This article presents a survey of the developments in digital relays for protection of transmission lines. For a modern power
system, selective high speed clearance of faults on high voltage transmission lines is critical and this survey indicates the
efficient and promising implementations for fault detection, classification and fault location in power transmission line
protection. The work done in this area favor computerized relays, digital communication technologies and other technical
developments, to avoid cascading failures and facilitate safer, secure and reliable power systems. Efforts have been made to
include almost all the techniques and philosophies of transmission line protection reported in the literature up to October 2010. The focus of this article is on the most recent techniques, like artificial neural network, fuzzy logic, fuzzy-neuro, fuzzy logicwavelet based and phasor measurement unit-based concepts as well as other conventional methods used in transmission line protection.

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Recent techniques used in transmission line protection: A review

According to the theory of equal transfer process of transmission lines (ETPTL), the voltages along the line and the current through the line transformed by the same linear transferring link still satisfy the original distributed parameter-based transmission-line model. It is proved that the voltage signals near power frequency along the line follow the law of linear distribution. On the basis of the aforementioned analytical results, an ETPTL-based new current differential protection scheme for long transmission lines by using restructured instantaneous value was presented. The primary voltage and current experience equal transfer processes and are transformed to be virtual instantaneous values before they are used by differential protection. According to the instantaneous voltage value of the transmission line, the instantaneous values of the capacitive current can be calculated. After removing this current, the instantaneous value-based differential criterion can be implemented. The results of Alternate Transients Program simulation test results show that the proposed technique has highly reliability, fast speed, excellent performance under high-resistance earth-fault conditions, and phase selection ability.

Instantaneous Value and Equal Transfer Processes-Based Current Differential Protection for Long Transmission Lines

Increased ratio error of capacitor voltage transformers (CVTs) has been recently encountered in several substations in Iran. The results of the performed diagnostic tests indicate that short-circuited capacitor elements, especially in the low-voltage capacitor, have increased the CVT error. In this paper, some simple and effective techniques are suggested to solve this problem. One of the proposed methods to compensate the increased error is utilization of an auxiliary voltage transformer (AVT), which does not require disassembling the CVT. The practical aspects of this method, its effects on the CVT transient response, and the influence of the AVT improper design on the performance of distance relay are scrutinized in this paper. Furthermore, the design requirements of the AVT to avoid distance relay malfunctions due to the AVT ferroresonance are discussed.

Compensation of CVT Increased Error and Its Impacts on Distance Relays

Measurement errors of a capacitive voltage transformer (CVT) are relevant to its equivalent parameters for which its capacitive divider contributes the most. In daily operation, dielectric aging, moisture, dielectric breakdown, etc., it will exert mixing effects on a capacitive divider’s insulation characteristics, leading to fluctuation in equivalent parameters which result in the measurement error. This paper proposes an equivalent circuit model to represent a CVT which incorporates insulation characteristics of a capacitive divider. After software simulation and laboratory experiments, the relationship between measurement errors and insulation parameters is obtained. It indicates that variation of insulation parameters in a CVT will cause a reasonable measurement error. From field tests and calculation, equivalent capacitance mainly affects magnitude error, while dielectric loss mainly affects phase error. As capacitance changes 0.2%, magnitude error can reach −0.2%. As dielectric loss factor changes 0.2%, phase error can reach 5′. An increase of equivalent capacitance and dielectric loss factor in the high-voltage capacitor will cause a positive real power measurement error. An increase of equivalent capacitance and dielectric loss factor in the low-voltage capacitor will cause a negative real power measurement error.

https://www.mdpi.com/1996-1073/10/3/357/pdf

Measurement Error Estimation for Capacitive Voltage Transformer by Insulation Parameters

Research on the reliability of capacitor voltage transformers calibration results

Simple delay solutions are usually used to prevent transient overreach caused by the transient error of a capacitor voltage transformer (CVT), which is very harmful to the safety and stability of operation of the power system. A proposed real-time CVT transient error estimation approach based on the chosen fundamental wave algorithm and the rated CVT parameters consists of two stages. The first stage obtains the error coefficient. The second stage estimates the measured error of the voltage amplitude according to the secondary side voltage. A novel adaptive distance relay approach is proposed, which can adjust operating thresholds according to the error. The approach hardly affects the performance for lines of normal length and operates rapidly for short lines with close-in faults, which is verified by the simulation studies. The overall performance is improved greatly in comparison with the general approach for distance relays

An adaptive distance relay based on transient error estimation of CVT

With the development of electric internet of things, substation focuses on building an intelligent system with intelligent information processing and convenient and flexible application. The secondary equipment is updated frequently, and the method of manual test configuration has been difficult to meet the work requirements. This paper presents an automatic configuration method of secondary equipment based on knowledge graph technology. Build the test knowledge graph of secondary equipment, and establish the knowledge association between intelligent electronic device (TED) file and test configuration, test equipment, configuration information point and information path. Based on the word2vec model, the word embedding vector of the secondary equipment test proprietary vocabulary is fused, and then the mapping relationship is deduced based on the information retrieval path and the text similarity of the configuration file. The experimental results show that the method of automatic configuration of secondary equipment test based on knowledge graph is scientific, effective, and has high accuracy, which is suitable for practical engineering application.

Research on Automatic Configuration Technology of Secondary Equipment Configuration Test in Intelligent Substation

The turbofan engine is an important part of the aircraft. If the equipment life cycle can be accurately predicted, it can not only bring huge benefits to the airline company, but also reduce the safety accidents caused by turbofan engine failure. In the field of life cycle prediction, long-short-term Memory (LSTM) network is particularly favored by the field of prediction maintenance because of its ability to learn from sequences. It can use time series data for a longer time review, so it is suitable for device life prediction using time series data. In this paper, the c-MAPSS data set of rotary motor is taken as the research object, and its life prediction model is studied based on LSTM. In this paper, principal component analysis algorithm and SNM optimization algorithm are used to optimize experimental data and extract features, and the traversal parameters of LSTM model are optimized. Finally, the cross-validation method is used to learn and integrate the data model. The experimental results show that compared with the original algorithm model, the integrated model can improve the precision and recall rate of the model by optimizing the original data, reducing the data dimension and duplicate data, and reducing the operation complexity.

A prediction model of turbofan engine remaining life based on improved algorithm

The signal configuration workload of the whole station simulation test of the intelligent substation is large, and the non-standard signal model of the secondary equipment makes it difficult to realize the automatic signal configuration. In order to solve the above problems, this paper proposes a self-configuration technology of the whole station simulation test of intelligent substation. Based on the signal configuration requirements of the whole station simulation test and the relevant specifications of relay protection, a standardized secondary equipment signal model is established. Based on the primary main wiring diagram of the substation, the unconfigured SSD file is generated. The improved edit distance similarity algorithm is used to realize the automatic mapping of the secondary equipment signal model to the standardized secondary equipment signal model, so as to realize the automatic configuration of the simulation test of the whole station. The actual example shows that the configuration method proposed in this paper can overcome the problem of non-standard signal models of secondary equipment of different manufacturers, and realize the automatic configuration of the simulation test signal of the whole station based on the similarity calculation of the signal model of the secondary equipment.

Research on the self-configuration technology of the whole station simulation test of intelligent substation

When the measurement information is missing, the Kirchhoff synthetic current method is usually used to replace the current information at the missing measuring point. However, in some specific cases, the inrush current of the transformer and the saturation of the bus CT will occur, which affects the accuracy of the synthetic current, and then leads to the misjudgement of the differential protection using the equivalent current, which endangers the safety and stability of the smart substation and the power system. In this paper, an information loss protection is proposed to eliminate the influence of inrush current and CT saturation, and PSCAD / EMTDC simulation is carried out. The results show that the reliability of power system is effectively improved when the measurement information of transformer and bus connection line is missing.

Yiquan Li

Papers

An adaptive distance relay based on transient error estimation of CVT

Research on Automatic Configuration Technology of Secondary Equipment Configuration Test in Intelligent Substation

A prediction model of turbofan engine remaining life based on improved algorithm

Research on the self-configuration technology of the whole station simulation test of intelligent substation

Missing Information Protection Considering Inrush Current and CT Saturation