Research On Power System Survivability Assessment And Disturbance Source Location Method

As an important infrastructure to guarantee social and economic development, security issues of power systems have always been highly concerned. Occurrence of blackout accidents in recent years has revealed the inherent potential safety hazard of power grid itself. Extreme natural disasters exposed the vulnerability of the grid under extreme conditions. Coping capacity of power systems in deliberate attack scenarios should cause alarm. Power systems survivability in conditions of both domestic trouble and foreign invasion is worth thinking about.Existing power survivability assessment or vulnerability assessment theory has obtained many achievements but there are still some imperfections, such as most theory focus on one aspect of power grid vulnerability, lack of comprehensive evaluation of power grid in normal and disturbance conditions from the internal and external perspective. If a power transmission grid in normal operation mode is smooth, generally it has more hub of higher degree of nodes and branches. However, when a high degree of node or branch fails, the impact on power grid will be more serious, and will have much higher degree of vulnerability. To solve the survival problems of power systems under normal condition and disturbance, from the perspective of power transmission efficiency, this paper established power system survivability index system and its evaluation method as well as disturbance location scheme.Power transfer path analysis method is proposed based on power flow tracing, and is able to deep analyze power transfer characteristics through the surface of the power flow and obtain all power transmission paths between generator and load. On the basis of power transfer path analysis, power smoothness evaluation index and method is constructed to reflect grid electricity transmission efficiency. The proposed index is able to identify pivotal components in power transmission.Power system vulnerability index and its evaluation method are put forward with consideration of multi-disturbance and evenness of power grid structure. Power grid evenness index is proposed based on distribution differences of nodes and branches in power transfer process. Spatial distance between nodes and spatial distance between branches are respectively defined. Spatial distribution evenness index for key nodes and key branches are proposed. Considering comprehensive influence of component failure on power transfer, key component dependence index is established. Power system vulnerability is analyzed under random failures and deliberate attack.On the basis of smoothness, evenness and vulnerability index, power system survivability index and evaluation method is established. A combined weight hierarchical optimizing method based on analytic hierarchy process (AHP) and improved gray correlation method is proposed to solve and calculate index weights of the survivability index system.Power grid planning evaluation method based on power system survivability is proposed. Based on Southern Brazilian46-bus network, four planning cases are designed, and survivability level of each case is calculated. Case study indicates that there are some contradictions between the smoothness and vulnerability also proves the necessity of evaluating both smoothness and vulnerability.Against two typical component failure mode that threat power system survivability, the disturbance location method is proposed respectively. A novel criterion for exactly identifying the machine leading to overvoltage of the common bus among the machines working in parallel is developed, to overcome loss of selectivity of existing schemes in some cases. By mean of this scheme, the machine leading to the overvoltage of the common bus due to the exciter runaway can be discriminated and removed appropriately. In comparison, the overvoltage due to load shedding can be identified as the one due to the external reason. Then, the machines with healthy exciters will not be tripped incorrectly, which will allow the AVR operates appropriately to adjust the system voltage back to the normal level. Based on the analysis of truncated error, a universal wavefront positioning correction method on traveling-wave-based fault-location algorithms is proposed. The proposed correction method is able to control the location error within150m under a different sampling rate. The maximum error is reduced by order at a low sampling rate. In the case of a high sampling rate, the probability distributions of location error are improved significantly although the maximum error cannot be decreased significantly. The two disturbance location methods provide important foundation for power system survivability against typical component failures.