Investigations On The Theory And Application Of Fault Monitoring Of DC System

The DC operation power supply system (DC system) provides uninterrupted electrical source for such important facilities as electromagnetic actuator of circuit breakers, relay protecting devices, signal devices, lighting devices, etc., and its reliability has a direct influence on the safe operations of power plants and substations. Better reliability of DC system is required with the growing capacity of power system and the higher degree of grid voltage. Some in-depth investigations about the battery failure forecasting, the ground fault monitoring, the operation parameters of battery online monitoring and the battery grid-connected discharging of DC system are carried out in this paper.The abnormal failure of battery which works as the backup power supply for DC system when AC power failure occurs, will affect the safe operations of DC system seriously. On the base of many intensive studies of the existing grey forecasting models, this paper presents an improved battery failure grey forecasting model based on the genetic algorithm (GA). This model takes the battery capacity as the characteristic quantity, provides a basis for judging the battery failure, and then avoids the shortcomings of the traditional capacity experiment. This method can realize the early failure prediction of battery, and reduce the times of the traditional discharge test for battery capacity, thus prolong the service life of battery. Forecasting examples show that the improved GA-based battery failure grey forecasting model brought forward in this paper, compared with the traditional GM(1,1) forecasting model, has the higher modeling accuracy, and can satisfy the engineering requirements.In practical operations, the ground fault of DC system ranks first in electrical faults. It is a serious and potential danger for the safe operations of power system. Generally, the unbalanced degree of symmetrical bridge is used as a chief means for reflecting insulation of DC system. However, it becomes disabled when the insulation of positive and negative poles drop in the same proportion. A new method of monitoring real-timely for DC system insulation using double asymmetrical bridges in normal mode is adopted in this paper, and the shortcomings of symmetrical bridge are overcome. The detection method of low frequency signal injection, which is widely used now, is easily influenced by the distributed capacitor between the ground and branches. To solve the problem, this paper presents a new method on the base of low frequency injection, namely measurement basing on double different frequencies. Currently there are many wires of available centralized insulation monitoring systems in the field, and the field construction is complex, that makes it easy to be disturbed, and its reliability is hard to be guaranteed. A scheme of distributed ground supervision and measurement system based on the field bus is put forward. The structure, functions and design method of the proposed system are introduced in detail. The field application shows that the...