| Now power grid is in a stage of rapid development, the pace of building strong smart grid and UHV transmission is faster and faster, requirements for relay protection system are also increasing. High voltage transmission lines in China are equipped with double sets of main protection, generally pilot protection principle. Pilot protection is perfect in principle and has absolute selectivity in theory, needs less time for fault detection and isolation and has higher rate of correct action, it can meet the protective requirements of high-voltage system well. Even so, each single principle has certain deficiencies which can’t ensure satisfactory performance in any operating conditions.Therefore, this paper proposes the idea of unified pilot protection system, in which different protection principles are concentrated into one system, work together based on the same data source, learn from each other to improve the performance of protection system and automatic reclosure system, complete online calculation of transmission line parameters and other auxiliary functions. The main contents are as follows:The rapid development of IED and fiber optic digital communication is the strong technical support and guarantee of unified pilot protection system. This paper describes the structure of unified pilot protection system, the form of data frame and its auxiliary functions.In view of current differential protection is susceptible to TA characteristics inconsistency and TA saturation, the paper introduces a fault judging method by means of fault direction information, which is less affected by TA characteristics. The method doesn’t need to identify TA saturation, and won’t reduce sensitivity and reliability of protection, it can improve performance of protection system through mutual cooperation of different protection principles. On this basis, a current differential protection criterion based on the amplitude and phase difference of fault current is proposed, which has higher sensitivity in internal faults and higher levels of security in external faults. This criterion can be used in different devices to distinct internal and external failures rapidly and reliably at beginning of faults.Through exchanging all kinds of action information with fiber optical digital channel, the paper puts forward three-jumped self-adaptive phase splitting reclosure and elect-jumped self-adaptive phase splitting reclosure and that achieved by controlling operation sequence and time of switches on both sides. Distinguishing transient faults and permanent faults can avoid secondary impact to the system and improve performances of automatic reclosure system.Transmission line parameter is important for obtaining power network structure, generating power system node admittance matrix or impedance matrix to calculate power flow, calculating short-circuit current, and setting relaying protection devices. But actually, transmission line parameters applied in power system are mostly experience values or offline measuring values provided by manufacturers, they may quite different from real parameters. This will influence the stable operation of power system. This paper studies online calculation methods of transmission line parameters based on phasor and sampling value, provides real and accurate parameters to improve the accuracy and reliability of power system computation and ensure stable operation of grid. |
