Electrical Power Distribution PDF

ELECTRICAL POWER DISTRIBUTION Electric Power Distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. Distribution Substations connect to the transmission system and lower the transmission voltage...

ELECTRICAL POWER DISTRIBUTION Electric Power Distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. Distribution Substations connect to the transmission system and lower the transmission voltage to medium voltage ranging between 2 kv and 35 kv with the use of transformers. ELECTRICAL POWER DISTRIBUTION Primary Distribution Lines carry this medium voltage power to distribution transformers located near the customer's premises. distribution transformers again lower the voltage to the utilization voltage used by lighting, industrial equipment and household appliances. ELECTRICAL POWER DISTRIBUTION Often several customers are supplied from one transformer through secondary distribution lines. commercial and residential customers are connected to the secondary distribution lines through service drops. customers demanding a much larger amount of power may be connected directly to the primary distribution level or the sub-transmission level. ELECTRICAL POWER DISTRIBUTION The transition from transmission to distribution happens in a power substation, which has the following functions: Circuit breakers and switches enable the substation to be disconnected from the transmission grid or for distribution lines to be disconnected. ELECTRICAL POWER DISTRIBUTION transformers step down transmission voltages, 35 kv or more, down to primary distribution voltages. these are medium voltage circuits, usually 600–35000 v. from the transformer, power goes to the busbar that can split the distribution power off in multiple directions. the bus distributes power to distribution lines, which fan out to customers. OVERHEAD DISTRIBUTION LINE An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy across large distances. It consists of one or more uninsulated electrical cables (commonly multiples of three for three-phase power) suspended by towers or poles. OVERHEAD DISTRIBUTION LINE CONSTRUCTION Towers for support of the lines are made of wood either grown or laminated, steel or aluminum (either lattice structures or tubular poles), concrete, and occasionally reinforced plastics. the bare wire conductors on the line are generally made of aluminum (either plain or reinforced with steel or composite materials such as carbon and glass fiber), though some copper wires are used in medium-voltage distribution and low-voltage connections to customer premises. OVERHEAD DISTRIBUTION LINE Traditionally, the overhead cables or the bare conductors have been used for the transmission of electrical power and even for the distribution. These are simple in configuration and are usually commissioned using the towers or poles. The bare wire conductors on the line are generally made of aluminum (either plain or reinforced with steel or composite materials such as carbon and glass fiber), yet, some copper wires are used in medium voltage distribution and low- voltage connections to customer premises. DIFFERENCE BETWEEN TRANSMISSION AND DISTRIBUTION LINE The transmission line and distribution line both are used to carry power or electricity from one place to the other. the difference between transmission and distribution line are explained on the basis of the factors like the basic usage of the transmission and distribution line, their working supply phase, voltage level and level of conduction. DIFFERENCE BETWEEN TRANSMISSION AND DISTRIBUTION LINE BASIS TRANSMISSION LINE DISTRIBUTION LINE Usage Transmission Line helps The Distribution line in the movement of carries electricity from electricity from power the substation to the plant to the consumer’s end. substations. Phase It is carried out It requires a single electricity in three phase supply system phase supply system. for carrying electricity. DIFFERENCE BETWEEN TRANSMISSION AND DISTRIBUTION LINE Voltage level Carries electricity at a Carries electricity at a very high voltage. very low and safe level About 11000 volts. of about 220 volts. Current conduction They conduct current They conduct less than level at 69 kV or more. 69 kV Thickness Transmission lines are Distribution line are thick lines. thin as compared to the transmission line. DIFFERENCE BETWEEN TRANSMISSION AND DISTRIBUTION LINE Generation of electricity is a major factor, but how this electricity is transmitted from the power stations to the substations and finally to the consumers is also important. This process is done by transmission and distribution lines. DIFFERENCE BETWEEN TRANSMISSION AND DISTRIBUTION LINE Transmission lines are a high voltage line that carries electricity from power plant to the substation from it is further distributed to various areas for different purposes. Distribution lines are low voltage lines that carry electricity from the substations to the end users for residential and commercial use. DIFFERENCE BETWEEN TRANSMISSION AND DISTRIBUTION LINE 1. Transmission Line helps in the movement of electricity from a power plant or power station to the various substations whereas the distribution line carries electricity from the substation to the consumer’s end. i.e., to the residential and commercial customers. DIFFERENCE BETWEEN TRANSMISSION AND DISTRIBUTION LINE 2. Transmission line carries power or electricity in three phase supply system. Distribution system requires a single phase supply system for carrying electricity. DIFFERENCE BETWEEN TRANSMISSION AND DISTRIBUTION LINE 3. Transmission line carries electricity at a very high voltage that is of about 11000 volts whereas Distribution lines carries electricity at a very low and safe value level that is about 220 volts. DIFFERENCE BETWEEN TRANSMISSION AND DISTRIBUTION LINE 4. Transmission line, conducts current at 69 kilo volts or more, but distribution line conduct current at less than 69 kilo Volt. 5. Distribution line are thin as compared to the transmission line. DIFFERENCE BETWEEN POWER TRANSFORMER AND DISTRIBUTION TRANSFORMER Power Transformer The Power Transformer is installed at various power stations for generation and transmission of power. It acts as a step-up or a step-down transformer for increasing and decreasing the level of voltages as per the requirement, and it’s also used as an interconnection between two power stations. DIFFERENCE BETWEEN POWER TRANSFORMER AND DISTRIBUTION TRANSFORMER Distribution Transformer The Distribution Transformer is used to bring down or step down the voltage and current level of a transmission line to a predefined level, which is called safety level for the end-user consumer in domestic and industrial purpose. DIFFERENCE BETWEEN POWER TRANSFORMER AND DISTRIBUTION TRANSFORMER DISTRIBUTION BASIS OF DIFFERENCE POWER TRANSFORMER TRANSFORMER Type of network It is used in transmission It is used in the network of higher distribution network for voltages lower voltages. Availability of ratings 400 kV, 200 kV, 110 kV , 11 Kv, 6.6 Kv, 3.3 Kv, 440 66 kV, 33 kV. V,230 V Maximum rating of usage Power transformers are Distribution transformers used for rating above 200 are used for rating less MVA than 200 MVA DIFFERENCE BETWEEN POWER TRANSFORMER AND DISTRIBUTION TRANSFORMER Size Larger in size as compared Smaller in size of distribution transformers Designed Efficiency Designed for maximum Designed for 50-70% efficiency of 100% efficiency Efficiency formula Efficiency is measured as Here All Day Efficiency is the ratio of output to the considered. It is the ratio of input power output in kilowatt hour (kWh) or watt hour (Wh) to the input in kWh or Wh of a transformer over 24 hours. DIFFERENCE BETWEEN POWER TRANSFORMER AND DISTRIBUTION TRANSFORMER Application Used in generating Used in distribution stations and stations, also for transmission industrial and substations domestic purposes Losses Copper and iron Iron losses take place losses take place for 24 hours and throughout the day copper losses are based on load cycle DIFFERENCE BETWEEN POWER TRANSFORMER AND DISTRIBUTION TRANSFORMER Load fluctuation In power transformer Load fluctuations are the load fluctuations very high are very less Operating condition Always operated at Operated at load less full load than full load as load cycle fluctuates Considering time It is independent of It is time dependent time DIFFERENCE BETWEEN POWER TRANSFORMER AND DISTRIBUTION TRANSFORMER Flux density In power transformer flux As compared to power density is higher transformer the flux density is lower in distribution transformer Designing of the core Designed to utilize the core As compared to power for maximum and will operate transformer the flux density is near to the saturation point lower in distribution of the B-H curve, which helps transformer to bring down the mass of core Usage Used to step up and step Used as an end user down voltages connectivity DIFFERENCE BETWEEN POWER TRANSFORMER AND DISTRIBUTION TRANSFORMER 1. POWER TRANSFORMERS ARE USED IN THE TRANSMISSION NETWORK OF HIGHER VOLTAGES WHEREAS THE DISTRIBUTION TRANSFORMERS ARE USED IN THE DISTRIBUTION NETWORK OF LOWER VOLTAGES. 2. THE POWER TRANSFORMERS ARE AVAILABLE IN VARIOUS RATINGS OF 400 KV, 200 KV, 110 KV, 66 KV, 33 KV IN THE MARKET AND THE DISTRIBUTION TRANSFORMER ARE AVAILABLE IN 11 KV, 6.6 KV, 3.3 KV, 440 V, 230 VOLTS. 3. THE POWER TRANSFORMER ALWAYS OPERATES ON RATED FULL LOAD AS THE LOAD FLUCTUATION IS VERY LESS BUT THE DISTRIBUTION TRANSFORMER IS OPERATED AT THE LOAD LESS THAN FULL LOAD AS THE VARIATION IN THE LOADS ARE VERY HIGH. DIFFERENCE BETWEEN POWER TRANSFORMER AND DISTRIBUTION TRANSFORMER 4. THE POWER TRANSFORMERS ARE DESIGNED FOR MAXIMUM EFFICIENCY OF 100%, AND THE EFFICIENCY IS SIMPLY CALCULATED BY THE RATIO OF OUTPUT POWER TO THE INPUT POWER, WHEREAS THE DISTRIBUTION TRANSFORMER THE MAXIMUM EFFICIENCY VARIES BETWEEN 50- 70% AND CALCULATED BY ALL DAY EFFICIENCY. 5. POWER TRANSFORMERS ARE USED IN POWER GENERATING STATIONS AND TRANSMISSION SUBSTATIONS, AND THE DISTRIBUTION TRANSFORMER IS INSTALLED AT THE DISTRIBUTION STATIONS FROM WHERE THE POWER IS DISTRIBUTED FOR THE INDUSTRIAL AND DOMESTIC PURPOSES. DIFFERENCE BETWEEN POWER TRANSFORMER AND DISTRIBUTION TRANSFORMER 6. THE SIZE OF THE POWER TRANSFORMER IS LARGE AS COMPARED TO THE DISTRIBUTION TRANSFORMERS. 7. IN POWER TRANSFORMER, THE IRON AND COPPER LOSSES TAKE PLACE THROUGHOUT THE DAY BUT IN DISTRIBUTION TRANSFORMER, THE IRON LOSS TAKES PLACE 24 HOURS I.E., THROUGHOUT THE DAY, AND THE COPPER LOSSES DEPEND ON THE LOAD CYCLE. DIFFERENCE BETWEEN POWER TRANSFORMER AND DISTRIBUTION TRANSFORMER 6. THE SIZE OF THE POWER TRANSFORMER IS LARGE AS COMPARED TO THE DISTRIBUTION TRANSFORMERS. 7. IN POWER TRANSFORMER, THE IRON AND COPPER LOSSES TAKE PLACE THROUGHOUT THE DAY BUT IN DISTRIBUTION TRANSFORMER, THE IRON LOSS TAKES PLACE 24 HOURS I.E., THROUGHOUT THE DAY, AND THE COPPER LOSSES DEPEND ON THE LOAD CYCLE. DIFFERENCE BETWEEN POWER TRANSFORMER AND DISTRIBUTION TRANSFORMER 6. THE SIZE OF THE POWER TRANSFORMER IS LARGE AS COMPARED TO THE DISTRIBUTION TRANSFORMERS. 7. IN POWER TRANSFORMER, THE IRON AND COPPER LOSSES TAKE PLACE THROUGHOUT THE DAY BUT IN DISTRIBUTION TRANSFORMER, THE IRON LOSS TAKES PLACE 24 HOURS I.E., THROUGHOUT THE DAY, AND THE COPPER LOSSES DEPEND ON THE LOAD CYCLE. AC TRANSMISSION LINE The transmission line has Resistance R, Inductance l, Capacitance C and the shunt or leakage conductance g. these parameters along with the load and the transmission line determine the performance of the line. the term performance means the sending end voltage, sending end currents, sending end power factor, power loss in the line, efficiency of the transmission line, regulate and limit of power flow during efficiency and transmission, regulation and limits of power during steady state and transient condition. the comparison chart of the transmission line is shown in the figure below. CLASSIFICATION OF TRANSMISSION LINES The classification of the transmission lines depends on its voltage and the length of the conductor. The transmission line is the medium of transferring the power from the generating station to the load center. It is mainly classified into two types. They are the: 1. AC Transmission Line a. Short-transmission Line b. Medium-transmission Line c. Long-transmission Line 2. DC Transmission Line SHORT TRANSMISSION LINE If the line is not more than 80 kv or if the voltage is not over than 66 kv then the line is known as the short transmission line. the capacitance of the line is governed by their length. The effect of capacitance on the short transmission line is negligible, but for cable where the distance between the conductor is small, the effect of capacitance cannot be ignored. While studying the performance of the short transmission line only resistance and the inductance of the line is calculated. SHORT TRANSMISSION LINE MEDIUM TRANSMISSION LINE the line which is ranging from 80 to 240 km is termed as a medium transmission line. the capacitance of the medium transmission line cannot be ignored. the capacitance of the medium transmission line is considered to be lumped at one or more point of the lines. the effect of the line is more at high frequency, and their leakages inductance and capacitance is considered to be neglected. the medium transmission line is sub-divided into pi – model and t – model. MEDIUM TRANSMISSION LINE In nominal pi model, it is assumed that the half of the capacitance concentrate at the each end of the line. MEDIUM TRANSMISSION LINE In T model, it is assumed that the capacitance is concentrated at the center of the line. MEDIUM TRANSMISSION LINE In T model, it is assumed that the capacitance is concentrated at the center of the line. LONG TRANSMISSION LINE The line having a length more than 240 km is considered a long transmission line. all the four parameters (resistance, inductance, capacitance, and leakage conductance) are found to be equally distributed along the entire length of the line. LONG TRANSMISSION LINE LONG TRANSMISSION LINE The line having a length more than 240 km is considered a long transmission line. all the four parameters (resistance, inductance, capacitance, and leakage conductance) are found to be equally distributed along the entire length of the line. DC TRANSMISSION LINE The DC transmission is mainly used for the bulk power transmission. for long distance transmission, the dc is less expensive and have low electrical losses. The cost of the dc transmission systems is higher for short distance transmission line because it requires more convertible equipment as compared to an ac system. DC TRANSMISSION LINE DC TRANSMISSION LINE The converter station converts the ac to dc at the sending end and dc to ac at the load end of the line. One of the major advantage of the dc system is that it allows the power transmission between two unsynchronized ac system. AC TRANSMISSION LINE The AC transmission line is used for transmitting the bulk of the power generation end to the consumer end. The power is generated in the generating station. the transmission line transmits the power from generation to the consumer end. The power is transmitted from one end to another with the help of step-up and step down transformer. AC TRANSMISSION LINE DC TRANSMISSION LINE In dc transmission line, the mercury arc rectifier converts the alternating current into the dc. the dc transmission line transmits the bulk power over long distance. at the consumer ends the thyratron converts the dc into the ac. DC TRANSMISSION LINE DIFFERENCES BETWEEN AC AND DC TRANSMISSION LINE 1. THE AC TRANSMISSION LINE TRANSMITS THE ALTERNATING CURRENT OVER A LONG DISTANCE. WHEREAS, THE DC TRANSMISSION LINE IS USED FOR TRANSMITTING THE DC OVER THE LONG DISTANCE. 2. THE AC TRANSMISSION LINE USES THREE CONDUCTORS FOR LONG POWER TRANSMISSION. AND THE DC TRANSMISSION LINE USES TWO CONDUCTORS FOR POWER TRANSMISSION. DIFFERENCES BETWEEN AC AND DC TRANSMISSION LINE 3. THE AC TRANSMISSION LINE HAS INDUCTANCE AND SURGES WHEREAS THE DC TRANSMISSION LINE IS FREE FROM INDUCTANCE AND SURGES. THE INDUCTANCE AND THE SURGES ARE NOTHING BUT THE WAVE OF THE HIGH VOLTAGE WHICH OCCURS FOR SHORT DURATION. 4. THE HIGH VOLTAGE DROP OCCURS ACROSS THE AC TERMINAL LINES WHEN THEIR END TERMINALS VOLTAGE ARE EQUAL. THE DC TRANSMISSION LINE IS FREE FROM INDUCTANCE, AND HENCE NO VOLTAGE DROP OCCURS ACROSS THE LINE. DIFFERENCES BETWEEN AC AND DC TRANSMISSION LINE 5. THE PHENOMENON OF THE SKIN EFFECT OCCURS ONLY IN THE AC TRANSMISSION LINE. THE SKIN EFFECT CAUSES THE LOSSES, AND THIS CAN BE REDUCED BY DECREASING THE CROSS-SECTION AREA OF THE CONDUCTOR. THE PHENOMENON OF SKIN EFFECT IS COMPLETELY ABSENT IN THE DC TRANSMISSION LINE. 6. AT SAME VOLTAGE, THE DC TRANSMISSION LINE HAS LESS STRESS AS COMPARED TO THE AC TRANSMISSION LINE. HENCE, DC REQUIRES THE LESS INSULATION AS COMPARED TO AC. DIFFERENCES BETWEEN AC AND DC TRANSMISSION LINE 7. THE COMMUNICATION LINE INTERFERENCE IS MORE IN THE AC TRANSMISSION LINE AS COMPARED TO THE DC TRANSMISSION LINE. 8. THE CORONA EFFECT IS THE PHENOMENON THROUGH WHICH THE IONIZATION OCCURS ACROSS THE CONDUCTOR. AND THIS IONIZATION CAUSES THE LOSSES IN THE CONDUCTOR. THE PHENOMENON OF CORONA EFFECT OCCURS ONLY IN THE AC TRANSMISSION LINE AND NOT IN THE DC TRANSMISSION LINE. DIFFERENCES BETWEEN AC AND DC TRANSMISSION LINE 9. THE DIELECTRIC LOSS OCCURS IN THE AC TRANSMISSION LINE AND NOT IN THE DC TRANSMISSION LINE. 10. THE AC TRANSMISSION LINE HAS THE DIFFICULTIES OF SYNCHRONIZATION AND STABILITY WHEREAS THE DC TRANSMISSION LINE IS FREE FROM STABILITY AND SYNCHRONIZATION. 11. THE AC TRANSMISSION LINE IS LESS EXPENSIVE AS COMPARED TO THE DC TRANSMISSION LINE. DIFFERENCES BETWEEN AC AND DC TRANSMISSION LINE 12. THE SMALL CONDUCTOR IS USED FOR AC POWER TRANSMISSION AS COMPARED TO THE DC TRANSMISSION. 13. THE AC TRANSMISSION LINE REQUIRES THE TRANSFORMER FOR STEP-UP AND STEP-DOWN THE VOLTAGE. WHEREAS IN DC TRANSMISSION LINE THE BOOSTER AND CHOPPER ARE USED FOR STEP-UP AND STEP-DOWN THE VOLTAGE. DIFFERENCES BETWEEN AC AND DC TRANSMISSION LINE The ac transmissions line is used for small power transmission. and for large distance power transmission, the dc transmission system is used. DIFFERENCES BETWEEN AC AND DC TRANSMISSION LINE Basis for Comparison AC Transmission Line DC Transmission Line Definition The ac transmission The dc transmission line transmit the line is used for alternating current. transmitting the direct current. Number of Three Two Conductors DIFFERENCES BETWEEN AC AND DC TRANSMISSION LINE Inductance & surges Have Don’t Have Voltage drop High Low Skin Effect Occurs Absent Need of Insulation More Less DIFFERENCES BETWEEN AC AND DC TRANSMISSION LINE Interference Have Don’t Have Corona Loss Occur Don’t occur Dielectric Loss Have Don’t have Synchronizing and No difficulties Difficulties Stability Problem DIFFERENCES BETWEEN AC AND DC TRANSMISSION LINE Cost Expensive Cheap Length of conductors Small More Repairing and Easy and Inexpensive Difficult and Expensive Maintenance Transformer Requires Not Requires UNDERGROUND TRANSMISSION LINE An electrical supply system employing underground stru ctures, cables, and other equipment located under desig nated areas along public ways or utility easements; does not include service cables in the customer’s duct. UNDERGROUND TRANSMISSION LINE The general understanding is that the underground cables are laid beneath the ground and the overhead cables are visible overhead. But apart from this, there are many significant features of both the types of these cables from the perspectives of electrical power transmission or distribution. UNDERGROUND TRANSMISSION LINE In the changed scenario of the power system design, particularly, the distribution system, the cables and their characteristics have become highly selective and the technological advancements have also made the selection of cable for a particular application more flexible. UNDERGROUND TRANSMISSION LINE The underground cables provide the uninterruptable power supply which is not possible with the overhead lines due to the limitations mentioned earlier. However, there are other technical factors which also have made the underground cable to have an edge over the overhead cables which include reduced risks of fault due to external factors like rain, wind and adverse climatic conditions. UNDERGROUND TRANSMISSION LINE The underground cables are also free from radio interference. The transmission towers are not required except for the local transformers in the system without considerable height of the tower. However, the underground cables are not free from limitations. Damage to underground cable is difficult to locate, and restoration of the system once the faults are located might take considerably long time. UNDERGROUND TRANSMISSION LINE The construction mechanism of the underground cable involving duct bank, vaults, splices and terminations not only increase the overall cost but also might reduce the overall system reliability. This problem further might increase with the increased line length with the additional necessity of the intermediate equipment. UNDERGROUND TRANSMISSION LINE Due to the concealed operating conditions, the heat dissipation from the underground system can also be one of the major bottlenecks for the successful operation of the system. Summarizing all these points, the following table gives a brief comparison between underground and overhead cables. COMPARISON THANK YOU AND GODBLESS EE LANG MALAKAS!