# Understanding and solving short-term voltage stability problems

In addition, supplementary control of generator excitation systems, static Var compensators, and HVDC converters is increasingly being used to solve system oscillation problems. The indicator of the voltage stability of the load bus j will be easily obtained: Thereby an indicator is derived from the fundamental Kirchoff-Laws.

Through the indicator of voltage stability, it is easy to find the most vulnerable area in a system, to find the impacts of other loads, areas and power transactions.

Increase loading of bus 5 from zero to the voltage collapse point, keeping the load at other buses fixed at the normal value. When the load at a load bus changes, it will influence the indicator. What areas are involved? For this reason, the approach based on steady state analysis is more feasible, and it can also provide insights of the voltage reactive power problems. When does the voltage instability occur? This is abundantly clear from the increasing number of major power-grid blackouts that have been experienced in recent years; for example, Brazil blackout of March 11, ; Northeast USA-Canada blackout of August 14, ; Southern Sweden and Eastern Denmark blackout of September 23, ; and Italian blackout of September 28, From the indicator, it is allowed to predict the voltage instability or the proximity of a collapse.

What are the key contributing factors? Three case scenarios have been simulated to study the steady state voltage collapse at the load buses and their respective L index.

In , low capacity HVDC ties were also established between the east and west systems. CHAPTER 1 Overview of Power Quality and Power Quality Standards 1 1. About Author Edvard Csanyi Edvard – Electrical engineer, programmer and founder of EEP. The index of the voltage stability [3] predicts the voltage problem of the system with sufficient accuracy.

The authors describe actual incidents. This simple system can be described by the following equations where the dot above a letter represents a vector: Because the voltage stability problem is reactive power relative problem, and the generator bus can provide the reactive power to support the voltage magnitude of the bus, it is absolutely necessary that the all of buses be distinguished.

To compare the equation 17 and 2 , we can observe that they have an identical form, and the voltage stability of the multi-bus system has been equivalent to a simple single generator and load system.

As the complexity of power systems increased, and interconnections were found to be economically attractive, the complexity of the stability problems also increased and systems could no longer be treated as two machine systems. How close is the system to voltage instability or collapse? Power factor is kept constant throughout the loading of buses.

Increasing load at bus 9 and de serving the index L for bus 5, 7 and bus 9 and identify the first collapse point. In general, the analysis of voltage stability problem of a given power system should cover the examination of these aspects: Once associated primarily with weak radial distribution systems, voltage stability problems are now a source of concern in highly developed and mature networks as a result of heavier loadings and power transfers over long distances.

Proper analysis requires dynamic modeling of aggregated motor loads, with equivalents for distribution feeders. Voltage Stability, Voltage Collapse, Reactive Power, Steady-State Voltage Stability, Transient Analysis I. Introduction Voltage stability is a major concern in planning and operations of power systems. Observe the effect on index L 5.