Abstract
This chapter presents a new reactive power loss index for identification of weak buses in the system. This index can be used for identification of weak buses in the systems. The new reactive power loss index is illustrated on sample 5-bus system, and tested on sample 10-bus equivalent system and 72-bus equivalent system of Indian southern region power grid. The validation of the weak buses identification from the reactive power loss index with that from other existing methods in the literature is carried out to demonstrate the effectiveness of the index. Simulation results show that the identification of weak buses in the system from the new reactive power loss index is completely non-iterative, and thus requires minimal computational efforts as compared with other existing methods in the literature.
TopIntroduction
The present day power system is being operated under stressed conditions due to rapidly growing power demand, and lacks of upgradation/augmentation of the existing infrastructure such as generation and transmission capacity in the system because of various operational, economical and environmental constraints. In addition, the situation becomes more worst if the system is perturbed by critical/severe network contingencies such as tripping of heavily loaded transmission lines or outage of large generating units. Under such situations, power system may result in voltage instability and susceptible to voltage collapse due to insufficient amount of reactive power reserve available in the system to support the voltage. Not only is reactive power necessary to operate the transmission system reliably, but it can also substantially improve the efficiency with which real power is delivered to customers/end users. Hence, the secure and reliable operation of power system has always been concern to the system operator.
In recent years, it has been observed that the voltage instability problem is the root cause for several major network blackouts in different countries such as France, Belgium, Sweden, Germany, Iran, Japan, USA and India (FERC, 2005; Srivastava, Velayutham, Agrawal, & Bakshi, 2012.). A system may be voltage unstable if it includes at least one voltage unstable bus (Ca˜nizares, De Souza, & Quintana, 1996). Therefore, the system operator must make sure that there are enough reactive reserve capacities available for the system to maintain voltage profiles. Properly planned reactive power reserve minimizes the risk of voltage collapse or low voltages as well as reduces transmission loss by keeping appropriate voltage profiles. For the above reason, the identification of critical/weak buses in the system is very much useful for installing additional voltage support devices to prevent possible voltage instability problem.
Key Terms in this Chapter
Voltage Stability: Voltage stability refers to the ability of a power system to maintain steady voltage at all buses in the system after being subjected to a disturbance from a given initial operating condition.
Fuzzy System: It is a component of machine learning techniques which takes membership values within 0 to 1 unlike crisp sets.
Electric Grid: An electric grid is a network of synchronized power providers and consumers that are connected by transmission and distribution lines and operated by one or more control centers.
Contingency: Contingency is an outage of a transmission line or transformer that may lead to over loads in other branches and/or sudden system voltage drop.
Optimization: A mathematical method to find the solution of a problem towards achieving better performance either in form of minimum or maximum under one or more given constraint.
Standard Deviation (STDEV): The standard deviation of the load voltage is used to quantify the amount of variation or dispersion of a set of load voltages.
Reactive Power: In electric power transmission and distribution, volt ampere reactive (VAR) is a unit by which reactive power is expressed in an AC electric power system.