Unit-1 Electrical Systems PDF

UNIT-1 ELECTRICAL SYSTEMS B.Arch Vth SEM By, Ar.Srilatha marru Course content: CLASS1  Introduction to the scope and purpose of electricity in the building.  Sources of electricity.  Power generation.  Transmission.  Distribution and consumption. SCOPE AND PURPOSE OF ELECTRICITY IN BUILDIN...

UNIT-1 ELECTRICAL SYSTEMS B.Arch Vth SEM By, Ar.Srilatha marru Course content: CLASS1  Introduction to the scope and purpose of electricity in the building.  Sources of electricity.  Power generation.  Transmission.  Distribution and consumption. SCOPE AND PURPOSE OF ELECTRICITY IN BUILDING  ELECTRICITY The first use of electric supply were established in 1882 by THOMAS EDISON, Thereafter there have been constant effort throughout the world to set-up power stations for more than one purposes. With the advent of fluorescent lamp by EDMUND GERMER that is compatible with daylight, cheap to run and not emitting heat gain in buildings, it made possible to install electric lighting supplementing day light and in extreme cases provide the only source of light in a windowless environment. Since the end of the nineteenth century virtually all buildings are provided with electric lightings installation for use at night. Several factors can exercise a critical influence on the success of lighting installations apart from proper level of illumination on the work plane.  ELECTRICITY Electrical energy is the term given to energy that has been converted from electric potential energy. This electric potential energy has usually been in turn converted from another source of energy, through a process known as generation. Electrical energy is supplied by a voltage (or electrical potential) delivered via an electric current. Electrical power is defined as the rate at which electrical energy is transferred via an electrical circuit over a given amount of time. It is therefore the rate of ‘doing work’. The SI unit of electrical power is the watt, which equates to an energy transfer rate of 1 joule per second. In the context of buildings, electrical energy is typically converted into other forms of energy, to serve useful purposes such as heating, lighting, motion or other forms of electrical power conversion. Scope of electricity in the building: The scope of electricity in a building includes the design, installation, maintenance, and repair of electrical systems: Design  This includes the design of the power source, load calculation, substation design, and backup power source. Installation  This includes the installation of internal and external electrical systems, wiring, transformers, and power poles. Maintenance and repair  This includes the maintenance and repair of electrical systems, fixtures, and equipment. Safety  This includes ensuring that the work is performed safely and that safety compliance is maintained.  Electricians are skilled professionals who perform these tasks. They have expertise in electrical systems, tools, and safety regulations. SCOPE OF ELECTRICAL WORK The modern building, besides electric wiring, has to provide for following services: Telephone wiring.  Solar Energy system. Communication cabling.  Photo voltaic power system. Computer cabling,  Other specific lighting services etc. networking,  Building management system. Dedicated earthing.  (HVAC)Heating, ventilation and air Audiovisual systems. conditioning design and other Security systems. mechanical systems, Sound re-inforcement.  Water supply system. Stage lighting.  Automation External lighting. Architectural in-built lighting. Purpose of electricity in the building. Electricity has become the lifeline of modern society. Homes, Offices, Industry, Schools, Hospitals, Transportation, Communication, Road Lighting, Markets all depend on reliable Electric Supply. Life comes to a standstill without electricity. Electricity has become an integral and inevitable part of every body’s life. In terms of thermal comfort (heating or cooling) and air quality, most of the energy used in buildings is used to maintain a comfortable indoor environment (ventilation). Other applications of energy include electric lighting, hot water, kitchen appliances or other electrical equipment (refrigerators, computers, TVs etc.). It is also necessary to remember that electricity becomes destructive and dangerous, if not handled with care, safety conforming to laid down safety standards and norms. In case of building fires, which often destroy property and lives causing sufferings to the affected people, the first culprit is often supposed to be ‘Electric Short Circuit’. Purpose of electricity: Electricity in a building has many purposes, including: Lighting: Lighting is used to illuminate both inside and outside of a building. Heating and cooling: Electricity is used for heating and cooling to maintain a comfortable indoor environment. Appliances: Electricity is used to power household appliances, computers, electronics, and machinery. Other electrical equipment: Electricity is used for other electrical equipment, such as exhaust fans, air conditioning, sound systems, and lifts. Protection: Electricity is used for protection against lightning and fire. Telecommunication and networking: Electricity is used for telecommunication and networking. SOURCES OF ELECTRICITY Sources of Electricity Electricity is generated from a variety of sources, including:  Fossil fuels Coal, natural gas, and oil are the cheapest way to generate electricity, but they are also the most harmful to the environment. Burning fossil fuels releases carbon dioxide into the atmosphere, which contributes to climate change, air pollution, and other environmental issues.  Renewable sources Wind, solar, geothermal, and hydropower are renewable sources of electricity.  Nuclear energy Nuclear energy is another primary source of electricity.  Electrochemical Batteries are a common source of electrochemical electricity, which is the direct conversion of chemical energy into electricity.  Piezoelectric Piezoelectric materials, such as quartz and Rochelle salt, can convert pressure, force, vibration, or shock into electrical energy. Sources of Electricity Electricity is a secondary energy water source, meaning it is produced by converting primary energy sources into coal electrical power. Electricity can also be converted back into other forms of energy, such as heat or mechanical Diesel or gas energy. wind solar POWER GENERATION Power generation-HYDRO  Hydroelectric power, is electricity generated from hydropower (water power).  Hydropower supplies 15% of the world's electricity, almost 4,210 TWh in 2023, which is more than all other renewable sources combined and also more than nuclear power.  Hydropower can provide large amounts of low-carbon electricity on demand, making it a key element for creating secure and clean electricity supply systems.  A hydroelectric power station that has a dam and reservoir is a flexible source, since the amount of electricity produced can be increased or decreased in seconds or minutes in response to varying electricity demand.  Once a hydroelectric complex is constructed, it produces no direct waste, and almost always emits considerably less greenhouse gas than fossil fuel-powered energy plants.  However, when constructed in lowland rainforest areas, where part of the forest is inundated, substantial amounts of greenhouse gases may be emitted. Power generation-HYDRO Power generation-HYDRO Hydropower, or hydroelectric power, is a renewable source of energy that generates power by using a dam or diversion structure to alter the natural flow of a river or other body of water. Hydropower relies on the endless, constantly recharging system of the water cycle to produce electricity, using a fuel—water—that is not reduced or eliminated in the process. There are many types of hydropower facilities, though they are all powered by the kinetic energy of flowing water as it moves downstream. Hydropower utilizes turbines and generators to convert that kinetic energy into electricity, which is then fed into the electrical grid to power homes, businesses, and industries. Power generation-HYDRO HOW EXACTLY IS ELECTRICITY GENERATED AT HYDROPOWER PLANTS? Because hydropower uses water to generate electricity, plants are usually located on or near a water source. The energy available from the moving water depends on both the volume of the water flow and the change in elevation—also known as the head—from one point to another. The greater the flow and the higher the head, the more the electricity that can be generated. At the plant level, water flows through a pipe—also known as a penstock—and then spins the blades in a turbine, which, in turn, spins a generator that ultimately produces electricity. Most conventional hydroelectric facilities operate this way, including run-of-the-river systems and pumped storage systems. The country’s top five hydroelectric power plants hail from the states of Uttarakhand, Maharashtra, Andhra Pradesh, Himachal Pradesh and Gujarat.  Power generation-THERMAL Generation of thermal power takes place in different “thermal power plants”. The energy generation takes place with the support of steam power which is created by burning coal, natural gas, oil, liquid and other substances. The steam power created by the burning of different substances is being used to rotate the generators and electricity is being produced by the rotation of these generators. Within the power plants, various boilers are present on which different substances are being burnt; mainly coal is used for producing steam. In order to produce a large amount of steam power, million tons of coals get burnt within the large boilers. As a result of this, a large volume of steam gets evolved from the boilers. The steam produced by the boiler is used as a driving force for rotating the wheels of the turbines.  Power generation-THERMAL At first, the steam is passed through the “high pressure turbine”. After that it goes to a “low pressure turbine”. A generator machine is found to connect with the “low pressure turbine”. The output of this “low pressure boiler” is the mechanical energy which is used as the driving force for rotating the shaft of the generator. Finally, this “mechanical energy” is being converted into “electrical energy” with the help of a generator. Thus the production of thermal power takes place in the different “thermal power plants” in various countries. The generated electricity is being used for meeting different energy demands all over the country. Different organisations such as NTPC, WBSEDCL, and CSE are the main distributors of thermal power throughout the country. There are different thermal power plants in different states of India especially in Maharashtra, Uttar Pradesh, Madhya Pradesh, and Gujarat and West Bengal. Chandrapur, Sholapur in Maharashtra, singrauli, amarkantak, satpura in Madhya Pradesh, Bokaro in Jharkhand are some major “thermal power stations” in India. Power generation-THERMAL Power generation-SOLAR Power generation-SOLAR Solar power works by converting energy from the sun into power. There are two forms of energy generated from the sun for our use – electricity and heat. Both are generated through the use of solar panels, which range in size from residential rooftops to ‘solar farms’ stretching over acres of rural land. Solar panels are usually made from silicon, or another semiconductor material installed in a metal panel frame with a glass casing. When this material is exposed to photons of sunlight (very small packets of energy) it releases electrons and produces an electric charge. This PV charge creates an electric current (specifically, direct current or DC), which is captured by the wiring in solar panels. This DC electricity is then converted to alternating current (AC) by an inverter. AC is the type of electrical current used when you plug appliances into normal wall sockets.  Power generation-WIND The Power of Wind: Wind turbines harness the wind—a clean, free, and widely available renewable energy source—to generate electric power. How a Wind Turbine Works A wind turbine turns wind energy into electricity using the aerodynamic force from the rotor blades, which work like an airplane wing or helicopter rotor blade. When wind flows across the blade, the air pressure on one side of the blade decreases. The difference in air pressure across the two sides of the blade creates both lift and drag. The force of the lift is stronger than the drag and this causes the rotor to spin. The rotor connects to the generator, either directly (if it's a direct drive turbine) or through a shaft and a series of gears (a gearbox) that speed up the rotation and allow for a physically smaller generator. This translation of aerodynamic force to rotation of a generator creates electricity. Power generation-WIND TRANSMISSION  What is transmission system The transmission system makes it possible to efficiently transport large amounts of power over long distances. Without transmission,electricity would have to be produced close to where it is used. Generators produce electricity, which is then increased to high voltage by transformers and sent to transmission lines. The transmission system moves the electricity over long distances to local distribution systems, where it is transformed to a lower voltage, so it can be safely delivered to consumers. One way to think about this system is in terms of an interstate road trip. A driver starts the trip on local roads and then uses an onramp to join the faster-flowing traffic on the interstate highway. At the end of the journey, the driver uses an off-ramp to join a local road system, slowing down from highway speed to reach the destination.  What is transmission system Generated Power Steps Up to the Transmission System Transmission begins at generating stations that produce electricity with voltages ranging from 2,300 to 24,000 volts. In switchyards, or substations, outside of these generating stations, there are large transformers that raise, or “step up,” the voltage to levels suitable for transporting large amounts of power at the transmission level – 100 kV (100,000volts) and higher.  What is transmission system Transmission Lines Move Electricity Over Long Distances Electricity is transmitted from one point to another by conductors, which are made up of many strands of aluminum and steel wire. Interconnected transmission lines form a network; therefore, if one line fails, others can take up the load. The AC transmission lines carry three-phase current – three separate streams of electricity traveling through separate conductors. Transmission towers generally support at least three wires, sometimes bundled with six conductors, if they carry two circuits on the same pole or tower. Consumers may recognize transmission lines as the larger, taller poles and towers. These carry many wires over long distances and differ from the utility poles found on a local street. These smaller utility poles and lines are part of the distribution system – the final leg in electricity’s journey from generators to consumers. CLASS-2 DISTRIBUTION AND CONSUMPTION Distribution: High-Voltage Electricity Steps Down for Consumption Wholesale power is transmitted at voltages that are too high for business and residential use. A series of step-down transformers that reduce voltage for distribution are the counterpart to the step-up transformers that raise voltage as power emerges from the generating station. When electricity approaches its destination, it is routed through large transformers in substations. These transformers reduce, or “step down,” the voltage to levels suitable for distribution to consumers at the retail level. In this step, the power that is over 100 kV from the transmission lines is reduced to voltages ranging from 4,160 to 34,500 volts. What Else Happens in a Substation? Substations also contain other devices such as circuit breakers, switches, meters, relay protection and control devices – all connected by hundreds of wires. Devices called regulators, for example, react to changes in customer demand to help maintain steady voltage. Successful operation of the electric grid requires the continuous balance of the power being supplied and consumed. Many substations use a capacitor bank to boost the voltages to counteract or correct imbalances in the supply and demand. Distribution: From Substations to Consumers: Conductors or cables, commonly known as distribution feeders, leave substations in various directions, carrying power to local distribution points at the retail level. Distribution transformers then reduce the voltage further for use by homes and businesses. Standard voltage at the consumer level is 120 or 240 volts. The transmission system is an essential part of the bulk electric system. Without the ability to move electricity across long distances, each community would have to depend on power generated locally. A robust transmission system gives different geographic areas access to power from distant generators, regardless of their location. Distribution: Distribution System: "The part of power system which distributes electrical power for local use is known as DISTRIBUTION SYSTEM.“ This system is the electrical system between the substation fed by the transmission system and consumer meter. Distribution line generally consist of: Feeders Distributers Service mains Distribution: Distribution: FEEDER: A Feeder is conductor which connects the substation to the area where power is to be distributed. Feeder are used to feed the electrical power from the generating station to the substation No tapings are taken from the feeder So the current in it remains the same throughout Main consideration in the design of feeder is the Current carrying capacity. DISTRIBUTER: A distributer is a conductor from which tapings are taken from pole mounted transformer to the consumer The current through a distributer is not constant because tapings are taken at various places along its length Voltage drop is main consideration Limit of variation is 6% of rated at consumer Distribution: SERVICE MAINS: A service mains is a generally a small cable which connects the distributer to the consumer 's meter. The connecting links between the distributor and the consumer terminals. Distribution: Classification of Distribution Systems: A distribution system may be classified according to ; (1) Nature of current:According to nature of current, distribution system may be classified as (a) D.C distribution system (b) A.C distribution system. Now-a-days, A.C system is universally adopted for distribution of electric power as it is simpler and more economical than direct current method. (2) Type of construction: According to type of construction distribution system may be classified as: (a) overhead system (b) underground system. The overhead system is generally employed for distribution as it is 5 to 10 times cheaper than the equivalent underground system. In general, the underground system is used at places where overhead construction is impracticable or prohibited by the local laws. Distribution: (3) Scheme of connection: According to scheme of connection, the distribution system may be classified as (a) Radial system (b) Ring main system (c) Inter connected system. Each scheme has its own advantages and disadvantages A.C Distribution: Now-a-days electrical energy is generated, transmitted and distributed in the form of alternating current. One important reason for the widespread use of alternating current in preference to direct current is the fact that alternating voltage can be conveniently changed in magnitude by means of a transformer.High transmission and distribution voltages have greatly reduced the current in the conductor and the resulting line losses. The a.c. distribution system is classified into (i) Primary distribution system and (ii) Secondary distribution system.  A.C Distribution: (1) Primary distribution system: The most commonly used primary distribution voltages are 11kv, 6.6kv and 3.3kv. Due to economic considerations, primary consideration is carried out by 3-phase, 3-wire system. Electric power from the generating station is transmitted at high voltage to the substation located in or near the city. At this substation, voltage is stepped down to 11 kV with the help of step-down transformer. Power is supplied to various substations for distribution or to big consumers at this voltage. This forms the high voltage distribution or primary distribution.  A.C Distribution: (2) Secondary distribution system: The secondary distribution system employs 400/230 V, 3-phase,4-wire system. The primary distribution circuit delivers power to various substations, called distribution substations. The substations are situated near the consumers’ localities and contain stepdown transformers. At each distribution substation, the voltage is stepped down to 400 V and power is delivered by 3-phase,4-wire a.c. system. The voltage between any two phases is 400 V and between any phase and neutral is 230 V. The single phase domestic loads are connected between any one phase and the neutral,. Motor loads are connected across 3-phase lines directly. D.C Distribution: For certain applications, d.c. supply is absolutely necessary. d.c. supply is required for the operation of variable speed machinery (i.e., d.c. motors storage battery.) For this purpose,a.c. power is converted into d.c. power at the substation by using converting machinery e.g.,mercury arc rectifiers, rotary converters and motor- generator sets. The d.c. supply obtained in the form of (i) 2-wire or (ii) 3-wire for distribution. D.C Distribution: 2-WIRE D.C. SYSTEM: As the name implies, this system of distribution consists of two wires. One is the outgoing or positive wire and the other is the return or negative wire. The loads such as lamps, motors etc. are connected in parallel between the two wires as shown in Fig. This system is never used for distrubution purposes due to low efficiency but may be employed for distribution of d.c.power. D.C Distribution: 3-WIRE D.C. SYSTEM: It consists of two outers and a middle or neutral wire which is earthed at the substation. The voltage between the outers is twice the voltage between either outer and neutral. The principal advantage of this system is that it makes available two voltages at the consumer terminals, V between any outer and the neutral and 2V between the outers. Loads requiring high voltage (e.g., motors) are connected across the outers, whereas lamps and heating circuits requiring less voltage are connected between either outer and the neutral. COMPARISON OF D.C. AND A.C. DISTRIBUTION: The electric power can be distributed either by means of d.c. or a.c. Each system has its own merits and demerits D.C DISTRIBUTION: ADVANTAGES: (i) It requires only two conductors as compared to three for a.c. distribution. (ii) There is no inductance, capacitance, phase displacement and surge problems in d.c. distribution. (iii) Due to the absence of inductance, the voltage drop in a d.c. distribution line is less than the a.c. line for the same load and sending end voltage. For this reason, a d.c. distribution line has better voltage regulation. (iv) There is no skin effect in a d.c. system. Therefore, entire cross-section of the line conductor is utilized. (v) For the same working voltage, the potential stress on the insulation is less in case of d.c. system than that in a.c. system. Therefore, a d.c. line requires less insulation. (vi) A d.c. line has less corona loss and reduced interference with communication circuits. (vii) The high voltage d.c. distrubution is free from the dielectric losses, particularly in the case of cables. (viii) In d.c. distrubution, there are no stability problems and synchronising difficulties. DISADVANTAGES: (i) Electric power cannot be generated at high d.c. voltage due to commutation problems. (ii) The d.c. voltage cannot be stepped up for distrubution of power at high voltages. (iii) The d.c. switches and circuit breakers have their own limitations. A.C. DISTRIBUTION: ADVANTAGES: (i) The power can be generated at high voltages. (ii) The maintenance of a.c. sub-stations is easy andcheaper. (iii)The a.c. voltage can be stepped up or stepped down by transformers with ease and efficiency.This permits to transmit power at high voltages and distribute it at safepotentials. DISADVANTAGES: (i) An a.c. line requires more copper than a d.c. line. (ii) The construction of a.c. distrubution line is more complicated than a d.c. distrubution line. (iii) Due to skin effect in the a.c. system, the effective resistance of the line is increased. (iv) An a.c. line has capacitance. Therefore, there is a continuous loss of power due to charging current even when the line is open  OVERHEAD DISTRIBUTION SYSTEM: In overhead power lines, a structure based network is used to transmit electrical energy from one point to another. It consists of adequate size of conductors , commonly three conductor in 66 KV , 33 KV or 11 KV lines or four conductor in 11 KV lines or 5 conductor in LT lines ( 5th conductor for street lighting) for three phase lines and two conductors for single phase lines etc. Suspended by towers or poles and generally comprising of the items- such as Poles, Conductors, Cross arms, pin insulators, Stay Wires, Stay Rod, Stay Anchor, Guy Insulator, earthing materials, Guard wire, Barbed wire and Danger plate etc. The Poles for the electrical network may be a Steel Poles (Tubular Poles, Rolled Steel Joists and Rails),Concrete Poles (RCCPoles,PCC poles and Pre-Stressed Concrete -PSC Pole) of various heights of 9 meters to 13 meters (IS: 5613 (Part 1, 2, 3) depending on site location, minimum safety clearance and Voltage (230Volts, 415Volts,11KV and 33KV etc) of the overhead network system. Along with these poles, Railpoles, which have more strength then other poles, are generally used in overhead network along and across the Road, Public Places, Residential areas, River crossing etc.  OVERHEAD DISTRIBUTION SYSTEM: Sometimes, for supporting different voltages on the same poles and to maintain the adequate clearance between the different lines of different voltage levels, poles with higher heights are used, and in such cases, guard wires are also provided to prevent accidental over charging of lines of lower voltage system due to conductor snapping etc. The conductors for the overhead network can be a bare conductor or an insulated conductor ( ABC) depending on the requirement. It is an important component of overhead electrical transmission and distribution systems. The choice of conductor depends on the power carrying capacity, cost, growth of the load, and reliability & efficiency. While selecting an ideal conductor, some of the following features such as i) maximum electrical & ii) thermal capacity and iii) cost effectiveness etc are considered.  UNDERGROUND DISTRIBUTION SYSTEM: In Under Ground cable system, the power is transferred from one point to another through underground cables laid in the ground in place of overhead lines on poles/ towers. As these cables are not exposed to the air/ atmosphere, this makes the U/G cabling system less susceptible to outages due to various atmospheric conditions like high wind, storm, thunder storms, heavy snow or ice storms etc. As these cables are not visible on ground, these provide an aesthetic look to the area where these are laid as compare to OH lines. However, the U/G cables have to be laid in the proper tranches and also have more restoration time in case of any fault as compare to OH lines.  UNDERGROUND DISTRIBUTION SYSTEM: While selecting the rating of cables to be used, some of the parameters such as Current carrying capacity, Voltage drop and short circuit rating are important factors to select the economical and optimum size of cable. The cable generally comprises of the conductor, insulation material, bedding, beading/armoring, and outer sheath etc. Although, the armoring and outer sheath takes care of the physical safety of cable , adequate care has to be taken by cable manufactures during manufacturing of the cable. Normally the lifespan of a cable is about 40 to 50 years. But over the time, the insulation of cable may get damaged or weakened due to ageing. Wrong handling of cabals, such as damages due to wrong handling/laying of cable also weakens the insulation of the cables. Normally, some of cable faults may be as 1. A short circuit fault between two conductor due to failure of insulation between the two conductors 2. A earth fault, i.e., fault between conductor and ground due to failure of outer insulation sheath 3. An open circuit fault, caused due to disconnection of the conductor etc.  OVERHEAD VERSUS UNDERGROUND SYSTEM: The distribution system can be overhead or underground. Overhead lines are generally mounted on wooden, concrete or steel poles which are arranged to carry distribution transformers in addition to the conductors. The underground system uses conduits, cables and manholes under the surface of streets and sidewalks. The choice between overhead and underground system depends upon a number of widely differing factors. 1. Public safety: The underground system is more safe than overhead system because all distribution wiring is placed underground and there are little chances of any hazard. 2. Initial cost: The underground system is more expensive due to the high cost of trenching,conduits, cables, manholes and other special equipment. The initial cost of an underground system may be five to ten times than that of an overhead system. 3. Flexibility: The overhead system is much more flexible than the underground system. In the latter case, manholes, duct lines etc., are permanently placed once installed and the load expansion can only be met by laying new lines. However, on an overhead system, poles, wires,transformers etc., can be easily shifted to meet the changes in load conditions.  OVERHEAD VERSUS UNDERGROUND SYSTEM: 4. Faults: The chances of faults in underground system are very rare as the cables are laid underground and are generally provided with better insulation. 5. Appearance: The general appearance of an underground system is better as all the distribution lines are invisible. This factor is exerting considerable public pressure on electric supply companies to switch over to underground system. 6. Fault location and repairs: In general, there are little chances of faults in an underground system. However, if a fault does occur, it is difficult to locate and repair on this system. On an overhead system, the conductors are visible and easily accessible so that fault locations and repairs can be easily made. 7. Current carrying capacity and voltage drop: An overhead distribution conductor has a considerably higher current carrying capacity than an underground cable conductor of the same material and cross-section. On the other hand, under ground cable conductor has much lower inductive reactance than that of an overhead conductor because of closer spacing of conductors. The choice of whether to use overhead line (OHL) or underground cable (UGC) must be made keeping in view the safety, reliability and operational constraints.The choice between OHL and UGC is driven by technical, environmental and economic considerations.  OVERHEAD VERSUS UNDERGROUND SYSTEM: (viii) Useful life: The useful life of underground system is much longer than that of an over head system. An overhead system may have a useful life of 25 years, whereas an underground system may have a useful life of more than 50 years. (ix) Maintenance cost: The maintenance cost of underground system is very low as compared with that of overhead system because of less chance of faults and service interruptions from wind, ice, lightning as well as from traffic hazards. (x) Interference with communication circuits: An overhead system causes electromagnetic interference with the telephone lines. The power line currents are superimposed on speech currents, resulting in the potential of the communication channel being raised to an undesirable level. However, there is no such interference with the underground system. It is clear from the above comparison that each system has its own advantages and disadvantage  RADIAL SYSTEM In this system, separate feeders radiate from a single substation and feed the distributors at one end only. Fig. (i) shows a single line diagram of a radial system for d.c. distribution where a feeder OC supplies a distributor AB at point A. distributor is fed at one end only i.e., point A is this case. Fig. (ii) shows a single line diagram of radial system for a.c. distribution. This is the simplest distribution circuit and has the lowest initial cost. DRAWBACKS : (a) The end of the distributor nearest to the feeding point will be heavily loaded. (b any fault on the feeder or distributor cuts off supply to the consumers who are on the side of the fault. (c) The consumers at the distant end of the distributor would be subjected to serious voltage fluctuations when the load on the distributor changes. Due to these limitations, this system is used for short distances only.  RING MAIN SYSTEM In this system, the primaries of distribution transformers form a loop.The loop circuit starts from the substation bus- bars, makes a loop through the area to be served,and returns to the substation. Fig. shows the single line diagram of ring mainsystem for a.c. distribution where substatio n supplies to the closed feeder LMNOPQRS. The distributors are tapped from different points M, O and Q of the feeder through distribution transformers. ADVANTAGES : (a) There are less voltage fluctuations at consumer’sterminals. (b) The system is very reliable as each distributor is fed via *two feeders. In the event of fault on any section of the feeder, the continuity of supply is maintained  Interconnected system When the feeder ring is energised by two or more than two generating stations or substations, it is called inter-connected system. Fig. shows the single line diagram of interconnected system where the closed feeder ring ABCD is supplied bytwo substations S1 and S2 at points D and C respectively. Distributors are connected to points O, P, Q and R of the feeder ring through distribution transformers. ADVANTAGES : (a) It increases the service reliability. (b) Any area fed from one generating station during peak load hours can be fed from the other generating station. This reduces reserve power capacity and increases efficiency of the system  DESIGN CONSIDERATIONS IN DISTRIBUTION SYSTEM Good voltage regulation of a distribution network is probably the most important factor responsible for delivering good service to the consumers. For this purpose, design of feeders and distributors requires careful consideration. (i) Feeders: A feeder is designed from the point of view of its current carrying capacity while the voltage drop consideration is relatively unimportant. It is because voltage drop in a feeder can be compensated by means of voltage regulating equipment at thesubstation. (ii) Distributors: A distributor is designed from the point of view of the voltage drop in it. It is because a distributor supplies power to the consumers and there is a statutory limit of voltage variations at the consumer’s terminals (± 6% of rated value). The size and length of the distributor should be such that voltage at the consumer’s terminals is within the permissible limits. REQUIREMENTS OF A DISTRIBUTION SYSTEM Requirements of a good distribution system are : proper voltage, availability of power on demand and reliability. (i) Proper voltage: One important requirement of a distribution system is that voltage variations at consumer’s terminals should be as low as possible. The changes in voltage are generally caused due to the variation of load on the system. Low voltage causes loss of revenue, inefficient lighting and possible burning out of motors. High voltage causes lamps to burn out permanently and may cause failure of other appliances. Therefore, a good distribution system should ensure that the voltage variations at consumer’s terminals are within permissible limits. The statutory limit of voltage variations is ± 6% of the rated value at the consumer’s terminals. Thus, if the declared voltage is 230 V, then the highest voltage of the consumer should not exceed 244 V while the lowest voltage of the consumer should not be less than 216 V. REQUIREMENTS OF A DISTRIBUTION SYSTEM (ii) Availability of power on demand: Power must be available to the consumers in any amount that they may require from time to time. For example, motors may be started or shut down, lights may be turned on or off,without advance warning to the electric supply company. As electrical energy ca nnot be stored,therefore, the distribution system must be capable of supplying load demands of the consumers. This necessitates that operating staff must continuously study load patterns to predict in advance those major load changes that follow the known schedules. (iii) Reliability: Modern industry is almost dependent on electric power for its operation. Homes and office buildings are lighted, heated, cooled and ventilated by electric power. This calls for reliable service. Unfortunately, electric power, like everything else that is man- made, can never be absolutely reliable. However, the reliability can be improved to a considerable extent by (a)interconnected system (b) reliable automatic control system (c) providing additional reserve facilities CONSUMPTION Energy consumption in different types of buildings Residential buildings consume 1–3 kWh/m2/month, while commercial buildings consume 5–25 kWh/m2/month. Energy consumption in different areas of a building The main areas of energy consumption in buildings are:Heating, ventilation, and air conditioning: Consumes 35% of total building energy Lighting: Consumes 11% of total building energy Major appliances: Consumes 18% of total building energy Class-3 Course content CLASS3:  Introduce to the electrical circuit- single and three phase,  types of wiring system, distribution system and supply – HT & LT, AC/DC Current-generators,Transformers,  Methods of wiring- joint box and open and concealed circuit, etc.  Wiring materials, lighting accessories wires and cables- materials types, sizes, switch boards, M.C.B, ELCB, INTRODUCE TO THE ELECTRICAL CIRCUIT- SINGLE AND THREE PHASE SINGLE PHASE Single Phase power is a two wire Alternating Current (AC) power circuit. Typically, there's one power wire and one neutral wire and power flows between the power wire (through the load) and the neutral wire. It is common in households. THREE PHASE Three Phase power is a three wire Alternating Current (AC) power circuit. A 3-phase power arrangement provides 1.732 (the square root of 3) times more power with the same current and provides (7) power circuits. Multistorey buildings and manufacturing plants have three-phase power. Difference between single phase and three phase supply:- Three-phase current offers a A three-phase system is usually more economical steadier source of power. than an equivalent single-phase or two-phase system -Magnetic force which, causes at the same voltage because it uses less conductor motor rotation is strongest when material to transmit electrical power.Most current flow is at its peak in the read414243444546 The main advantage of 3 phase cycle.-Single-phase current peaks is that it is more efficient for running AC motors than twice during one cycle, whereas, one or two phase.Properties of three phase three-phase current peaks six times supply Three-phase has properties that make it very during one cycle.-A balanced desirable in electric power systems:1) The phase three-phase, three-wire circuit with currents tend to cancel out one another, summing to equal voltages uses 75% of the zero in the case of a linear balanced load. This copper required for conductors makes it possible to eliminate or reduce the size of the neutral conductor; all the phase conductors carry the same current and so can be the same size, for a balanced load.2) Power transfer into a linear balanced load is constant, which helps to reduce generator and motor vibrations.Electrical system3) Three-phase systems can produce a magnetic field that rotates in a specified direction, TYPES OF WIRING SYSTEM, Wiring systems  Wiring in buildings is run either on the surface or conceled in the construction. Surface wiring is cheaper but its appearance limits its use. The type of wiring system available for use in buildings are sheated and conduit. Two or more wires consisting of metal conductors each having its own inuation is enclosed in a protective sheath known as TRSC tough rubber sheated.  Use of PVC for insulation and sheating is preferred as it gives smoother and neater cables. This type of wire are well suited to surface use. For use in concealed wiring, conduit or metal channels should provide to protect wiring. Types of wiring There is wide choice of wiring; however one must keep in mind the safety of men & material. The various types of wiring used are discussed below 1. Cleat Wiring 2. Wooden Casing , Capping Wire 3. Lead Casing Wire 4. C.T.S & T.R.S or PVC wire 5. Conduit wiring Cleat wiring  In this system of wiring, V.I.R or PVC Insulated wires are held to the walls and ceiling by means of porcelain cleats which are fixed at distance of 0.5 m horizontally and 0.75 m vertically above the walls The cleat are made on two halves, one is known as base and the other is known as cap. The wirings are drawn in groves and finally tightened. This wiring is cheapest and require little skill and can be quickly installed. Wooden Casing , Capping Wire  In this type of wiring, the casing is fitted on the walls and ceilings on the wooden gutties which are fixed The size of casing and capping generally used is 20 mm x 12 mm for house wiring. This type of wiring is generally used for house wiring. It is cheaper as compared to lead sheated and conduit wiring, easy to Install. Lead Casing Wire  In this system of wiring, the wiring procedure is same except the wire used in VIR covered with an outer sheath made of lead-aluminum alloy It is used in houses and industrial wiring. It has good mechanical protection and possibility of fire is less. C.T.S & T.R.S or PVC wire  In this system of wiring first of all teaks wood is fitted on the walls and ceiling. The battern is tightened by drawing wooden screws in the gutties fitted in the wall an ceiling. PVC or CTS wire run on the battern and finally grappled by the joint clip. This type of wiring is suitable for domestic installations, commercial & Industrial buildings except where it is liable to mechanical injury. Conduit wiring  In this type of wiring system VIR or PVC are carried through steel or PVC tubes as conduit in case of surface conduit wiring, the conduit is fitted on the surface of the walls by means of saddles and in case of concealed conduit wiring the conduit to facilitate the drawing of wires DISTRIBUTION SYSTEM AND SUPPLY Electricity in buildings Electrical energy for use in buildings is often supplied via a grid connection, and typically originates at a power station, where it has been generated by electro- mechanical generators. Electrical energy can by generated by many means, such as chemical combustion, nuclear fission, or renewable means such as flowing water, wind, geothermal heat and solar voltaic. Equally, electrical energy may be generated at the building itself, typically either via solar voltaic, localised electromechanical generators or other renewable sources. Such energy may be used locally within the building or may be exported back into the grid for use by other consumers. Where this latter facility exists, the building and its system are referred to as a ‘prosumer’ – i.e. a simultaneous producer and consumer of electrical energy. Electricity in buildings Entry in the buildings In Urban areas electrical cables are Usually underground/overhead and are brought up to entry point at ground level or into basement service cable cannot be bent to small radiee and this should be borne in mind when considering point of entry. In small buildings the cable run is kept as short as possible, terminating in a distribution board at the first convenient position. In these buildings the distribution board will be fitted with a seal box to prevent moisture from entering the insulation of the service cable, a main fuse for the premises in a box sealed by the supply authority and the consumer unit or other switch and fuse gear belonging to the building. The position chosen for the distribution board should be readily accessible both for meter reading and for replacing fuses. In some cases special glasses are provided so that meter can be read without entering the premises. Electricity in buildings Electricity in buildings Power Distribution in Small buildings The distribution systems of small  From the meter, the power is commercial or residential transmitted into the building. buildings are simple. Wires transfer the electricity  The building's utility pole will be from the meter to a panel attached to the transformer board. which then trim down the  The panel board will have a voltage from 13.8kV down to main service breaker and a 120/240 or 120/208 volts and series of circuit breakers, which then passes the electricity to a control the flow of power to meter. various circuits in the building.  The meter, owned by the  Each branch circuit will serve a power company, is monitored device (some appliances for energy consumption. require heavy loads) or a number of devices like convenience outlets or lights.  Power Distribution in large buildings Large buildings have a much higher electrical  The bus or feeder is tapped as needed consumption than small buildings and a conductor is run to an electric  The building should have and maintain their closet, which serves a zone or floor of own step-down transformer. a building.  The electricity is then transmitted to  Each electrical closet will have switchgear. The role of the switchgear is to another step-down transformer. distribute electricity safely and efficiently to  That transformer will feed a branch the various electrical closets throughout the panel, which controls a series of building. branch circuits that cover a portion of  Circuit breakers are safety features which the building. allow power to be disrupted whenever  Each branch circuit covers a subset of maintenance and repair is needed. the electrical needs of the area - for  The electricity will leave the switchgear and instance: lighting, convenience outlets travel along a primary feeder or bus. The bus to a series of rooms, or electricity to a or feeder is a heavy gauge conductor that piece of equipment. is capable of carrying high amperage current throughout a building safely and efficiently. Ducts for Electrical Distribution  In addition to the wiring systems there are a number of ducts available specially designed to contain electric cables in particular building stations  Duct tube: It consists of an inflatable rubber tube, which is placed, in concrete formwork before pouring concrete. After the concrete has set the duct tube is deflated, withdrawn from concrete, leaving a duct for electric wiring, or other purpose.  Skirting trunking: It is very usual to run cable trunking in or above the skirting round the perimeter walls. This systems is mostly employed in office buildings.  Floor Trunking: System is employed in large offices where desks are placed remote from walls. Useful where there are comparatively few points, the positions of which are known, and where flexibility for future re-planning must be achieved.  Overhead distribution  Overhead distribution systems are clearly more economical and more flexible than under floor ones. They are mainly used in industrial units when pendants connection to apparatus is not considered unsightly. Ducts for Electrical Distribution Course content CLASS4:  Types of Earthing, Types of electric motors and pumps, distribution board and meter, Control switches.  Electrical Symbols and layout preparation.  Electric Vehicle Charging systems at residential and commercial level.  Share the knowledge of power systems, and power load factor;  Fundamental Principles of electricity as per standard norms,  Introduction to the energy conservation concepts.  National Electricity Grid network, Lightening, and substation operations at the buildings scale. ASSIGNMENTS Assignment1: Make a chart for electricity consumption for a day in your house/hostel. ASSIGNMENT2: Draw a plan of a residence/hostel and mark the  Mode of power entry into building  Ug/oh