The introduction of the microprocessor-based numerical relay in the 1980s resulted in multifunctional, multidimensional, communications-enabled complex protection systems for zone and system protection. The increasing capabilities of this technology created new unintended challenges: 1) complexity has increased and selecting coordinated settings is a challenge leading to occasional miscoordination; 2) protection functions still rely on a small number of measurements (typically three voltages and three currents) limiting the ability of protection functions to dependably identify the type of fault conditions; and 3) present approaches are incapable of dealing with hidden failures in the protection system. Statistically, 10% of protection operations are misoperations. This paper presents a new approach to protection that promises to eliminate the majority of the problems that lead to misoperations. The approach is described, demonstrated in the laboratory, compared to traditional protection functions and its application to a substation coordinated protection system capable of detecting and dealing with hidden failures is described. This paper also discusses the planned field testing of the approach.

Dynamic State Estimation-Based Protection: Status and Promise

Results of a literature survey done on microgrids from conception to installation is presented. The purpose is to evaluate the current status, major obstacles and existing research efforts directed toward establishing functional microgrids within utility systems. This review paper covers technical issues associated with frequency control and re-synchronization associated with typical distributed energy sources. Also evaluated are regulatory and policy issues associated with ownership, maintenance, availability, coordinated equipment control, obligation to provide adequate power quality, etc. associated with operating an islanded microgrid within a utility company's service territory. Actual microgrids in operation today are described. Benchmark test systems for steady state and dynamic simulations are also discussed.

Microgrids — A review of modeling, control, protection, simulation and future potential

In this study, a new algorithm for discrimination between internal faults and inrush current conditions in power transformers is presented. First, the proposed algorithm removes the pre-fault conditions of the fault currents. Then, those currents are processed using the discrete wavelet transform to obtain the wavelet matrix. The correlation matrix is computed from wavelet matrix to know the eigenvalues associated with each frequency scale and to reduce the analysed information. This algorithm, which the authors are going to call wavelet correlation modes, is used to identify inrush and internal fault currents in power transformer. To validate the proposed algorithm, simulations are carried out in power systems computer-aided design software, and the obtained signals are analysed in order to evaluate its performance and sensitivity.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-gtd.2015.1147

Algorithm for transformer differential protection based on wavelet correlation modes

Faults diagnosis in power transformers has been traditionally based on the insulation resistance measurement, polarisation index, analysis of dissolved gasses in oil, dissipation/power factor measurement, and partial discharges within many other alternatives. Originally, all these techniques presented an offline implementation, that is, with the transformer out of service. Currently, some of them, such as partial discharges measurement or gas analysis (gas chromatography), are carried out online in those cases in which the importance of a machine justifies it. These techniques have been recently complemented with new alternatives, such as frequency response analysis, an offline application technique. At the same time, in recent years, development of online diagnostic strategies has been carried out only based in monitoring of electrical variables. These techniques have the advantage of being economical in relation to traditional ones. Its development are incipient and with high growth potential. This study presents a review of the most important techniques and a critical comparison between them.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-gtd.2017.2086

Power transformers monitoring based on electrical measurements: state of the art

Current transformer (CT) saturation can cause the maloperation of transformer differential protection under external faults. To avoid this problem, a method based on the histogram of the normalized rotated current (NRC) is proposed. NRC is obtained by a symmetric waveform transformation of a part differential current. An index based on the histogram is defined to evaluate the NRC frequency distribution. The external faults with different degrees of CT saturation, internal faults, and transferring faults can be clearly distinguished by the proposed method. Moreover, the detection time is invariably less than a half cycle after the obvious increase of the differential current. Simulation results validated the proposed method.

Histogram-Based Method to Avoid Maloperation of Transformer Differential Protection Due to Current-Transformer Saturation Under External Faults

Setting the pickup current and slope of differential relays of power transformer protection is a well-known compromise. It has been the focus of study to improve both the security and sensitivity of transformer differential protection recently. However, it is difficult to achieve a high degree of security and sensitivity at the same time by conventional percentage restraint differential criteria based on a fixed predetermined characteristic curve. Therefore a novel adaptive protection criterion is proposed in this study, which can self-regulate the parameters of percentage differential characteristic (e.g. pickup current, restraint coefficient and restraint current at the knee point of the slope characteristic) on the basis of operating conditions of power transformers. The test results show that the proposed scheme provides a high operating sensitivity on internal faults, while retaining higher security on all external faults. Furthermore, because of self-regulation of the setting values of relays, it is more convenient for engineers in the field who only need to give the upper and lower limits but not the exact value of the settings of protective relay.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-gtd.2011.0739

Self-adaptive transformer differential protection

In the traditional feeder automation of distribution network, it's hard to coordinate switches with each other, the rapidity and selectivity of protection is irreconcilable. To solve this problem, this paper introduces wireless sensor network, which can collect date and communicate it. Together with the recloser and sectionalizer, which are widely used in distribution network currently, a new feeder automation scheme is presented. By putting up network model and fault analysis, a protection criterion, which reference to the adjacent Switch State, is given. Finally, to verify the feasibility of this scheme, the NS2 wireless simulation is given, which analyzes the delay of data transmission and packet loss rate.

A feeder automation scheme based on wireless sensor network

As a supporting technology in wireless sensor networks, time synchronization is a new focus topic in the research of Wireless Sensor Networks, and it is a challenge to acquire a high precision of synchronization with lower energy-consumption. Based on TPSN and RBS, an energy-aware time synchronization algorithm is presented. In this algorithm, the additional parameters including the remaining energy level of child-nodes and their degrees are synthetically considered to optimize the process of reference-node selection, thus to reduce and balance energy-consumption among the nodes, prolong the network lifetime efficiently. Experimental results show the validity of the algorithm.

Pei Liu

Papers

Self-adaptive transformer differential protection

A feeder automation scheme based on wireless sensor network

Research on the algorithm of energy-aware time synchronization for Wireless Sensor Networks