Intelligent system for detecting "hidden" errors in protection settings

Due to many developments taking place within the electricity supply industry, the network and its operation has grown ever more in recent years, which brings significant challenges for power system protection engineers. Apart from the significant efforts that are required to ensure that the protection setting process is effective, work also needs to be carried out to check the validity of the settings after initial calculation and application. However, solely relying on personnel and procedures to assess the validity of the protection relay setting files may occasionally result in a hidden error (or errors) remaining undetected until an in-service mal-operation event is experienced. This may bring significant consequences, in terms of economic costs, potential safety hazards and damage to the reputation of the utility company. This paper will present the initial research of making use of artificial intelligence technology (expert system) to help protection engineers validate the protection settings. Existing expert systems for protection settings applications will be reviewed and a new intelligent system that can open a setting file and interrogate the protection functions and settings in the file will be introduced. The advantages of this novel intelligent tool over existing protection setting expert systems will be discussed

Backup protection requirements in future low-inertia power systems

The content of this paper will illustrate how, in the future, the power transmission system in Great Britain (GB) may be much "weaker" than it is at present, and will describe the potential impact that this could have on the voltage profiles during faults, and how the operation of backup protection system operation, if required, needs to be considered carefully to ensure system integrity in the future. The potential for future problems associated with generators’, converter-interfaced infeeds’, and HVDC interconnectors’ potential inability to “ride through” during slow/backup protection operations, and the consequent risk of complete system collapse, will also be highlighted. The paper also contains a description of ongoing and future work concerned with investigation of the use of wide-area communications systems, which may already be in existence and used for other purposes, to enhance backup protection performance and possibly offer an alternative and improved solution compared with existing schemes. It is shown how such a system could potentially be "settings-free" and establish and maintain an image of the connectivity of the network from either SCADA data and/or analysing current flows during normal operation. Example results of simulations are included to demonstrate the concept of identifying fault locations and protection failures using measured voltages from phasor measurement units (PMUs). This may act as a foundation for a future backup protection scheme and this is discussed in the conclusions and future work sections

Traveling wave-based protection scheme for inverter-dominated microgrid using mathematical morphology

Inverter-dominated microgrids impose significant challenges on the distribution network, as inverters are well known for their limited contribution to fault current, undermining the performance of traditional overcurrent protection schemes. This paper introduces a new protection scheme based on the initial current traveling wave utilizing an improved mathematical morphology (MM) technology, with simplified polarity detection and new logics introduced for meshed networks and feeders with single-end measurement. The proposed protection scheme provides ultrafast response and can be adapted to varied system operational modes, topologies, fault conditions, and load conditions. Only low-bandwidth communication is required to achieve high-speed operation and adequate discrimination level in meshed networks. Simulation in PSCAD/EMTDC verifies both the sensitivity and stability of the proposed protection scheme under different microgrid operational scenarios

A novel protection scheme for inverter-dominated microgrid

Protecting an inverter-dominated microgrid is challenging for the traditional overcurrent protection scheme owing to the suppressed fault current from the inverter interfaced DGs (IIDGs). In this paper, a protection scheme based on the Discrete Wavelet Transform is developed in MATLAB/SIMULINK to detect the faults in the microgrid. The input voltage of the proposed scheme is first transformed into dq0 frame using the Park Transform. A filtering system based on the wavelet denoising approach is then implemented to reduce the sampling frequency and reject the switching noise generated by the inverters in the microgrid. The performance of the proposed scheme is evaluated in transient simulation by systematically applying different types of faults, including varied fault positions and impedances. Additionally, a high impedance arcing fault model is implemented to test the proposed protection scheme under nonlinear fault impedance conditions

Assessment of fault location techniques in voltage source converter based HVDC systems

This paper investigates fault location techniques in high voltage direct current (HVDC) transmission networks utilizing voltage source converters (VSCs). The subject has been extensively researched due to the fault locating actions associated with the supply restoration and the economic loss, and also because of the trending employment of VSC-HVDC transmission systems. However, the fast operation of HVDC protection has made fault localization more challenging as limited measurement data can be extracted. By broadly researching the existing fault locating approaches in such systems, a comprehensive literature review is presented. Then, two selected methods, active impedance method and travelling wave method (using Continuous Wavelet Transformation) are tested. These fault location techniques together with the power system models have been developed using Matlab/Simulink. The results are summarized and systematic comparative analysis of the two fault location techniques is performed

A model-based approach for automatic validation of protection settings

The reliable operation of protection systems depends on the correct setting of protective devices. Due to the increasing network complexity and the large number of protective devices (and their associated setting parameters), it is extremely laborious for engineers to manually validate the settings. Existing model-based (MB) systems that are capable of performing the validation task require significant manual input for network models creation, relay models configuration, simulation result analysis, etc., which is both time consuming and subject to human errors. This paper presents a methodology that adopts the principle of model-based reasoning (MBR) for automated validation of protection settings. Such a methodology is demonstrated through the design and implementation of a prototype tool Model-Based protection setting Smart Tool (MBST), which is capable of automatically populating network models, configuring relay models with settings to be validated, creating credible system events, and simulating the relays’ behaviour under these events. The automated process is achieved by an interface layer within MBST that allows interaction with a commercially available simulation engine to leverage its internal data and functions for the settings validation task. The simulated results are automatically analysed using a rule-based (RB) approach. The key advantage of the work is the mechanism to automate the entire settings validation process. The design of the interface layer to interact with existing simulation engine and models also demonstrates a solution for rapid prototyping of intelligent systems dedicated to validation of protection settings

Performance analysis of the overcurrent protection for the renewable distributed generation dominated microgrids

This paper aims to present a study of the conventional protection scheme i.e. overcurrent (OC) protection’s malfunctioning in the microgrids dominated by inverter interfaced distributed generator (IIDG) under a range of scenarios by injecting faults at different locations of the network. Due to low cost and inherent back-up protection, overcurrent scheme is considered to be the main protection for the distribution networks and microgrids. However, the integration of IIDG in large number might introduce several protection challenges for microgrids. Existing literature discusses the protection issues that might arise in microgrids due to addition of distributed generation, but those challenges are not practically studied. Hence, in this paper, several fault cases are simulated by changing fault positions and using different combinations of IIDGs in the network so that protection challenges can be fully explored and performance of the overcurrent relays in the IIDG dominated microgrids can be analysed under those simulated cases

Intelligent fault location in MTDC networks by recognising patterns in hybrid circuit breaker currents during fault clearance process

In this paper, a novel, learning-based method for accurate location of faults in MTDC networks is proposed. By assessing the DC circuit breaker currents during the fault clearance process, a pattern recognition approach is adopted from which the fault location is estimated. The implementation of the algorithm is allocated into three main stages, where similarity coefficients and weighted averaging functions (incorporating exponential kernels) are utilized. For the proposed algorithm, only a short-time window of data (equal to 6 ms) is required. The performance of the proposed method is assessed through detailed transient simulation using verified MATLAB/Simulink models. Training patterns have been retrieved by applying a series of different faults within an MTDC network. Simulation and experimental results revealed that the proposed scheme i) can reliably determine the type of fault ii) can accurately estimate the fault location (including the cases of highly resistive faults) and iii) is practically feasible

The case for redefinition of frequency and ROCOF to account for AC power system phase steps

All conventional techniques for measuring frequency result in large deviations to the perceived or calculated frequency when the AC waveform undergoes a phase step. The deviation magnitude and duration are dependent on the phase step magnitude, and the applied windowing/filtering. Such phase steps do occur in the power system, and the erroneous frequency calculation can result in inappropriate reactions by some rapidly-responding control and protection systems. If the frequency measurand is further differentiated to ROCOF (Rate of Change of Frequency), the excursion magnitudes can become far larger than any normally expected values of ROCOF. This paper discusses the meaning of the terms frequency and ROCOF, and presents a modified concept of frequency and ROCOF. This is done by allowing rapid phase steps to be disaggregated from frequency in the AC waveform model equation. This allows new measurands “underlying frequency”, and “underlying ROCOF” to be defined, as a pair of linked parameters, independent from a separate dynamic phase parameter. These new measurands have the potential to offer much more useful and stable information to be sent to fast-acting control and protection systems, than the existing measurands of AC frequency and ROCOF, particularly during fault events and large switching or disconnection events

Novel fault location in MTDC grids with non-homogeneous transmission lines utilizing distributed current sensing technology

This paper presents a new method for locating faults in multi-terminal direct current (MTDC) networks incorporating hybrid transmission media (HTMs), including segments of underground cables (UGCs) and overhead lines (OHLs). The proposed travelling wave (TW) type method uses continuous wavelet transform (CWT) applied to a series of line current measurements obtained from a network of distributed optical sensors. The technical feasibility of optically-based DC current measurement is evaluated through laboratory experiments using Fiber-Bragg Grating (FBG) sensors and other commercially available equipment. Simulation-based analysis has been used to assess the proposed technique under a variety of fault types and locations within an MTDC network. The proposed fault location scheme has been found to successfully identify the faulted segment of the transmission media as well as accurately estimating the fault position within the faulted segment. Systematic evaluation of the method is presented considering a wide range of fault resistances, mother wavelets, scaling factors and noisy inputs. Additionally, the principle of the proposed fault location scheme has been practically validated by applying a series of laboratory test sets