External diagnosis of Gas Circuit Breaker contact wearing
The internal inspection for a GCB (gas circuit breaker) is regularly performed to check and change contact parts in the case that the number of times of fault current breaking reaches a specified number, because TBM (time based maintenance) criteria is generally applied. Our new system, however, can change maintenance criteria to CBM (condition based maintenance). Current interval for internal inspection may be, however, redundant compared with the actual amount of contact wearing, because it is difficult to estimate the actual amount of contact wearing correctly from the outside. Then, in order to evaluate the precise amount of contact wearing from the outside, we developed a sophisticated system which can presume the accurate amount of contact wearing by using real breaking current and arcing time. Furthermore, this new system can evaluate the precise amount of contact wearing even if CT (current transformer) is saturated by DC in fault current and regardless of the current phase at the breaking. Therefore, the internal inspection period to replace contact materials can be extended up to nearly three-fold length compared with the traditional way.
Application of IED to Condition Based Maintenance of Medium Voltage GCB/VCB
— Time base maintenance (TBM) is conventionally applied by the power utilities to maintain circuit breakers (CBs), transformers, bus bars and cables, which may result in under maintenance or over maintenance. As information and communication technology (ICT) industry develops, the maintenance policies of many power utilities have gradually changed from TBM to condition base maintenance (CBM) to improve system operating efficiency, operation cost and power supply reliability. This paper discusses the feasibility of using intelligent electronic devices (IEDs) to construct a CB CBM management platform. CBs in power substations can be monitored using IEDs with additional logic configuration and wire connections. The CB monitoring data can be sent through intranet to a control center and be analyzed and integrated by the Elipse Power Studio software. Finally, a human-machine interface (HMI) of supervisory control and data acquisition (SCADA) system can be designed to construct a CBM management platform to provide maintenance decision information for the maintenance personnel, management personnel and CB manufacturers.
A probabilistic model of power system disturbances
Power system stability analysis involves the study of the state trajectories of a power system in response to a disturbance. The system is usually presumed to be in a static equilibrium state when the disturbance is initiated. The disturbance causes a dynamic motion of the system state variables to either a new equilibrium condition or an unstable condition, which we usually regard as a system failure in some sense. The disturbance that initiates system dynamic behavior is of primary interest here. Qualitatively, the system disturbance may be large or small, and may be a simple step change in some parameter or a complex sequence of changes. We are interested in describing the disturbance not just mathematically, but probabilistically. Thus we seek a definition that will permit us to associate probabilities with disturbance events, such that the probabilities conform to an axiomatic definition of probability.