The Analysis Of Generator Differential Protection Malfunctions Causing By The External Faults Of Taishan Power Plant

P-type current transformer is currently the most widely used current transformer inelectric power system, and the generator differential protection with a ratio restraintcharacteristic is the most important primary protection of generator stator phase faults. Whenan external short circuit faults occurs, due to defects in its transient saturation characteristicsoften lead generator differential protection malfunction, threaten the security and stability ofthe power system, but also lead to plants huge economic losses. Taishan Power Plant Phasegenerator differential protection uses P-type current transformers and typical ratio restraintdifferential protection, but had once lexternal faults caused generator differential protectionmalfunction. Because Taishan Power Plant is located in the typhoon, thunderstorm-proneareas, the fault outside the area is frequently occur, which threat to the safe operation ofgenerators. There is an urgent need to find a measure to prevent external faults lead generatordifferential protection malfunction.This paper points out external faults lead generator differential protection malfunction ismainly due to the defect of current saturation characteristics, and pointed out that the mainfactors leading to the current transformer saturation. Differential protection with a ratio ofbraking characteristics were analyzed, and noted the relevant measures. This paper alsoanalyzes a case of the external faults lead to a generator differential protection malfunction, anpoints out the process external fault current into a load current after the fault, partial transientsaturation is the main reason. From the perspective of practical application, this paperproposes a number of measures to mitigate or avoid saturation, such as short-circuit currentamplitude is reduced, reducing the load current transformer secondary current transformersecondary load excitation characteristics and optimal matching of the current transformerdemagnetization, using TP-type current transformers, using anti-saturation criterionprotection and from reality of Taishan power plant, each of these precautions is feasibilitilyanalysised. In the above measures,"t using TP-type current transformers " is an importantmeasure proposed by the relevant standard, so this paper analyzes in detail, pointing out thatthis measure does not have feasibility in Taishan power plant. Through the feasibility analysisof these precautions, concluded that "using anti-saturation criterion protection" measures ineffect and feasibility have greater advantages, the most suitable for implementation in TaishanPower Plant. After the implementation of this measure, generator differential protectionmalfunction incident did not happen again, achieve the desired results.