Cable & Its Types

Cable is assembly of two or more than two conductor in running side by side or bundled form. It is used in building wiring and used in industry and commercial places to aim of transmit power or signal from one to another, and it is very important to install wire of good quality otherwise it would burn down. It is very careful about selection of cable according to requirement. There are many types of cable that are found in market according to use like there are also communication cable used to transmit low power signal and for uses of electronic signal purposes and Fiber optical cable used for optical data through light source to receiving devices and  the cable which is used to transmit electric power is called Power cable.

  1. Basic parts of power cable: –
  • Conductor

Copper and aluminum are used as a conductor material in cable because of higher electrical conductivity solid or number of bare wires either made up of aluminum or copper to make a power cable.

The number of wire strands in conductors are 7, 19,37,61,91 etc. The size of conductor is represented by 7/A, 19/B, 37/C and so on, in which first represent the number of strands and second represent like A, B, C, represent diameter of individual wire in cm or mm. 

  • Insulator

Most used insulator in cable like insulated like poly vinyl chloride, impregnated paper, butyl rubber, cross linked polythene but paper insulated cable is preferred because of their high current capacity and generally reliable and having a long life.

The insulator must have following properties: –

  1. It must have high resistance so that it does not allow current flow in it.
  2. It must have high dielectric strength so that it does not allow any leakage current.
  3. It has high mechanical strength so that there is less chance of breakdown
  4. It must be capable of operating at high temperature
  5. It should have low thermal resistance.
  6. It should have low power factor.
  • Inner Sheath

It basically used for protecting the cable from moisture because moisture evaporate the property of insulation. It made of lead alloy, and these strengths withstand the internal pressure of pressurized cables. The material should have nonmagnetic material in inner sheath. In power cables there is an aluminum sheath is used because it is cheaper, smaller in weight and high mechanical strength than the lead sheath.

When there is an underground cable then protection from corrosion or electrolyte we use material like hessian or PVC.

  • Armouring

 Armouring is done by galvanized steel wire, or two layer of metal type are applied over sheath for protecting it from mechanical damage. The steel wire nis normally used because it has high longitudinal strength.

  • Oversheath

It gives the mechanical strength to cables. It protects from all over damage like moisture, corrosion, dirt, dust and so on. The thermoplastic material is used making over sheath.

  1. Types of Cable   
  • Ribbon Electric Cable

It consists of multiple insulated wiring running parallel with one another and used for multiple data transmission like this is used to connect the CPU with motherboard. And are generally used for interconnection of networking device.

     

  • Shielded Cables

It consists of one or two insulated which are covered by a woven braided shield or aluminium foil for better signal transmission and removing irregularities in frequency and power and external interference in radio. These cables are also used to transmit high voltage and are protected by shield.

 

  • Coaxial Cable

It consists of solid copper or steel conductor plated with copper which is enclosed in the metallic braid and metallic tape. This is entirely covered by with an insulated protective outer jacket. These types of electric cable are used for computer networking and audio video networking. It is used in telephone trunk line, broadband internet, high speed computer data busses, cable television and connecting radio transmitter.

 

  • Twisted Pair Cables

It has two or more insulated copper wires which are twisted with each other and are colour coded. These are used in telephone cable and resistance to external interference can be measured by number of wires.

 

  • Fiber Optical Cable

These types of cable are used to transport optical data through light source to the receiver. It is assembled similar to electrical cable but containing one or more optical fibre that are used to carry light. These optical fiber elements are typically individual coated with plastic layer and contained in protective tube suitable for environment

                                              

  • Instrumentation Cable

These are flexible and shielded cables for transmission of signal between equipment in industrial installation. Especially suitable for optimum data transmission with high level of electromagnetic interference.

                            

  • Underground Cable

Underground cables are employed to transmit and distribution of electrical power where there is impractical to use overhead transmission line, or this is used in congested area where there is impossible to use overhead transmission line. There are kind of cable used depend upon voltage level and service requirement. Underground cable consists of a central core or more than two or three core made of copper or sometime uses of aluminium and insulated from each other by impregnated paper and metallic sheath is provided to protect insulation from moisture.

Types of cable used in any particular location depend upon its mechanical strength and voltage level.

According to voltage level, there category can be divided.

Types of cable

Operating voltage

Low voltage cable

             Up to 1KV

High voltage cable

             Up to 11KV

Super tension cable

             Up to 33KV

Extra high-tension cable

             Up to 66KV

Extra super voltage cable

             Up to 132KV

 

 

  1. Selection of Cable

For consideration of cable for correct size and for type of application, some factor to be considered such as following:

  • System voltage
  • Current carrying capacity
  • permissible voltage drop
  • Short circuit rating
  1. References 

 

 

  Electrical panel and Its Type

 

Electrical panel is a combination of electrical devices which uses electrical power to control various mechanical function of industry equipment or machinery.

 An electrical panel includes two main categories

  1. Panel Structure
  2. Electrical component

Panel structure

The structure of an electrical panel is a combination of enclosure and back panel.

The enclosure a type of metal box which varies in size and is typically made of an aluminium or stainless steel. The number of doors usually one or two needed on enclosure. Enclosure have following properties like waterproof, dust proofing and indoor and outdoor use purpose and Hazardous condition rating and back panels a sheet mounted inside the enclosure that provide structure support for DIN rail mounting and wiring ducts.

Electrical component

There are eight types of mainly electrical component within an electrical panel enclosure which define and organize a several different functions carried out by panel.

This component includes:

    1. Main circuit breaker
    2. Surge arrestors
    3. Transformer
    4. Terminal blocks
    5. Programmable logic control
    6. Relays and contractors
    7. Circuit breakers
    8. Human machine interface

Types of Panels

  • HT panel

 

HT Panel are generally used to supply power to various electrical devices and distribution board. HT panels are installed for both outdoor and indoor application mostly used in every substation for controlling the power flow.

  • Power control center panel

It take directly supply from transformer and used to control power supply in large industry as well as commercial units. The power supplied into heavy machineries, equipments , transformer are controlled according to need of electrical load using these PCC panels. It is used in every industry like chemical, plastic, paper, power, oil, and natural gas, dairies. The main function of panel is to protect and control power distribution for large manufacturing industries.

  • Main LT panel

These are used as low voltage panel to obtain power from generator or transformer and distribution electricity to various electrical devices and distribution board. LT panel are designed to function at lower voltage up to 430V with low insulation level.

  • MCC panel

These panels are an assembly of starters, circuit breakers, fuses, relay and variable frequency drive to control drives from center location. It consists of multiple enclosed section having a common power bus and with each section containing combination starter, which in turn consist of motor starter, fuses or circuit breaker and power disconnect. Motor control center also includes push button, indicator, variable frequency drive, logic controller and starters and metering equipment. These panels are used in large commercial building, industry and where there are multiple drives that need to be controlled from a central location, such as mechanical room or electrical room.

Reference

https://www.squareone.ca/resource-centres/getting-to-know-your-home/electrical-panel

 

 

.

 

Programmable Logic Controller

PLC is an industrial grade computer used in automation industry to make system reliable through logic. It was invented by General motor, in America and Dick Morley was considered father of PLC. Dick Morley has identified the problem in industry that before PLC there is hardware wiring and this hardware nature made it difficult for design engineer to find troubleshooting and system is also not reliable. Now a days PLC is used in every automation industry and there are so many Industry providing automation digital solution like Schneider electric, Allen Bradley, Siemens industries and so on.

Working of PLC

PLC works in program of scan cycle where it read executes it program repeatedly and there is ladder logic and scan cycle consist of 3 steps.

  1. Read input
  2. Execute the program
  3. Write output

It follows the sequence of instruction and works in real time that is millisecond and in milliseconds for the processor to evaluate all the instruction and update all the output according to instruction.

Component of PLC

 They have three components, and these are: processor, power supply input/output section                               

  • Processor

It is brain of system of plc system, is a solid state device designed to perform a wide variety of production, machine tool and processor control function. Conventionally electromechanical device, relays and their associated wiring formerly performed these function. It operates in 5volt supply and supplied by power supply. Once the ladder diagram program is entered into processor, it remains until changed by the user with one of programming devices and program unaltered through power failure.

  • Power supply

It work is to convert line voltage into 24 dc voltage to provide internal circuitry. Basically, it is combination of transformer, rectifier and capacitor. In some cases, it also provides an isolated VDC supply to power dc input circuits, switches and indicators. There are so type power supply found in PLC like DC/DC converter power supply, Frequency converter plc power supply, Linear plc power supply and Switching plc power supply.

  • PLC Input/Output

Electrical noise like spike in power lines or load kick back would have series impact on PLC internal circuits this is where input/output portion play a very important role. The I/O both protect CPU from electrical noise. The I/O section is where status signal is filtered to remove noise level and CPU decision are made and put into operation. The PLC inputs provide their status to a storage area within the CPU AND outputs are driven from similar stored status in the CPU. Real world devices like push buttons, limit switches and sensor are connected through input modules in the PLC. These modules detect a change in state of input signal and provide a stored image to input element in ladder logic. The input element simulates action of relay contact within PLC. In turn, output element are energized which produces desired output signal to drive load such as motor controller, contactors, via output modules in the I/O.

  • PLC Programming

PLC are simply to program. They use a relay ladder language that is similar to magnetic relay circuitry. Engineers, and electrician can learn to program the PLC without extensive training or experience. There are numerous advantages in using PLC versus a relay or solid electronics. In a PLC, changes can be accomplished quickly and inmost cases, without hardware modification to the controller.

Advantages

The advantages one gets with PLC are-

  1. Less wiring.
  2. Easier and make faster response in real time.
  3. It make trouble shooting easier and reducing downtime.
  4. High reliable and flexible.
  5. Low power consumption.
  6. Capable of handling complex logic.

Conclusion

PLC applications are typically customized system. It is low compared to cost specific custom- built control design. It requires less maintenance due to absence of moving parts, thus making things they work better. Overall, PLC appear to be an excellent solution for many different problems.

References 

  1. https://www.unitronicsplc.com/what-is-plc-programmable-logic-controller/?__cf_chl_managed_tk__=pmd_fcc46ff256a5f8fc95b6a9ac40d67fed824816f5-1626427881-0-gqNtZGzNAuKjcnBszQgO
  2. https://www.galco.com/comp/prod/plc.htm#:~:text=Programmable%20Logic%20Controllers%20have%20three,(I%2FO)%20section.&text=The%20processor%2C%20or%20the%20brain,%2C%20and%20process%2Dcontrol%20functions.

 

Earthing

Earthing is arrangement by which an electrical installation is connected to means of earthing. This is usually for safety purposes although sometimes also for functional purposes, for example in case telegraph lines which use earth as conductor to save cost of return wire over a long circuit. If there is fault in electrical installation, a person could get an electric shock by touching a live metal part because electricity uses the body as path to earth. Earthing provides an alternate path for fault current to flow of earth. It can be seen in power system networks, industries, domestic homes, commercial buildings.  

In this below diagram, we can easily see that equipment body leakage current leakage from equipment body, pass to a human body as there is no grounding of equipment or device. This increases the risk of electrical shock. Hence earthing play an immense important role in industries, commercial building, home etc.

Electrical system without earthing

In this below diagram, with grounding of equipment, the whole leakage of current in equipment  body passes through low resistance path called ground wire so there is a negligible chance of electrical shock.                      

Electrical system with earthing

 

Method of earthing

There are various types of earthing is done like rod earthing, strip earthing, plate earthing, pipe earthing and earthing through water mains but pipe and plate earthing is preferred so much.

  • Earthing mat

 It is done by number of joining of rod through copper conductor and it reduces overall grounding resistance of system. Such type of earthing helps to limiting the potential. This type of earthing used in where there is a high fault current is to be experienced. While designing this system following points must consider.

  • Earthing electrode

 In this earthing, we may use wire, rod, pipe and inserted vertically or horizontally into ground and In distribution system there is rod of nearly 1m is used and inserted vertically into ground but in generating substations there is earthing mat is used rather than Earthing electrode.

  • Pipe earthing

This type of earthing is mostly used and this is considered best method as compared to other type of earthing for same soil condition. In this earthing, the galvanized steel or perforated pipe of approved length and diameter depend upon types of soil and current carried by that rod is placed upright in wet soil as shown in figure. Normally size of pipe is of 40mm diameter and 2.5m in length for ordinary soil but for dry soil length may increase. When there is summer then moisture of soil decrease which cause increase in ground resistance some arrangement of water is done for water accessible or 3 or 4 buckets of water is put into a pipe which is connected to soil pit. In soil pit, there is mixed of charcoal and salt around the pipe to reduce the effective resistance of soil.

  • Plate earthing

In this earthing, either copper plate of 60cm×60cm×3m or galvanized iron rod of 60 cm× 60 cm×6mm is buried in ground with it face vertically to ground and depth is not less than 3m from ground level. The ground wire connected to copper plate through nut or bolt. Copper wire is not used mostly because of high costing. The layer of soil and coke is placed in soil pit.

  • Earthing through water mains

In this type of grounding, the copper or GI wire is connected to water mains through water pipe and water pipe is directly connected to earth as shown in fig. when the fault condition occurs the whole leakage current passes through water steel pipe and earthed.                     

                                       

References 

  1. https://circuitglobe.com/methods-of-earthing.html
  2. https://www.electricalindia.in/electrical-safety-earthing/

 

Vacuum Circuit Breaker

The vacuum interrupter technology was first introduced in the year of 1960 but still is a developing technology.  A circuit breaker is a device that interrupts an electric circuit to prevent unwarranted current caused by short circuit, typically resulting from overload. It’s basically functionality is to interrupt current flow after a fault is deducted. This is kind of circuit breaker where arc quenching takes place in a vacuum medium. The operation of switching on and closing of current carrying contacts and interrelated arc interruption takes place in vacuum chamber in a breaker is called vacuum interrupter. Vacuum offers high insulating strength.

  1. Construction

The vacuum circuit breaker consists of fixed contact, moving contact and an arc shield mounted in a vacuum interrupter. The outer insulating body is made with glass and has high vacuum capacity. The movable part is connected to control mechanism by stainless steel bellows. Arc shield prevents deterioration of internal dielectric strength by preventing metallic vapors from falling on inside surface of outer insulating body. To reduce possibility of leak, permanent or tight sealing is done. Vacuum has high dielectric strength as compared to air so vacuum circuit breaker is preferred where arc interruption need high in place of air circuit breaker.

  1. Working principle

When breaker operates, the moving contact separates from fixed contact and an arc is struck between the contacts. The production of arc is due to ionization of metals ions and depend very much upon materials of contact. The arc is quickly extinguished because metallic vapours, electrons, and ions produced during arc are diffused in a short time and seized by surface of moving and fixed member and shields. Since vacuum has very fast rate of recovery of dielectric strength because dielectric strength of vacuum is eight times greater than air and four times greater than sf6.

Contact materials must have following properties:

  • High density.
  • Contact resistance must be less.
  • High arc resist capability.
  • A boiling point must be high to diminish arc erosion.
  • Thermal conductivity is high to dissipate quickly the large heat produced throughout arcing 

  1. Ratings and specification of vacuum circuit breaker

The rating of circuits breakers is generally given in MVA. VCB comes a wide variety ranging from 250 to 1500MVA. According to European standard, the commonly available preferred values for rated current are 25A, 32A, 40A, 50A, 63A, 80A, 100A, 125A

  1. Advantages
  • It does not require any additional filling of oil or gas.
  • The VCB is fast in operation so ideal for fault clearing and suitable for repeated operation comfortably
  • Vacuum circuit breaker is almost maintenance free and minimum maintenance required as compared to other circuit breakers.
  • No exhaust of gas to atmosphere and noiseless operation.
  • No fire hazards
  • The dielectric strength of vacuum is greater than air and sf6 circuit breaker. High dielectric strength makes possible to quench a vacuum arc within very small gap.

  1. Disadvantages 

  • The main disadvantages of this circuit breaker is that it become uneconomical at voltage exceeding 38kv because at more than 38kv, two number of vacuum circuit breaker are required to be connected in series.
  • VCB production is uneconomical if produced in small quantities.

  1. Conclusion

Now a days, vacuum circuit breakers applications to not only medium voltage power systems but also for in high voltage transmission systems. It is because it has so many advantages characteristics such as high interruption capability, long operation life, safety and high-cost performance. After Kyoto protocol in 1997, sf6 circuit breaker is one of major problem of global warming gases, since then vacuum circuit breaker uses become widespread.

  1. Reference

  1. https://www.elprocus.com/vacuum-circuit-breaker-working-applications/
  2. https://circuitglobe.com/vacuum-circuit-breaker.html

 

Transformer

It is static device used to step up and step down of voltage level without change in frequency and power. Transformer works on the mutual induction principle. This principle states that when electric current flows in primary winding supply then due to alternating nature of supply voltage, it develops varying nature of flux and whenever varying mutual flux linked to a secondary winding through core then according to faraday law, whenever either conductor cuts a magnetic flux or magnetic flux cuts a conductor, EMF produced in conductor, hence in this way, EMF developed on secondary winding.

The basic phenomenon behind working of transformer is mutual induction between two winding linked by a common magnetic flux. Transformer consist of two inductive coils, LV and HV winding. These windings are electrically separated but magnetically linked to each other. When LV or HV winding are supplied of ac supply then alternating magnetic flux developed in the winding and it get linked to load side by a common path that phenomenon is called mutual induction. Due to this, alternating EMF is produced in load side whenever circuit will be closed the current flows in load side.

  1. Types of Transformer

According to change in level of voltage, there are two type of transformer –

1.1.  Step up transformer

1.2.  Step down transformer

  • Step up transformer

 It is used to step up the level of voltage. This transformer increases voltage from primary to secondary winding. In this transformer, secondary turns are more than primary turns. This transformer has made long distance transmission power practical because it steps up the voltage and corresponding it decrease current at same ratio hence, due to decreases the current level there is much less power losses in line. This is used generally for long distribution.

  • Step down transformer

This transformer decreases level of voltage from primary to secondary. In this transformer, secondary turns are less than primary turns. It is used mainly in distribution and load side. This transformer has a wide variety of application like distribution side and electronic devices etc. When it comes to operating voltage, the step up transformer application can be roughly divided into two groups: LV (voltages up to 1kv) and HV (voltages above 1kv). 

  1. Construction of transformer

The construction of transformer is of iron core laminated with steel bands core lamination are constructed from insulated metal thin metal strips. These laminations are separated and wound around the limp using a sheet of coat. The laminations are separated and wound around the limb using a sheet of coat or parchment. The winding consists of two types, main and secondary winding. These winding are isolated from each other and are made by electrical coil.

  • Core

The core of transformer is typically built with high permeability materials, such as silicon steel laminations. Based upon configuration of main and secondary windings, a transformer core may be formed in two ways.

  • Core type construction

In core type construction, as shown in fig, the coils are wound around two limb of rectangular magnetic core. Each limb carries one half of primary winding and one half of secondary winding so as to reduce leakage reactance to minimum possible. The LV is wound on inside nearer to core while the HV winding wound on inside nearer to core while HV winding is wound over LV winding away from the core in order to reduce amount of insulation material required. 

  • Shell type construction

In shell type construction, the coils are wound on central limb of a three limb core. The entire flux passes through central limb and divides in two parts going to side limbs shown in fig. Sandwich type winding is used in such a construction. This type of construction is popular in low voltage application like transformer used in electronic devices, power electronics converters.                                     

                             

                            


                                                      Fig: Shell and core type construction

  • Conservator

A cylindrical tank plays a key role in transformer. It is arranged over the main tank roof so that sufficient space can be provided to expand to transformer oil. Once the temperature increases, then oil volume can also be increases, then oil volume can also be increased. Then oil goes to conservator tank after cooling down it returns to main tank. The shape of conservator tank in transformer is cylindrical where both ends of oil container are closed. One side of the container is provided for cleaning purpose.

 

   

                                                    Fig: Conservator tank

  • Breather

 As a temperature of transformer increases, the insulating oil in transformer heats up.   When oil heats up and spreads, the transformer breathes air in and oil is cooled down and oil level is consumed. The oil level in chamber rises and reduces as breather brings the air in and out to cool the air. The air carries moisture, which contaminates oil and thus deteriorates the consistency of oil. The breather is packed with silica gel to remove moisture content. The key feature of silica gel is to isolate moisture from oil while preserving the consistency of insulating oil. The color of silica gel becomes pink as it absorbs moisture from oil

                                                                 Fig: Breather

 

  • Radiator

The basic function of radiator is to cool down the transformer oil. Oil immersed power transformer is generally provided with detachable pressed sheet radiator with isolating valves. But in case of small size distributing transformer, the radiators are generally integrated parts of transformer body and projected from main tank. The working principle of radiator is very simple. It just increases the surface area for dissipating heat of oil. Under loaded condition, warm oil increases in volume and enter into upper portion of main tank. Then oil enters in radiator through top valve and cools down by dissipating heat through thin radiator wall. This cold oil comes back to main tank through bottom radiator valve.

  • Bushings

Bushings are the insulation system in construction of transformer that enables an electrical conductor to safely transfer electrical energy through it. When a significant volume of electrical energy travel through it, it provides electrical field power to withstand insulation of conductor. In small transformer, solid porcelain type bushing   is used, and in large transformer, oil filled condense type bushing is used.

                                                                 Fig: Bushing

                                                              

  • Buchholz relay

In order to protect of transformer from internal short circuit due to oil, buchholz relay is used for oil immersed transformer, buchholz relay is an oil and gas actuated relay which sense the fault occurring in the part immersed in transformer. Whenever short circuit occurs in transformer then oil generates enough heat and become decompose itself into hydrogen and monoxide gases and these gases travel through pipe and relay is also mounted on pipe between main tank and conservator tank and these relay sense the gas and activate the tripping circuit.

                                                            Fig: Buchholz                                                              

  1. Distribution voltages classes and standard ratings of transformer

Transformer are used wide variety of purposes, with complete range of voltage and power ratings as well as many special features for particular applications.

The following cover main types:

  • Small transformer

They are used for stationary, portable or hand held power supply units. They may be used to supply three phase power up to 40kva at frequencies up to 1mhz. 

  • Distribution Transformer

 They are used to distribute power to domestic premises. They may be single phase or three phase. They have rating ranging from16kva up to 2500kva and this type of transformer like 11, 6.6, 3.3, 440 sand 230V. 

  •  Supply Transformer 

They are used to supply larger industrial premises or distribution substations. Ratings ranging from 4mva to 30mva, with primary winding rated up to 66kv and secondary up to 36kv. The primary winding has a highest voltage ranging from 3.6kv to 36kv, the secondary winding voltage does not exceed 1.1kv. 

  • Transmission transformer

          They are among largest and highest voltage transformer in use. They are used to transmit power between high voltage networks and Rating ranging from 60mva to 1000mva and winding are rated at 33, 66,132, 275 and 400kv.       

  •  Power or step up transformer 

Power is usually generated in large power station at typically 11kv-20kv, and this transformer are used to step up voltage. These transformers are usually rated at 400, 500, 630,800 or 1000mva and transmit power at 66, 110,132,220, 400 and 765kv. 

  1. References 

  1. https://www.electricaleasy.com/2014/03/electrical-transformer-basic.html

Lightning Protection Unit

Lightning is an atmospheric discharge of electricity from thunder, occurs during thunderstorms. The atmospheric discharge lightning can travel at speed of light and its temperature can reach up to 30,000 degree Celsius. The effect of lightning strike may cause thousands of death every year. It is a natural phenomenon occurring at any day and this discharge produce a wide range of electromagnetic radiation.

Lightning protection unit are designed to protect the building structures, industrial appliances, commercial building, HT substation, electrical equipments, communication transmission lines  etc. from damage effect of lightning strike. It play a very important role in safety from lightning storms. A lightning strike could bring thousands of mega ampere current within milliseconds. As a result, failure of home and industrial appliances, fire in building structures, home etc. and may cause death also.

                                       Fig: Effect of lightning strike on building

                                         Fig: Building with lightning protection unit

 

As we can relate with both of the figure above , effect of lightning on building without and with light protection unit.

  1. Components of lightning protection devices

    • Air terminal

Air terminal is used to intercept lightning strike. It provide a low resistance path to lightning strike and it is connected to down conductor and down conductor is connected with earthing electrode which is directly kept into soil mud. Whenever lightning strike hits, the whole current is discharged through air terminal- which is  connected to ground electrode instead of building structure.      

  • Down conductor

Down conductor provide a low resistive path to lightning current from air terminal to ground electrode. It should be installed vertically and straight to avoid the bending of down conductor. This shall ensure minimum inductance because of resistance in the path of discharging current and surges.

  •     Grounding

 It play a very important role in discharging lightning current. It dissipates all the lightning current into a big mass of soil. The soil resistivity should be less than 10 ohm for comfortable discharge of current, according to electrical standard. A typically earth electrode of copper alloy is deep driven vertically into the soil. Soil have finit conductivity so that current discharges easily. The mixing of charcoal and salt is done in soil pit to decrease the resistivity of soil.

  1. Lightning Arrestor

These devices are designed to protect the transmission line, insulations, switchgears, transformers communication line by the effect of lightning strike. They directly installed to power substation , distribution system or telecommunication line. It has ground termininal and high voltage terminal and whenever lightning travel along the power line to arrestor then current through surges diverted by arrestor to earth. In telegraphy and telecommunication, it is placed where wires enter a structure so that preventing damage to electronic instrument and ensuring safety near to them. Their purpose is basically to limit the rise in voltage when power lines are struck by lightning.

    

                                                  Fig: Lightning arrestors

Small version of light arrestor is called surge arrestor. That are generally used for protection from surges produced in transient condition and they are not used directly to protect from lightning. The most common surge arrestor is non linear metal oxide resistor type in porcelain or silicon rubber housing that are fitted parallel to circuit and connected to earth griding.

 Types of Lightening Arrestors 

  • Station class

Typically used in power stations or substations  and other high voltages structure and areas. It is designed to protect equipment above 20MVA range. 

  • Intermediate class

Designed to used in medium voltage equuipment areas, electrical substaions, transformer or other substation equipment and it is designed in range of 1 to 20 MVA.

  • Distribution class

Most commonly found on transformers and are commonly used in equipments rated at 1000kva or less.

  • Secondary class

Found in homes and commercial buildings and provide  least amount of protection to electrical system.

  1. Conclusion

All electrical equipment in an electrical system needs to be protected from voltage surges. The rating of arrestor, the class of arrestor and location of arrestor all play a important role in the surge protection. In protection of substation, we use different class of lightning arrestors to protect the electrical equipment and In ships, water is used to discharge voltage.

  1. References

  1. https://www.electricaltechnology.org/2020/03/surge-arrester-suppressor-lightning-arrester-rod.html