Issues related to power system voltage levels have become increasingly important issue during last two and half decades. In power networks, low voltage situations may result in the loss of stability, voltage collapse and eventually to cascading power outages. Large number of incidents of voltage collapse has been reported in different countries across the globe. A simple indicator that has the potential in real time, i.e. L indicator has been used to find voltage profile at different switching condition and simulated using ANN in network reconfiguration for the improvement of voltage stability. A method for improving voltage stability in a power network comprising of multiple lines and switches has been suggested in this chapter based on system reconfiguration approach. ANN based fast and efficient methodology has been developed to obtain the optimum switching combination to achieve best voltage stability. The proposed scheme has been tested on an IEEE 14-bus system.
Top2. Overview Of Voltage Stability Issues In General
Issues related to power system voltage levels have become increasingly important during last two and half decades. In power networks, low voltage situations may result in the loss of stability, voltage collapse and eventually to cascading power outages. Large number of incidents of voltage collapse has been reported in different countries across the globe (Taylor, 1994) & (Aboytes & Arroys, 1987).
It is a well-established fact that there is a strong relationship between real power transmission (MW) and rotor angle (δ), and reactive power transmission (MVAR) and the voltage (Chakrabarti & Mukhopadhyay, 1989) & (Aboytes & Arroys, 1987). In other words, the availability of MW is dictated by machine angle, which in turn is decided by the input to the prime mover. On the other hand, voltage magnitude is related to MVAR availability at that point of time. Voltage instability can be ascribed to lack of VAR support necessary to maintain the voltage profile within specified levels (Davidson, 1975) at certain load condition.
Voltage stability is concerned with maintaining ‘acceptable voltage levels’ all system buses under normal conditions as well as when the system is being subjected to a disturbance. The main causes of voltage instability are lack of reactive power resources, heavy loading and severe contingencies. During instability, voltage magnitude of some of the system buses decrease gradually and then rapidly to reach the collapse point (Aboytes & Arroys, 1987). The excess load on the transmission lines, large distance of the generating sources, and lack in local reactive compensation (Chakrabarti & Mukhopadhyay, 1989) are the also caused the voltage instability.
Some of the researchers have been developed a number of voltage stability indicators in the last two decades. Due to this fact, accurate preventive control actions can be taken easily with the help of voltage stability index. Voltage stability assessment can be done with the help of different indicators (L-index indicator, V-Q sensitivity indicator, Voltage Collapse Proximity Indicator (Warwick, Ekwue, Arthur, & Aggarwal, 1997), which involves numerous load flow solutions under both normal and abnormal operating conditions like outage of transmission lines, outage of some generating source etc.