ELE 2303 Power Generation and Transmission CLO2 PDF

Power Generation and Transmission ELE-2303 Monday, July 1, 2024 ELE 2303: Power Generation and Transmission CLO-2 : Describe the power transmission process, from generation to distribution 2  CLO-2 - Describe the power transmi...

Power Generation and Transmission ELE-2303 Monday, July 1, 2024 ELE 2303: Power Generation and Transmission CLO-2 : Describe the power transmission process, from generation to distribution 2  CLO-2 - Describe the power transmission process, from generation to distribution. 2.1 Describe the components and layout of an electrical power system from generation to distribution and explain the purpose of using Super Grid. 2.2 Identify types of power lines, standard voltages, and components of high-voltage transmission lines (HVTL). 2.3 Describe the construction of a transmission line and perform calculation of power loss, voltage drop, and regulation. 2.4 Describe the problems related to transmission lines; this includes corona effect flashover, ambient effect on the transmission line and lightning strikes. 2.1 The components and layout of an electrical power system and the purpose of using Super grid. The first electric network was a DC line established in the USA in 1882 in New York City by Thomas Edison. The excessive power loss, RI2, at low voltage prevented Edison's companies deliver energy over long distances from their stations. With the invention of the transformer (William Stanley, 1885) the level of AC voltage for transmission and distribution could be increased and loses could be decreased. This made the AC networks more predominant over the DC networks. Another advantage of the AC system is that due to lack of commutators in AC generators, more power can be produced conveniently at higher voltages.  Edison’s Company installed the first three-phase system at 2.3 kV in 1893. In the beginning, power systems were operating at different frequencies, in the range of 25 Hz to 133 Hz. But, as the need for interconnection and parallel operation became evident, a standard frequency of either 60 Hz or 50 Hz was adopted. Transmission voltages have since then risen steadily. The 765 kV extra high voltage (EHV) was first put into operation in the United States in 1969.  An electrical network connecting and/or interconnecting different power stations and different load centers is called the Power Grid. The advantage of an interconnected system is that it requires fewer generators for peak load and spinning reserve. Also, interconnection makes the energy generation and transmission more economical and reliable, since power can readily be transferred from one area to others. Some times, it may be cheaper for a power system company to buy bulk power from neighboring utilities rather than producing it locally. A modern power system components can be divided into four main groups 1. Power generation stations (plants) 2. Transmission system(s) (operated at high and extra high voltage levels) 3. Distribution systems (operated and medium and low voltage levels) 4. Transformation and switched Substations, a) To connect the above three groups, b) To transfer voltage from one level to another, and c) To allow switching operations, isolation of faults and conducting safe maintenance.  Essential components in power generation stations (1/2) Power generation stations (plants) include one of the essential components of power systems:- The generators (known also as alternators). Generators convert mechanical power to electrical. The source of mechanical power, commonly known as the prime mover, can be hydraulic turbines, steam turbines, gas turbines or internal combustion engines. Steam turbines get energy from burning oil, gas, coal, nuclear fuel and some other renewable resources. More details about the different types of power generation plans based on the type of fuel and type of turbines was covered in CLO1.  Essential components in power generation stations (2/2) Other major components of power generation stations are the Transformers. Each generator will commonly have a step up transformer to transform the generated voltage (e.g. 15 kV) to a transmission voltage level (e.g. 220 kV). The high voltage terminals of step-up transformers are connected by means of circuit breakers and bus-bars to the transmission system. The facility, where circuit breakers, bus-bars, and other supporting components (such as isolators, voltage transformers (VTs), current transformers (CTs)) constitute what is called the high voltage substation in the power station. The high voltage substation is considered as the boundary between power generation station and transmission system. https://electricalschool.org/generatorstep-upgsu/  Transmission and Sub-transmission The purpose of a transmission network is to transfer electric energy from generating units at various locations to the distribution system. Transmission network also interconnect neighboring utilities which permit economic dispatch of power within regions and transfer of power between regions during emergencies.  High voltage transmission lines are terminated in substations, which are called high-voltage substations, receiving substations, or primary substations. The function of some substations is switching circuits in and out of service; they are referred to as switching stations. At the primary substations, the voltage is stepped down to a value more suitable for distribution. Very large industrial customers may be served from the transmission system. The portion of the transmission system that connects the high-voltage substations through step-down transformers to the distribution substations are called the sub-transmission network. Typically, the sub-transmission voltage level ranges from 69 to 138 kV. Some large industrial customers may be served from the sub-transmission system. https://electricalschool.org/sub-transmissionsystem/  Distribution System The distribution system is that part which connects the distribution substations to the consumers' service-entrance equipment. The primary distribution lines are usually in the range of 4 to 35 kV and supply the load in a well-defined geographical area. Some small industrial customers are served directly by the primary feeders. The secondary distribution network reduces the voltage for utilization by commercial and residential consumers. Lines and cables not exceeding a few hundred feet in length then deliver power to the individual consumers. The secondary distribution serves most of the customers at levels of 400/230 V, single-phase and three-phase, four-wire system. Distribution systems are both overhead and underground.  Purpose of Using Super Grid A “supergrid,” “megagrid,” or “supersmart grid” is a grid that interconnects various countries and regions with a high-voltage direct current (HVDC) power grid. It is a wide-area transmission network capable of large-scale transmission of electricity, which allows trade high amounts of (renewable) electricity across great distances. * - https://www.sciencedirect.com/topics/engineering/supergrids 2.2 Identify types of power lines, standard voltages, and components of high- voltage transmission lines (HVTL).  TL - Parameters, Types, and Theory What is a Transmission Line? Transmission line is the long conductor with special design (bundled) to carry bulk amount of generated power at very high voltage from one station to another as per variation of the voltage level.  Watch the video: https://www.youtube.com/watch?v=PaaUwwLR0v8 The major types of Transmission Towers 1. Suspension Tower: are on the straight line of TL. It may also vary maximum to degree of 5 angle. The high voltage suspension towers are design to carry the only weight of the conductor in straight line position. Most of towers in any TL fall into this type of tower category and construction cost of suspension type transmission lines are much cheaper compare to other types of TL. These type of towers are used on the lines for straight run or for small angle of deviation up to 2° or 5°. 2. Tension Tower: are used at locations where the angel of deviation is more than degree of 5. These towers are also known as angle towers and the tower are designed to take the tension load of the cable. Tension towers are mostly use for turning points and for the section isolate locations. 3. Transposition Tower: are specially used for transpose the conductors of three-phase line. These type of towers are widely used in long TL. 4. Special Tower: These towers are used at locations such as those involving long-span river crossings, valley crossings, power line crossings from above existing lines, power lines crossings bellow existing lines (Gantry type structures) , tapping to existing lines, special termination towers, etc.  The structures, the pylons (1/2) Structures for overhead lines take a variety of shapes depending on the type of line. Structures may be as simple as wood poles directly set in the earth, carrying one or more cross-arm beams to support conductors, or “armless” construction with conductors supported on insulators attached to the side of the pole. Tubular steel poles are typically used in urban areas. High-voltage lines are often carried on A B C lattice-type steel towers or pylons.  The structures, the pylons (2/2) (A): Anchor pylons or strainer pylons are employed at branch points as branch pylons and must occur at a maximum interval of 5 km, due to technical limitations on conductor length.; (B): Branch pylon is a pylon that is used to start a line branch. The branch pylon is responsible for holding up both the main-line and the start of the branch line, and must be structured so as to resist forces from both lines.; (C): A tension tower with phase transposition of a traction current line for single phase AC 110 kV, 16.67 Hz.  TL Structures (1/4) Pole type structures are generally used In such cases, steel structures become for voltages of 345-kV or less, the cost-effective option. Lattice steel structures can be used for Also, if greater longitudinal loads are the highest of voltage levels, included in the design criteria to cover Wood pole structures can be various unbalanced loading economically used for relatively contingencies, H-frame structures are shorter spans and lower voltages, less efficient at withstanding these loads. In areas with severe climatic loads and/or on higher voltage lines with Steel lattice towers can be designed multiple sub-conductors per phase, efficiently for any magnitude or designing wood or concrete structures orientation of load. to meet the large loads can be uneconomical. TL Structures (2/4) TL Structures (3/4) TL Structures (4/4)  Power Lines, Standard Voltages The IEC 60038, IEC standard voltages, divide the voltage ratings into four categories: Band 1 - A.C. systems 100 V to 1000 V* (Low voltage): Nominal Voltage, V Three-phase four-wire or three-wire systems Single-phase three-wire systems 50 Hz 60 Hz 60 Hz - 208/120 240/120 - 240 - 400/230 4808/277 - 690/400 480 - - 600/347 - 1000 600 - Supply voltage range ±10 % at the supply terminals Supply terminal to final equipment maximum 4% voltage drop https://myelectrical.com/notes/entryid/203/voltage-levels-to-iec-60038  Band 2 - A.C and D.C traction systems *: Voltage, V Lowest Nominal Highest Frequency D.C. Systems (400) (600) (720) 500 750 900 1000 1500 1600 2000 3000 3600 A.C. Single Phase Systems (4750) (6250) (6900) 50 or 60 2 12000 15000 17250 16 /3 19000 25000 27500 50 or 60 Bracketed are non preferred and should not be used if possible * - https://myelectrical.com/notes/entryid/203/voltage-levels-to-iec-60038 Band 3 - A.C. systems above 1 kV to 35 kV * (Medium voltage) Voltage, kV Series I Series 2 Highest Nominal Highest Nominal 3.6 3.3 3 4.40 4.16 7.2 6.6 6 12 11 10 13.2 12.47 13.97 13.2 14.52 13.8 (17.5) (15) 24 22 20 26.47 24.94 36 33 36.5 34.5 40.5 35 It is recommended that only one series be used. * - https://myelectrical.com/notes/entryid/203/voltage-levels-to-iec-60038  Band 4 - A.C. systems above 35 kV to 230 kV * (High voltage) Voltage, kV Highest Nominal Voltage, V (52) (45) 7.25 66 69 123 110 115 145 132 138 (170) (150) 245 220 230 Only one series should be used in each country * - https://myelectrical.com/notes/entryid/203/voltage-levels-to-iec-60038  Band 5 - A.C. systems above 245 kV * (Extra high voltage) Highest Voltage, kV The IEC is the most popular standard in the word; however, many countries follow the American standard or they have their own standards. (300) 362 In the UAE, according to TRANSCO document “THE ELECTRICITY TRANSMISSION CODE” **, A voltage exceeding 50 volts AC but not 420 exceeding 1000 volts AC is defined as Low Voltage. 550 800 Any voltage exceeding the Low Voltage is defined as High voltage. 1050 1200 * - https://myelectrical.com/notes/entryid/203/voltage-levels-to-iec-60038 ** - https://www.transco.ae/documents/The%20Electricity%20Transmission%20Code.pdf  The American National Standards Institute (ANSI) Standard Voltages Standard transmission voltages are also established in the United States by the American National Standards Institute (ANSI). Transmission voltage lines operat- ing at more than 60 kV are standardized at 69 kV, 115 kV, 138 kV, 161 kV, 230 kV, 345 kV, 500 kV, and 765 kV line-to-line. Transmission voltages above 230 kV are usually referred to as extra-high voltage (EHV).  2.3 Describe the construction of a TL and perform calculation of power loss, voltage drop, and regulation. Construction of a TL starts with: Material procurement, Structure design, Foundation design, Conductor sag-tension design, Insulation design, Tower design, and Structure spotting.  Construction Of Transmission Lines (TL) TL are used in transmission systems for the transfer of power, usually over long distances, from one point to another. TL are commonly interconnected forming what is called “power transmission grid”. The main components of a TL are the Structure, Conductors, Insulators and other fittings (dampers, spacers, arcing horns and warning signs). Structure cost usually accounts for 30 to 40% of the total cost of a transmission line. Selecting an optimum structure becomes an integral part of a cost-effective TL design.  Types of Transmission Lines The transmission line design is based on technical and economical considerations. TLs can either be Overhead TLs (OHTL) or Underground Cables (UGC). The cost of UGC is several times more expensive than OHTL, therefore the later is more commonly used in power transmission systems. The TL design should guarantee transfer of power with limited voltage drop, high efficiency, minimum line losses, low voltage regulation and power system stability; all at minimum construction (capital) and operation costs. These indicators are highly dependent on the parameters (R, L and C) of the TL conductors and TL nominal voltage. Different types of calculations and simulations are performed, these include: Power flow, short circuit and power system stability.  Transmission Line Modeling (1/2) In order to perform the above mentioned calculations and simulations, the different power system components, which are directly involved in the transfer of power from generators to loads, including generators, transformers, TLs and distributions lines, should be represented with accurate and appropriate mathematical models. TLs are represented using one of three models, depending on the length of the line and its nominal voltage; these models are: Short TL model, Medium TL model, Long TL model.  Transmission Line Modeling (2/2) Medium Transmission Line Medium TL model is used for TL with: Short Transmission Line  a length more than 80 km (50 miles) but less than 250 km (150 miles) Short TL model is used for TL with:  a voltage level from 66 kV to approx. 132 kV  a length less than 80km (50 miles)  All line parameters (R,L and C) are included in the model. and/or  Lumped line parameters are used in a (π or T) model.  a voltage level less than 66 kV, Long Transmission Line  Line capacitance (C) effect is neglected, Long TL model is used for TL with:  a length more than 250 km (150 miles), and/or  Only line resistance and inductance are  a Voltage level above 132 kV included in calculation.  Distributed Line parameters are used in the Long TL model.  1. Short Transmission Model The short line model is obtained by multiplying the series impedance per unit length by the line length. The phase voltage and line current at the sending end are: Once sending end voltage and current are calculated all other values can be derived (voltage drop, line losses, efficiency and voltage regulation):  2. Medium Transmission Line Model For medium length lines, half of the shunt capacitance may be considered to be lumped at each end of the line. This is referred to as the nominal π model, as shown: Y is the total shunt admittance of the line given by: The sending end voltage and current are:  3. Long Transmission Line Model For long length lines, the TL is represented using distributed line parameters. Series impedance and shunt admittance are given per unit length (per km): z = r + jωC, y = g + jωC Propagation constant: Characteristic impedance: Then:  What are ABCD Parameters of a TL? (1/4) ABCD parameters are generalized circuit constants used to help model transmission lines. ABCD parameters are used in the two port network representation of a transmission line. ABCD parameters and a two-port model is used to simplify these complex calculations. Given to the output port power (PR QR): 1. Receiving end voltage = VR ABCD parameters can be used for the three TLs 2. Receiving end current = IR models (short, medium and long). What are the variables for the input port (VS IS)? The circuit of such a two-port network is shown:  What are ABCD Parameters of a TL? (2/4) Now the ABCD parameters of the transmission line provide the link between the supply and receiving end voltages and currents, considering the circuit elements to be linear in nature. Thus the relation between the sending and receiving end specifications is given using ABCD parameters by the equations below.  What are ABCD Parameters of a TL? (3/4) Applied to Short TL model, by comparing the coefficients of VR and IR : the ABCD parameters can be noticed: Applied to medium TL model, the ABCD parameters can be noticed: Applied to Long TL model, the ABCD parameters can be noticed: Units of ABCD Parameters of the TL (4/4)  Efficiency of Transmission Line Transmission efficiency is defined as the ratio of receiving end power PR to the sending end power PS and it is expressed in percentage value. Assume:  COS θs is the sending end power factor.  COS θR is the receiving end power factor.  Vs is the sending end voltage per phase.  VR is the receiving end voltage per phase.  TL efficiency is given by:  Voltage Regulation of Transmission Line Voltage regulation (VR) of transmission line is a parameter defined as the percentage change of the receiving end voltage as the load at that end changes from no-load (zero load) to full load: 𝑉𝑉𝑛𝑛𝑛𝑛 −𝑉𝑉𝑓𝑓𝑓𝑓 𝑉𝑉𝑉𝑉 = 100% 𝑉𝑉𝑓𝑓𝑓𝑓 Where Vnl is the receiving end no-load voltage and Vfl is the full load voltage. For short transmission lines, VS = VR at no-load; the voltage regulation in this case can also be 𝑉𝑉𝑆𝑆 −𝑉𝑉𝑅𝑅 found using the equation: 𝑉𝑉𝑉𝑉 = 100% 𝑉𝑉𝑅𝑅 Where, Vs is the sending end voltage per phase and VR is the receiving end voltage per phase. Note: VS is assumed constant when voltage regulation is calculated.  Load Power Factor on Efficiency of TL (1/3) Efficiency of TL is: For short TL, IR=IS=I So, for a three phase short TL Therefore It is clear that to transmit given amount of power, the load current is inversely proportional to receiving end power factor.  Load Power Factor on Efficiency of TL (2/3) For Medium TL represented with a π model: 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑝𝑝𝑝𝑝𝑝𝑝 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 = x 100% 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑝𝑝𝑝𝑝𝑝𝑝 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝+𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 𝑝𝑝𝑝𝑝𝑝𝑝 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 𝑉𝑉𝑅𝑅 𝐼𝐼𝑅𝑅 cos 𝜃𝜃𝑅𝑅 𝜂𝜂 = 2 x 100% 𝑉𝑉𝑅𝑅 𝐼𝐼𝑅𝑅 cos 𝜃𝜃𝑅𝑅 + 𝐼𝐼𝐿𝐿 𝑅𝑅 Where IL is the line current, R is the total line resistance. Note: IL is not equal to IR  Effect of Load Power Factor on VR of TL (3/3) The percentage VR of transmission line is influenced by the load power factor. For loads with lagging or unity power factors, VR is likely to be positive value. For loads with leading power factor, VR is expected to be negative. The following phasor diagrams show the full load voltages for lagging, unity and leading power factors conditions. The diagrams prove the above statements.  Perform calculation of power losses Transmission system consists of several key components: step-up transformers, transmission lines, substations, primary voltage distribution lines, line or step-down transformers. Electricity losses occur at each stage of the power transfer process, such as in: Step-up transformers that connect power plants to the transmission system, Transmission Lines connecting the step-up and the step-down transformers, and Ending with the customer wiring beyond the retail meter. These electricity losses are often referred to “line losses,” even though the losses associated with the conductor lines themselves represent only one type of electricity loss that occurs during the process of transmitting electricity. System average line losses are in the range of 6 to 10 %.  Transmission System (TS) Losses Calculation TS Losses energy losses due to the physical properties of electric and magnetic circuits in the transmission systems. Two types of losses occur in transmission systems. Fixed Losses and Variable Losses. (Details are next slides)  Fixed Losses (FL) vs Variable Losses (VL) The following are examples of FL: VL are the “classic” losses which vary Hysteresis and eddy current losses in the iron with the current running in the windings core of transformers. of transformers and in the conductors of Electric field losses on transmission lines transmission and distribution line and (corona, noise, light) due to cables and cables. overhead lines, whenever the circuit is energized. TS losses mainly have the form of heat dissipation from iron core of The magnitude of FL is not dependent on transformers and current carrying the magnitude of the current being carried conductors. by the conductor but rather the voltage of energized circuits. Some losses have the form of noise and light. As the voltage is more or less constant, these losses are also considered non- varying.  Transmission Line (TL) Losses Calculation The losses in a conductor carrying an alternating current is given by: PLoss = 𝐼𝐼 2 𝑅𝑅 where I is the current and R is the resistance of that conductor. R causes energy to be absorbed by the conductor and results in conductor heating up. This energy is lost to the surroundings. R is proportional to the resistivity of the conductor material and its length and inversely proportional to the conductor cross sectional area. 𝑙𝑙 𝑅𝑅 = 𝜌𝜌 𝐴𝐴 To reduce losses, a conductor with lower resistivity and/or bigger cross sectional area should be used. This should however be optimized with the cost.  What is Voltage Drop in a TL? Voltage drop is the change of electrical potential along the path of a current currying conductor in an electrical circuit. The line voltage drop in the TL is mainly due to the transmission line parameters (resistance ❲R❳, inductance ❲L❳, capacitance ❲C❳, and shunt conductance ❲G❳). These parameters offer impedance to the flow of current and voltage drops across the length of the transmission line. When the line voltage drop increases, the receiving-end voltage VR decreases accordingly relative to the sending end voltage.  Voltage Drop 1. Approximate method Voltage drop: EVD = IR cos θ + IX sin θ where abbreviations are same as below. 2. Accurate method o If sending end voltage and load PF are known. o If receiving end voltage, load current and PF are known. 2.4 Describe the problems related to transmission lines; this includes corona effect, flashover, ambient effect on the transmission line and lightning strikes.  Corona Effect in Transmission Lines There is a hissing noise with violet glow phenomenon termed as corona effect which is commonly observed in high voltage transmission lines. The corona effects leads to voltage drop and energy loss in in TLs in form of heat, noise and light with release of ozone gas. It also can cause radio interference with communication systems  What is Corona Effect? When a TL is energized with high AC voltage, electrostatic field is induced around the conductors. In TL, conductors are surrounded by the air. Air acts as a dielectric medium. When the potential gradient of the induced electrostatic field is less than 30kV/cm, this field will not be sufficient to ionize the air around the conductors. However, if it is greater than 30 kV/cm, air will be ionized. The ionized air act as a virtual conductor, producing a hissing sound with a violet glow, particularly when humidity of air is high. This electrical discharge caused by ionization of air is known as Electrical Corona Discharge or Corona Effect.  Disadvantages of Corona Effect A non-sinusoidal voltage drop occurs in transmission line due to non-sinusoidal corona current, which causes interference with neighboring communication circuits due to electromagnetic transients and electrostatic induction effects. Ozone gas is produced due to the formation of corona, which chemically reacts with the conductor and causes corrosion. The energy dissipated in the system due to corona effect is called as Corona loss. The power loss due to corona is undesirable and uneconomical. The efficiency of transmission line is reduced due to the loss of power or energy.  Advantages of Corona Effect Due to corona across the conductor, the sheath of air surrounding the conductor becomes conductive, which rises the conductor diameter virtually. This virtual increase in the conductor diameter, reduces the maximum potential gradient or maximum electrostatic stress. Thus, probability of flash-over is reduced. Effects of transients produced by lightning or electrical surges are also reduced due to corona effect. As, the charges induced on the line by surge or other causes, will be partially dissipated as a corona loss. In this way, corona protects the transmission lines by reducing the effect of transients, which are produced by voltage surges.  Factors Affecting Corona Discharge The phenomenon of electric discharge associated with energized electrical devices, including transmission lines results in a power loss, reducing the efficiency of the transmission lines. The following factors can change the magnitude of the Corona Effect: Supply Voltage - if the applied voltage is high, the corona discharge will cause excessive corona loss in the TL. Conductor Surface - The effect depends on the shape, material, and conditions of the conductors. The rough and irregular surface, decreases the value of breakdown voltage. This decrease in breakdown voltage due to concentrated electric field at rough spots, give rise to more corona effect. Air Density Factor - The corona loss in inversely proportional to air density factor. Space between Conductors - If the distance between two conductors is very large compared to conductor diameter, the corona effect may not happen because the larger distance between conductors reduces the electro-static stress at the conductor surface, thus avoiding corona formation. Atmosphere - As corona is formed due to ionization of air surrounding the conductors, therefore, it is affected by the physical state of atmosphere.  Methods of Reducing Corona Effects The corona effect can be reduced by: Corona rings are metallic rings of Increasing Conductor Size: The voltage at which toroidal shaped, which are fixed at the end corona occurs can be raised by increasing conductor size. Hence, the corona effect may be reduced. This of bushings and insulator strings to reduce method however is not practical; bigger conductors are heavier and require more expensive structures. the chance of flash over the insulators. Bigger size conductors are also more expensive. Increasing Conductor Spacing: The corona effect can be reduced by increasing the spacing between conductors, which raises the voltage at which corona occurs. However, increase in conductor spacing is limited due to the cost of supporting structure as bigger cross arms and supports to accompany the increase in conductor spacing, increases the cost of TL. Bundling TL conductors: Using bundles of conductors per phase (two or more conductors per phase) can highly increase the effective diameters of the conductors and reduce corona effect substantially. This method is the most practical one.  Power Loss Due to Corona The formation of corona is always accompanied by the loss of energy which is dissipated in the form of light, heat, sound, and chemical action. When disruptive voltage is exceeded, the power loss due to corona is given by: “d” is the distance between conductors. δ is the breakdown strength of air at a barometric pressure of b cm of Hg and temp of t 0C becomes Under standard conditions, the value of δ = 1  Ambient effect on the TL The electric system is made up of thousands of components connected together that are mostly electromechanical and its functionality can be affected by weather conditions. We can identify 5 impacts of weather on Power Systems: oImpact of Temperature, oImpact of Humidity, oImpact of Pressure, oImpact of Wind Speed and Direction, and oImpact of Contamination  1. Impact of Pressure on TL (1/2) Normally Sag calculation is performed for the normal temperature conditions. However, in practical scenario there are some special cases in cold climate areas and in winter seasons. The wind pressure also got an effect on sag and the length of sag can vary due to this conditions. So wind pressures and the weight of ice on the conductor also need to take into consideration while performing sag calculation for high voltage power lines. When the ice coating surrounded by the conductor get to increase the net diameter of the conductor and its weight also get higher.  1. Impact of Pressure on TL (2/2) Factors affecting the sag Conductor weight – Sag of the conductor is directly proportional to its weight. The weight of the conductors is increased due to ice loading. Span – Sag is directly proportional to the square of the span length. Longer span gives more sag. Tension -The sag is inversely proportional to the tension in the conductor. Higher tension increases the stress in the insulators and supporting structures. Wind – It increases sag in the inclined direction. Temperature – The sag is reduced at low temperatures and is increases at higher temperatures.  2. Impact of Humidity on TL IMPACT OF ICE & SNOW ACCRETION (Air humidity affects the intensity of corona loss because of the dirt accumulated on the conductor surface become rehydrated, increasing the intensity of corona activity and it increases the probability of failure.) MECHANICAL ISSUES o Galloping (wind-induced instability) of Conductors & Ground Wires, o Ice & Snow Shedding from Conductors & Ground Wires, o Rolling of Bundle Conductors. ELECTRICAL ISSUES o Partial discharges and local arcs; o Corona noise and power loss; o Electromagnetic interference; o Flashovers of insulators. https://www.powerandcables.com/impact-mitigation-of-icing-on-power-network-equipment/  3. Impact of Temperature on Power Systems Most mechanical or electrical devices have an operating The temperature of a conductor depends on a number of temperature which is the temperature at which the device will factors including: operate effectively. Transformers, electric motors, among others, could get seriously damaged if the ventilation is poor. Current flowing in the conductor It’s important to grant good ventilation and cooling for every single element that requires it. Ambient temperature Temperature also affects metals in numerous ways. When the temperature of a conductor goes up the resistance goes up - directly proportional. Solar radiation level While designing a transmission line, those factors must be taken into account given that the cable conductor could expand Wind speed. or contract according to the temperature causing the line to violate minimum clearance between the line and any obstacle. Considering that temperature varies several times within a day, at some point the cable length will change permanently. This is called “Creep Effect” and it can be predicted to avoid clearance restrictions in the future. High temperatures cause conductors to expand and hence increase in length. The converse is true for low temperature conditions. The change in length varies from one conductor to another depending on its thermal expansivity.  4. Impact of Contamination on TL (1/2) This contamination is one of the fundamental driver of flashover in the insulators. The pollution on insulators is one of the biggest problems for power transmission. The pollutants that exist in the air settle in the surface of the insulator becoming conductor and allowing the pass of currents that could facilitate the conditions of short circuit. The degree of pollution is generally determined by measuring the equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD) in the area of interest and later used to determine the type and number of insulators to be used.  4. Impact of Contamination on TL (2/2) Water washing - Energized transmission insulators is often the fastest method to maximize system performance. It’s a short- term solution and has safety implications The performance of high voltage insulators because a flashover might occur during is strongly affected by environmental energized washing. Additionally, it has pollution in contaminated regions. extensive lifetime costs. Increase the creepage level - Creepage Extreme weather conditions, ocean spray, extenders have been used to prevent pollution salt fog, cement dust, airborne agricultural flashover on insulators for over 20 years. dust and all other kinds of pollution can Silicone grease - Since the 1960’s, utilities cause an insulator flashover. have used "silicone grease" with good results to prevent the effects of pollution on the insulators surface. The 4 known ways to mitigate insulator Room Temperature Coatings (RTV) are flashovers: specifically formulated for high voltage insulators  B. Ambient effect on Lightning Strikes When lightning hits a power line, a “flashover” occurs. Most people recognize them when they see bright arcs hit their power lines. Flashovers are the main cause of short-circuited power lines as well as power surges that can damage appliances. There are, on average, approximately 100 lightning strikes per second across the planet. Each lighting heats up the air to temperatures of about 30,000°C, much hotter than the surface of the sun. Lightning falls broadly into three main categories based on where it starts and ends: o Intra-cloud (IC) that happens within a single cloud, o Cloud-to-cloud (CC) starts and ends between two clouds, and o Cloud-to-ground lightning (CG) originates from a storm cloud and ends somewhere on Earth’s surface.  What Causes Lightning? Lightning is defined as an electrical discharge that occurs because of imbalances between either the ground and the storm clouds, or within the clouds themselves. When the upper atmosphere possesses cold, dense air and the lower atmosphere consists of warm, moist are, thunderclouds will develop. As this warm air starts to rise, cold air descends, and the moisture forms clouds. As this cycle continues, friction between the frozen and liquid water particles create electrical charges inside these clouds. Once the electrical charge is great enough, the air between the ground and bottom of the cloud breaks down. This effectively causes some of the electrical charge to reach the earth below: This is what we know as a lightning strike.  Lightning Strikes to the Transmission Line The lightning strike injects a current into the power system when it hits a transmission line. The magnitude of the generated voltages depends on the current waveform and the impedances through which it flows. The steepness of the voltage wave governs the insulation flashover. The charge on the leader’s head, its potential, or capacitance are such that they generate the flow of tens or hundreds of thousands of amperes when impacting the power line. Through impedances on the order of hundreds of ohms, these high currents create voltages of megavolts or tens of megavolts. How Do Power Lines Get Protection From Flashovers? Circuit Breakers. TL gets circuit breakers too. When breakers pick up on signs of a short, they cut power to the affected area temporarily to help stop the short from spreading. Shield Wires. Are specialized wires that are meant to reduce the chances of flashovers. Adding more to power lines can help absorb the “blow” of a lightning strike. However, it’s important that they are placed correctly, as a poorly positioned shield wire can allow a large number of lightning strikes to hit phase conductors, and result in flashovers. Tower Grounding. When lightning strikes a power line, the power will run through the lines and eventually hit the ground. Having better grounding means that the towers that support the line will have better mechanisms to neutralize electricity—either through structural engineering or electrical means. Insulation. Insulated electrical wiring will be less likely to experience a flashover, especially if it’s an induced flashover. Although it is difficult to increase insulation on existing lines, even small increases in length will improve insulation and reduce the risk of flashovers. Transmission Line Surge Arresters. Also abbreviated as TLSAs, these devices are meant to help decrease the amount of energy transmitted as a result of a lightning-induced power surge. Their job is to limit the voltages between the tower structure and the phase conductors, which can prevent flashovers in both poorly shield designs and high-footing-resistance areas.