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

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

Differential relays are the main protection for power transformers including transmission and industrial transformers. Protection against internal fault is generally relegated to these relays. The most probable internal fault of the industrial transformer is phase to ground type. To limit the fault current in this condition, a limiter resistor is utilised in the transformer. However, it has considerable impact on sensitivity of the differential and restricted earth fault (REF) protections. In this study, an effective approach is proposed to improve the differential and REF protections sensitivity of the industrial transformers. The proposed technique not only realises the fault current limitation function, but preserves sensitivity of the protections. In this method, a developed fault current limiter is utilised in the transformer neutral instead of the neutral grounding resistor. The performance of the proposed technique is evaluated by some simulations and experiments. The results confirm the high capability of the proposed technique in different conditions.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-gtd.2015.1343

New approach to improve sensitivity of differential and restricted earth fault protections for industrial transformers

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

The structure of intelligent substation SCD file is complex, and there are many layers of information. Different functions have corresponding information basis, and often need to be associated across multiple information nodes, resulting in poor visualization. This paper presents a multi-dimensional visualization method of SCD file information of smart substation based on knowledge graph. Firstly, the file structure and function structure of SCD text expression are analyzed. Then the SCD file node is extended and the seven-step method is adopted to construct the intelligent substation ontology, which is realized by Protégé. The knowledge graph of substation is constructed by using ontology and relationship between SCD nodes. The graph expression of SCD is completed, and the visualization of file structure information is realized. The information path of functions such as the correlation between primary and secondary devices and the correlation between virtual and real circuits is mined. The information nodes in the path are searched in the SCD knowledge graph to realize the visualization of functional structure information. The above work was done through Neoj4, Python. The simulation results show that knowledge graph can decouple SCD information and realize multi-dimensional visualization of information with a high degree of visualization, which can provide guidance for operation and maintenance and information retrieval.

Multi-dimensional Visualization Method of SCD File Information of Intelligent Substation Based on Knowledge Graph

With the scale of the power grid is becoming larger and larger. The corresponding operation and maintenance work of the distribution network is becoming increasingly intelligent, which also puts forward corresponding requirements for the reliability of safe and stable operation of the power grid. The condition assessment of relay protection applies the scientific concept of condition-based maintenance to the actual work site, which is of great significance. To judge the operation status of the equipment and provide a scientific basis for maintenance, in this paper, based on the application of digital twin technology in microgrid operation and maintenance, the method of calculating reliability probability density by function is applied to solve the problems of fuzziness, gray, and randomness of the relay protection status index. The invention can evaluate the state of the relay protection of the power system and can timely and accurately put forward the corresponding relay protection inspection and maintenance scheme, thereby improving the maintenance efficiency of the relay protection and further strengthening the power supply reliability of the power system. It can ensure the security and stability of the power system and reduce the reliable power consumption of the majority of power users.

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Operation and Maintenance Technology of Relay Protection Equipment Based on Digital Twin Technology

In view of the sharp increase in the amount of data in intelligent substations at present, the gap between the data transmission mode and the data storage mode is large, resulting in the problem of low data storage efficiency. This paper presents a data storage method of intelligent substation based on physical model. Firstly, this paper analyzes the data transmission mode of IEC 61850, introduces the object-oriented modeling technology of IEC 61850, the relationship between various configuration files, and the tree structure of the transmitted data. Then, this paper introduces the concept, structure and characteristics of the physical model. Build a physical model of the device based on the CID (Configured IED Description) file of the device, and form a device self-describing JSON file. After then, according to the characteristics of each service in the physical model, this paper uses different types of databases to store the data under this service. Finally, this paper develops and applies the method, and completes the back-to-back data storage model of a substation equipment. The experimental results show that the functional requirements and performance indicators of the developed substation data storage method can achieve the desired goals and effectively improve the efficiency of data storage.

A Data Storage Method of Intelligent Substation Based on Physical Model

The network security situation plays a key role in the operation and maintenance of smart electric power grid, the Long Short-term Memory (LSTM) recurrent neural network is used to predict the network security situation based on the historical sequence data. Since hyperparameters of LSMT such as the number of neurons, learning rate are difficult to determine, we apply the improved Simple Particle Swarm Optimization algorithm (SPSO) to optimize these parameters. The SPSO-LSTM network was proposed to obtain the final prediction result. Experimental results show that this method can obtain good prediction results in various application scenarios.

Qian Tan

Papers

Self-adaptive transformer differential protection

Multi-dimensional Visualization Method of SCD File Information of Intelligent Substation Based on Knowledge Graph

Operation and Maintenance Technology of Relay Protection Equipment Based on Digital Twin Technology

A Data Storage Method of Intelligent Substation Based on Physical Model

A LSTM-Based Method for Prediction of Network Security Situation in Smart Electric Power Grid