Interactive security evaluation in power-system operation

Abstract

The real-time operation of power systems requires security assessment and enhancement computations to ensure that the system stays in the normal state for as long as possible. The paper describes an interactive computer package with colour graphics for power-system operational studies. The package includes load flows, fault analysis and security enhancement. A decoupled algorithm is used for security enhancement, and offers the operator a choice of feasible corrective actions to alleviate line overloads. These corrective actions include generator rescheduling, network voltage adjustments, switching of reactive compensation and the control of phase shifters. Experiments on three test systems are summarised and discussed. ,7 max mm List of symbols nb -number of busbars nl = number of lines 5,-= voltage angle at busbar i V t = voltage magnitude at busbar i 8 a = loss angle of a line /-/ given by sin (R/Z) = current flow between busbars / and / = capacity of line i-j = nominal phase angular displacement of line i-j maximum phase angular displacement minimum phase angular displacement nominal real busbar load new real busbar load after load shedding nominal reactive busbar load new reactive busbar load after load shedding real-power generation rescheduled real-power generation sum of the operating generation and spinning reserve vector of the deviations of abnormal load busbar voltages vector of the deviations of the controlling variables consisting of tap-changing transformer ratios and reactive-power sources Kh = nominal transformer tap ratio n max _ maximujn transformer tap ratio «™ m = minimum transformer tap ratio M = number of overloaded lines K = number of phase-shifters DSEA = decoupled security enhancement algorithm NLP = nonlinear programming method LP = linear programming method bij = series admittance of line i-j = series impedance of line /-/ = impedance matrix q

Decoupled Secure Economic Dispatch Algorithm for Power Systems Operation

“…(23) as it adjusts itself to maintain the conservation of power in the network. The use of sensitivity analysis for security enhancement has been described previously by the authors of [15,16].…”

Improved sensitivities in MW dispatch for control of voltage

“…Many references describing the formulation of a matrix of sensitivities of active power flows to active controls have required some pseudo-inverse matrix to be found, for example [12]. The approach adopted here, however, avoids that and allows fast sparse matrix techniques to be used.…”

“…and comprises only the active power equations. The changes in slack bus power and nodal voltage angles can be related to changes in active power transmitted along each transmission line or through each transformer from general node to node by (15) Hence, a matrix directly relating changes in active power injections and phase shifter angles and changes in active power flow may be found such that (16) and (17) If equation (12) is re-expressed as (18) then can be found by sparse matrix methods and premultiplied by to obtain . Since , can be used to determine the effects of changes inactive power controls on active power flows measured at each end of each branch.…”