Research On Data Acquisition System Of Digital Substation And The Protection Theory For Transformer Based On It

The data acquisition in the digital substation provides a data platform with excellent performance for the transformer protection, which lay a good foundation for the realization of new protection theory. Aiming to the situation status in quo, this paper start with the construction of data acquisition for transformer protection, pay attention to the key technology about the factors having impacts on protection performance, and provide the related solutions. On this base, the paper takes some research on the new theory for transformer protection, to achieve an integrated transformer protection scheme in the digital substation.The Merging Unit (MU) is the key equipment to realize the acquisition control of voltage, current, and switch status, and it is also a plant collecting information and providing a standard data interface. The mapping scheme from the functions defined in IEC61850-9-1 to a hardware system is proposed by using the sampling cards, data processing cards, and communication card, to realize the data acquisition system for digital substation. To meet the demand of synchronization for the plants on processing-level, bay-level, substation-level in digital substation, a hierarchical method of time synchronization is proposed. In this method, the pulse per second is used as time synchronization signal for merging unit, and the SNTP protocol is used for time synchronization of plants on bay-level and substation-level. What more, aiming to request of the clock for substation, a method to producing clock of high accuracy based on error analysis is proposed to provide a stable, accurate clock signal.This paper analyses the accuracy of Rogowski coil and resistive voltage divider basing on their measuring principle. The analysis shows that they can have a good transient performance if suitably designed. To solve the problem that the sampling rate of merging unit may differ from the request of protection algorithm, a data processing method based on Filtered- Interpolated-Extraction is provided. The criterion for network testing is also discussed. On these research bases, the paper takes theoretical analysis and stimulant authentication on the protection theory based on transformer equivalent circuit. The research shows that this theory has a good capacity on the identification of inrush current, inter-turn fault. But because of the increased complexity of algorithm, the measurement error of the signals can make a greater affection on protection algorithm. So, a restraint criterion is necessary and provided to avoid maloperation caused by calculation error.Paper does research works about some key technologies for digital substation on a practical view. Finally, the research direction of data acquisition system for substation and its use for relay protection is discussed after the conclusion of the work.