This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TSG.2016.2607318, IEEE Transactions on Smart Grid
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A D-S Evidence Theory-based Relay Protection System Hidden Failures Detection Method in Smart Grid Zaibin Jiao, Member, IEEE, Heteng Gong, and Yifei Wang
power system reliability, aiming at identifying the weak link of power systems. The occurrence probability of N-K contingencies is calculated in [4]-[5]. Reference [6] proposes a new method for evaluating the effects of consequence circumstances caused by hidden failures based on vulnerable regions. Then the reliability evaluation method in consideration of relay protection system failures is presented in [7]-[10]. Subsequently, [11] focuses on the analysis of protection system hidden failures in circuit breakers and the risk of system collapse, considering that hidden failures in relay protection systems are accurately evaluated in [12]. In addition, some studies have proposed some techniques to minimize potential hidden failures or reduce and mitigate the impact hidden failures. Reference [13] applies pattern recognition techniques and machine learning in a hidden semi-Markov model for effective online failure prediction. Reference [14] proposes a relay supervisory system (RSS) as part of relay protection systems to improve condition-based maintenance and mitigate the impact of hidden failures. Smart grid provides Index Terms--D-S evidence theory; hidden failures; redundan- us with an intelligent platform to enhance the connection of the cy and coordination of relay protection; smart grid devices. Under one disturbance event, many sequence of event (SOE) records can be obtained from the relay protection manI. INTRODUCTION agement information systems (RPMIS). Meanwhile, wide area ower system blackouts caused by cascading failures result measurement systems (WAMS) provide a new information in large economic losses, although they are a rare event [1], integration platform to achieve dynamically real-time monitor[2]. Early in 1996, Phadke and Thorp [3] indicated that hidden ing and reaction, and the information of relay devices is exfailures in relay protection systems are one of the reasons for pected to be uploaded and shared constantly. Therefore, in cascading failures. Hidden failures are permanent defects that smart grid, combining all the information to detect the hidden exist in relay protection systems, but they can only be exposed failures before the hidden failures have been triggered is a new when the power systems are under faulty or abnormal condi- research direction. Based on the RPMIS and WAMS in smart grid, this paper tions. Such problems lead directly to undesirable relay tripping and deterioration of the system operation, which can finally reveals information under faulty or disturbance conditions, result in cascading failures and even large-scale blackouts. uses the mutual coordination of relay protection and simple Therefore, in order to prevent blackouts and ensure power fault location result, and combines all the information with Dsystem security, a detection method for hidden failures is inev- S evidence theory to finally propose a method for detecting the no-triggered hidden failures in relay protection systems. itable in smart grids. The rest of this paper is organized as follows. Section II Most studies consider the risk assessment or impact evaluation of relay protection systems with hidden failures to bolster constructs several pieces of evidence on the basis of the coordination relationship among relays. Section III proposes the detection algorithm that uses fault location information. In The authors are with the School of Electrical Engineering, Xi’an Jiaotong Section IV, the evidence concluded from Sections II and III is University, Xi’an 710049, China (the corresponding author is Zaibin Jiao, ecombined to obtain reliable results based on the D-S evidence mail:
[email protected]). Abstract--Hidden failures in relay protection systems are the primary factors for triggering the cascading outages and bulk blackouts of power systems, but it is difficult to detect these when power systems operate normally. In smart grids, relay protection management information systems (RPMIS) allow us to obtain many sequence of event (SOE) records under disturbances and faulty conditions. By studying such record information, this paper proposes a detection method for hidden failures based on the features of relay protection systems. In this method, certain evidence is constructed by analysis of redundancy and coordination between the primary and backup protections or within the backup protection. Meanwhile, uncertain evidence is constructed by utilizing the fault location. Then, by combining all the evidence with D-S evidence theory, detection criteria for detecting hidden failures in relay protection systems are presented. Last, the effectiveness of the proposed algorithm is verified on the IEEE 39 bus system case. The results indicate that this method can detect hidden failures in relay protection systems and send alarm information. Thus, it is of great importance to ensure the security operation of power systems in smart grids.
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theory. Section V verifies the effectiveness of this method on the IEEE 39 bus system case. Finally, conclusions are given in Section VI. II. COORDINATION AMONG RELAY PROTECTIONS In general, primary and backup protection work together to detect and isolate faults on transmission lines reliably. In some cases, even duplicate primary protections are used to ensure reliability. Namely, protection configuration is redundant. Therefore, when certain disturbances or faults occur in power systems, more than one relay responds normally. If some of these relays should pick up but they do not, hidden failures might exist in these abnormal relays. Take Fig. 1 as an example, and assume that differential current protection and complete three-zone distance relays are configured on line sections AB，BC, and CD. The coordination relationship between these protections at bus B is analyzed in the paragraphs that follow Fig. 1. jX
Ⅲ A
B Ⅰ
Ⅱ C Ⅰ
jX
jX
Ⅱ
Ⅰ D
E
For those relays on the upstream of the transmission line, namely the relays at Bus A, the principle is that the protection area of the Zone-III distance relay at Bus A cannot exceed the protection area of the Zone-II distance relay at Bus B. This means that the Zone-II distance relay at Bus B must pick up if the Zone-III distance relay at Bus A also picks up. Moreover, if the differential current protection at Bus B does not pick up and the Zone-III distance relay at Bus A picks up, the Zone-II distance relay at Bus B must pick up. In summary, the diagram shown in Fig. 2 can be obtained to determine whether the Zone-II distance relay picks up correctly. Upstream zone-III pick up, Upstream differential not pick up
( Opposite ) Zone-I pick up
Zone-II pick up
Differential pick up
Differential not pick up, Downstream zone-I not pick up
Zone-II not pick up
Zone-III not pick up
Fig. 2. Diagram of coordination relationship among relays.
Assuming z is the protection to be tested, the protection set X = {x1, x2, x3…} combines those protections whose protection areas are contained in the area of z, and the protection set Y = {y1, y2, y3…} combines those protections whose protecR R R tion areas contain the area of z. Furthermore, the elements in sets X and Y can be the combination of several relay protecFig. 1. Diagram of a simple power system. tions. Thus far, two principles can be obtained to determine Normally, distance relays with different thresholds are in- whether protection z pick up correctly: stalled at Bus B for line section BC, and they are called Zone-I, 1. x X , x pick up z pick up Zone-II, and Zone-III distance relays. According to the setting 2. y Y , y not pick up z not pick up criteria, the protection area for the Zone-I distance relay is Therefore, the logical relationship is that “x pick up” is a included in the protection area for the Zone-II distance relay. sufficient condition to “z pick up,” and “y pick up” is a necesThis means that the Zone-II distance relay must pick up if the sary condition to “z pick up.” If the inferred conclusion above Zone-I distance relay has already picked up. Similarly, the is inconsistent with the practical situation, protection z is conZone-II distance relay cannot pick up if the Zone-III distance sidered to have hidden failures. relay does not pick up. In addition, the protection capability of differential current III. IDENTIFYING HIDDEN FAILURES USING FAULT LOCATION protection covers the entire line, whereas the protection capaINFORMATION bility for the Zone-II distance relay exceeds the entire line. The comparison between the fault location information and Therefore, if the differential current protection picks up, the Zone-II distance relay must also pick up. Moreover, if the re- distance relay threshold determines whether to pick up the mote side of this section line is also configured with distance corresponding protection. Therefore, the fault location inforrelays, the Zone-II distance relay for this section line must pick mation can also be used to identify the hidden failures of the corresponding protection. Combining the fault location inforup once the Zone-I distance relay in the remote side picks up. For those relays on the downstream of the transmission line, mation of two sides is preferable because the combination of namely the relays at Bus C, the principle is that the protection the fault location information of two terminals can identify area of the Zone-II distance relay at Bus B cannot exceed the whether a fault exists on this line. For the internal fault, the area of the Zone-I distance relay at Bus C. This means that the combined location information of this line can be used directly Zone-II distance relay at Bus B does not pick up if the Zone-I to distinguish internal and external faults, and to determine distance relay also does not pick up. Moreover, the differential whether to pick up the primary and backup protections. Such combined location information is similar to the logical sufficurrent protection does not pick up in this case, obviously. cient and necessary conditions that can be classified as the
1949-3053 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TSG.2016.2607318, IEEE Transactions on Smart Grid
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elements in sets X and Y. For the fault on the downstream line, specific location values for such line are required in order to compare with the backup protection threshold and determine whether to pick up the backup protection. Taking the analysis of the Zone-II distance relay at Bus B in Fig. 1 as an example, the logical relationship is shown in Fig. 3, as follows: Zone-II at B pick up
Internal fault f1 d+
C
K f2
1.15d1 u 2( ) 1 0.8
D
External fault f2: dmcd-
Zone-II at B pick up
External fault f3: dmc>d+
Zone-II at B not pick up
External fault f3: dmD
