OPTIMUM VOLTAGE REGULATOR PLACEMENT IN A RADIAL DISTRIBUTION SYSTEM USING FUZZY LOGIC
seminar surveyer Active In SP Posts: 3,541 Joined: Sep 2010 
22122010, 05:09 PM
PRO DOC.doc (Size: 624.5 KB / Downloads: 111) 1. DISTRIBUTION SYSTEM 1.1 General description of Distribution System: Distribution system is that part of the electric power system which connects the high voltage transmission network to the low voltage consumer service point In any distribution system the power is distributed to various uses through feeders, distributors and service mains. Feeders are conductors of large current carrying capacity which carry the current in bulk to the feeding points. Distributors are conductors from which the current is tapped of for the supply to the consumer premises. 1.1.1 Basic Distribution Systems There are two basic structures for distribution system namely (i) Radial distribution system (ii) Ring main distribution system (i) Radial Distribution System: If the distributor is connected to the supply system on one end only then is system is said to be a radial distribution system. A radial Distribution System is shown in fig 1.2. In such a case the end of the distributor nearest to the generating station would be heavily loaded and the consumers at the distance end of the distributor would be subjected to large voltage variations as the load varies. The consumer is dependent upon a single feeder so that a fault on any feeder or distributor cuts off the supply to the consumers who are on the side of fault away from the station. (ii) Ring Main Distribution System: Ring main employs a feeder which covers the whole area of supply finally returns to the generating station. The feeder is closed on itself. This arrangement is similar to two feeders in parallel on different buses. The distribution system in India has low load density in rural areas. Losses in rural distribution system are higher and power factor is also poor as compared to urdistribution system. The length of distribution network is generally 20 to 25 times the transmission network and involves considerable operation and maintenance. Though radial arrangement of distribution system has disadvantages, most of the rural distribution system in India is of this type and in India the length of the rural distribution is more than urban distribution network. So, it is important to study the radial distribution system. 1.2 Distribution System Losses It has been established that 70% of the total losses occur in the primary and secondary distribution system, while transmission and sub transmission lines account for only 30% of the total losses. Distribution losses are 15.5% of the generation capacity and target level is 7.5%. Therefore the primary and secondary distribution must be properly planned to ensure losses within the acceptability limits. 1.2.1 Factors Effecting Distribution System Losses Factors contributing to the increase in the line losses in primary and secondary distribution system are: 1. Inadequate size of conductor: Rural load is usually scattered and generally fed by radial feeders. The conductor size of the feeders must be adequate. The size of the conductor should be selected on the basis of length, KVA capacity of the stranded conductors. 2. Feeder Length: In practice, 11KV and 415V lines in rural areas are extended radially over long distances to feed loads scattered over large areas. This results in high line resistance, low voltage and high current that leads to high I2 R losses in the line. 3. Location of Distribution Transformers: Often the distribution transformers are not located centrally with respect to the customer. Consequently, the farthest customers obtain an extremely low voltage even though a reasonably good voltage level is maintained at the transformer secondary which again leads to higher line losses. 4. Low Voltage: Whenever the voltage applied to an induction motor deviates from rated voltage, its performance is adversely affected. A reduced voltage in case of induction motor results in higher currents drawn from the same output leads to higher losses. This can be overcome by installing the tap changing transformers. 5. Use of over rated Distribution transformers: Studies on 11KV feeders have revealed that often the rating of distribution transformers is much higher than the maximum KVA demand on the LT feeder. Over rated transformer produces unnecessarily high iron losses. 6. Poor workmanship in fittings: Bad workmanship contributes significantly towards increasing distribution losses, as joints are sources of power losses. So, the number of joints should be kept to a minimum and at the same time care must be taken to avoid sparking and heating of contacts. 7. Low Power Factor: In most of the LT distribution systems, it is found that the power factor varies from 0.65 to 0.75. For a given load, the low power factor contributes high current which results high distribution losses. 1.3 Reduction of line losses: The losses in Indian power system are on the higher side. So, the government of India has decided to reduce the line losses and set a target for reduction of T&D losses by 1% per annum in order to realize an overall reduction of 5% in the national average. Methods for the reduction of line losses: The following methods are adopted for reduction of distribution losses. (1) HV distribution system (2) Feeder reconfiguration (3) Reinforcement of the feeder (4) Grading of conductor (5) Construction of new substation (6) Reactive power compensation (7) Installing Voltage regulators. (1) HV distribution system: The low voltage distribution system contributes about 1/3 of the total losses. The main contributing factors for the losses in this system are the wrong distribution system practice chosen by our country coupled with the nonadherence of prescribed norm for voltage drops. The LT distribution system based on European practice where loads are concentrated in small areas with high load densities and that too with high power factor and load factor is most ill suited to cater the scattered highly inductive load with very low load densities, low power factor and low load factor prevalent in our country. The situation prevailing is that LV lines are extended irrespective of voltage drops up to full capacity of the distribution transformer, some times over and above the transformer capacity. Hence, no purpose will be served by prescribing low KVAKm loading limits for LV lines when the existing norms are not adhered to at all. The only practice and feasible solution is to eliminate or minimize LV lines by switching over to single phase high voltage distribution. By, adopting HV distribution, the losses in the LV distribution can be reduced by 85%. Advantages of HV distribution systems: It will eliminate losses on lengthy LT lines It will have better voltage regulation. It will improve the power factor as starting and running capacitors are inherently provided to single phase motors. It will improve the supply reliability. It virtually eliminates pilferage by direct tapping of energy from LT over head lines. Line losses will be reduced by 85% of the LT line losses (2) Feeder Reconfiguration: Feeder reconfiguration is defined as the process of altering the topological structure of distribution feeders by changing the open/closed status of the sectionalizing and ties switches. Feeder reconfiguration allows the transfer of loads from heavily loaded feeders to less heavily loaded feeders. Such transfers are effective not only in terms of altering the levels of loads on the feeders being switched, but also in improving the voltage profile along the feeders and effecting reduction in the overall system power losses. (3) Reinforcement of the feeder conductor: Studies on several distribution feeders have indicated that first few main sections of the feeder contribute to 60% to 80% of the feeder total losses. This is mainly due to the fact that the conductor size used at the time of erection of feeders is no more optimal with reference to the increased total load. The total cost is the increased sum of fixed cost of investment of the line and variable cost of energy losses in the conductor due to the power flow. Addition of a new load on existing feeder is limited by its current carrying capacity. So if the existing feeder gets overloaded, the alternative for catering the extra load is only reinforcement of the feeder. This method is considered to be good for short term planning measures. Reinforcement of the conductor is considered necessary as the smaller sized conductor’s results in high losses due to non standard planning. However at the time of reinforcement much supply interruptions will take place, which leads in loss of revenue. (4) Grading of conductors: In normal practice, the conductor used for radial distribution feeder is of uniform cross section. However the load magnitude at the substation is high and it reduce as we proceed on to the tail end of the feeder. This indicates that the use of a higher size conductor, which is capable of supplying load from the source point, is not necessary at the tail end point. Similarly use of different conductor cross section for intermediate sections will lead to a minimum both in respect of capital investment cost and line loss point of view. The use of larger number of conductors of different cross section will result in increased cost of inventory. A judicious choice can however be made in the selection of number and size of cross section for considering the optimal design. If tie lines exist already it is the most economical method to reduce losses but in practice in rural India tie lines are uncommon. Constructing new tie lines for small excess loads leads to unnecessary increase in capital investment. (5) Construction of new substation: If a substation is to be constructed and connected to an existing network, several possible solutions are to be studied. These solutions may include various connection schemes of the substation and several feasible solutions, while the principle connection scheme is defined by a limited number of possibilities. The number of possibilities of newly constructed HT line and thus its location determines the cost of their construction and operation. Due to the large number of possible sites, an economical comparison may over look the optimum technical solution. The final decision is easily influenced by additional factors such as topography, land owner ship, environment considerations etc. The optimum size for a substation is defined as that location which will result in minimum cost for construction and minimum losses. These include both the investments for the 11Kv and 33Kv voltage systems and the cost of operating the system. So, by constructing a new substation at load centers, the line losses will be reduced due to improvement in voltage profile and reduction in length of the lines. But for an excess small quantum of load, the decision for construction of new substation cannot be made as the capital investment is high and the substation will run under load condition for a long time resulting in poor return on the capital. So, in such situations alternate arrangements can be attempted. (6)Reactive power compensation: It is universally acknowledged that the voltage reactive power control function has pivotal role to play in the distribution automation. The problem of reactive power compensation can be attempted by providing static capacitors. The present practice to compensate reactive power component is to increase reactive power by increasing the terminal voltage of the generator or by increasing the field current of the synchronous machine in condenser mode at generating stations. This procedure is not effective because the power system losses will be further increased due to increase of reactive power in the transmission system. An alternate method for compensating the reactive power is the use of capacitors in distribution systems at customer points. There are two methods in capacitor compensation. They are 1. Series compensation. (Capacitors are placed in series with line) 2. Shunt compensation. (Capacitors are placed in parallel with load ) The fundamental function of capacitors whether they are in series or in shunt in a power system is to generate reactive power to improve power factor and voltage, there by enhancing the system capacity and reducing losses. In series capacitors the reactive power is proportional to the square of the load current where as in shunt capacitors it is proportional to the square of the voltage. (7) Installing Voltage Regulators: Voltage regulator or Automatic voltage booster is essentially an auto transformer consisting of a primary or existing winding connected in parallel with the circuit and a second winding with taps connected in series with the circuit. Taps of series winding are connected to an automatic tap changing mechanism. AVB is also considered a tool for loss reduction and voltage control is a statutory obligation. AVB provides 10% boost of voltage. It boosts voltage in four steps of 2.5% each and it also boosts voltage in 32 steps of 0.625% each. It has line drop compensation to maintain constant voltage at its location. KVA rating = rated voltage × %boost of booster × rated current/100 It causes sudden voltage rise in discrete steps at its location leading to better voltage profile and reduction in losses. Benefits of AVB When a booster is installed at a bus, it causes a sudden voltage rise at its point of location and improves the voltage at the buses beyond the location of AVB. The % of voltage improvement is equal to the setting of % boost of AVB. The increase in voltage in turn causes the reduction in losses in the lines beyond the location of AVB. Multiple units can be installed in series to the feeder to maintain the voltage within the limits and to reduce the line losses. It can be removed and relocated, whenever and wherever required easily. 


seminar class Active In SP Posts: 5,361 Joined: Feb 2011 
23032011, 12:19 PM
OPTIMAL VOLTAGE REGULATOR PLACEMENT IN A RADIAL DISTRIBUTION SYSTEM USING FUZZY LOGIC.doc (Size: 80.5 KB / Downloads: 60) Abstract: The operation and planning studies of a distribution system require a steady state condition of the system for various load demands. Our aim is to obtain optimal voltage control with voltage regulators and then to decrease the total cost of voltage regulators and losses, to obtain the net saving. An algorithm is proposed which determines the initial selection and tap setting of the voltage regulators to provide a smooth voltage profile along the network. The same algorithm is used to obtain the minimum number of the initially selected voltage regulators, by moving them in such a way so as to control the network voltage at the minimum cost. The algorithm has been implemented using MATLAB along with Fuzzy Logic and the result of both conventional and Fuzzy Logic are compared. Introduction: General description of Distribution System Distribution system is that part of the electric power system which connects the high voltage transmission network to the low voltage consumer service point In any distribution system the power is distributed to various uses through feeders, distributors and service mains. Feeders are conductors of large current carrying capacity which carry the current in bulk to the feeding points. Distributors are conductors from which the current is tapped of from the supply to the consumer premises. A typical distribution system with all its elements is shown 1.1.1 Basic Distribution Systems There are two basic structures for distribution system namely (i) Radial distribution system (ii) Ring main distribution system Radial Distribution System: If the distributor is connected to the supply system on one end only then the system is said to be a radial distribution system. A Radial Distribution System is shown in fig 1.2. In such a case the end of the distributor nearest to the generating station would be heavily loaded and the consumers at the far end of the distributor would be subjected to large voltage variations as the load varies. The consumer is dependent upon a single feeder so that a fault on any feeder or distributor cuts off the supply to the consumers who are on the side of fault away from the station. 1.2 Distribution System Losses It has been established that 70% of the total losses occur in the primary and secondary distribution system, while transmission and sub transmission lines account for only 30% of the total losses. Distribution losses are 15.5% of the generation capacity and target level is 7.5%. Therefore the primary and secondary distribution must be properly planned to ensure losses within the acceptability limits. 1.2.1 Factors Effecting Distribution System Losses Factors contributing to the increase in the line losses in primary and secondary distribution system are: 1. Inadequate size of conductor: 2. Feeder Length: 3. Location of Distribution Transformers: 4. Low Voltage: 5. Low Power Factor: 1.3 Reduction of line losses: The losses in Indian power system are on the higher side. So, the government of India has decided to reduce the line losses and set a target for reduction of T&D losses by 1% per annum in order to realize an overall reduction of 5% in the national average. Methods for the reduction of line losses: The following methods are adopted for reduction of distribution losses. (1) HV distribution system (2) Feeder reconfiguration (3) Reinforcement of the feeder (4) Grading of conductor (5) Construction of new substation (6) Reactive power compensation (7) Installing Voltage regulators. Installing Voltage Regulators: Voltage regulator or Automatic voltage booster is essentially an auto transformer consisting of a primary or existing winding connected in parallel with the circuit and a second winding with taps connected in series with the circuit. Taps of series winding are connected to an automatic tap changing mechanism. AVB is also considered a tool for loss reduction and voltage control is a statutory obligation. Benefits of AVB When a booster is installed at a bus, it causes a sudden voltage rise at its point of location and improves the voltage at the buses beyond the location of AVB. The % of voltage improvement is equal to the setting of % boost of AVB. The increase in voltage in turn causes the reduction in losses in the lines beyond the location of AVB. Multiple units can be installed in series to the feeder to maintain the voltage within the limits and to reduce the line losses. It can be removed and relocated, whenever and wherever required easily. FUZZY LOGIC 2.1 Introduction Fuzzy logic, invented by Professor Lotfi Zadeh of UCBerkeley in the mid 1960s, provides a representation scheme and a calculus for dealing with vague or uncertain concepts. It provides a mathematical way to represent vagueness in humanistic systems. The crisp set is defined in such a way as to dichotomize the individuals in some given universe of discourse into two groups as below: a) Members (those who certainly belong to the set.) b) Nonmembers (those who certainly do not belong to the set.) 2.2 Fuzzy Logic in Power Systems Analytical approaches have been used over the years for many power system operation, planning and control problems. However, the mathematical formulations of real world problems are derived under certain restrictive assumptions and even with these assumptions, the solutions of large – scale power systems problems are not trivial. On the other hand, there are many uncertainties in various power system problems because power systems are large, complex, geographically widely distributed systems and influenced by unexpected events. More recently, the deregulation of power utilities has introduced new issues into the existing problems. These facts make it difficult to effectively deal with many power systems problems through strict mathematical formulations alone. Although a large number of AI techniques have been employed in power systems, fuzzy logic is a powerful tool in meeting challenging problems in power systems. This is so because fuzzy logic is the only technique, which can handle in precise, vague or ‘fuzzy’ information. 


