Unit Protection Scheme Research Articles

A New Unit Protection Scheme Applied to Transmission Lines

A New Unit Protection Scheme Applied to Transmission Lines

Fault Current Improved Grey Slope Relational Analysis Based Unit Protection Scheme for DC Distribution Lines

Fault Current Improved Grey Slope Relational Analysis Based Unit Protection Scheme for DC Distribution Lines

Time-Domain Techniques for Line Protection Using Three-Dimensional Cartesian Coordinates

Today high speed protection of power system elements is necessary and realizable. This paper introduces time-domain protection techniques for transmission lines using voltage and current signals in Cartesian coordinates. Three techniques are proposed using this approach for line protection. Direction of fault is obtained using change in angle between Cartesian planes of voltage and current. In the second application on unit protection scheme, internal and external faults in transmission lines are discriminated using dot product of the normals to both end current planes. Fault type identification is obtained using the angle between incremental changes in currents in Cartesian coordinates. The output of each protection function using the new concept is derived in a quarter-cycle. The performance of each of the proposed techniques is tested for load variation, high resistance fault, different fault types, power swing, fault inception angles and signal with noise. Further, the proposed techniques are evaluated using field data from a 400 kV double circuit line.

Unit Protection of Tapped Line DC Microgrid

DC microgrids are attractive options for being more efficient and less complex than ac microgrids. Several protection methods exist for ring main and radial dc microgrid architecture, but the development of protection techniques for tapped line-based dc microgrids is still in the beginning stage. Usually, the loads and distributed energy resources (DERs) are tapped at any section of the line in the microgrid. When there is no communication link from the tapped line to any bus in the microgrid, the existing unit protection schemes fail to identify the fault in the tapped line-based medium-voltage direct current (MVDC) microgrid. In that case, the existing unit protection scheme fails to identify the fault in the tapped line-based MVDC microgrid. Therefore, this article proposes a new unit protection scheme for the tapped line MVDC system based on the superimposed resistance. The proposed method identifies the tapping status using the prefault current data. The technique is robust during load changes and power generation variation at the tapping station. The proposed scheme is validated using a two-bus tapped dc microgrid for distinct fault scenarios like high-resistance fault, varying fault location, and different modes of distributed generation operation under MATLAB/Simulink environment. Also, the performance of the proposed scheme is verified on a lab-implemented dc microgrid hardware bed and tested for different types of fault scenarios.

A communication-free active unit protection scheme for inverter dominated islanded microgrids

Large-scale integration of different renewable energy resources introduces significant challenges to the protection of microgrids (particularly those that may operate in islanded mode), including variable and low fault levels, difficulty in operation of main and backup protection with their coordination, and bidirectional power flow during faults. As a solution to such challenges, this paper presents a novel active protection strategy for the inverter dominated islanded microgrids that coordinates protection actions with the inverter control strategy. The proposed scheme dictates specific actions from the inverter interfaced distributed generator (IIDG) controller to inject specific harmonic components into the microgrid during the fault. Relays throughout the network detect and analyse the injected harmonic components to identify the faulted section, and take appropriate isolating actions, without any requirement for relay-to-relay communication. The scheme achieves selectivity and coordination using definite time delay settings. To verify the performance of the scheme, a realistic microgrid model incorporating the proposed protection strategy has been developed in MATLAB Simulink, where a wide range of fault scenarios have been simulated with variations in fault location, type, fault resistance, line impedance, and different combinations of IIDGs (including with and without connection of a synchronous generator). Additionally, case studies using a real-time digital simulator (RTDS) platform have also been conducted to validate the performance of the proposed solution in real-time, with multiple relays implemented as hardware prototypes running on the OPAL-RT platform — thereby demonstrating the system operation in a hardware-in-the-loop (HiL) configuration. It is shown that the scheme is highly effective in detecting and isolating faults, with proper discrimination, stability and provision of backup, under all investigated scenarios.

Analysis of 3 kV DC Contact Line High-Speed Circuit Breaker Unit Protection Scheme Limitations

The High-Speed Circuit Breaker (HSCB) is a de-facto electro-mechanical contact line protection device employed in the 3 kV DC traction power supply system. The breakers installed at the terminal ends of the contact line make a unit protection scheme configuration. While the HSCBs seem to trip under fault conditions, there is an unknown source that keeps on supplying residual current into the faults. This necessitates some explanation of the source of energy of the continual flow of residual energy. This paper makes an analysis of the limitations in the HSCB unit protection scheme using MATLAB simulation and how the scheme can be optimized with digital protection devices augmented with a peer-to-peer transfer trip as an end-to-end protection solution.

Identification of fault and section identification in multi-terminal HVDC system using unit protection scheme

Identification of fault and section identification in multi-terminal HVDC system using unit protection scheme

A pilot-based unit protection scheme for meshed microgrids using apparent resistance estimation

Microgrids (MGs) are very attractive for electrical power generation/consumption owing to increased reliability and resiliency, however, protection against different short-circuit faults is a major challenge in implementation. This paper proposes a simple algorithm for on-line estimation of apparent resistance per-phase of a three-phase ac power line. The idea is to compare the estimated apparent resistance with the real resistance per-phase of the power line. Then, any reasonable difference between the two resistances will indicate a short-circuit fault occurrence along the line; hence, the line has to be tripped immediately. This pilot-based unit protection scheme presents salient advantages when applied to protect the power lines in the meshed MGs. Effectiveness of the proposed protection scheme is verified by simulation in the MATLAB/SIMULINK environment using a test MG with inverter-based distributed generations. The results confirm reasonable performance of the protection scheme for the meshed MGs with various topologies under both the grid-connected and islanded modes of operation and with different faults including the symmetrical/asymmetrical short-circuit faults, high impedance short-circuit faults, and close-in-internal short-circuit faults.

Decentralized Plug-and-Play Protection Scheme for Low Voltage DC Grids

Since the voltages and currents in dc grids do not have a natural zero-crossing, the protection of these grids is more challenging than the protection of conventional ac grids. Literature presents several unit and non-unit protection schemes that rely on communication, or knowledge about the system’s topology and parameters in order to achieve selective protection in these grids. However, communication complicates fast fault detection and interruption, and a system’s parameters are subject to uncertainty and change. This paper demonstrates that, in low voltage dc grids, faults propagate fast through the grid and interrupted inductive currents commutate to non-faulted sections of the grid, which both can cause circuit breakers in non-faulted sections to trip. A decentralized plug-and-play protection scheme is proposed that ensures selectivity via an augmented solid-state circuit breaker topology and by utilizing the proposed time-current characteristic. It is experimentally shown that the proposed scheme provides secure and selective fault interruption for radial and meshed low voltage dc grids under various conditions.

Hybrid Signal Processing and Machine Learning Algorithm for Adaptive Fault Classification of Wind Farm Integrated Transmission Line Protection

The technological advancement in integration of Renewable Green Energy Sources (RGES) like Wind Farm Generators (WFG), and Photovoltaic (PV) system into conventional power system as a future solution to meet the increase in global energy demands in order to reduce the cost of power generation, and improve on the climate change impact. This innovation also introduces challenges in the power system protection by it being compromised due to injected fault current infeeds on existing facilities. These infeed lead to the undesired trip of a healthy section of the line, and protection system failure. This paper presents a soft computational approach to adaptive fault classification model on High Voltage Transmission Line (HVTL) with and without RGES-WFG integration topologies, using extracted one-cycle fault signature of voltage and current signals with wavelet statistical approach in Matlab. The results are unique signatures across all fault types and fault distances with distinct entropy energy values on proposed network architecture. The supervised machine learning algorithm from Bayesian network classified 99.15 % faults correctly with the operation time of 0.01 s to produced best-generalized model with an RMS error value of 0.05 for single line-to-ground (SLG) fault identification and classification. Best suitable for adaptive unit protection scheme integration.

DC Ring Bus Microgrid Protection Using the Oscillation Frequency and Transient Power

A fast and accurate protection scheme for a dc microgrid enhances the service reliability and improves the power quality. A fault in any section of a dc microgrid results in oscillation in current, where its frequency is a function of fault position. The frequency and associated transient power of the first cycle of the oscillation are used for fault detection and faulted section identification, respectively. Based on the inverse-time transient power, a relay coordination scheme is proposed for the faulted section isolation in a dc ring bus microgrid. The maloperation of a relay due to the communication failure in the unit protection scheme can be averted by applying the proposed method using local data. The performance of the method is tested using data obtained from PSCAD/EMTDC simulations for numerous cases including bidirectional power flow situation, high fault resistance, and different fault types. The proposed algorithm is also validated on a scaled-down hardware setup in the laboratory.

A Superimposed Current Based Unit Protection Scheme for DC Microgrid

With enhanced processing capacity and communication infrastructure available in smart grid platform, unit protection scheme is a promising technique. High resistance fault is a problem with current differential and current direction based unit protection solutions. In this letter, a protection scheme capable of fast fault detection and reliable selectivity for DC microgrid is proposed. The method uses superimposed currents of both ends of a line segment presented on Δi-plane during fault to derive protection decision. Using PSCAD/EMTDC simulations, performance of the proposed method is evaluated, compared and found to be accurate.

Distributed Photonic Instrumentation for Power System Protection and Control

We report on recent developments in hybrid optical protection schemes that make use of passive fiber Bragg grating-based transducers for the distributed measurement of voltage and current. In addition to the details of the hybrid optical sensor technology, and its full integration with a commercial busbar protection relay, we report on the first-time laboratory demonstration of a centralized three-ended unit protection scheme featuring hybrid optical sensors capable of passive and wide-area coverage. Furthermore, we discuss the impact of this technology on present and future protection applications that may be improved or enabled by the proposed scheme.

Protection Planning and System Design to Reduce Arc-Flash Incident Energy in a Multi-Voltage-Level Distribution System to 8 $\hbox{cal}/\hbox{cm}^{2}$ (HRC 2) or Less—Part II: Analysis

This paper demonstrates that, in a multi-voltage-level (medium and low voltages) distribution system, the incident energy can be reduced to 8 cal/cm2 (hazard risk category 2) or even less, so that a personal protective equipment outfit of greater than two is not required. This is achieved with the current state-of-the-art equipment and protective devices. It is recognized that, in the existing distribution systems, not specifically designed with this objective, it may not be possible to reduce the arc-Flash hazard to this low level, unless major changes in the system design and protection are made. A typical industrial distribution system is analyzed, and tables and time-coordination plots are provided to support the analysis. Unit protection schemes and practical guidelines for arc-Flash reduction are provided. The methodology of IEEE 1584 is used for the analyses. Reducing HRC also reduces the fault damage to the equipment.

Modelling and Analysis of a Unit Protection Scheme

This paper presents the modelling and analysis of unit protection of feeders. The protection system module is linked to the primary power system module in such a way that it acts as a feedback loop. The primary power system module provides the three-phase voltages and/or currents at the transducer locations. The protection system module then processes this data, and outputs a circuit breaker status, which can then be feedback to the primary power system module. The paper also describes the operating principles of the protection unit. Finally, practical applications of the model under fault conditions are examined.

The impact of large steel mill loads on power generating units

Large steel mills can be potentially harsh loads on an electric power system, producing harmonic currents and unbalanced system loading. Since these large loads are typically supplied from the EHV power system grid, it must be recognized that not only will the system of the host utility be impacted, but neighboring utility systems could be impacted as well. Existing IEEE Standard 519-1992, IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems, does not fully address the interharmonic problems generated by steel mill loads. This paper identifies the limits of existing unit protection schemes to detect the potentially damaging impacts which large mill loads can have on nearby power generating units. Preoperational studies are needed to assess the impact of the mill on the power system, followed by field tests to verify the study results. Potential mitigation schemes to protect generating units are identified. Issues are discussed from both a utility and mill perspective. Additionally, the paper provides information needed by both the utility protection engineer and the mill's operators during initial planning discussions prior to operation.

A novel non-unit protection for series compensated EHV transmission lines based on fault generated high frequency voltage signals

A new high-speed protection technique based on fault generated high frequency (HF) voltage signals is developed and applied to the protection of EHV series compensated power transmission lines. It is a nonunit protection technique as it relies totally on locally derived information, but it has the discriminative properties normally associated with unit protection schemes. The protection scheme has been designed using CAD techniques including emulation of analogue interfaces and hardware. It is shown that the new relay scheme is able to overcome many difficult protection problems encountered on such EHV power lines using conventional methods, and discriminates clearly between internal and external faults, producing a fast trip output.

Computer-aided design of a new nonunit protection scheme for EHV teed circuits

The paper describes a new technique for protecting EHV teed transmission lines that is based on nonunit principles but exhibits the properties of a unit protection scheme. Fault generated high frequency (HF) signals are extracted from the coupling capacitor of a conventional capacitor voltage transformer (CVT) with a specially designed measurement circuit. Power line carrier line traps are used to confine the HF signals to the protected zone and their bandstop characteristics are used as a basis for discriminating between internal and external faults. A digital signal processing unit is used to process the signals and produce a trip output. Some simulated results are presented to show the ability of the scheme to rapidly detect faults on different teed circuits under a variety of system and fault conditions encountered in practice.

Method of using data from computer simulations to test protection equipment

The paper describes a computer-aided protection evaluation equipment which has been developed primarily to investigate protective relay performance during the period immediately following fault inception. Modern mathematical techniques allow the transient behaviour of a power system to be determined and the equipment described permits this calculated information to be used to evaluate relay performance. The equipment comprises two main elements—a simulation executed on a computer and a means of using the simulation to test protective relays. Novel techniques are described for removing sampling effects from the analogue signals, for small signal modelling of transducers and for the evaluation of unit protection schemes by the simultaneous application of currents and voltages from two points on a power system. Both the hardware and operating software are detailed and information is given concerning the computer simulation of the power system.