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Electrical basics

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To Know more about Electrical Components.

To Know more about Electrical Components.

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  • 1. Electrical basics
  • 2. Contents
    • Fuse
    • 3. A circuit breaker
    • 4. A relay
    • 5. A contactor
    • 6. Suppression Diodes:
    • 7. Wiring
    • 8. American wire gauge (AWG)
    • 9. Current transformer
    • 10. Phase monitoring relay
    • 11. Ground fault interrupter (GFI)
    • 12. Emergency off (EMO) Switch
    • 13. Cable Basics
    • 14. Heat Shrink tubing
    • 15. Busbar
    • 16. Restriction of Hazardous Substances Directive (ROHS)
    • Fuse - is a type of over current protection device. Its essential component is a metal wire or strip that melts when too much current flows, which interrupts the circuit in which it is connected. Short circuit, overload or device failure is often the reason for excessive current. A fuse interrupts excessive current (blows) so that further damage by overheating or fire is prevented.
    • A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.
    • 17. In - rated current of a circuit breaker for low voltage distribution applications as the current that the breaker is designed to carry continuously (at an ambient air temperature of 30 °C).
    • 18. Instantaneous tripping current, that is the minimum value of current that causes the circuit-breaker to trip without intentional time delay (i.e., in less than 100 ms), expressed in terms of In
  • Type B devices are generally suitable for domestic applications. They may also be used in light commercial applications where switching surges are low or non-existent.
    Type C devices are the normal choice for commercial and industrial applications where fluorescent lighting, motors etc. are in use.
    Type D devices have more limited applications, normally in industrial use where high inrush currents may be expected. Examples include large battery charging systems, winding motors, transformers, X-ray machines and some types of discharge lighting.
    Type B devices are designed to trip at fault currents of 3-5 times rated current (In). For example a 10A device will trip at 30-50A.
    Type C devices are designed to trip at 5-10 times In (50-100A for a 10A device).
    Type D devices are designed to trip at 10-20 times In (100-200A for a 10A device).
  • 19.
    • A relay is an electrically operated switch. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal.
    • 20. A relay is used to isolate one electrical circuit from another. It allows a low current control circuit to make or break an electrically isolated high current circuit path.
    • 21. A relay will switch one or more poles, each of whose contacts can be thrown by energizing the coil in one of two ways:
    • 22. Normally-open (NO) contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive.
    • 23. Normally-closed (NC) contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive
  • 24.
    • A contactor is an electrically controlled switch used for switching a power circuit, similar to a relay except with higher current ratings. A contactor is controlled by a circuit which has a much lower power level than the switched circuit. Unlike a circuit breaker, a contactor is not intended to interrupt a short circuit current.
    • 25. A type of relay that can handle the high power required to directly control an electric motor is called a contactor.
    • 26. Contactors typically have multiple contacts, and those contacts are usually (but not always) normally-open, so that power to the load is shut off when the coil is de-energized. Perhaps the most common industrial use for contactors is the control of electric motors.
    • The top three contacts switch the respective phases of the incoming 3-phase AC power, typically at least 480 Volts for motors 1 horsepower or greater. The lowest contact is an "auxiliary" contact which has a current rating much lower than that of the large motor power contacts, but is actuated by the same armature as the power contacts. The auxiliary contact is often used in a relay logic circuit, or for some other part of the motor control scheme, typically switching 120 Volt AC power instead of the motor voltage. One contactor may have several auxiliary contacts, either normally-open or normally-closed, if required.
    • 27. Unlike general-purpose relays, contactors are designed to be directly connected to high-current load devices. Relays tend to be of lower capacity and are usually designed for both normally closed and normally open applications. Devices switching more than 15 amperes or in circuits rated more than a few kilowatts are usually called contactors. Apart from optional auxiliary low current contacts, contactors are almost exclusively fitted with normally open contacts. Unlike relays, contactors are designed with features to control and suppress the arc produced when interrupting heavy motor currents
    • 28. Applications - Contactors are used to control electric motors, lighting, heating, capacitor banks, and other electrical loads.
  • Suppression Diodes:Anytime that a relay coil is driven by a circuit that is not specifically designed to drive a relay, you should use a quenching/suppression diode connected in parallel with the relay coil. The diagram below will show the connection of the diode. Initially, you may think the diode serves no purpose because the voltage applied to the relay cannot pass through the diode. This is true when the relay is energized. The diode comes into play when the power source is removed from the relay coil. When power is applied to the relay coil, a magnetic field is created and energy is stored in the coil. When power is removed, the magnetic field collapses causing a reverse voltage to be generated (it's called inductive kickback or back EMF). The back EMF can easily reach 200 volts. The diode will absorb the reverse voltage spike. This voltage, if not absorbed by the diode, will cause premature failure of switch contacts and may cause the failure of power switching transistors. You can use virtually any type of rectifier or switching diode (i.e. 1N4001, 1N4002, 1N400x... )
  • 29.
    • Wiring- Three-phase electric power is a common method of alternating current electric power generation, transmission, and distribution.
    3Ph, 4 wire - Three-phase systems may have a neutral wire. A neutral wire allows the three-phase system to use a higher voltage while still supporting lower-voltage single-phase appliances.
    3-Phase 5-Wire 208 V- This is the simply 3-phase power (3 hot wires and a ground) with a neutral wire to provide 120 V.
    Terminology:
    Hot is any conductor (wire or otherwise) connected with an electrical system that has electric potential relative to electrical ground or neutral.
    A neutral wire is the return leg of a circuit; in building wiring systems the neutral wire is connected to earth ground at least at one point
    Ground is a conductor with continuity to earth
  • 30.
    • American wire gauge (AWG) is a standardized wire gauge system used predominantly in the United States and Canada for the diameters of round, solid, nonferrous, electrically conducting wire. The cross-sectional area of each gauge is an important factor for determining its current-carrying capacity.
    • Current transformer In electrical engineering, a current transformer (CT) is used for measurement of electric currents. Current transformers, together with voltage transformers (VT) (potential transformers (PT)), are known as instrument transformers. When current in a circuit is too high to directly apply to measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be conveniently connected to measuring and recording instruments.
    • 31. A current transformer also isolates the measuring instruments from what may be very high voltage in the monitored circuit. Current transformers are commonly used in metering and protective relays in the electrical power industry.
    • 32. The primary circuit is largely unaffected by the insertion of the CT. The rated secondary current is commonly standardized at 1 or 5 amperes. For example, a 4000:5 CT would provide an output current of 5 amperes when the primary was passing 4000 amperes.
    • Phase monitoring relay is designed to monitor the correct phase rotation or sequence of 3 phase system L1, L2, L3. Rotation machines are particularly vulnerable to incorrect phase sequence. Three Phase motors rotate in the wrong direction, potentially leading to physical damage or the risk of injury to personal, yet voltage & current reading may appear normal. If one phase is lost because of a blown fuse, electric motors can continue to operate (single phase) which can result in severe electrical or mechanical damage.
    • 33. This relay should be used to monitor the incoming supply, protecting all equipment against incorrect connection at initial installation or after maintenance work. Rotating machines that cannot tolerate reverse rotation or pose significant risk to personal under this condition should be individually protected with this relay. The possibility of incorrect supply connection is much more likely in portable equipment or marine applications.
  • 34.
    • Ground fault interrupter (GFI) - is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor. Such an imbalance is sometimes caused by current leakage through the body of a person who is grounded and accidentally touching the energized part of the circuit. A lethal shock can result from these conditions. GFIs are designed to disconnect quickly enough to mitigate the harm caused by such shocks although they are not intended to provide protection against overload or short-circuit conditions.
    • 35. GFIs are designed to prevent electrocution by detecting the leakage current, which can be far smaller (typically 5–30 milli amperes) than the currents needed to operate conventional circuit breakers or fuses (several amperes). GFIs are intended to operate within 25-40 milliseconds, before electric shock can drive the heart into ventricular fibrillation, the most common cause of death through electric shock.
    • 36. GFIs are also commonly known as Ground fault circuit interruptor (GFCI), Residual current device (RCD), Earth leakage circuit breaker (ELCB).
    • Emergency off (EMO) Switch -is a switch when deactivated, places the equipment into a safe shutdown condition and will restrict all hazardous potentials to the main power enclosure. This is a condition in which all hazardous voltage has been removed from the equipment, all hazardous production materials flow has been stopped, any radiation sources have been de-energized or totally contained, any capacitors have been grounded, all moving parts stopped, internal and external heat sources shut off, and the equipment presents minimum hazard to personnel or the facility.
  • 37.
    • Cable Basics
    • 38. Conductor is a material which contains movable electric charges.
    • 39. Of the metals commonly used for conductors, copper has a high conductivity. Silver is more conductive, but due to cost it is not practical in most cases. Aluminium has been used as a conductor in housing applications for cost reasons.
    • 40. Electrical Wires are either solid or stranded Conductors. "Solid Conductors" are exactly that, one solid Wire. "Stranded Conductors" consist of a Wire made of a number of smaller Wire strands wrapped around each other. The choice between solid or stranded depends on the need for flexibility in handling and working with the Wire. Smaller electrical Wire Sizes are generally made of solid Conductors; while Wires larger than Number 6 AWG are generally stranded.
    • Insulation separates conductors electrically and physically within a cable.
    • 41. The jacket physically protects the internal components of a cable, improves the cable’s appearance and provides flame retardancy.
    • 42. –Protects from the environment
    • 43. –Protects from the rigors of installation
    • 44. Drain Wire Metallic conductor frequently used in contact with foil-type signal-cable shielding to provide a low-resistance ground return at any point along the shield.
    • 45. Twisted pair cabling is a type of wiring in which two conductors (the forward and return conductors of a single circuit) are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighboring pairs.
    • Shielding - Contains electrical energy so that the signal on the cable does not radiate and interfere with signals in other nearby cables and circuitry.
    •Protects the signal from external interference.
    Shielding materials-
    • Heat Shrink tubing- is a sleeve ordinarily made of nylon or polyolefin, which shrinks in diameter when heated. Its diameter and thickness can vary. Heat shrink tubing is rated by its expansion ratio, a comparative of the differences in expansion and recovery rate. Heat shrink is used to insulate wires offering abrasion resistance and environmental protection for stranded and solid wire conductors, connections, joints and terminals in electrical engineering. It can also be used to repair the insulation on wires or to bundle them together, to protect wires or small parts from minor abrasion, and to create cable entry seals, offering environmental sealing protection between bulkheads and adding sealability to electrical junction boxes.
    • 50. Common shrink ratio is 2:1, while high-grade polyolefin heat shrink is available in 3:1
    • The tubing is placed over the connection to be protected and then heated with an oven, hot air gun or similar tool. Convenient, but less effective, methods for shrinking the tube include a soldering iron (held in close proximity, but not touching the tube) or the heat from a lighter. These processes cause the tubing to contract as far as one sixth of its original diameter (dependent on the heat shrink, 2:1 is the most common), providing a snug fit over irregularly shaped joints. This provides good electrical insulation, protection from dust, solvents and other foreign materials, as well as strain relief. If overheated, heat shrink tubing can melt, scorch or catch fire like any other plastic.
    • 51. Heat-shrink tubing is manufactured from a thermoplastic material such as polyolefin, fluoropolymer (such as FEP, PTFE or Kynar), PVC, neoprene, silicone elastomer or Viton.
    • 52. Heat shrink tubing is available in a variety of colors to allow easier color coding of wires and connections.
    • Busbar - In electrical power distribution, a busbar is a thick strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus. Busbars are used to carry very large currents, or to distribute current to multiple devices within switchgear or equipment. Busbars are typically either flat strips or hollow tubes as these shapes allow heat to dissipate more efficiently due to their high surface area to cross-sectional area ratio.
    • 53. A busbar may either be supported on insulators, or else insulation may completely surround it. Busbars are protected from accidental contact either by a metal earthed enclosure or by elevation out of normal reach. Neutral busbars may also be insulated. Earth busbars are typically bolted directly onto any metal chassis of their enclosure.
    • Restriction of Hazardous Substances Directive (ROHS) -The Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment 2002/95/EC (listen; commonly referred to as the Restriction of Hazardous Substances Directive or RoHS) was adopted in February 2003 by the European Union. The RoHS directive took effect on 1 July 2006, and is required to be enforced and become law in each member state. This directive restricts the use of six hazardous materials in the manufacture of various types of electronic and electrical equipment. It is closely linked with the Waste Electrical and Electronic Equipment Directive (WEEE) 2002/96/EC which sets collection, recycling and recovery targets for electrical goods and is part of a legislative initiative to solve the problem of huge amounts of toxic e-waste.
    RoHS is often referred to as the lead-free directive, but it restricts the use of the following six substances:
    • Lead (Pb)
    • 54. Mercury (Hg)
    • 55. Cadmium (Cd)
    • 56. Hexavalent chromium (Cr6+)
    • 57. Polybrominated biphenyls (PBB)
    • 58. Polybrominated diphenyl ether (PBDE)
    The maximum permitted concentrations are 0.1% or 1000 ppm (except for cadmium, which is limited to 0.01% or 100 ppm) by weight of homogeneous material.