Current Transformer Saturation Detection Based On Mathematical Morphological Skeleton And Development Of On-chip Protection System Based On FPGA

Relay protection is an integral part of the power system and guarantee the stableoperation of power systems. Because the theory of current differential protection is simpleand reliable, it is widely used for a variety of occasions in power system, such as lineprotection, busbar-protection and transformer protection. However, the accuracy andreliability of differential protection are mainly subject to unbalance current. One of the maincauses of unbalanced current is the current transformer saturation caused by external fault indifferential protection. Therefore, it required the study of CT saturation and developingstrategies to avoid differential protection maloperation caused by it. There are two mainanti-saturation strategies: blocking strategy and compensation strategies, both of which havetheir pros and cons. This paper chooses more practical blocking strategy to do research. Inconsideration of shortcomings of traditional blocking strategies, we propose a CT saturationdetection algorithm based on morphological skeleton. It has a very high reliability, because ofthe full use of saturation distortion of waveform information. Compared to the traditionallocking strategies, it has a shorter delay, which is about a quarter of fundamental cycle.Due to microprocessor-based protection device with high reliability, selectivity andsensitivity, it is widely applied to the modern power system. But as continuously improvementof power systems automation technology, especially the development of the smart grid, thehigher performance of microprocessor-based protection is required. For this requirement, wehave developed on-chip protection system based on FPGA. It has more computing capacity,can run a variety of complex algorithms; higher-speed communication features to meetcommunication between substation devices based on IEC61850standards. It delivers a morereliable, more cost-effective, more flexible and less power consuming protection relay and thevolume of device is more micro.This paper is composed of following chapters:1th chapter summarizes CT saturation andmicrocomputer protection, proposed research topics;2nd chapter introduced causes, andeffects and simulation method of CT saturation;3rd chapter firstly introduced fundamentals ofmathematics morphology, then based on it, morphology skeleton is extended to1-dimensionsignal processing;4th chapter proposes a CT saturated detection algorithm based onmorphology skeleton, for the blocking strategy of differential protection; beginning with5thchapter, the content of paper changed from CT saturation to the description of on-chipprotection system based on FPGA, this chapter mainly focuses on the illustration of hardware platform of the protection system; the6th chapter shows the software system design of theprotection system and shows the test result of CT saturation detection technologyimplemented in on-chip protection system based on the OMICRON test device. the finalchapter makes the summary and expectation of full paper.