Research On The Local And Regional Area Information-based Adaptive Protection

With the increasingly complex structure and operation modes of power grids,the setting calculation and coordination of relay protection face severe challenges.The settings of the traditional multi-stage protection are usually off-line calculated according to the maximum and minimum operation modes.When the system operation mode changes complexly,it not only increases the difficulty in selecting the maximum and minimum operation modes,but also the protection performance will deteriorate even under normal operating modes.There are serious challenges,such as insufficiency of protection range and difficulty in protection coordination,existing in the traditional multi-stage protection.In addition,since the protection based on local information cannot accurately determine the fault at the end of the line and the adjacent line,the multi-stage definite time delay is utilized to maintain the selectivity of protection.However,the overlong delay of protection is more and more difficult to meet the customers' high requirement for power quality and reliability.In this dissertation,a local measurement-based adaptive setting method for overcurrent protection and the regional area information-based adaptive protection schemes are proposed.The primary contents and results of this research include:(1)A local information-based distribution network operation mode awareness method is proposed.It is difficult to off-line calculate proper relay settings if the system operates with various modes.An optimized Thevenin equivalent parameter estimation method is proposed based on the irrelevant relationship between the source and load side variations.The optimized estimation results are achieved by solving a Gaussian denoising problem.Then,the primary-dual hybrid gradient algorithm and the taut-string-multiresolution algorithm are utilized to solve the problem,respectively.The proposed methods can improve the accuracy of the Thevenin equivalent parameter estimation and the system operating mode awareness,which is important to implement the adaptive settings of the overcurrent relay.(2)A local prefault information-based adaptive setting method for overcurrent protection in distribution system is proposed.Considering the system operating mode changes as well as the fault analysis model of the inverter-interfaced DGs(IIDGs),a fault current online estimation method is established.According to the estimated fault current values,an adaptive setting method is proposed to adjust the coefficient and realize the adaptive setting for the multi-stage current protection.The proposed method has improved the sensitivity and selectivity of the traditional current protection,and enhanced the coordination between the adjacent protection relays.(3)A regional area information-based distribution network protection method is proposed.Under fault conditions,the pick-up information of local relays within the predefined area are collected by the regional area protection system(RAPS);then several RAPS logic criteria are executed to adjust the time delay settings of local relays adaptively.The fault isolation is accelerated and the protection coordination is enhanced by this method.Also the fault tolerance capability of protection is improved by the effective utilizing of the redundant digital information.The proposed RAPS can improve the selectivity,sensitivity,quickness,and fault tolerance capability of the protection system,which can deal with the failure of a single communication or protection device.(4)Local backup protection of transformer and corresponding substation area backup protection methods are proposed.To solve problems existing in the conventional transformer backup protection,such as increasing complexity of setting calculation,extending time delay of fault isolation,and aggravating deficiency of sensitivity,a local backup protection configuration and setting method for transformer is presented.Then,a substation area backup protection scheme is proposed based on the multi-point redundant digital information with substation area.The substation area backup protection scheme can not only adjust the time delay of local relays,but also accelerate the faulty component identification and isolation processes.