Electrical Installation:Electrical Installation: Components of LT Switchgear: Switch Fuse Unit (SFU), MCB, ELCB, MCCB, Types of Wires and Cables, Earthing. Types of Batteries, Important Characteristics for Batteries..pptx.pptx

Electrical Installation: Components of LT Switchgear: Switch Fuse Unit (SFU), MCB, ELCB, MCCB, Types of Wires and Cables, Earthing. Types of Batteries, Important Characteristics for Batteries..pptx

1. 1. SWITCH FUSE UNITS (SFU) Switch fuse unit is compact combination, generally metal enclosed of a switch and a fuse. It is very widely used for low and medium voltages. The ratings of switch fuse units are in the range of 30,60,100,200, 400, 600 and 800 amperes. Switch fuse units are available as 3 pole and 4 pole units. They are developed for making capacities up to 46 kA. They can safely break, depending upon ratings, currents of the order of 3 times the load current. Switch fuse units can be installed on metal-clad switchgear. A complete range of Fuse Switch & Switch Fuse units are offered to suit varied power distribution applications. The heavy duty Fuse Switches are fully type tested with short circuit breaking capacity of 80 KA at 415V suitable for utilization category AC-22A/ AC-23A. Four frame sizes cover the full range. The Switch Fuse units are suitable for utilization category AC-22A. The accurate current limiting operation and high breaking capacity office has resulted in a number of ingenious combination of switches and fuse to get an economical unit combining the best performance of each . The accurate current limiting operation and high breaking capacity office has resulted in a number of ingenious combination of switches and fuse to get an economical unit combining the best performance of each . Features of Fuse Switches i . Double break with side handle operation ii. Positive indication of contacts iii. Suitable for surface mounting iv. Door interlock facility v. Sheet steel enclosure duly phosphatized and powder painted

2. Features of Switch Fuses: i . Side handle operation ii. Suitable for surface mounting iii. Sheet steel enclosure duly phosphatised and powder painted iv. Provision of conduit knockouts and detachable gland plates . Construction of Fuse Switch Fuse Switch units are fitted with sturdy side operating handle which drives the quick make break mechanism incorporating operating springs. Liberal sized silver plated terminals, suitable for aluminium cable/bus-bar termination, are provided with terminal cover shields to prevent any accidental contact with live metal parts. Positive ON-OFF indication is provided on the switch door. 1. Contacts Contacts are made of electrolytic copper, electro-plated with silver, for better contact and greater resistance to corrosion. Specially designed female contacts ensure low contact resistance and better arc-control. 2. Fuses Fuse switches are designed for use with HBC Cartridge fuse links conforming to IS:13703. 3. Enclosures The enclosure is made of sheet steel, rust protected, phosphatized and powder coated. They are fitted with removable top and bottom end plates provided with knock-outs for bus bars/cables entry. Front accessible door, fitted with dust- excluding gasket, is interlocked to prevent opening when the switch is in 'ON' condition. They are suitable for surface mounting.

3. Construction of Switch Fuse Switch Fuse Unit comprises of vitreous steatite porcelain rewritable fuses or HBC fuse fittings complete with their conducting parts. The switch is fitted with sturdy side operating handle with quick make-break type mechanism. 1. Contacts Contacts are made of electrolytic copper, silver-plated. The fixed contacts are provided with removable shield. 2. Fuses Switch Fuse units are provided with rewritable fuse or HBC Fuse Links. 3. Enclosures The Enclosure is made of sheet steel duly phosphatised and power-coated. They are provided with conduit knock-outs and have detachable gland plates. Door interlock is provided to prevent opening when the switch is in 'ON' condition.

4. Write a note on Switch Fuse Unit (SFU). A) The construction of SFU is as shown in figure. In SFU the switches and fuses are separated from each other. The fuses are connected external to the switches. The fuses are power fuses with current ratings of few hundred amperes. The switches can be operated simultaneously with the help of handle as shown in figure. The range of SFU for single phase applications is 16A to 63A where as for three phase applications is 16A to 320A. Unlike fuse the SFU can also be operated manually. The three phase SFU consists of three switches and three fuses (one each per phase). SFU can also work as switch to connect or disconnect the supply. Q.2) Write short notes on MCB. A) MCB is an electromagnetic device which operates and disconnects the circuit when the current reaches a pre-determine value. It is normally operated at 1.25 times its rated current. It is an overcurrent protection device. Overcurrent may result from short circuit or overload. MCB is better than fuse since it does not require replacement once the overload is detected. In simple terms MCB is a switch which turns off when the current passing through it passes the maximum allowable limit. It is basically operated on two type of working principles.

5. Thermal operation (overload protection): Whenever continuous overcurrent flows through MCB, the bimetallic strip is heated & deflects by bending. As the bimetal bends, it pulls the trip bar which open the breakers contact. Time required for bimetal to bend varies inversely with current. Magnetic operation (short circuit protection): When short circuit occurs the rising current passes through coils creating a magnetic field that attracts the movable contact towards the fixed contact. This causes the opening of breaker contacts. It takes time around 5 milliseconds. Write a note on Molded Case Circuit Breaker (MCCB). A.) The main difference between MCB and MCCB is about their capacities. MCB is rated below 100 amps with an interrupting range below 18,000 amps. The trip characteristics of MCB are not adjustable and it is used for low energy requirements like domestic wiring. The MCCB on the other hand comes with adjustable trip characteristics which has rating as high as 2500 amps and their interrupting rating ranges from 10,000 amps to 2,00,000 amps. MCCB is used for providing energy to high power equipment. The main functions of MCCB are: It provides protection against overload. 2) It provides protection against electrical faults such as short circuit. 3) It helps in switching the circuit ON and OFF. The tripping mechanism is done by magnetic and thermal sensitive devices. The tripping mechanisms are assembled in a moulded case therefore the name is Moulded Case Circuit Breaker. The principle of operation of MCCB is same as the MCB.

6. Compare fuse and MCB Compare MCB and MCCB

7. V.V.P. Q.5) Compare MCB and MCCB SR NO MCB MCCB 1 It stands for Miniature circuit breaker It stands for Moulded case circuit breaker 2 It trips for over-current conditions It also trips for over-load conditions 3 Capacity upto only 100 amps Capacity upto 2500 amps 4 Interrupting capacity 18000 amps Interrupting capacity 2,00,000 amps 5 Used for domestic applications Used for industrial applications 6 Tripping mechanism not adjustable Tripping mechanism is adjustable Q.6) Write short notes on ELCB. Write short notes on ELCB. A.) For the protection of human body from the electric shock protective device like fuse or MCB are used. But generally this device are incapable of measuring small current flowing in human body, so requirement is to have a device which can sense small current and cut-off the supply instantly. The device used for this purpose is known as Earth Leakage Circuit Breaker (ELCB). Working of ELCB It is current operated device designed to operate when a leakage current exceeds the predefined value. It consists of a operating coil and a trip mechanism which operated the circuit when required. The coil is supplied through 1-Ф supply so current in phase & neutral wire will be same.

8. This current will produce flux linkages same in magnitude but of opposite direction. This will result zero net flux in tripping coil of relay. When fault or leakage current exceeds the limit higher current will flow in phase conductor than neutral current. Resultant flux now is out of balance in tripping coil of relay. Difference of flux will induce emf in the coil which opens the contact of ELCB and isolate the circuit from the supply. Explain different types of wires. Following are the different types of wires used for electrical installations: 1) V.I.R wires, 2) C.T.S. or T.R.S wires, 3) P.V.S wires, 4) Lead alloy sheathe wires, 5) Weather proof wires and 6) Flexible wires 1) V.I.R ( Vulcanised Indian Rubber) wires: It mainly consists of tinned conductor with rubber coating. Tinning of conductor prevents sticking of rubber to the conductor. Thickness of rubber depends on the voltage ratings for which wire is to be designed. Coating of this wires is done to prevent moisture from damaging the wire. 2) C.T.S (Cab type sheathed) or T.R.S (Tough rubber sheathed) This is the modified V.I.R type wire. It consists of rubber coated conductors with additional sheath of tough rubber. This provides better protection against moisture & mechanical wear-tear. 3) P.V.C (Poly vinyl chloride) It is most commonly used for wiring purpose. The conductor is insulated by poly vinyl chloride which has the properties such as moisture proof, toughness, durability and chemical inertness 4 ) Lead alloy sheathe wires Ordinary wires can be used at dry places but places where moisture content is more lead sheathed wires are used. The layer of lead covering is 0.12 cm thick. 5) Weather proof wire This type of wire has outdoor application such as providing a service connection from overhead line to building. Here the conductors are covered with fibrous material with water proof compound .

9. 6) Flexible wires: These wires have number of strands instead of single conductor. The conductor is insulated with P.V.C. material. These wires are used for household application where flexibility is needed Explain Cleat wiring and Conduit wiring with figure. Cleat wiring : This is the cheapest and simplest system of wiring used for temporary purpose. For example it can be used in birthday & marriage functions. Conductor are held to walls or ceiling with the help of plastic cleats. Cleat consists of a cover portion and a base portion. Grooves are provided in the base portion of cleat for accommodation of wires. Wires are passed from the base portion of cleat through the grooves. After the wire is run into the base portion, cover portion is placed over it. Advantages : 1) It is the cheapest and simplest system of wiring. 2) Very quick installation can be done. 3) It is suitable for temporary purpose. 4) It requires very little skill for installation. Disadvantages: 1) It gives rubbish look. 2) It can’t be used for permanent purpose. 3) Oil, smoke and dust can damage the conductor .

10. Conduit wiring: This system is best for domestic and commercial purposes. It can be used for permanent purpose. It consist of plastic or metallic pipes known as conduit & a junction box. Conduit are installed on walls or ceiling. From the junction box two or more conduit come out depending upon the design. Wires or cables are run from this conduit so that they are well protected inside it. Advantages : 1) It provides protection against mechanical injury. 2) It provides protection against chemicals, moisture, dust, gas, etc. 3) It has longer life and better look. Disadvantages : 1) This system is very costly. 2) It requires time for installation. 3) Highly skilled labor is required for installation.

11. Explain Construction of cable with suitable diagram. (1) Conductors: Conductors used for cables are generally made up of tinned copper or aluminum. To provide the sufficient flexibility conductors are used in stranded form. Cable may consists of one, two, three of four conductors depending upon the service required. (2) Insulation: The type and thickness of insulation depends upon the voltage level. Insulating materials should provide the following properties: High insulation resistance, High mechanical strength, Non-porous, Chemically inert, High die-electric strength, Non-inflammable etc. Following are the different materials used for cable insulation: Rubber, Vulcanized India Rubber, Impregnated paper, PVC etc. (3) Metallic Sheath: As the cable is placed under ground, soil may present, moisture, gases and some other liquids. Therefore to protect the cable metallic sheath made up of lead or aluminium is provided over the insulation. (4) Bedding : To protect the metallic sheath from corrosion and some mechanical injury, bedding is provided . It is made up of some fibrous material such as jute . (5) Armouring : Armouring is used to protect the cable from mechanical injury while handling. It consists of one or two layers of galvanised steel wire or steel tape.

12. (6) Serving: Serving is provided to protect the armouring from atmospheric conditions. It is made up of some fibrous material like jute. Write a note of different types of cables. A) Cables can be classified as: 1) As per the voltage lever 1.1 Low tension cables: These cables are generally used for voltages up to 1000V. It consists of one core of tinned copper conductor insulated by multiple layers of impregnated paper. Insulation is surrounded by lead sheath which gives protection against moisture. In order to protect lead sheath from corrosion serving layer of fibrous material is provided. 1.2 High tension cables: These cables are used up to 11000 Volts. It consists of three cores of stranded copper or aluminum conductor. These cores are insulated from each other by multiple layers of impregnated paper. Lead sheath is used for protection against moisture. Cable is provided by armouring to protect cable against mechanical injury. 1.3 Super tension cables: For voltages above 11,000 V these types of cables are used. It is further divided into (1) H-type cables: These cables were invented by H. Hochstadter and hence the name is H-type cable. It consists of three cores, each core is insulated by impregnated paper. The insulation of each core is covered with metallic screen which is made up of aluminum foil. Additional conducting tape is also wrapped round all the three cores . Cable is provided by lead sheath, bedding, armouring and serving levels for its protection. This type of construction provides less electrical stress and also dielectrical losses are reduced. Another advantage of metal screen is that, heat dissipating capacity of cable increases

13. (2) S.L. type cable: These types of cables are used upto 66 kV. The construction of S.L. type cable is same as that of H-type cable, only difference is that here each core is covered with separate lead sheath. The three cores are just equivalent to three separate cables. Here armouring and serving level are provided but there is no separate lead sheath. Advantages of this type of cables are less possibility of core to core break down and bending of cable becomes easy as there is no overall lead sheath. 1.3 Extra high tension cables: In order to meet the increased voltage demand the extra high tension and extra super power cables are used for 132 kV and 275 kV. There are two types of extra high tension cables: (1) Oil filled cables: Here the ducts or channels are provided in the cable for oil circulation. This type of cable consists of oil channel at the centre of core by stranding the conductor wire. Oil used in this cables is mineral oil of low viscosity. The oil is constantly supplied to the channel by using external oil reservoir. The oil pressure prevents the possibility of void formation. The system is so designed that when oil gets expanded due to increase in temperature at heavy load condition, extra oil gets collected in the external reservoir. When there is fall in temperature during light load condition same oil is sent back due to contraction . (2) Pressure cable: In construction, pressure cable is similar to any solid cable the difference is that pressure cable has triangular shape. Triangular formation helps to reduce the weight of the cable. Also the thickness of lead sheath is 75 percent of that of solid type of cable. Bedding and serving are not provided in pressure cable which helps in decreasing the thermal resistance . But the cable is provided with thin layer of armouring . Cable is installed in gas tight metal pipes of some larger area and the pipe is filled with nitrogen gas at a pressure of 12 to 15 atmosphere .

14. What is Earthing ? Explain the purpose of Earthing . A) “The earthing is the connection of general mass of earth to electrical apparatus in such a manner that fault current will flow to earth without danger.” The earth is made up of a material that is electrically conductive. A fault current will flow to earth through the live conductor, provided it is earthed. The Conventional system of Earthing is done by digging of a large pit into which a GI pipe or a Copper plate is positioned with the layers of charcoal and salt. When system is without earthing and if short circuit occurs and human body touches the metal part, current will get return path through human body.When system is properly earthed and if short circuit occurs and human body touches the metal part, current will not get path through human body, because circuit is already provided with low resistance path through earthing . Purpose of Earthing Provide an alternative path for the fault current to flow so that it will not put in danger the user Ensure that all exposed conductive parts do not reach a dangerous potential Maintain the voltage at any part of an electrical system. The qualities of a good Earthing : Must be of low electrical resistance Must be of good corrosion resistance Must be able to dissipate high fault current repeatedly

15. Write short note on Pipe Earthing . Earthing electrode shall consist of a CI pipe not less than 40 mm diameter and 3 meters long. The electrode shall be buried vertically in the ground as far as practicable below permanent moisture level, but in any case not less than 3 m below ground level. Wherever possible, earth electrodes shall be located close to water tap. The electrode shall be in one piece and no joints shall be allowed in the electrode. The pipe earth electrode shall be kept vertically and surrounded with 150 mm thick layer of charcoal dust and salt mixture up to a height of 2.5 meters from the bottom. At the top of the electrode a G.I. threaded cap shall be provided for watering the earth. The main earth conductors shall be connected to the electrode just below the G.I. cap with proper terminal lugs and check nuts . The G.I. cap over the pipe and earth connection shall be housed in a brickwork chamber, approximately 300 mm length x 300 mm wide and 300 mm deep. The brickwork chamber shall be provided with a cast iron inspection cover resting over a C.I. frame, embedded in masonry .

16. Earthing electrode shall consist of plate, not less than 600 mm x 600 mm x 12 mm thick. The plate electrode shall be buried as far as practicable below permanent moisture level but, in any case, not less than 3 meters below ground level. Wherever possible, earth electrodes shall be located as near the water tap, water drain or near down take pipe. The earth plate shall be set vertically and surrounded with 150 mm thick layer of charcoal dust and salt mixture. The G.I. cap over the GI pipe shall be housed in a brickwork chamber, approximately 300 mm x 300 mm x 300 mm deep. The brickwork chamber shall be provided with a cast iron inspection cover resting over a GI frame, embedded in brickwork. No earth electrode should have a resistance more than 3 ohm measured by an earth resistance meter. In rocky soil the resistance may be up to 8 ohm. Explain different safety precautions for electrical installations. 1) Insulation of the conductors used must be proper and in good condition. It must be so to avoid the leakage of current by conductor. If insulation is not proper the person coming in contact with it may receive electric shock. 2) To measure the insulation of wire, device known as megger must be used. Before starting use of new wire, megger tests should be conducted. 3) Earth connections should be always maintained in proper condition. 4) Before starting work with any installation, make the main supply off and remove the fuse. 5) Fuse must be of correct ratings to avoid the fault during running conditions. 6) While working with the electric installations use rubber shoes to avoid accidents. Use some wooden support under the feet to avoid contact with the earth. 7) While coming in direct contact with conductor, terminal or removing insulation layer from conductor, make use of rubber gloves.

17. 8) Use a line tester to check whether a live terminal carries any current with the help of a test lamp. 9) Always make use of insulated line testers, screw drivers, etc. 10) Never touch two different terminals at the same time. 11) The electrical socket should be fixed at a height beyond the reach of children. 12) Never try to repair any electrical equipment with wet hands, as it increases the possibility of shock. 13) Always use standard ISI marked materials and equipments . 14) Never use an aluminum or steel ladder to work with electrical appliance at height. 15) Plug points of high power appliances like refrigerator, water heaters, etc must be properly earthed. Explain the construction & working of Lead acid battery OR Explain working of any one type of battery you know .

18. Construction: Container: It consists of electrodes, electrolyte and water. Electrodes: These are positive and negative metal plates. Anode (PbO2) is connected to positive terminal & cathode ( Pb ) is connected to negative terminal. Electrolyte: It is an dilute chemical solution. Sulphuric acid (H2SO4) Working: Chemical Changes During Discharging: When a lead acid battery is fully charged the anode and cathode of it’s cells are converted into Lead Peroxide ( PbO2) and Sponge Lead ( Pb ) respectively. During the process of discharge , The current within the cell is moving from cathode to anode , So the Hydrogen ions moves to anode and Sulfate ions moves to the cathode. At Anode, Hydrogen combines with Lead Peroxide and reacts with Sulfuric acid to form Lead Sulfate. or, PbO2 + H2 + H2SO4 = PbSO4 + 2H2O And at the cathode, the Lead and Sulfate combines to form Lead Sulfate. Or, Pb + SO4 = PbSO4 So, during the discharging of lead acid battery the plates of cells are both converted into Lead Sulfate which is whitish in colour , Due to formation of water the specific gravity of the cells decreases and also the EMF of the cell decreases. Chemical Changes During Charging: Now, When the cell is recharged again , The hydrogen ions moves to cathode and Sulfate Ions moves to anode, At cathode , The lead sulfate reacts with Hydrogen to give Lead and Sulfuric acid, Or, PbSO4 + H2 = Pb + H2SO4 And at anode the Sulfate reacts with Lead sulfate along with water to give Lead Peroxide and Sulfuric acid. Or, PbSO4 + 2H2O + SO4 = PbO2 + 2H2SO4 So, during the process of recharging the plates gets reverted back into their original conditions, The specific gravity of the cells increases due to formation of Sulfuric acid and the EMF of cells or battery increases.

19. Explain important characteristics for batteries. Some of the important characteristics of battery are: EMF: Potential difference between battery terminals is called EMF of the battery. A battery converts chemical energy into electrical energy and produces emf between its two electrodes. This emf has value between 1.8 V and 2.2 V. When the cell discharges, the emf is reduced where as the emf increases when the cells are charged. The emf is denoted by the symbol E. 2) Terminal voltage: When the switch is closed the external load is connected across the battery terminals, the voltage available at the external terminals of the battery will be less than the emf of the battery by the voltage drop of the battery. Voltage available at the external terminal of the battery is called as terminal voltage. It will be less than the emf of the battery. It is denoted by V. 3 ) Internal resistance: When the switch is closed, the current flows from positive terminal to negative terminal through external load. The resistance offered by the electrodes and electrolyte is called internal resistance of the battery. It is measured in ‘r’ and measured in Ohms. Relation between EMF and terminal voltage: V = E – Ir Where, V = terminal voltage E = EMF I = current flowing in the circuit r = internal resistance of the battery 4) Current capacity and cell ratings: The capacity of battery is expressed in Ampere hour (AH). It is defines as product of constant discharge current and the time duration. If a battery has a capacity of say 10 AH it means that this battery is capable of supplying 10 A current for one hour.

20. 5) Cell efficiency: Ampere Hour efficiency (AH) It is defined as ratio of ampere hour during discharging to the ampere hour supplied during charging. AH efficiency = The typical value of AH efficiency is 90 to 95% Watt-Hour efficiency (WH) It is defined as product of AH efficiency and the ratio of Average voltage during discharging to average voltage while charging .   The WH efficiency is less than AH efficiency. Typically is it 75 to 80%. Charging and Discharging curves: If the battery voltage is 12 V, then 6 cells each of 2 volts terminal voltage are connected in series. The battery is said to be fully discharged if the cell voltage reaches 1.8 volts. Hence 1.8 V/cell is called as the final discharge voltage. No further discharge of cell is advisable. Figure shows charging and discharging curves of a battery, it shows during discharge the cell voltage decreases from 2 V to 1.8 V and during discharge the cell voltage increases from 2 to 2.4V. If the cell is further charged upt o 2.6 V it is called as boost charging.

21. In the realm of electrical systems and safety measures, terms like earthing , grounding, and bonding often surface, each playing crucial roles in ensuring the safety and efficiency of electrical installations. While these terms are closely related, they serve distinct purposes that are essential to comprehend for anyone dealing with electrical systems, whether in industrial, residential, or commercial settings. Earthing Earthing , often interchangeably referred to as grounding, is the process of connecting electrical systems to the earth through conductors to provide a safe pathway for electrical currents in case of a fault. The primary objective of earthing is to prevent electrical shock and to ensure the proper functioning of protective devices, such as fuses and circuit breakers, by directing fault currents safely into the ground. This protective measure is critical in preventing fires and minimizing damage to electrical equipment and appliances. The key components of an earthing system typically include grounding electrodes (such as rods or plates buried in the ground), conductors (usually made of copper or aluminum), and bonding connections to ensure low impedance paths for fault currents. In residential buildings, for instance, earthing is achieved by connecting the neutral conductor of the electrical system to a grounding electrode buried in the soil near the building. Difference between Earthing and Grounding

22. Grounding Grounding, although often used synonymously with earthing , can also refer to the act of connecting electrical equipment or devices to the earth or to an appropriate conductor to ensure safe operation. In this context, grounding ensures that equipment and appliances have a stable reference point, often referred to as "ground potential," which helps prevent electrical noise, interference, and static buildup that could disrupt operations or cause damage. Proper grounding is crucial in sensitive environments such as data centers, where equipment must operate with minimal electrical interference to maintain data integrity and operational reliability. Bonding Bonding, on the other hand, involves connecting various conductive parts of electrical equipment, structures, and appliances together to ensure electrical continuity and to prevent potential differences that could lead to electric shocks or equipment damage. Bonding also facilitates the effective operation of overcurrent protection devices by ensuring that fault currents can flow uninterrupted to the earth or to the electrical supply system. In practical terms, bonding is achieved through the use of bonding conductors or bonding jumpers that securely connect metal components (such as equipment enclosures, metal piping systems, and structural elements) to the main earthing system or grounding electrode. This practice helps to equalize potential differences and reduce the risk of electrical hazards caused by stray currents or lightning strikes.

23. Earthing (Grounding): Establishes a direct connection to the earth to safely dissipate fault currents and prevent electrical shocks. - Grounding: Provides a stable electrical reference point for equipment and systems to ensure reliable operation and minimize interference. - Bonding: Ensures electrical continuity between conductive materials to prevent potential differences that could lead to hazards or equipment damage.