Category: electrical Safety

Precautions Against Highly Flammable Contents In an industry, the presence of highly inflammable materials, increase the risk of hazard to its container (structure) and to the persons working close to it. The events can turn more dangerous if the structure gets hit by a lightening stroke. That is the reason; for such areas, a higher degree of safety and protection scheme needs to be followed. If a structure contains highly flammable solid, liquids or gas vapours then consider the following recommendations − Use all-metal structure for storage of flammable materials Keep flammable liquid or gas inside an all-metal structure. In case the degree of hazard is high, it is better to go for a gas-tight structure. Close any openings in the structure Sometimes, due to lack of inspection, a small opening in the gas or vapour chamber leads to trouble. It directs the lightening flames to enter inside thereby causing explosion. So, it is highly recommended to seal those openings. Regular maintenance of containers It is the duty of the safety inspector to put the containers for daily/weekly checks. A keen follow-up will make the flaws public beforehand and the safety officer can take appropriate step to avoid the possible dangerous consequences. Avoid the accumulation of flammable air-vapour mixtures about such structures Lightning flames can charge the flammable air-vapour particles easily and can travel through them to their source. In this regard, it is important to keep the air-vapour mixture of these structures away from the contact of lightning by any mean. Reduce the spark gaps between the metallic conductors Inside the structure, there may be some conductors having space between them. In due course of time, the accumulation of flammable air or vapours inside those gaps can create hazardous situation on being exposed to lightning. When lightning strikes, the flammable air or vapours turn into charged particles and may possibly cause sparks between the conductors. Thus, on a regular safety check, it is required to reduce the spark gaps. Location of the structure Some locations are prone to lightning and if the structure is present in such areas, then it is likely to get hit by lightning every now and then. Here, the primary duty is to move the structure from that place to another place, more immune to lightning strike, almost immediately. Otherwise, it will lead to catastrophic hazards not only to the instruments present inside but also to the personnel working near to that. Create multiple zones of protection This is in line to the point that we discussed just before. If the structure is not in a condition of getting transferred from the position of a high prone lightning area, then it is important to create multiple zones of protection around the structure. The lightning has to go through a number of protection layers before reaching the structure. Learning working make money

Electrical Safety – Test Certifications We will now understand what electrical safety test certifications are. Let us begin with the concept of Electrical Product Certification. Electrical Product Certification A product must pass the performance test, quality assurance test and meet the specifications for certification scheme. The certification scheme includes Federal Communications Commission (FCC) Telecommunication Certification Body (TCB) program Environmental Protection Agency Energy Star Program International Commission on the Rules for the Approval of Electrical Equipment Product Safety Certification Body Scheme Material Analytical Services Certified Green IEQ program Worldwide Accreditation Bodies All recognized bodies are listed for accreditation to the ISO 65 standard by the International Accreditation Forum (IAF). The recognized bodies are − American National Standards Institute (ANSI) Accreditation Board (a sub-division of ANSI) American Association for Laboratory Accreditation (A2LA) International Accreditation Service (IAS) United Accreditation Foundation (UAF) Technischer Überwachungsverein (TÜV)- Germany Korean Accreditation Board (KAB)- Korea Safe Electrical Work Certification The regulatory system promotes safety satisfying the standards. The work should be controlled and enforced through the certification system. Therefore, certification is required for such work. The Energy Provision Act 2006 defines two different classes of electrical works – Controlled work and Restricted work. The scope of both the works has been established by the Commission for Energy Regulation. Controlled Electrical Work There are some electrical works, which need experienced people to work for safety reasons. Controlled work comes under the scope of the regulatory system at outset. A Registered Electrical Contractor must do the certified controlled works or an inspector from the Safety Supervisory Bodies may also do the work. The certificate describes the confirmation that the electrical work has been tested properly. Safety verification with national standards according to the national wiring rules is an important category of certification. The work must be significant enough in the context of electrical safety and needs to be controlled through the issuance of a completion certificate. The likelihood for like replacements of switches, sockets, lightning fitting to an existing circuit must be done as per the compliance with the Technical Rules. Such works define the Scope of Controlled Works. This involves installation, commissioning, inspection and testing work as defined in Part 7 of the National Wiring Rules ET101 and ET105. The inspection of the electrical installations must confirm the Regulation 89 of Sl. No. 732 of 2007. Restricted Electrical work The current scope of restricted works was decided in 2013. It involves the electrical installation in any locations listed in part 7 of National Rules for Electrical Installations. The inspection, testing or certification of existing Electrical Installations is described in Chapter 62 of the National Rules for Electrical Installation. This work is only applicable to domestic environments. Testing of Equipment In this section, we will learn about the testing of equipment undertaken by different recognized organizations − CPRI The Central Power Research Institute tests the electrical equipment such as transformer, reactor, switchgear, cable, duct, capacitor, arrestors relay, insulator and renewable energy products and thereby, generates a test report. BSI The BSI provides Certification Board (CB) report for the apparatus of IT equipment, control & wiring accessories, electronic component, medical equipment, cables, and environment. ERDA The Electrical Research and Development Association shows the excellence in testing, calibration, R & D with the support of Council of Scientific and Industrial Research (CSIR) for different products such as cables, transformer oil, energy meter, switchgear, T & D lines, lamps & luminaries, dielectrics, polymers and photovoltaic cell. ITC The ITC Pvt Ltd. provides testing services for ingress protection, LED products, battery, PV module, cable gland and domestic appliances, etc. NRTL The Nationally Recognized Testing Laboratory is a private organization under OSHA and ensures OSHA electrical safety standards. It authorizes the manufacturer to apply the registered certification for a particular product. The testing service of any organization must follow several IEC standards such as − Sr.No. Standards & Testing Equipment 1 IEC 61010-1 Lab Instruments 2 IEC 60204-1 Control Panel 3 IEC 60595 LED Luminary 4 IEC 61347 Lamp control gear 5 IEC 60950 Information technology equipment 6 IEC 60601 Electro-medical equipment 7 IEC 60065 Audio video & similar product 8 IEC 61439 Low voltage switchgear & control gear assemblies 9 IEC 60034 Rotating electrical machine Questions 1. Who can include any organization as accreditation body in worldwide? a) IAF b) ANSI c) KAB d) UAF Ans: a Explanation All recognized bodies are listed for accreditation to the ISO 65 standard by International Accreditation Forum (IAF). 2. What is name of the laboratory recognized by OSHA? a) CPRI b) ERDA c) NRTL d) None of these Ans: c Explanation Nationally Recognized Testing Laboratory is a private organization under OSHA and ensures OSHA electrical safety standards. 3. What is the standard code of testing LED luminaries? a) IEC 60065 b) IEC 60595 c) IEC 60601 d) IEC 60034 Ans: b Explanation Any organization must follow LED luminaries testing services according to the International Electro-technical Commission 60595 standards. Learning working make money

Procedure to Mark Unprotected Equipment We will now learn about the procedure to mark unprotected equipment. To begin with, we will look into the industry safety practices. Industry Safety Practices Let us now look into the safety practices in the electrical industry. Intended use Select the device according to the purpose and use within the specified limit. Do not use the external auxiliary device Instruction and safety Contact the technical assistant to ensure how to use the device according to the safety labels and tags. Installation Refer Material Safety Data Sheet (MSDS) and understand the processing characteristics of the material. Ground the equipment and install protective devices. Operation Use safety devices like guards, interlocks, and protect yourself with Personal Protective Equipment. Ensure that you see the signs of potential in a proper manner. Maintenance & repair Do a scheduled maintenance at intervals and confirm the correct operation of the device. If any fault occurs, replace it or repair it. Equipment safety information The specific conditions that an equipment can withstand are mentioned in the manual for the equipment or on the equipment. We also need to abide by a few precautions while handling and working with the electrical equipment. Avoid open flame in the site area Check the pressure daily to protect the equipment from wear, damage or leaks Do not point dispensing handgun at anyone Do not remove the molten hot melt cable with bare skin If you encounter a disaster, seek medical attention immediately Shut down the equipment safely as the level of shut down varies from one device to another. General safety warning and caution Every equipment comes with warning and caution symbols provided by the manufacturer. It is important that an electrician understand the warnings and symbols and handles the equipment accordingly. The following table shows a few safety label and their description − Sr.No. Safety Label Description 1 Warning − Risk of electrical shock. It may cause injury or equipment damage if not observed correctly. 2 Warning − Potential hazardous situation. It can cause serious injury including death. 3 Caution − Potential hazardous situation. It can cause minor or moderate personal injury. It is recommended to carefully understand the type of equipment. It is also important to know the placement of equipment and what is to be kept away from it. HM – Hot Melt – Caution: To stay away from the hot surface. If hot metal gets in contact with a hot surface, then it might lead to a disaster. PC – Process Control – Warning: Untrained or inexperienced personnel may lead to equipment damage and personal injuries. CA – Cold Adhesive – Warning: Do not use high pressure. It may release cold adhesive causing personal injury. Approved symbols present on devices The following table lists down a few approved symbols present on devices Sr.No. Icons Meaning 1 Corrosive product 2 Product hazardous to health 3 Toxic product 4 Product harmful to the environment 5 Explosive product 6 Product meets European safety requirements 7 Restriction of certain hazardous substances in electrical/electronic equipment 8 Safety Extra Low Voltage Marking at Site In this section, we will the different marks on a site and understand what they mean. Barricading and signage There are different types of barricades use at the location. The following table shows a few barricades − Type Description Example Caution Access permitted but caution required. It highlights hazardous area. Danger Access permitted under the instruction of authority. Restricted area: hot work, falling object, unprotected edge. Don’t Enter/ Electrical Work Used for switchboard, distribution line maintenance. Radiation Access permitted under the instruction of Radiation safety officer. Incident scene No access for any unauthorized person if an incident has occurred. Barrier mesh/ Bunting flag It is used to highlight the boundary of the work area. Solid Barricade This signage means establishing a safe distance from plant or equipment Questions 1. What is required to understand about the equipment at the time of installation? a) barricade b) Symbols c) MSDS d) None of these Ans: c Explanation Material Safety Data Sheet (MSDS) is referred before the installation of an equipment. 2. Which barricade is/are required to highlight the boundary of work area? a) Barrier mesh b) Radiation c) Bunting flag d) Both A & C Ans: d Explanation According to the safety standards, Barrier mesh and Bunting flag are used to highlight the boundary of work location. 3. Which symbol represents the product that is harmful to the environment? a. b. c. d. Ans: b Explanation Each symbol defines a product such as A represents hazardous to health, B represents harmful to the environment, C represents corrosive material and D represents explosive material. Learning working make money

Maintenance of Unprotected Equipment We will now understand the maintenance of unprotected equipment. Here, we will also delve into the different types of maintenance. Types of Maintenance The technical actions regulate the normal operation of equipment that is divided into two major groups − Preventive Corrective Preventive/ Predictive Maintenance Preventive maintenance does not mean to maintain the equipment at the time of malfunctioning but to prevent the failures before it arises. It is applicable to prevent the breakdown. This type of maintenance is performed over a period of time, then it is called as Scheduled Maintenance that reduces the risk of malfunction and degradation of equipment. Preventive maintenance focuses on equipment’s type that manages to adopt predictive and conditional maintenance. The predictive maintenance defines the equipment status through utilization of various non-destructive testing and measuring techniques. The predictive preventive maintenance program ensures efficient, reliable and safe production. Corrective Maintenance When any fault, failure or malfunction is detected, corrective maintenance is applied to the equipment. As the name suggests, it is useful in order to correct the issues. It cannot be pre-determined like preventive maintenance. It focuses on the infrastructure of equipment. It is referred as emergency maintenance. Such maintenance must be carried out efficiently in the equipment. Preventive Checks A routine preventive maintenance needs checking to prevent damages in electrical equipment. Consider the checklists given below to follow preventive checks − Cleaning Machines Clean the machine at regular intervals and apply oil to the unprotected metal surface. Lube the Machine A good lubrication can keep safe the turret, spindle, dry gears, bearings and oil reservoir and protect from wear and corrosion. Skim oil off the machine Oil skimmer is used on the surface of the machine to create a perfect breeding ground and removes dermatitis, dry skin, nasty smells and poor tool life. Monitor machine-cutting fluid A refractometer monitors the water-based fluid concentration weekly. Another kit checks the PH level. The backlash and alignment should be checked quarterly. Repairs If there is any issue with the maintenance, the equipment requires repairs for smooth functioning. The art of repair facility is responsible to repair and modify all types of electrical equipment parts. There are certain parts of devices that need to be checked frequently and repaired accordingly. Transformer Repairing of leaks, bushings, housings, radiator fins, gaskets and indicators is done and damages can be replaced. Transformer oil will be replaced if the air level is degraded. Circuit breaker Obsolete parts should be supplied otherwise, circuit breaker can be replaced. A trained professional should diagnose and ensure the fault. Switchgear If there is any tear, accident or electrical fault found in switchgear and control gear by experienced engineers, then repair facility repair the broken parts or replace the equipment. Protective relay During troubleshooting, engineer should check if the operation of relay meets the specifications or not. If something wrong is reported, then it is repaired, recalibrated or replaced. Cables A Cable is an equipment in the electrical system. A single fault in the cable can shut down the whole system. The splicing is checked and the cable is replaced immediately. Statutory Audit In case of maintenance, the repairing and replacement process requires some financial support and generation of reports. Thus, statutory audit pitches in. It is to define a fair view of the financial statements such as balance sheet, income and expenditure account, receipt and payment. It shows the distribution of fund regarding electrical material repairing, purchase, etc. Scope of SA According to the financial management system, the scope includes − Adequacy of project financial system: Effectiveness of accounting, financing, operation control, compliance with plans, policies, procedures, the reliability of accounting system, data and reports and verifying assets and liabilities. All documents, records and accounts must be kept carefully for a project. Questions 1. Which maintenance is applicable after a fault occurs? a) Preventive maintenance b) Corrective maintenance c) Both A & B d) None of these Ans: b Explanation When any fault, failure or malfunction is detected, corrective maintenance is applied to the equipment. 2. If preventive maintenance is offered monthly, then it is called ______. a) Corrective maintenance b) Emergency maintenance c) Scheduled maintenance d) Protective maintenance Ans: c Explanation When preventive maintenance is performed over a period of time, then it is called Scheduled Maintenance. 3. Which device measures the concentration of fluid? a) Barometer b) Thermistor c) Refractometer d) None of these Ans: c Explanation Barometer measures air pressure. Thermistor measures temperature. Refractometer measures the concentration of the fluid. Learning working make money

Types of the Supply System We will now learn the different types of the supply system. Before we begin, we need to know what power supply is. Power Supply The supply of electric power to an electrical load is called power supply. The main function of the power supply is to convert electric current from a source to the correct voltage, current and frequency to power the load. Electrical outlet, energy storage device such as batteries, fuel cells, generator, solar power converters are generally known as power sources. Power supply is classified into different categories. In our subsequent sections, we will see what the different categories are. DC Power Supply Such type of supply supplies a constant DC voltage to the loads. It may deliver from a DC source or an AC source. AC-DC Supply AC energy can deliver DC power with the help of a rectifier, which converts the transformer output voltage to a varying DC voltage. The DC voltage passes through an electronic filter, which turns it into an unregulated DC voltage. There is also a register in series with the output to limit charging current and the final output power is fed to the load. Switched Mode Power Supply (SMPS) The main input is converted to DC voltage via rectifier and filter and then switched on and off at a high frequency (10 KHz- 1 MHz) by an electronic switch. It has a safety feature to protect the device and the user. Linear Regulator Linear regulator converts a varying DC voltage to a constant. There is a current limiting function to protect the power supply and load from overcurrent. It is independent of fluctuation in input voltage and loads impedance to provide a steady value. AC Power Supply AC power supply can be taken from the main supply transferred to the desired voltage with the help of step up and step down transformer. This supply is divided into a single-phase and a three-phase system. Programmable Power Supply A PPS provides remote control operation through an analog input or digital interface such as RS 232. The controlled properties include voltage, current and frequency (in case of AC). Uninterruptible Power Supply UPS has a feature to take power from two or more sources simultaneously. It is used as a backup supply as it takes over the load in dropout or failure condition of main supply. The process is so fast that the load never experiences an interruption. High Voltage Power Supply HDPS supplies the bulk of energy, which is hundreds or thousands of volts for applications above 20KV. It includes voltage multiplier or high turns ratio, high voltage transformer or both to produce a high voltage. Principle of Power Supply In modern power stations, the generation of electricity is at 25 KV and it is transformed to 400 KV. The number of generator sets are designed to provide the flexibility required power for seasonal variations in loads. The principle is to supply the power to any consumer with a ring system and fed from two directions carefully with proper protection and loss of supply. The following image shows the distribution of power supply from power station to consumer − Practice A trained employee should be engaged in the practice of electrical works. Every electrical work must follow the following codes and standards including − OSHA’s electrical safety requirements for employee National Electrical Codes NFPA 70 Practice for external power supply is applicable for computer, electric vehicle, welding purpose, aircraft power supply and plug-in adapters. Characteristics of Power Supply The electrical characteristics of power supply refers to the quality of the power. Form factor Ripple Factor Rated Wattage Nominal Voltage Operating Voltage Range Input Frequency Range Efficiency Load Regulation Line Regulation Transient Response Hold-up Time Protections Peak Inrush Current Questions 1. Which type of power supply needs an analog input? a) High Voltage Power Supply b) Programmable Power Supply c) Switched Mode Power Supply d) AC-DC Supply Ans: b 2. Which of the followings are not required in AC-DC supply? a) Transformer b) Rectifier c) Filter d) Inductor Ans: d 3. Which of the following is not characteristic of the power supply? a) Trip time b) Inrush current c) Line regulation d) Ripple factor Ans: a Learning working make money

Measures Related to Gas/Ducts/Fibre material It is very important to consider safety measures while working with gas, ducts, fibre material. It is recommended that a person working with these should wear the required safety attire and carry all the necessary tools. Safety measures related to gas The incident rate has reached 6% because of electrical cases in oil and gas companies all over the world. Safety precautions play a vital role and help in avoiding electrical hazards. For reliability and safety reasons, checking periodically and keeping electrical system in good condition is necessary after the installation. Proper care and experience are needed for the expansion, modification, revamping of existing facilities when working with a live plant. Need to be professional to choose perfect electrical equipment for installing in a gas industry. For example, HRC fuse is suitable for such industries instead of a kit-kat fuse. Electrical equipment installation, design, testing and maintenance must follow the standards of respective nationalities to ensure the expected quality as well as the safety. Safety measures related to duct/ fibres The duct or conduits are the pathway of cables and protect them. The electrical conduits must follow the standard specifications of – ASTM F2160 NEMA TC7 UL 651A & B and UL 2024 National Electrical Code (Chapter-9) It is essential to focus on the diameter of conduit ∓ inner duct, number of inner duct, length & direction, the composition of the duct, the coefficient of friction, jam combination, pull speed, temperature, elevation, inner duct weight, mechanical stress, tension and bending radii, etc. Trained professionals must choose the ducts as per the requirement of the environment including underwater, underground, outdoor location or indoor location. Use symbols for the underground cabling that can restrict the people from digging and facing accidents. Electrician must use tension meter, cable lubricants and required electrical equipment. Safety measures related to fibre material Fibre optic cables need to be handled with care with proper knowledge about bending radius, and cable twisting. Use laser beam to find damages in the optical communication cable. Do not stick the broken ends or drop fibre pieces on the floor. Avoid skin contact with the fibre material. Remember not to drink or eat anything near installation area. Group classification of flammable gas/ vapor A flammable gas or vapor can be ignited from an arc or spark at the electrical system and results in dangerous accidents. There are four Class I group classifications in section 500-5(a) as per NEC. Group A: Acetylene Group B: Hydrogen and gases equivalent to hazardous in nature Group C: Ethyl Ether or gases or vapors which are equivalent to hazardous nature Group D: Gasoline, alcohol, acetone, natural gas & similar material These groups were made as per the level of hazard related to the explosion pressures of the specific atmosphere. Besides these engineers should follow ‘Practice for the classification of flammable liquids, gases or vapours’ in NFPA 497. Group classification of Duct There are different types of electrical ducts or conduits used for various applications. Galvanized Rigid Conduit The thickness of galvanized steel tube protects the electrical wiring and become the choice of an electrician in commercial and industrial applications. Electrical Metallic Tubing Such conduits are made of steel or aluminum and restricted to a specific radius for bending. It is very popular in commercial, residential and industrial buildings. Electrical Nonmetallic Tubing It is moisture resistant and flame retardant and it is easy to bend by hand due to the flexibility. Flexible Metallic Conduit It is known as “Greenfield of flex” means it doesn’t maintain permanent bend. It is recommended for dry areas. Liquid-tight Flexible Metal Conduit These are covered by a plastic waterproof coating which is applicable for general wiring in wet or damp locations. Rigid Metallic Conduit It is made up of coated stainless steel or aluminum which prevents corrosion. Liquid-tight Flexible Non-metallic Conduit These are the flame resistant type which is recommended as a raceway for installation of approved conductors (Rating- 600 volts). Aluminum Conduit It is used in large amounts of water areas and corrosion prone areas as it prevents corrosion. PVC Conduit It resists moisture and corrosion, which has also the higher thermal coefficient of expansion. Based on the design and shape electrical ducts are classified as follows − Individual Round Pipe Extended Plenum Reducing Trunk Multiple Return Air The following figure shows the different supply duct systems − The following figure shows a typical duct connection and has – Elbow Tee Reducing Tee Cross Lateral Questions 1. Class I group classification of flammable gas/ vapor/liquid is described in ______. a) NFPA 70 b) NEC Article 500 c) IS d) None of these Ans: b 2. Which group does flammable gas Hydrogen belong to? a) Group D b) Group C c) Group B d) Group A Ans: c 3. Which one of the followings is known as “Greenfield Flex”? a) Liquid-tight Flexible Metal Conduit b) Galvanized Rigid Conduit c) PVC Conduit d) Flexible Metallic Conduit Ans: d Learning working make money

Safety Measures During Handling Lighting Protection Equipment For buildings containing highly flammable liquid or gas, it is important to guard them from lightning. However, handling lightning protection equipment is not a child’s play. A single mistake can cause serious hazards to the structure and the persons working near to it. Depending on the type of building to which the lightening protection equipment have been integrated, there are different handling methodologies. Let us understand what the methodologies are. Building with explosive dust or flammable vapour risk For such type of building, it is recommended to add an integrally mounted lightening protection system. It should have vertical air terminals and horizontal air terminals. Depending on the type of storage inside the building the height of the vertical terminals must be set at minimum 1.5 metre whereas the horizontal air terminals must be spaced 3 to 7.5 metre from each other. Explosive storage building and explosive workshops Here, it is required to add integrally mounted systems. The vertical and horizontal spacing in this case should be 0.3m high and 7.5m spaced respectively. Small explosive storage buildings Buildings of such type are very less to get hit by lightning. The integral mounted systems are not necessary over here. Only a vertical pole type lightning protection scheme can work wonders. Storage of explosives in buildings There are some buildings that contain explosives such as Nitroglycerine (NG). These structures need suspended horizontal air terminations as integrally mounted systems and vertical pole types will not be able to provide the desired protection. These suspended horizontal air terminations should be placed at a minimum height of 2m above the structure. About the internal spacing, it should be minimum 3m between the terminations. Learning working make money

Electrical Safety – Cables A cable is a group of wires swathed in sheathing that ensures a smooth electricity supply. It needs to be installed carefully following the National Electricity Code and National Building Code for various electrical applications. Types of Cables There are more than 20 different types of cables according to the design and application. Let us consider a few important types here − Non-Metallic Sheathed Cable (NM Cable) These cables have a flexible plastic jacket with two to four wires that are commonly used for indoor residential cabling and special varieties are for underground and outdoor cabling. Underground Feeder Cable (UF Cable) The wires in such cables are grouped together and embedded in the flexible material. These are useful for outdoor lighting and in-ground application. Metallic Sheathed Cable (BX cable) There are three stranded copper wires insulated with cross-linked Polyethylene and PVC sheathing. These cables are used for outdoor application and high-stress installation. The following images show the different types of cables − Multi-Conductor Cable (MC Cable) More than one conductor that is insulated individually. The outer insulation gives extra security. The different varieties of MC cables are used in homes and music industries. For example, the audio multicore ‘snake cable’. Coaxial Cable (Heliax cable) A tubular insulating layer with a tubular conducting shield protects the inner conductor of the cable. As the two inner sheaths share the same geometrical axis, the name coaxial is justified. It is used for carrying television signals and connecting video equipment. Unshielded Twisted Pair Cable (UTP) UTP cable consists of two wires twisted together with solid copper cores and not insulated individually. These are often used in telephones, security cameras and data networks. Ribbon Cable It has various conducting wires running parallel to each other on a flat plane. Ribbon cables are applicable for low voltage applications such as in computers and its peripherals. Direct Buried Cable (DB cable) It either is a specially designed coaxial cable or bundled fiber optic cables, which have many layers of banded metal sheathing, heavy rubber coverings, and shock absorbing gel waterproof wrapped thread-fortified tape. This is considered a popular choice for transmission and communication requirements. Twin Lead Cable (TL cable) The TL cable consists of two wires that are generally used in the transmission of a signal from the antenna to receivers like TV and radio. Paired Cable There are two individually insulated conductors, which are used in DC or low frequency AC applications. Twisted Pair Cable The inner insulated wires in TPC are twisted or intertwined; otherwise, it is same as paired cable. Importance of Thermal Resistance Thermal resistance is the optimum temperature at which the insulation cable melts down. It depends upon the area of cabling the thermal phenomenon has taken into consideration when underground electricity network is designed. In an underground power system, the core temperature of cable should not exceed the maximum temperature of cable operation (65ᵒ C). The following figure shows the variation of cable core temperature with increase in soil thermal conductivity − The thermal conductivity varies according to the material used in cable layer as the cable needs to dissipate heat to its surroundings. Cable Layer Material Thermal Conductivity () Conductor Copper 400.00 Insulation XLPE 0.3232 The thermal conductivity of soil changes the intensity of heat transfer from the power cable. As the conductivity increases, the soil receives heat faster and the cable temperature lowers down. The soil conductivity depends upon the water content (caused by rainfalls or droughts) and moisture. The distribution of temperature should be done effectively while working in the underground electrical network system. Safety precautions Let us now consider a few safety precautions − Do a safety plan, which includes emergency activities, evacuations suitable to the codes and standards. Professional and trained electricians should be employed, who understand the safety protocols and surrounding workplace environment. Workers must use non-conducting gloves, safety eyewear, shoes and protective clothing to protect from electrical risks. Maintenance and testing should be done periodically. Questions 1. Which material is used to cross-link the core in Metallic Sheathed Cable? a) Copper b) PVC c) Polyethylene d) Aluminum Ans: c 2. Which cable is suitable for cameras and data networks? a) Twin Lead Cable b) Unshielded Twisted Pair Cable c) Direct Buried Cable d) Twisted Pair Cable Ans: b 3. What happens to the cable core temperature with increase in soil thermal conductivity? a) Increases b) Decreases c) No Change d) Can’t be predicted Ans: b Learning working make money

Electrical Safety – Transformer Safety Transformers are a major source of power supply to any industry. The conversion of voltage level can cause serious damage to a person or to the nearby area if not kept under tight protection measures. It is the duty of safety inspector to run the following condition assessments on the transformer with the following checklist − Main transformer inspection check list Task Yes No N/A Comments Main Tank Paint System in Good condition Rust Observed Tank grounds in Good condition Conduits and fittings secure External core ground provider Oil Leakage observed Cooling system Radiator or cooler fins cleaned All valves to main tank open and secure All fins in place and operational All oil pumps in place and operational Oil flow indicators function properly Excessive vibration or noise observed Leaking of oil if any Oil Preservation Positive pressure of inert gas Proper setting of regulator of Nitrogen blanket Correct pressure check of gas blanket Bushing All clean and zero defect Proper check of oil levels Oil leakage if any De-energized tap changer (DETC) Location of Position indicator tap Locking mechanism checked Load Tap Changer (LTC) Location of Position indicator tap Silica gel breather Oil leakage if any Control Cabinet Connections/components in good condition Weather tight seals checked Strip heaters checked Protective devices Oil Temp indicator reading Oil Temp indicator set points Winding Temp indicator reading Winding Temp indicator set points Buchholtz relay alarm/trip Gas detector alarm/trip Learning working make money

Electrical Safety – Earthing The process of transferring an unintended electrical energy directly to the earth through a low resistance wire is called electrical earthing. It refers to the connection of a noncurrent-carrying part of the equipment or neutral of supply system to the ground, which represents the zero potential. The leakage current chooses the simple low resistance path to flow. Thus, the electrical system and equipment are protected from damage. Types of Electrical Earthing The electrical equipment has two non-current carrying parts such as neutral of the system and frame of the equipment. Earthing system is also classified into two types. Neutral Earthing The process of connecting neutral of the system to the earth through a GI wire is known as Neutral earthing or System earthing. It is used in star winding systems including generator, transformer, etc. Equipment Earthing When the metallic frame of the equipment is connected to the earth by the help of a conducting wire then it is called Equipment earthing. In fault condition in the apparatus, the fault current flows to the earth and the system is protected. Need of Earthing Earthing is needed for the following reasons − To protect the user from electrical shock. Earthing system shows the easiest path to the fault current even after the insulation failure. It protects the electrical apparatus used in the circuit from short circuit current, high voltage surges and lightning discharges. Explanation We will now understand the need of earthing considering the following conditions − Normal Condition Earthing of a system is done in the installation to connect the respective parts with electrical conductors or electrodes. The electrode is placed near the soil or below the ground level, which has flat iron riser under the ground. The noncurrent-carrying parts are connected with the flat iron. The following figure shows the flow of fault current without earthing system − Fault Condition In a fault condition, the fault current flows from the equipment to the earth through the earthing system. Thus, the apparatus is protected from short circuit or fault current. At the fault time, the voltage of the electrode increases and equals to the resistance of the electrode and the ground fault. The following figure shows the flow of fault current with an earthing system − Ground Resistance Measurement The ground resistance of an electrode is measured by the fall of potential method. The total set up is shows in the figure given below, where – E is the earth electrode under test P & C are two auxiliary electrodes placed at a suitable distance from E I is the amount of current that passes between E and C V is the measured voltage between E and P The following figure shows the setup to measure ground resistance − There is no appreciable effect on the resistance of E, if C is at an adequate distance from E. As the current into electrode P is very small, the electrode also has a negligible effect on resistance. Now varying the distance of electrode P from E, the resistance is measured. The following figure shows the true resistance from the R vs d curve − From the figure, the portion of the curve is marked as R of E, which is a nearly horizontal slope in the curve. The upward slope indicates the effect of the resistance of C. For the field measurement earth tester calibration, the ratio is directly used. Risk reduction The earthing system must follow the rules and regulations for the risk reduction according to the following standards. Indian Standards: IS 3043- Code of practice for Earthing (latest) National Electricity Code (NEC): 1985 of BIS IEEE guide for safety in AC substation grounding No. ANSI/IEEE standard, 80-1986. Proper inspection and field survey is necessary before the installation. A flowchart needs to be followed for the different steps: Inspection & Survey – Design – Testing – Installation – Maintenance – Preparing Report. Electrode resistance, soil resistivity is measured periodically and megger test should be exercised. Do not use copper or aluminium wire as substitute, paint, enamel and grease on the electrode. Protect the electrode lead from mechanical stress and corrosion. Proper training and management can reduce the risk factor. Learning working make money