Voltage collapse precipitated by the immediate change in stability when generator reactive power limits are encountered

Abstract

When a generator of a heavily loaded electric power system reaches a reacthe power limit, the system can become immediately unstable and a dynamic voltage collapse leading to blackout may follow.We study the statics and dynamics of this mechanism for voltage collapse by example and by the generic theory of saddle node and transcritical bifurcations. Load power margin calculations can be misleading if the immediate instability phenomenon is neglected.

The irrelevance of electric power system dynamics for the loading margin to voltage collapse and its sensitivities

“…We can compute loading margins and their sensitivities using the better known and 263 simpler static load models, while assuming a very general form for the poorly known dynamics which underlie the static equations. This observation generalizes more limited results in [5][6][7] and supports the reductions in [8] of differential-algebraic power system equations to static models. Moreover, this observation is a result underlying advanced industry software to monitor and avoid voltage collapse blackouts, for example [9].…”

“…A stable equilibrium may disappear or become unstable when the differential equations undergo discrete changes. For example, when a generator encounters a reactive power limit, the system equations change in such a way that the equilibrium persists but can possibly change stability [6]. If a line or generator is tripped, then the system equations change in such a way that equilibrium can possibly be lost.…”

From Hierarchical to Open Access Electric Power Systems

“…Time consuming off-line simulations of regional systems are carried out to simulate the worst case scenarios and to create lists of critical forced outages. Contingencies leading to fast transient instabilities [66], nonrobust response to small deviations in states, parameters, and inputs away from nominal [76], and occurrence of uncontrollable voltage collapse [15] are found and preventive adjustments of thermally limited power transfers are made in order to ensure that during such forced outages no problems of this type take place.…”

Fuzzy Load-Shedding Strategy Considering Photovoltaic Output Fluctuation Characteristics and Static Voltage Stability

“…As shown in Figure 1, in the P-V curve, the SNB point is the saddle-node bifurcation point of the power grid. Regardless of the UHB or the limit induced bifurcation (LIB) [9,27], the SNB point is usually used as the voltage collapse critical point in power grids. The upper half of the P-V curve is the voltage's stable region and the lower half is the voltage's unstable region.…”