Cause of Disturbances
Power demand varies during the day. Morning increase in power consumption is caused by turning on of home or industrial appliances. Evening rise in power demand is caused by lights turning ON. Significant changes can lead to disturbances and even blackouts.
High levels or even changes in power consumption at a given generator site can lead to disturbances that will affect the normal operation of neighboring generators. The system can become unstable and fail, costing the industries hours of production time in the hours it takes to restart the plant. If the disturbance is detected early appropriate control measures can be applied to ensure system stability. For example, additional damping can be inserted to attenuate potentially dangerous oscillations. Power system load is reduced with various intelligent load shedding procedures. Disturbance monitoring considered in research is detection of disturbances by estimating:
- damping of post disturbance oscillations,
- changes in generator frequencies.
Faults
70 % of blackouts are caused by malfunction in protection devices such as unnecessary tripping of power system components, in an event of a disturbance. Many blackouts are caused by cascading events initiated by failures of one or more of power system devices. There are two main types of power line faults symmetrical and asymmetrical. Symmetrical faults cause high currents and major disturbances due to three phase current flow. Unbalanced or asymmetrical faults are not as severe and include the following types: phase-to-phase, phase-to-ground and phase-to-phase-to-ground-fault.
Variation in Power Demand
Power demand depends on time of the day, day of the week and seasons. Daily Load Curve (DLC) of Single Wire Earth Return (SWER) networks used in rural areas shows peaks at morning (6:40 am) and evenings (5:00 pm to 8:30 pm). In the morning power consumption rises due to turning on of home or industrial appliances. In some cases the load doubles from 8:00 am to 9:00 am. At night lights rise in power is caused by turning on of lights. Power demand is low on weekends. In major Australian cities various independent processes contribute to the total load.