Study On10kV Zero Sequence CT Characteristics And Detection Methods

With the development of the Dongguan City, the Dongguan power grid to accelerate reform of citynetwork, most distribution network will gradually replace the cables overhead lines, power grid structurewill also by a single power supply, power supply for the development of radiation shaped multi power looppower supply, in order to improve the reliability of power supply. Neutral grounding via low resistancemode configuration is simple, quick action, more suitable for large and medium-sized city with the cabledistribution network. However, with respect to the neutral point of arc suppression coil grounding mode,10kV distribution network with neutral grounding via small resistance in China put into operation time is notlong, many problems still need to be further studied.According to statistics, at present, Dongguan power grid has many incidents caused by the twodevice disorders, which is related to selection, installation, detection and maintenance of zero sequencecurrent transformers. As one of the core components, the zero sequence current transformer is important toprotection and measurement means, its rational forthputting and operation will greatly enhance the safetyand reliability of the grid. Therefore, systematic study, investigation on selection and installation problems,improvements for operation and maintenance aspects, will be able to effectively improve operationalefficiency of Dongguan grid, and contribute to the accumulated experience of domestic distributionnetwork construction and operation.In this paper, the working principles and characteristics of current transformers have been analyzed,the error cause and its composition, the models and indicators meanings have all been introduced. Afterclassification of the current transformers, accuracy and selection requirements of protective currenttransformer have been cited. On this basis, the differences between current transformer and zero-sequencecurrent transformer is described, applications and principles of zero-sequence current transformer workingfor zero-sequence protection, transformer zero sequence protection, zero-sequence generator protection,small ground fault line selection system, leakage protection have been analyzed. From the practical projectangle, the selecting principles, installation requirements, attention points, and operation and maintenance ofthe zero-sequence were introduced. One case about10kV transformer protection grade trip of DongguanPower Supply Bureau was retrospectively analyzed, and the zero sequence TA typical error connection wasdiscovered, as a result, an improved installation process of this TA has been developed. Besides, against thedeficiencies of low-pressure zero sequence TA up flow tests, an innovative up-flow test, which use a zerosequence TA up flow line, is proposed and significantly improved the operational efficiency and safetyfactor of Dongguan Power Supply Bureau.