Reliability and Stability in Power Systems


Do you ever image what may happen to our life if there is no electricity someday? In fact, electrical power systems are one of the keys elements elementsof modern soceity, which providing clean and convenient energy to drive motors, light homes and streets, run manufacturing plants and business. Furthmores the modern soceity has come to expect that the supply of electrical energy will be continuously available on demand. The primary function of an electric power is to provide electrical energy to its customers as economically as possible and with acceptable degree of continuity and quality.

Since electricity supply generally involves a very comples and highly integrated systems. Failure in any parts of systems can cause interruptions which range from inconveniencing a small number of local residents to major and disruptions of supply. In order to reduce to the probability, frequency and duration of the effect, on the one hand, it is necessary to increase investment in the planning, design process. The designers should make sure that design limits are not exceeded, to be alert to conditions that affect reliability,and be ready to take action to prevent hazardous situations from developing.On the other hand, it is also very important to increase investment in operating and maintainece process. Since no matter how advanced the system is, it is still operated by the human being. As the result, it is responsibility of the operatorof the systems to perform their functuionso that maximum reliability and stability will be realized.

Some Useful Definitions

The term has very wide range of meaning and cannot be considered with a single specific definition. In a general rather than specific sense, all aspects of ability of the system to satisfy the consumer requirement can be considered as reliability. There are three major stability conditions must be considered:
Steady-State Stability
The ability of an electric power system to maintain synchronism between machines within the systems and on external tie lines following relatively slow or normally expected load changes.
Transient Stability
The ability of the system adequate to withstand the shock of the relatively large of generation or load is lost or fault occurs on a transmission line. It is the ability of the system to remain in synchronism following a system disturbances.
Dynamic Stability
The ability of a power system to remain in synchronism after the transient stability period until the system has settled down to the new stead-state equilibrium.

General Methods Used for Studying Reliability and Stability

The probability and statistic methods play very important roles. In specific, both security monitoring system, which consists of predicting the outcome of potential disturbances of the system on a real-time base; and SCADA( Supervisory Control And Data Acquisition)system are used widely.


Stable operation of a power system requires a continuous match between energy supply to the prime movers and electrical load on the system.

For more Information:

Links to Reliability Engineerng
Links to Reliability Analysis Center
Links to Power Engineering

Sau-Shing Kot (