Analysis Of Influencing Factors In Synchronized Sampling Based On Electrical Quantities And Research On The Threshold Of Impedance Relay Based On Sampled Values

Segregated current differential protection is the best protection of transmission line. Both current start-up and differential current are used as conditions of starting protection, which can not prevent the misoperation caused by light loading. So synchronized sampling based on electrical quantities is proposed, it can be another condition of starting protection.Some influencing factors are analyzed in this article, which is about to detect synchronous of phase segregated current differential protection by using synchronized sampling based on electrical quantities, some methods are proposed to reduce the deviations and prevent the error judgments, when the deviations can not be neglected. In addition, threshold setting and judging methods are discussed in this paper, including two methods for threshold setting:superposition method and compensation method, and simulation verification show that compensation method is preferable. This paper provides more theoretical basis for the engineering of synchronized sampling based on electrical quantities.The protection consisted by superimposed component impedance relay based on sampled values is proposed to satisfy the demand of action time when the fault is near the power source and bus, which use sampled values to calculate, and can identify the fault within one cycle after it occurred. But, it will be influenced by transient components at the beginning of the fault.In order to reduce the undesirable effect of transient process on superimposed component impedance relay based on sampled values, a new method about floating threshold setting is proposed in this paper. According to theoretical derivation and analysis of the worst influence, the floating threshold value is determined and action threshold can flaot continuously in one cycle after fault, so the action speed of protection is improved, by the premise of assuranced reliability. This floating threshold which is coposed of the sampled values of measuring voltage and current, is very simple, it has short computing time and low computational complexity, although the process of derivation is complex. Finally, the floating threshold can be proved to meet the requirement of the protection by simulation verification.