【作者】 徐习东；

【导师】 邱家驹；

【作者基本信息】 浙江大学 ， 电力系统及其自动化， 2005， 博士

【摘要】 本文首先阐述了变压器纵差保护的基本原理,组成环节并介绍了一些最近研究成果。 在综述目前各种涌流及过励磁电流识别方法后,介绍了间断角原理的特点,指出了在大涌流小故障情况下间断角原理能快速判断故障的存在。分析并指出了在发展性故障中,由于一个周波中存在多个状态过程,因此波形不对称,含二次谐波,可能导致谐波制动元件发出制动信号,但这种情况不影响间断角的测量。 描述了在TA饱和后,TA二次侧涌流波形出现间断角消失的现象,并阐述了目前保护装置采用的一、二阶导数恢复间断角的方法。证明了二阶导数判据不受故障电流中的非周期分量影响。在数字式保护中,常用差分代替微分,本文分析了差分对噪声误差的放大,并提出采用分段最小二乘法测量一、二阶导数的方法,降低了噪声误差,提高了间断角测量的准确性及保护的灵敏度。 区外故障时,TA饱和会引起误差增大,易导致保护误动。本文通过大量数字仿真找出了TA饱和后,波形相关系数与传变误差之间的关系,由此提出了基于波形识别的自适应比率制动原理。该方法在区外转区内故障情况下,不会因制动电流比差动电流先升高而盲目提高比率制动元件的制动比率。使得大电流下,能更合理地提高制动比率,从而提高了比率差动保护的灵敏度与可靠性。 指出了一种传统保护未考虑的不平衡电流因素的存在,即:对Y0/△接线的变压器,如仅在Y0侧有电源并在该侧发生区外接地故障时,Y0侧零序故障电流可能造成差动回路有较大的不平衡电流,然而,目前保护中未采取足够的措施对此进行制动。文章对此进行了详细分析,并提出了零序制动原理。消除了变压器纵差保护长期存在的一个隐患。 介绍了实现上述原理与方法的保护装置。 介绍了对上述保护装置进行的动模试验及结果,并对结果进行了分析。试更多还原

【Abstract】 This paper reviews the concepts and the component elements of the transformer longitudinal differential protective relay, and introduces some new approaches.After the existing methods is evaluated for discriminating internal faults from inrush and overexcitation conditions, the dead angle principle is discussed in detail. Then, it is concluded that the protective relay based on dead angle principle can identify the small faults currents with large inrush currents. It is also discussed that if a fault current increases quickly due to the change of fault parameters, the current wave will be dissymmetry, where there is a second harmonic content. This case may cause the harmonic blocking unit issues restrain signal, but it doesn’t cause the miscalculation of dead angles.When a CT（current transformer） is saturated, the dead angles will disappear in the CT second winding. The measure is usually taken to revert the dead angle by calculating the first and the second derivatives of the differential current. In this paper, it is proved that the transient dc component of the primary current can not invalidate the measure. In digital relays, derivation calculus is substituted by sampled difference. This paper analyzes the percentage of noise which is magnified by sampled difference, and proposes the approaches to reduce the noise which calculate the first and the second derivatives by using fragment functions integrated with the least square algorithm. The approaches improve both the accuracy of the dead angle calculation and the sensitivity of the relay.For external faults, the increase of the CT error introduced by the CT saturation may produce relay misoperation. In this paper ,by calculating and analyzing a great deal of simulated data, the ratio-relationship between CT errors and waveform correlation coefficients of the CT secondary current has been established, then, a principle of self-adaptive restraint ratio coefficients based on waveform correlation coefficients is presented. If external faults and internal faults occur in succession, the restraining current will increase earlier than the operating current. In this case ,the relay based on the self-adaptive restraint ratio coefficients doesn’t raise the bias threshold inherently, instead ,it can raise the restraint ratio properly by the magnitude of the CT error, so it has high reliability and sensitivity.A new unbalanced current is pointed out, for a Y₀/ △ transformer, which Yo side is connected to the power source. If an external fault on Yo side occur, there will be unbalanced differential current introduced by the zero sequence currents in Yo side because of CT errors, but there is no corresponding restraining current. The paper analyzes this case in detail, than proposes a new approach based on zero sequence current restrain, which eliminates a hidden defect exiting in transformer longitudinaldifferential protection for a long time.The relay based on the approaches proposed in this paper is described.The dynamic simulation system, where the relay is tested, is described, and the test results are discussed. The test results prove that the approaches proposed in this paper can improve the reliability and sensitivity of the transformer longitudinal differential protective relay.更多还原