supervision and power-system control all working together in a coordinated automatic fashion. The commands are generated automatically and then transmitted in the same fashion as operator initiated commands.


Hardware structure of the power-system automation


Data acquisition system

The instrument transformers with protective relays are used to sense the power-system voltage and current. They are physically connected to power-system apparatus and convert the actual power-system signals. The transducers convert the analog output of an instrument transformer from one magnitude to another or from one value type to another, such as from an ac current to dc voltage. Also the input data is taken from the auxiliary contacts of switch gears and power-system control equipment.


Main processing instrumentation and control (I&C) device

The I&C devices built using microprocessors are commonly referred to as intelligent electronic devices (IEDs). Microprocessors are single chip computers that allow the devices into which they are built to process data, accept commands, and communicate information like a computer. Automatic processes can be run in the IEDs. Some IEDs used in power-system automation are: ;
Remote Terminal Unit A remote terminal unit(RTU) is a microprocessor-controlled electronic device that interfaces objects in the physical world to a distributed control system or SCADA (supervisory control and data acquisition) system by transmitting telemetry data to ...
(RTU): A remote terminal unit is an IED that can be installed in a remote location, and acts as a termination point for field contacts. A dedicated pair of copper conductors is used to sense every contact and transducer value. These conductors originate at the power-system device, are installed in trenches or overhead cable trays, and are then terminated on panels within the RTU. The RTU can transfer collected data to other devices and receive data and control commands from other devices. User programmable RTUs are referred to as “smart RTUs.” ;Meter: A
meter The metre (British spelling) or meter (American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure"), symbol m, is the primary unit of length in the International System of Units (SI), though its prefi ...
is an IED that is used to create accurate measurements of power-system current, voltage, and power values. Metering values such as demand and peak are saved within the meter to create historical information about the activity of the power system. ;Digital fault recorder: A digital fault recorder (DFR) is an IED that records information about power-system disturbances. It is capable of storing data in a digital format when triggered by conditions detected on the power system. Harmonics, frequency, and voltage are examples of data captured by DFRs. ;Programmable logic controller (PLC): A
Programmable Logic Controller A programmable logic controller (PLC) or programmable controller is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity tha ...
can be programmed to perform logical control. As with the RTU, a dedicated pair of copper conductors for each contact and transducer value is terminated on panels within the PLC.It is like a work-horse which work upon the command given by their master. ;
Protective relay In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected. The first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detecti ...
: A protective relay is an IED designed to sense power-system disturbances and automatically perform control actions on the I&C system and the power system to protect personnel and equipment. The relay has local termination so that the copper conductors for each contact do not have to be routed to a central termination panel associated with RTU.


Controlling (output) devices

;Load tap changer (LTC): Load tap changers are devices used to change the tap position on transformers. These devices work automatically or can be controlled via another local IED or from a remote operator or process. ;
Recloser In electric power distribution, automatic circuit reclosers (ACRs) are a class of switchgear designed for use on overhead electricity distribution networks to detect and interrupt transient faults. Also known as reclosers or autoreclosers, ACRs a ...
controller: Recloser controllers remotely control the operation of automated reclosers and switches. These devices monitor and store power-system conditions and determine when to perform control actions. They also accept commands from a remote operator or process.


Communications devices

;Communications processor: A communications processor is a substation controller that incorporates the functions of many other I&C devices into one IED. It has many communications ports to support multiple simultaneous communications links. The communications processor performs data acquisition and control of the other substation IEDs and also concentrates the data it acquires for transmission to one or many masters inside and outside the substation.


Applications


Overcurrent protection

All lines and all electrical equipment must be protected against prolonged
overcurrent In an electric power system, overcurrent or excess current is a situation where a larger than intended electric current exists through a conductor, leading to excessive generation of heat, and the risk of fire or damage to equipment. Possible caus ...
. If the cause of the overcurrent is nearby then automatically that current is interrupted immediately. But if the cause of the overcurrent is outside the local area then a
backup In information technology, a backup, or data backup is a copy of computer data taken and stored elsewhere so that it may be used to restore the original after a data loss event. The verb form, referring to the process of doing so, is "back up", w ...
provision automatically disconnects all affected circuits after a suitable time delay. Note that disconnection can, unfortunately, have a
cascade Cascade, Cascades or Cascading may refer to: Science and technology Science *Cascade waterfalls, or series of waterfalls * Cascade, the CRISPR-associated complex for antiviral defense (a protein complex) * Cascade (grape), a type of fruit * Bioc ...
effect, leading to overcurrent in other circuits that then also must therefore disconnect automatically. Also note that
generator Generator may refer to: * Signal generator, electronic devices that generate repeating or non-repeating electronic signals * Electric generator, a device that converts mechanical energy to electrical energy. * Generator (circuit theory), an eleme ...
s that suddenly have lost their load because of such a protection operation will have to shut down automatically immediately, and it may take many hours to restore a proper balance between
demand and supply In microeconomics, supply and demand is an economic model of price determination in a market. It postulates that, holding all else equal, in a competitive market, the unit price for a particular good, or other traded item such as labor or l ...
in the system, partly because there must be proper
synchronization Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...
before any two parts of the system can be reconnected. Reclosing operations of
circuit breakers A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to interrupt current flow to protect equipment and to prevent the risk ...
usually are attempted automatically, and often are successful during thunderstorms, for example.


Supervisory control and data acquisition

A ''supervisory control and data acquisition system'' (
SCADA Supervisory control and data acquisition (SCADA) is a control system architecture comprising computers, networked data communications and graphical user interfaces for high-level supervision of machines and processes. It also covers sensors and ...
) transmits and receives commands or data from process instruments and equipment. Power system elements ranging from pole-mounted switches to entire power plants can be controlled remotely over long distance communication links. Remote switching, telemetering of
grid Grid, The Grid, or GRID may refer to: Common usage * Cattle grid or stock grid, a type of obstacle is used to prevent livestock from crossing the road * Grid reference, used to define a location on a map Arts, entertainment, and media * News g ...
s (showing voltage, current, power, direction, consumption in kWh, etc.), even automatic synchronization is used in some power systems.


Optical fibers

Power utility companies protect high voltage lines by monitoring them constantly. This
supervision Supervision is an act or instance of directing, managing, or oversight. Etymology The English noun "supervision" derives from the two Latin words "super" (above) and "videre" (see, observe). Spelling The spelling is "Supervision" in Standard E ...
requires the transmission of information between the power substations in order to ensure correct operation while controlling every alarm and failure. Legacy telecom networks were interconnected with metallic wires, but the substation environment is characterized by a high level of electromagnetic fields that may disturb copper wires. Authorities use a tele-protection scheme to enable substations to communicate with one another to selectively isolate faults on high voltage lines,
transformer A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
s, reactors and other important elements of the electrical plants. This functionality requires the continuous exchange of critical data in order to assure correct operation. In order to warranty the operation the telecom network should always be in perfect conditions in terms of availability, performance, quality and delays. Initially these networks were made of metallic conductive media, however the vulnerability of the 56–64 kbit/s channels to
electromagnetic interference Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electros ...
, signal ground loops, and ground potential rise made them too unreliable for the power industry. Strong electromagnetic fields caused by the high voltages and currents in
power lines Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines that facilitate this movement form a ''transmission network''. This is d ...
occur regularly in electric substations. Moreover, during fault conditions electromagnetic perturbations may rise significantly and disturb those communications channels based on copper wires. The reliability of the communications link interconnecting the protection relays is critical and therefore must be resistant to effects encountered in high voltage areas, such as high frequency induction and ground potential rise. Consequently, the power industry moved to
optical fiber An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to ...
s to interconnect the different items installed in substations. Fiber optics need not be grounded and are immune to the interferences caused by electrical noise, eliminating many of the errors commonly seen with electrical connections. The use of fully optical links from power relays to multiplexers as described by IEEE C37.94 became standard. A more sophisticated architecture for the protection scheme emphasizes the notion of
fault tolerant Fault tolerance is the property that enables a system to continue operating properly in the event of the failure of one or more faults within some of its components. If its operating quality decreases at all, the decrease is proportional to the ...
networks. Instead of using a direct relay connection and dedicated fibers, redundant connections make the protection process more reliable by increasing the availability of critical data interchanges.


C37.94

IEEE C37.94 , full title ''IEEE Standard for N Times 64 Kilobit Per Second Optical Fiber Interfaces Between Teleprotection and Multiplexer Equipment'', is an
IEEE The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operation ...
standard, published in 2002, that defines the rules to interconnect tele-protection and multiplexer devices of power utility companies. The standard defines a data frame format for optical interconnection, and references standards for the physical connector for
multi-mode optical fiber Multi-mode optical fiber is a type of optical fiber mostly used for communication over short distances, such as within a building or on a campus. Multi-mode links can be used for data rates up to 100 Gbit/s. Multi-mode fiber has a fairly large ...
. Furthermore, it defines behavior of connected equipment on failure of the link, and the timing and optical
signal In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...
characteristics. Teleprotection systems must isolate faults very quickly to prevent damage to the network and power outages. The IEEE committee defined C37.94 as a programmable n x 64 kbit/s (n=1...12) multimode optical fiber interface to provide transparent communications between teleprotection relays and multiplexers for distances of up to 2 km. To reach longer distances, the power industry later adopted a single mode optical fiber interface as well. The standard defines the protection and communications equipment inside a substation using optical fibers, the method for clock recovery, the jitter tolerances allowed in the signals, the physical connection method, and the actions the protection equipment must follow when any kind of network anomalies and faults occur. C37.94 was already implemented by many protection relay manufacturers such as ABB, SEL, RFL, and RAD; and tester manufacturers such as Net Research (NetProbe 2000), ALBEDO and VEEX. Teleprotection equipment once offered a choice of transmission interfaces, such as the IEEE C37.94 compliant optical fiber interface for transmission over fiber pairs, and
G.703 G.703 is a 2016 ITU-T standard for encoding voice or data over digital carriers such as T1 and E1. G.703 provides specifications for pulse-code modulation (PCM). G.703 also specifies E0 (64kbit/s). For information about E0 audio see G.711. ...
, 64kbit/s co-directional and E1 interfaces.


References

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See also

* Automatic generation control *
Smart grid A smart grid is an electrical grid which includes a variety of operation and energy measures including: *Advanced metering infrastructure (of which smart meters are a generic name for any utility side device even if it is more capable e.g. a f ...
*
Smart meter A smart meter is an electronic device that records information such as consumption of electric energy, voltage levels, current, and power factor. Smart meters communicate the information to the consumer for greater clarity of consumption beha ...
*
International Council on Large Electric Systems The International Council on Large Electric Systems (CIGRE) is a global nonprofit organisation in the field of high voltage electricity. It was founded in Paris, France in 1921. The scope of its activities include the technical and economical ...
(CIGRE) *
SCADA Supervisory control and data acquisition (SCADA) is a control system architecture comprising computers, networked data communications and graphical user interfaces for high-level supervision of machines and processes. It also covers sensors and ...
* Power-system automation Electric power Smart grid Electric power transmission Electrical engineering