Electric power transmission
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 which facilitate this movement are known as a transmission network; this is distinct from the local wiring between high-voltage substations and customers, referred to as electric power distribution. The combined transmission and distribution network is known as the "power grid" in North America, or just "the grid". In the United Kingdom, Myanmar and New Zealand, the network is known as the "National Grid". A wide area synchronous grid known as an "interconnection" in North America, directly connects a large number of generators delivering AC power with the same relative frequency to a large number of consumers. For example, there are four major interconnections in North America. In Europe one large grid connects most of continental Europe. Transmission and distribution lines were owned by the same company, but starting in the 1990s, many countries have liberalized the regulation of the electricity market in ways that have led to the separation of the electricity transmission business from the distribution business.
Most transmission lines are high-voltage three-phase alternating current, although single phase AC is sometimes used in railway electrification systems. High-voltage direct-current technology is used for greater efficiency over long distances. HVDC technology is used in submarine power cables, in the interchange of power between grids that are not mutually synchronized. HVDC links are used to stabilize large power distribution networks where sudden new loads, or blackouts, in one part of a network can result in synchronization problems and cascading failures. Electricity is transmitted at high voltages to reduce the energy loss which occurs in long-distance transmission. Power is transmitted through overhead power lines. Underground power transmission has a higher installation cost and greater operational limitations, but reduced maintenance costs. Underground transmission is sometimes used in environmentally sensitive locations. A lack of electrical energy storage facilities in transmission systems leads to a key limitation.
Electrical energy must be generated at the same rate. A sophisticated control system is required to ensure that the power generation closely matches the demand. If the demand for power exceeds supply, the imbalance can cause generation plant and transmission equipment to automatically disconnect or shut down to prevent damage. In the worst case, this may lead to a cascading series of a major regional blackout. Examples include the US Northeast blackouts of 1965, 1977, 2003, major blackouts in other US regions in 1996 and 2011. Electric transmission networks are interconnected into regional and continent wide networks to reduce the risk of such a failure by providing multiple redundant, alternative routes for power to flow should such shut downs occur. Transmission companies determine the maximum reliable capacity of each line to ensure that spare capacity is available in the event of a failure in another part of the network. High-voltage overhead conductors are not covered by insulation; the conductor material is nearly always an aluminum alloy, made into several strands and reinforced with steel strands.
Copper was sometimes used for overhead transmission, but aluminum is lighter, yields only marginally reduced performance and costs much less. Overhead conductors are a commodity supplied by several companies worldwide. Improved conductor material and shapes are used to allow increased capacity and modernize transmission circuits. Conductor sizes range from 12 mm2 with varying resistance and current-carrying capacity. For normal AC lines thicker wires would lead to a small increase in capacity due to the skin effect; because of this current limitation, multiple parallel cables are used when higher capacity is needed. Bundle conductors are used at high voltages to reduce energy loss caused by corona discharge. Today, transmission-level voltages are considered to be 110 kV and above. Lower voltages, such as 66 kV and 33 kV, are considered subtransmission voltages, but are used on long lines with light loads. Voltages less than 33 kV are used for distribution. Voltages above 765 kV are considered extra high voltage and require different designs compared to equipment used at lower voltages.
Since overhead transmission wires depend on air for insulation, the design of these lines requires minimum clearances to be observed to maintain safety. Adverse weather conditions, such as high wind and low temperatures, can lead to power outages. Wind speeds as low as 23 knots can permit conductors to encroach operating clearances, resulting in a flashover and loss of supply. Oscillatory motion of the physical line can be termed gallop or flutter depending on the frequency and amplitude of oscillation. Electric power can be transmitted by underground power cables instead of overhead power lines. Underground cables take up less right-of-way than overhead lines, have lower visibility, are less affected by bad weather. However, costs of insulated cable and excavation are much higher
Frequency is the number of occurrences of a repeating event per unit of time. It is referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency; the period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a newborn baby's heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals, radio waves, light. For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles per unit time. In physics and engineering disciplines, such as optics and radio, frequency is denoted by a Latin letter f or by the Greek letter ν or ν; the relation between the frequency and the period T of a repeating event or oscillation is given by f = 1 T.
The SI derived unit of frequency is the hertz, named after the German physicist Heinrich Hertz. One hertz means. If a TV has a refresh rate of 1 hertz the TV's screen will change its picture once a second. A previous name for this unit was cycles per second; the SI unit for period is the second. A traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. 60 rpm equals one hertz. As a matter of convenience and slower waves, such as ocean surface waves, tend to be described by wave period rather than frequency. Short and fast waves, like audio and radio, are described by their frequency instead of period; these used conversions are listed below: Angular frequency denoted by the Greek letter ω, is defined as the rate of change of angular displacement, θ, or the rate of change of the phase of a sinusoidal waveform, or as the rate of change of the argument to the sine function: y = sin = sin = sin d θ d t = ω = 2 π f Angular frequency is measured in radians per second but, for discrete-time signals, can be expressed as radians per sampling interval, a dimensionless quantity.
Angular frequency is larger than regular frequency by a factor of 2π. Spatial frequency is analogous to temporal frequency, but the time axis is replaced by one or more spatial displacement axes. E.g.: y = sin = sin d θ d x = k Wavenumber, k, is the spatial frequency analogue of angular temporal frequency and is measured in radians per meter. In the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has an inverse relationship to the wavelength, λ. In dispersive media, the frequency f of a sinusoidal wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave: f = v λ. In the special case of electromagnetic waves moving through a vacuum v = c, where c is the speed of light in a vacuum, this expression becomes: f = c λ; when waves from a monochrome source travel from one medium to another, their frequency remains the same—only their wavelength and speed change. Measurement of frequency can done in the following ways, Calculating the frequency of a repeating event is accomplished by counting the number of times that event occurs within a specific time period dividing the count by the length of the time period.
For example, if 71 events occur within 15 seconds the frequency is: f = 71 15 s ≈ 4.73 Hz If the number of counts is not large, it is more accurate to measure the time interval for a predetermined number of occurrences, rather than the number of occurrences within a specified time. The latter method introduces a random error into the count of between zero and one count, so on average half a count; this is called gating error and causes an average error in the calculated frequency of Δ f = 1 2 T
A transmission medium is a material substance that can propagate energy waves. For example, the transmission medium for sounds is a gas, but solids and liquids may act as a transmission medium for sound; the absence of a material medium in vacuum may constitute a transmission medium for electromagnetic waves such as light and radio waves. While material substance is not required for electromagnetic waves to propagate, such waves are affected by the transmission media they pass through, for instance by absorption or by reflection or refraction at the interfaces between media; the term transmission medium refers to a technical device that employs the material substance to transmit or guide waves. Thus, an optical fiber or a copper cable is a transmission medium. Not only this but is able to guide the transmission of networks. A transmission medium can be classified as a: Linear medium, if different waves at any particular point in the medium can be superposed. Electromagnetic radiation can be transmitted through an optical medium, such as optical fiber, or through twisted pair wires, coaxial cable, or dielectric-slab waveguides.
It may pass through any physical material, transparent to the specific wavelength, such as water, glass, or concrete. Sound is, by definition, the vibration of matter, so it requires a physical medium for transmission, as do other kinds of mechanical waves and heat energy. Science incorporated various aether theories to explain the transmission medium. However, it is now known that electromagnetic waves do not require a physical transmission medium, so can travel through the "vacuum" of free space. Regions of the insulative vacuum can become conductive for electrical conduction through the presence of free electrons, holes, or ions. A physical medium in data communications is the transmission path over. Many transmission media are used as communications channel. For telecommunications purposes in the United States, Federal Standard 1037C, transmission media are classified as one of the following: Guided —waves are guided along a solid medium such as a transmission line. Wireless —transmission and reception are achieved by means of an antenna.
One of the most common physical medias used in networking is copper wire. Copper wire to carry signals to long distances using low amounts of power; the unshielded twisted pair is eight strands of copper wire, organized into four pairs. Another example of a physical medium is optical fiber, which has emerged as the most used transmission medium for long-distance communications. Optical fiber is a thin strand of glass. Four major factors favor optical fiber over copper- data rates, distance and costs. Optical fiber can carry huge amounts of data compared to copper, it can be run for hundreds of miles without the need for signal repeaters, in turn, reducing maintenance costs and improving the reliability of the communication system because repeaters are a common source of network failures. Glass is lighter than copper allowing for less need for specialized heavy-lifting equipment when installing long-distance optical fiber. Optical fiber for indoor applications cost a dollar a foot, the same as copper.
Multimode and single mode are two types of used optical fiber. Multimode fiber uses LEDs as the light source and can carry signals over shorter distances, about 2 kilometers. Single mode can carry signals over distances of tens of miles. Wireless media may carry surface waves or skywaves, either longitudinally or transversely, are so classified. In both communications, communication is in the form of electromagnetic waves. With guided transmission media, the waves are guided along a physical path. Unguided transmission media are methods that allow the transmission of data without the use of physical means to define the path it takes. Examples of this include radio or infrared. Unguided media do not guide them; the term direct link is used to refer to the transmission path between two devices in which signals propagate directly from transmitters to receivers with no intermediate devices, other than amplifiers or repeaters used to increase signal strength. This term can apply to unguided media. A transmission may be simplex, full-duplex.
In simplex transmission, signals are transmitted in only one direction. In the half-duplex operation, both stations may only one at a time. In full duplex operation, both stations may transmit simultaneously. In the latter case, the medium is carrying signals in both directions at same time. There are two types of transmission media: guided and unguided. Guided Media: Unshielded Twisted Pair Shielded Twisted Pair Coaxial Cable Optical Fiber hubUnguided Media: Transmission media looking at analysis of using them unguided transmission media is data signals that flow through the air, they are not bound to a channel to follow. Following are unguided media used for data communication: Radio Transmission Microwave Transmission and reception of data is performed in four steps; the data is coded as binary numbers at the sender end A carrie
Telecommunication is the transmission of signs, messages, writings and sounds or information of any nature by wire, optical or other electromagnetic systems. Telecommunication occurs when the exchange of information between communication participants includes the use of technology, it is transmitted either electrically over physical media, such as cables, or via electromagnetic radiation. Such transmission paths are divided into communication channels which afford the advantages of multiplexing. Since the Latin term communicatio is considered the social process of information exchange, the term telecommunications is used in its plural form because it involves many different technologies. Early means of communicating over a distance included visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, optical heliographs. Other examples of pre-modern long-distance communication included audio messages such as coded drumbeats, lung-blown horns, loud whistles. 20th- and 21st-century technologies for long-distance communication involve electrical and electromagnetic technologies, such as telegraph and teleprinter, radio, microwave transmission, fiber optics, communications satellites.
A revolution in wireless communication began in the first decade of the 20th century with the pioneering developments in radio communications by Guglielmo Marconi, who won the Nobel Prize in Physics in 1909, other notable pioneering inventors and developers in the field of electrical and electronic telecommunications. These included Charles Wheatstone and Samuel Morse, Alexander Graham Bell, Edwin Armstrong and Lee de Forest, as well as Vladimir K. Zworykin, John Logie Baird and Philo Farnsworth; the word telecommunication is a compound of the Greek prefix tele, meaning distant, far off, or afar, the Latin communicare, meaning to share. Its modern use is adapted from the French, because its written use was recorded in 1904 by the French engineer and novelist Édouard Estaunié. Communication was first used as an English word in the late 14th century, it comes from Old French comunicacion, from Latin communicationem, noun of action from past participle stem of communicare "to share, divide out.
Homing pigeons have been used throughout history by different cultures. Pigeon post had Persian roots, was used by the Romans to aid their military. Frontinus said; the Greeks conveyed the names of the victors at the Olympic Games to various cities using homing pigeons. In the early 19th century, the Dutch government used the system in Sumatra, and in 1849, Paul Julius Reuter started a pigeon service to fly stock prices between Aachen and Brussels, a service that operated for a year until the gap in the telegraph link was closed. In the Middle Ages, chains of beacons were used on hilltops as a means of relaying a signal. Beacon chains suffered the drawback that they could only pass a single bit of information, so the meaning of the message such as "the enemy has been sighted" had to be agreed upon in advance. One notable instance of their use was during the Spanish Armada, when a beacon chain relayed a signal from Plymouth to London. In 1792, Claude Chappe, a French engineer, built the first fixed visual telegraphy system between Lille and Paris.
However semaphore suffered from the need for skilled operators and expensive towers at intervals of ten to thirty kilometres. As a result of competition from the electrical telegraph, the last commercial line was abandoned in 1880. On 25 July 1837 the first commercial electrical telegraph was demonstrated by English inventor Sir William Fothergill Cooke, English scientist Sir Charles Wheatstone. Both inventors viewed their device as "an improvement to the electromagnetic telegraph" not as a new device. Samuel Morse independently developed a version of the electrical telegraph that he unsuccessfully demonstrated on 2 September 1837, his code was an important advance over Wheatstone's signaling method. The first transatlantic telegraph cable was completed on 27 July 1866, allowing transatlantic telecommunication for the first time; the conventional telephone was invented independently by Alexander Bell and Elisha Gray in 1876. Antonio Meucci invented the first device that allowed the electrical transmission of voice over a line in 1849.
However Meucci's device was of little practical value because it relied upon the electrophonic effect and thus required users to place the receiver in their mouth to "hear" what was being said. The first commercial telephone services were set-up in 1878 and 1879 on both sides of the Atlantic in the cities of New Haven and London. Starting in 1894, Italian inventor Guglielmo Marconi began developing a wireless communication using the newly discovered phenomenon of radio waves, showing by 1901 that they could be transmitted across the Atlantic Ocean; this was the start of wireless telegraphy by radio. Voice and music had little early success. World War I accelerated the development of radio for military communications. After the war, commercial radio AM broadcasting began in the 1920s and became an important mass medium for entertainment and news. World War II again accelerated development of radio for the wartime purposes of aircraft and land communication, radio navigation and radar. Development of stereo FM broadcasting of radio
In electronics and telecommunications, a transmitter or radio transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, applied to the antenna; when excited by this alternating current, the antenna radiates radio waves. Transmitters are necessary component parts of all electronic devices that communicate by radio, such as radio and television broadcasting stations, cell phones, walkie-talkies, wireless computer networks, Bluetooth enabled devices, garage door openers, two-way radios in aircraft, spacecraft, radar sets and navigational beacons; the term transmitter is limited to equipment that generates radio waves for communication purposes. Generators of radio waves for heating or industrial purposes, such as microwave ovens or diathermy equipment, are not called transmitters though they have similar circuits; the term is popularly used more to refer to a broadcast transmitter, a transmitter used in broadcasting, as in FM radio transmitter or television transmitter.
This usage includes both the transmitter proper, the antenna, the building it is housed in. A transmitter can be a separate piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and a receiver combined in one unit is called a transceiver; the term transmitter is abbreviated "XMTR" or "TX" in technical documents. The purpose of most transmitters is radio communication of information over a distance; the information is provided to the transmitter in the form of an electronic signal, such as an audio signal from a microphone, a video signal from a video camera, or in wireless networking devices, a digital signal from a computer. The transmitter combines the information signal to be carried with the radio frequency signal which generates the radio waves, called the carrier signal; this process is called modulation. The information can be added to the carrier in several different ways, in different types of transmitters. In an amplitude modulation transmitter, the information is added to the radio signal by varying its amplitude.
In a frequency modulation transmitter, it is added by varying the radio signal's frequency slightly. Many other types of modulation are used; the radio signal from the transmitter is applied to the antenna, which radiates the energy as radio waves. The antenna may be enclosed inside the case or attached to the outside of the transmitter, as in portable devices such as cell phones, walkie-talkies, garage door openers. In more powerful transmitters, the antenna may be located on top of a building or on a separate tower, connected to the transmitter by a feed line, a transmission line. Electromagnetic waves are radiated by electric charges undergoing acceleration. Radio waves, electromagnetic waves of radio frequency, are generated by time-varying electric currents, consisting of electrons flowing through a metal conductor called an antenna which are changing their velocity or direction and thus accelerating. An alternating current flowing back and forth in an antenna will create an oscillating magnetic field around the conductor.
The alternating voltage will charge the ends of the conductor alternately positive and negative, creating an oscillating electric field around the conductor. If the frequency of the oscillations is high enough, in the radio frequency range above about 20 kHz, the oscillating coupled electric and magnetic fields will radiate away from the antenna into space as an electromagnetic wave, a radio wave. A radio transmitter is an electronic circuit which transforms electric power from a power source into a radio frequency alternating current to apply to the antenna, the antenna radiates the energy from this current as radio waves; the transmitter impresses information such as an audio or video signal onto the radio frequency current to be carried by the radio waves. When they strike the antenna of a radio receiver, the waves excite similar radio frequency currents in it; the radio receiver extracts the information from the received waves. A practical radio transmitter consists of these parts: A power supply circuit to transform the input electrical power to the higher voltages needed to produce the required power output.
An electronic oscillator circuit to generate the radio frequency signal. This generates a sine wave of constant amplitude called the carrier wave, because it serves to "carry" the information through space. In most modern transmitters, this is a crystal oscillator in which the frequency is controlled by the vibrations of a quartz crystal; the frequency of the carrier wave is considered the frequency of the transmitter. A modulator circuit to add the information to be transmitted to the carrier wave produced by the oscillator; this is done by varying some aspect of the carrier wave. The information is provided to the transmitter either in the form of an audio signal, which represents sound, a video signal which represents moving images, or for data in the form of a binary digital signal which represents a sequence of bits, a bitstream. Different types of transmitters use different modulation methods to transmit information: In an AM transmitter the amplitude of the carrier wave is varied in proportion to the modulation signal.
In an FM transmitter the frequency of the carrier is varied by the modulation signal. In an FSK transmitter, which transmits digital data, the frequency of the carrier is shifted between two frequencies which represent the two binary digits, 0 and 1. Many oth
High-voltage direct current
A high-voltage, direct current electric power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses. For underwater power cables, HVDC avoids the heavy currents required to charge and discharge the cable capacitance each cycle. For shorter distances, the higher cost of DC conversion equipment compared to an AC system may still be justified, due to other benefits of direct current links. HVDC uses voltages between 100 kV and 1,500 kV. HVDC allows power transmission between unsynchronized AC transmission systems. Since the power flow through an HVDC link can be controlled independently of the phase angle between source and load, it can stabilize a network against disturbances due to rapid changes in power. HVDC allows transfer of power between grid systems running at different frequencies, such as 50 Hz and 60 Hz.
This improves the stability and economy of each grid, by allowing exchange of power between incompatible networks. The modern form of HVDC transmission uses technology developed extensively in the 1930s in Sweden and in Germany. Early commercial installations included one in the Soviet Union in 1951 between Moscow and Kashira, a 100 kV, 20 MW system between Gotland and mainland Sweden in 1954; the longest HVDC link in the world is the Rio Madeira link in Brazil, which consists of two bipoles of ±600 kV, 3150 MW each, connecting Porto Velho in the state of Rondônia to the São Paulo area. The length of the DC line is 2,375 km. In July 2016, ABB Group received a contract in China to build an ultrahigh-voltage direct-current land link with a 1100 kV voltage, a 3,000 km length and 12 GW of power, setting world records for highest voltage, longest distance, largest transmission capacity. High voltage is used for electric power transmission to reduce the energy lost in the resistance of the wires. For a given quantity of power transmitted, doubling the voltage will deliver the same power at only half the current.
Since the power lost as heat in the wires is directly proportional to the square of the current, doubling the voltage reduces the line losses by a factor of 4. While power lost in transmission can be reduced by increasing the conductor size, larger conductors are heavier and more expensive. High voltage cannot be used for lighting or motors, so transmission-level voltages must be reduced for end-use equipment. Transformers are used to change the voltage levels in alternating current transmission circuits. Transformers made voltage changes practical, AC generators were more efficient than those using DC; because of this, AC became dominant after the conclusion of the War of Currents in 1892. The War of Currents was a competition fought in the US between the DC system of Thomas Edison and the AC system of George Westinghouse. Practical conversion of power between AC and DC became possible with the development of power electronics devices such as mercury-arc valves and, starting in the 1970s, semiconductor devices as thyristors, integrated gate-commutated thyristors, MOS-controlled thyristors and insulated-gate bipolar transistors.
The first long-distance transmission of electric power was demonstrated using direct current in 1882 at Miesbach-Munich Power Transmission, but only 1.5 kW was transmitted. An early method of high-voltage DC transmission was developed by the Swiss engineer René Thury and his method was put into practice by 1889 in Italy by the Acquedotto De Ferrari-Galliera company; this system used series-connected motor-generator sets to increase the voltage. Each set was driven by insulated shafts from a prime mover; the transmission line was operated in a'constant current' mode, with up to 5,000 volts across each machine, some machines having double commutators to reduce the voltage on each commutator. This system transmitted 630 kW at 14 kV DC over a distance of 120 km; the Moutiers–Lyon system transmitted 8,600 kW of hydroelectric power a distance of 200 km, including 10 km of underground cable. This system used eight series-connected generators with dual commutators for a total voltage of 150 kV between the positive and negative poles, operated from c.1906 until 1936.
Fifteen Thury systems were in operation by 1913. Other Thury systems operating at up to 100 kV DC worked into the 1930s, but the rotating machinery required high maintenance and had high energy loss. Various other electromechanical devices were tested during the first half of the 20th century with little commercial success. One technique attempted for conversion of direct current from a high transmission voltage to lower utilization voltage was to charge series-connected batteries reconnect the batteries in parallel to serve distribution loads. While at least two commercial installations were tried around the turn of the 20th century, the technique was not useful owing to the limited capacity of batteries, difficulties in switching between series and parallel connections, the inherent energy inefficiency of a battery charge/discharge cycle. First proposed in 1914, the grid controlled mercury-arc valve became available for power transmission during the period 1920 to 1940. Starting in 1932, General Electric tested mercury-vapor valves and a 12 kV DC transmission line, which served to convert 40 Hz generation to serve 60 Hz loads, at Mechanicville, New York.
In 1941, a 60 MW, ±200 kV, 115 km buried cable
An electrical connector is an electro-mechanical device used to join electrical terminations and create an electrical circuit. Electrical connectors consist of jacks; the connection may be temporary, as for portable equipment, require a tool for assembly and removal, or serve as a permanent electrical joint between two wires or devices. An adapter can be used to bring together dissimilar connectors. Hundreds of types of electrical connectors are manufactured for power and control applications. Connectors may join two lengths of flexible copper wire or cable, or connect a wire or cable to an electrical terminal. In computing, an electrical connector can be known as a physical interface. Cable glands, known as cable connectors in the US, connect wires to devices mechanically rather than electrically and are distinct from quick-disconnects performing the latter. Electrical connectors are characterised by their pinout and physical construction, contact resistance, insulation between pins and resistance to vibration, resistance to entry of water or other contaminants, resistance to pressure, reliability and ease of connecting and disconnecting.
They may be keyed to prevent insertion in the wrong orientation, connecting the wrong pins to each other, have locking mechanisms to ensure that they are inserted and cannot work loose or fall out. Some connectors are designed such that certain pins make contact before others when inserted, break first on disconnection, it is desirable for a connector to be easy to identify visually, rapid to assemble, require only simple tooling, be inexpensive. In some cases an equipment manufacturer might choose a connector because it is not compatible with those from other sources, allowing control of what may be connected. No single connector has all the ideal properties. Fretting is a common failure mode in electrical connectors that have not been designed to prevent it. Many connectors are keyed, with some mechanical component which prevents mating except with a oriented matching connector; this can be used to prevent incorrect or damaging interconnections, either preventing pins from being damaged by being jammed in at the wrong angle or fitting into imperfectly fitting plugs, or to prevent damaging connections, such as plugging an audio cable into a power outlet.
For instance, XLR connectors have a notch to ensure proper orientation, while Mini-DIN plugs have a plastic projection, which fits into a corresponding hole in the socket and prevent different connectors from being pushed together. Some connector housings are designed with locking mechanisms to prevent inadvertent disconnection or poor environmental sealing. Locking mechanism designs include locking levers of various sorts, screw locking, toggle or bayonet locking. Depending on application requirements, housings with locking mechanisms may be tested under various environmental simulations that include physical shock and vibration, water spray, etc. to ensure the integrity of the electrical connection and housing seals. A terminal is a simple type of electrical connector that connects two or more wires to a single connection point. Wire nuts are another type of single point connector. Terminal blocks provide a convenient means of connecting individual electrical wires without a splice or physically joining the ends.
They are used to connect wiring among various items of equipment within an enclosure or to make connections among individually enclosed items. Since terminal blocks are available for a wide range of wire sizes and terminal quantity, they are one of the most flexible types of electrical connector available; some disadvantages are that connecting wires is more difficult than plugging in a cable and the terminals are not well protected from contact with persons or foreign conducting materials. One type of terminal block accepts wires that are prepared only by removing a short length of insulation from the end. Another type accepts wires that have spade terminal lugs crimped onto the wires. Printed circuit board mounted terminal blocks allow individual wires to be connected to the circuit board. PCB mounted terminal blocks are soldered to the board, but they are available in a pull-apart version that allows the wire-connecting half of the block to be unplugged from the part, soldered to the PCB.
A general type of connector that screws or clamps bare wire to a post. Many, but not all binding posts will accept a banana connector plug. Crimp-on connectors are a type of solderless connection. Since stripping the insulation from wires is time-consuming, many connectors intended for rapid assembly use insulation-displacement connectors so that insulation need not be removed from the wire; these take the form of a fork-shaped opening in the terminal, into which the insulated wire is pressed and which cut through the insulation to contact the conductor within. To make these connections reliably on a production line, special tools are used which control the forces applied during assembly. If properly assembled, the resulting terminations are gas-tight and will last the life of the product. A common example is the multi