Zhencun Pan

Detection and Location of Ground Faults Using a Discernible Signal

It is very difficult to correctly detect the faulty line and fault location when a single phase to ground fault (SFG) occurs in distribution system with non-effectively grounded neutral. After analyzing the characteristics of the loop of faulty circuit including the potential transformer (PT), it is found that the faulted phase of PT is idle during a SFG. According to fact described above, an approach for ground fault localization and faulted feeder identification using a discernible signal on non-effectively grounded neutral systems is described. The discernible signal is supplied by a special signal generator and is coupled to the primary distribution system through PT when a fault occurs. After the faulty feeder and fault location are determined, the signal generator will be removed. The feasibility of the approach has been verified in field distribution systems

An Integrated Automatic Control System for Distributed Generation Hierarchical Islanding

The penetration of distributed generation causes unintentional islanding, failure of re-closing, unsynchronized re- closing, etc. Existing anti-islanding techniques can be susceptible to common mode tripping, which could decrease the stability of total system and increase the requirement for secure spinning reserve. The strategy of hierarchical islanding of DG is described in this paper, which includes Mini Islanding and Substation Islanding. The main purposes of hierarchical islanding are to achieve stable islanding and utilize the DG contribution to system availability under conditions of major system disturbance. Substation Islanding is the first choice. When the inter-ties faults occur, the Substation Island is split from the grid and achieves stable islanding. If the stable islanding can not be obtained, the Substation Island would split into several Mini Islands. A hierarchical distributed control system integrated splitting, realtime load shedding and resynchronization is introduced to maintain stability of hierarchical islanding.

A Wide Area Protection System and Division of Protection lED Associated Area Based on Petri Net

In wide area protection system the operation performance of relaying protection IED is improved by receiving and utilizing wide area fault information. The utilization of wide area fault information should be selective. That is, when fault occurs, corresponding protection lEDs only accept and utilize information that is related closely with fault, ignore that contributes little to fault calculation. So it is necessary to divide associated area for protection IED. Operation manner of wide area relaying protection system are discussed first in this paper. The principle to divide protection IED associated area is determined based on Petri net theory. Double-bus and double-circuit connection and one and a half circuit breaker connection are taken as the examples to study network topology to meet the requirements of protection associated area division. Analysis results show that the method to divide protection associated area is effective, which can meet information transmission requirement of wide area relaying protection system

A method to estimate voltage sag profile for power distribution systems

In recent years, the need to characterize the feeder-level power quality performance has emerged. It is driven by the interest to compare the PQ performance among utility companies or among various feeders. This is a very challenging task, however, since the voltage sag profile along a feeder is needed for calculating the feeder-level PQ indices. It is impossible to measure the voltage sag level at each customer site. In response to this emerging need, we propose to estimate the sag profile of a feeder based on limited number of metering points. The proposed sag estimation method has the following characteristics: 1) it makes use of the radial connection characteristic of a distribution feeder, 2) it requires only a limited number of metering results, 3) it employs a least-square method to predict the sag profile along a distribution line. One of the potential applications of the proposed method is to calculate the feeder power quality performance indices such as System Average RMS Frequency Index (SARFIx).

A Fault Determination Algorithm for Relaying Protection System Based on Wide Area Information

A fault determination algorithm for wide area relaying protection system based on fault direction information is proposed. IED of wide area relaying protection system collects fault direction information in specific protection zone and estimates fault site in virtue of protection action factor (AF) that is defined in this paper. The failure operation of IED is considered and its influence on fault determination algorithm is analyzed. Relaying protection strategy anti failure operation of IED is proposed. Results of case study show that fault determination algorithm for wide area relaying protection system proposed in this paper is simple, reliable and convenient to estimate fault section. The fault estimation results are correct and immune against IED failure operation, which can improve the performance of relaying protection system markedly.

An Automatic Shedding Decision System for the Backup Protection of a Transmission Network

In recent years, many wide spread blackouts is caused by incorrect operations of the backup protection relays that result from the overloading of some transmission lines after one faulted transmission line is tripped. This paper gives a new solution to this event. A new conception of RCTL(relative cluster of the transmission line ) is introduced firstly in this paper. Then the method for searching RCTL based on decision tree theory and the method for calculating distribution coefficient of RCTL is introduced in detail, among them the key techniques are emphasized in the paper. On this basis, an automatic shedding decision system for the backup protection is proposed to prevent cascading outages. The simulation of CEPRI standard model shows that the automatic shedding decision system for the backup protection against cascading outages works well.

Transformer and Bus Backup Protection Based on Longitudinal Comparison Principle

A new transformer backup protection based on longitudinal comparison principle (LCP) is introduced in this paper. The fault can be located by comparing action of measurement elements on all sides of transformer simultaneously. If the transformer internal faults occur, backup protection trips the breakers of all sides with a short time delay to avoid nuisance tripping caused by inrush current. If an external fault occurs, the backup protection can determine the fault side and trip the corresponding breaker after a predetermined time coordinated with downstream relays. The coordination of operation time and reach among overcurrent relays on different side is not needed. The backup protection can provide good protection performance for transformer and adjacent buses. It can shorten the operation time and improve selectivity and sensitivity

Voltage sag state estimation for power distribution systems

Summary form only given. The increased awareness on power quality has resulted in the need to quantify the voltage sag performance of a distribution feeder, similar to what has been done on characterizing the reliability performance of a feeder. Since it is impossible to measure the sag level at every node of a distribution feeder, estimation of sag characteristics at un-metered nodes becomes necessary. This paper proposes the concept of voltage sag state estimation and associated algorithms to achieve this goal. The proposed method has the following characteristics: 1) it makes use of the radial connection characteristic of a distribution feeder, 2) it is based on a limited number of metering points, 3) it employs a least-square method to predict the sag profile along a distribution line. The results of the proposed sag state estimator can be used to calculate the feeder power quality performance indices such as the system average RMS frequency index (SARFIx).