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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 UC-Berkeley 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) Non-members (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.