Differential Protection System Research Articles

Transformer Internal and Inrush Current Fault Detection Using Machine Learning

Preventive maintenance in the transformer is performed through a differential relay protection system, and it protects the transformer from internal and external faults. However, the Current Transformer (CT) in the differential protection system mal-operates during inrush currents. CT saturates due to magnetizing inrush currents and causes false tripping of the differential relays. Moreover, identification of tripping in protection relay either due to inrush current or internal faults needs to be diagnosed. For the above problem, continuous monitoring of transformer breather and CT terminals with thermal camera helps detect the tripping in relay due to inrush or internal fault. The transformer’s internal fault leads to high breathing process in the transformer breather, never for inrush currents. During inrush currents, CT temperature is increased. Continuous monitoring of breather and CT of the transformer through thermal imaging and radiometric pixels detect the causes of CT saturation and differentiates maloperation. Hybrid wavelet threshold image analytics (HWT-IA) based radiometric pixels analysis of the transformer breather and CT after de-noising provides an accurate result of about 95% for identification of the false tripping of differential protection system of transformer.

Change detection filter technique-based fault analysis of HVDC transmission line

PurposeThis research paper aims to investigate the change detection filter technique with a decision tree-based event (fault type) classifier for recognizing and categorizing power system disturbances on the high-voltage DC (HVDC) transmission link.Design/methodology/approachA change detection filter is used to the average and differential current components, which detects the point of fault initiation and records a change detection point (CDP). The half-cycle differential and average currents on both sides of the CDP are sent through the signal processing unit, which produces the respective target. The extracted target indices are sent through a decision tree-based fault classifier mechanism for fault classification.FindingsIn comparison with conventional differential current protection systems, the developed framework is faster in fault detection and classification and provides great accuracy. The new technology allows for prompt identification of the fault category, allowing electrical grids to be restored as quickly as possible to minimize economic losses. This novel technology enhances efficiency in terms of reducing computing complexity.Research limitations/implicationsSetting a threshold value for identification is one of the limitations. To bring the designed system into stability condition before creating faults on it is another limitation. Reducing the computational burden is one of the limitations.Practical implicationsCreating a practical system in laboratory is difficult as it is a HVDC transmission line. Apart from that, installing rectifier and converter section for HVDC transmission line is difficult in a laboratory setting.Originality/valueThe suggested scheme’s importance and accuracy have been rigorously validated for the standard HVDC transmission system, subjected to various types of DC fault, and the results show the proposed algorithm would be a feasible alternative to real-time applications.

A new differential protection algorithm for transmission lines connected to large-scale wind farms

The fluctuated output power of the large-scale wind farms (WF) and their fault transient characteristics have an adverse effect on the current differential protection systems of the transmission lines. With increased transmission line length and in the case of weak output power from the WF, the differential current between both line ends increases in normal conditions since the capacitive current is comparable to the load current. This paper proposes a new differential protection algorithm for transmission lines connected to large-scale wind farms. The proposed current differential protection algorithm is developed based on the signs of the phase current samples at both line ends, instead of utilizing directly the current magnitudes. The similarity between the signs of the phase current samples at both line ends is evaluated utilizing the signed correlation criterion, and the fault detection index is calculated to discriminate the internal faults from other events. In addition, a new online technique is introduced to adjust the protection settings considering the different output power levels of the WF. The conducted PSCAD/EMTDC simulation studies confirm the acceptable performance of the proposed protection algorithm for numerous normal and fault scenarios, including different fault resistances and inception angles as well as all fault types. The effect of line length, type of wind turbine generator, and different values of WF output power are also considered.

Adaptive Differential Protection System for Microgrid

Microgrids are the small version of power system which grants us the integration of distributed generation resources to insure the facilities to the remotely located electric loads as well as have so many advantages over traditional power system like reduced transmission loss, green energy solution and proper use of renewable energy resources. However the resilience offered by microgrid is inconvenient if it is not be able to protect properly in case of any disturbance occurs which is very common in microgrid due to load dynamics. Protective devices used in traditional power grid cannot actually protect microgrid due to variable loads and different fault levels at grid connected modes and islanded modes. The available research about this concern has not been very successful, therefore options like distance, directional over current and differential relay remains effective protection scheme from present standard. Even though these relays are very useful in power system but their effectiveness for microgrid is yet to be analyzed. This paper is presenting the MATLAB simulation based analysis for differential relay type adaptive protection system by taking a complex microgrid model and generating various fault and generation capacities and analyzing it. In this paper different scenarios has been discussed where differential relay seems to be better than distance and directional over current relay protection scheme.

An Adaptive Differential Protection and Fast Auto-Closing System for 10 kV Distribution Networks Based on 4G LTE Wireless Communication

With the development of wireless communication technology and computer technology, more and more smart technologies have been applied in electricity distribution networks. This paper presents an adaptive current differential protection and fast auto-closing system for application in 10 kV distribution networks in China Southern Power Grid. The current differential protection can adaptively change its settings according to the topology change of the primary distribution networks, thus the system effectively reduces the operation and maintenance cost of the power distribution network. In order to restore the power supply for the healthy part of the 10 kV networks quickly after a power system fault is cleared, the protection and control system provides wide area control function for automatic fault isolation and automatic switching. The traditional overcurrent protection and control system have no fault location function, it may take several minutes or even hours to manually locate a fault and then restore the power supply. Compared with the protection and control system of the traditional 10 kV distribution networks, the system developed can locate and isolate faults within 900 ms (assuming that the operating time of the load switch is 700 ms), and can quickly restore power supply in less than one second after a power system fault is cleared.

Investigating the impact of network security on the line current differential protection system

This paper analyses the influence of network security measures on the system behaviour of a power system protection device. In this particular case, an IP-based Ethernet protection interface of a line current differential protection system is considered. IPsec has previously been proposed to be part of the security concept of the protection interface. Therefore, the authors conduct a trade-off analysis regarding the influence of IPsec on the protection function and consequently on the system safety. This work shows that the protection function of the relay is not impaired as long as the additional CPU performance for the encryption by the protection relay is available and the necessary bandwidth on the communication channel is provided.

Design, implementation, and evaluation of secure communication for line current differential protection systems over packet switched networks

In this work we propose a secure communication concept for the protection of critical power supply and distribution infrastructure. Especially, we consider the line current differential protection method for modern smart grid implementations. This protection system operates on critical infrastructure, and it requires a precise time behavior on the communication between devices on both ends of a protected power line. Therefore, the communication has to fulfill deterministic constraints and low-delay requirements and additionally needs to be protected against cyber attacks. Existing systems are often either costly and based on deprecated technology or suffering from maloperations. In order to allow for both, economical and reliable operation, we present the first holistic communication concept capable of using state-of-the-art packet switched networks. Our solution consists of three parts: (i) we develop a list of design requirements for line current differential protection systems communication; (ii) we propose a communication concept obeying these design requirements by combining cryptographical and physical security approaches; and (iii) we evaluate our solution in a practical setup. Our evaluation shows a clock accuracy of 3 µs with a resilience to asymmetric delay attacks down to 8 ns/s. This demonstrates the secure and fault-free operation of a line current differential protection system communicating over a state-of-the-art network.

Adaptive CWT‐based transmission line differential protection scheme considering cross‐country faults and CT saturation

In this study a new adaptive continuous wavelet transform (CWT)-based current differential protection scheme is proposed to cope with problems of conventional current differential protection in transmission lines. Current transformer (CT) saturation is a major problem for protection engineers in current differential protection systems. The mentioned problem is highlighted when an external fault occurs and causes mal-operation of differential protection. In this study, three phase currents at both ends of transmission line have been sampled and used as input signals to the proposed method using appropriate communication link. In addition, CWT with the aid of Mexican hat as a mother wavelet has been employed to extract high-frequency information of signals and detect fault occurrence and CT saturation in each phase. As a result, the proposed technique is able to prevent unwanted trip due to CT saturation during external faults. Nevertheless, simulation results confirm sensitivity and security of the proposed protection technique in facing with second internal fault of cross-country faults after a short delay.

The Effect of Harmonic Distortion on the Performance of Differential Relay for Distribution Transformer Protection

This paper aims to analyzing and probing the influences of power system harmonics on a differential relay used for distribution transformer protection. The increased use of nonlinear devices in industry, commercial and residential areas can lead to a significant increase the level of harmonic distortion in the power system. This harmonic has the significant effects to the differential protection systems components such as current transformer (CT) and relay. The CT tends to saturate due to the presence of current harmonics in power system, so it will produce magnitude secondary current error and make the differential relay to miss operations. The harmonic distortion effects on the differential protection have been investigated through laboratory test. To determine the CT errors when operates under harmonic condition, the CT has been test with certain level of THDi. The result of this testing was found that with increasing of the THDi, the magnitude of secondary current error increased and differential relay will operate at no fault conditions.

IP系汎用・標準技術を用いた広域系統監視・保護制御システムの開発と検証

This paper proposes a network system architecture for next-generation wide-area monitoring, protection and control (WAMPAC) of power systems, featuring a wide-area Ethernet (L2-network) and time synchronization such as IEEE 1588 and other schemes associated with decentralized modular devices. Based on the architecture, a prototype WAMPAC system has been constructed and installed in an analog power system simulator to examine its communication performance, including time synchronism and show the validity of an actual application, wide-area integrated primary and backup protection with a current differential scheme. Fundamental analyses with respect to end-to-end transmission delay, system unavailability and scalability for double redundant current differential line protection systems with 4-repeater/5-span communication links were conducted to examine its applicability to an actual power system.

Protection relay of phase-shifting device with thyristor switch for high voltage power transmission lines

Problems of functioning of differential current protection systems of phase shifting devices (PSD) with mechanically changed coefficient of transformation of shunt transformer are analyzed. Requirements for devices of protection of PSD with thyristor switch are formulated. Based on use of nonlinear models of series-wound and shunt transformers of PSD modes of operation of major protection during PSD, switching to zero load operation and to operation under load and during short circuit operation were studied for testing PSD with failures. Use of the principle of duplicating by devices of differential current protection (with realization of functions of breaking) of failures of separate pares of PSD with thyristor switch was substantiated. To ensure protection sensitivity to the shunt transformer winding short circuit, in particular, to a short circuit that is not implemented in the current differential protection for PSD with mechanical switch, the differential current protection reacting to the amount of primary ampere-turns of high-voltage and low-voltage winding of this transformer was designed. Studies have shown that the use of differential current cutoff instead of overcurrent protection for the shunt transformer wndings allows one to provide the sensitivity during thyristor failure with the formation of a short circuit. The results of simulation mode for the PSD with switch thyristor designed to be installed as switching point of Voskhod-Tatarskaya-Barabinsk 220 kV transmission line point out the efficiency of the developed solutions that ensure reliable functioning of the PSD.

Line Differential Protection Modeling with Composite Current and Voltage Signal Comparison Method

This paper discusses the protection system which is the most important part in a power system. Increased protection system reliability determines to improve the performance of the entire electrical system. Differential scheme denoted a very reliable method to secure the protection zone. There have been some studies on this topic. However, still need further study in order to obtain a better system, simple and reliable. The resulting model is made in gradually. Each stage is verified to reduce operational errors. Validation was done using the composite method of current and voltage signals, and the sigma delta algorithm as the analog to digital converter. Numerous computing were done to simulate the differential protection system on the underground cable transmission line 420 kV along the 58.5 km, using Matlab / Simulink. The results showed that the proposed method is effective enough to minimize the percentage of errors.

Line Differential Protection Modeling with Composite Current and Voltage Signal Comparison Method

This paper discusses the protection system which is the most important part in a power system. Increased protection system reliability determines to improve the performance of the entire electrical system. Differential scheme denoted a very reliable method to secure the protection zone. There have been some studies on this topic. However, still need further study in order to obtain a better system, simple and reliable. The resulting model is made in gradually. Each stage is verified to reduce operational errors. Validation was done using the composite method of current and voltage signals, and the sigma delta algorithm as the analog to digital converter. Numerous computing were done to simulate the differential protection system on the underground cable transmission line 420 kV along the 58.5 km, using Matlab / Simulink. The results showed that the proposed method is effective enough to minimize the percentage of errors.

Innovative Differential Protection of Power Transformers Using Low-Energy Current Sensors

Traditional differential protection systems are applied on large power transformers using current transformers (CTs). However, because of high secondary currents (often exceeding 100 kARMS), differential protection systems for electric arc furnace transformers have not been applied in the past due to the lack of commercially available CTs. This paper will present differential protection systems that have been in use for many years using Rogowski coil current sensors. These protection systems use high-precision printed circuit board Rogowski coil current sensors. This paper reviews the characteristics, designs, and application of these Rogowski coil sensors for advanced protection, control, and metering systems with new multifunction relays. This paper compares performance characteristics of new solutions based on Rogowski coil sensors with the conventional differential protection systems based on CTs, demonstrating that the new systems do not have the limitations of conventional technology. Operating experience from several site applications is included.

Adaptive Agent-Based Wide-Area Current Differential Protection System

This paper proposes a multiagent-based adaptive wide-area current differential protection system. A power grid is divided into primary and backup protection zones dynamically online with the help of a developed expert system, and the relay agents of these zones cooperate to perform a differential relaying function. Predictive self-healing strategies have been proposed to prevent misoperation of the relay agent, and the communication system has been simulated. The performance of the proposed adaptive wide-area current differential protection system based on computer simulation is presented in this paper.

Redes neurais aplicadas a relés diferenciais para transformadores de potência

Este trabalho apresenta um sistema completo de proteção diferencial para transformadores de potência, através da teoria de Redes Neurais Artificiais (RNAs). O método proposto trata a classificação do sistema de proteção como um problema de reconhecimento de padrões e constitui um método alternativo aos algoritmos convencionais. Muitos fatores, tais como a energização do transformador e a saturação dos TCs, podem causar uma operação inadequada do relé de proteção. Um sistema de proteção completo foi desenvolvido, incluindo um módulo baseado em RNA em substituição aos filtros harmônicos, usados no algoritmo convencional. Este módulo se constituiu de uma RNA tipo MLP Backpropagation para a classificação de sinais. Abordagens baseadas na reconstrução dos sinais distorcidos causados pela saturação dos TCs são também propostas. Essa análise foi realizada através do emprego de RNAs Recorrentes de Elman, utilizadas para reconstruir os sinais distorcidos pela saturação dos TCs. Essas rotinas foram adicionadas ao algoritmo final de proteção. O desempenho dos algoritmos propostos foi comparado ao do algoritmo convencional de proteção de transformadores, em termos de velocidade e precisão de resposta. Com a utilização de uma ferramenta de inteligência artificial em um algoritmo completo de proteção de transformadores, uma solução precisa, rápida e eficiente foi obtida, se comparada aos métodos convencionais.

A Wide Area Differential Backup Protection Scheme For Shipboard Application

A new wide area differential protection (WADP) system is proposed to suit the need of the shipboard application where short cables make conventional backup schemes impractical. The close proximity of all the components in a shipboard power system makes communication less of an issue than in a land-based system. With an overall view of the protected system and by use of a differential search algorithm, a minimum fault isolation area is decided. A built-in confirmation mechanism avoids unnecessary or false tripping due to protection component failure. The principle of the WADP system is described in detail in this paper. Simulation results are shown for a small Shipboard Power System (SPS).

A Wireless Differential Protection System for Air-Core Inductors

This paper describes a new wireless differential protection system for detection of turn-to-turn faults in air-core inductors. The proposed system is composed of a pair of floating magnetic field sensors placed at opposite ends of an air-core inductor, which wirelessly communicate their measurements to a remote receiver. The receiver compares the magnetic field measurements from the sensors and triggers an alarm or circuit interruption system if the mean-squared field difference exceeds a specified threshold. The main contributions of this paper are a description of a specific realization of this differential air-core inductor protection system with several novel features and experimental results that demonstrate the sensitivity and latency of the proposed protection system. Our results suggest that deployment of the proposed system in shunt-connected inductors could help to prevent catastrophic damage resulting from turn-to-turn faults by detecting and arresting these faults in their incipient stages.

Modified Differential Ground Fault Protection for Systems Having Multiple Sources and Grounds

This paper discusses the modified differential ground fault protection system, for the purpose of illustrating that 1) such systems are suitable for application on service equipment having multiple sources of electrical power, each of which may have multiple grounds, 2) such systems may be applied using conventional equipment that is currently available from several suppliers, 3) such systems can meet requirements for generator grounding without the use of four-pole transfer switches and switched neutrals, 4) such systems may be analyzed for effectiveness using conventional circuit analysis techniques.

Summary: Comparative performance of amplitude-comparator pilot-wire differential-protection systems

A new relay circuit, applicable to asymmetrical pilot circuits, is described. In the steady state for relays at both ends, the circuit provides identical unit-diameter circular stability areas on the complex plane, centred on (1, 0), and it is suggested that this relay circuit constitutes a preferred characteristic of marginal operation. Certain alternative relay configurations are compared, to ascertain relative susceptibilities to the effects of induced interference voltages and the presence of d.c. components in the relaying quantities derived from the protected system. Homogeneous pilot circuits are assumed for simplicity, and the relay schemes considered include: (i) that referred to above which provides the preferred relay characteristic (ii) that which provides termination of the pilot circuit in characteristic impedance (iii) that which provides compensation for pilot-circuit phase-shift and a self-inverse characteristic.