An open platform for rapid-prototyping protection and control schemes with IEC 61850

Communications is becoming increasingly important to the operation of protection and control schemes. Although offering many benefits, using standards-based communications, particularly IEC 61850, in the course of the research and development of novel schemes can be complex. This paper describes an open-source platform which enables the rapid prototyping of communications-enhanced schemes. The platform automatically generates the data model and communications code required for an intelligent electronic device to implement a publisher-subscriber generic object-oriented substation event and sampled-value messaging. The generated code is tailored to a particular system configuration description (SCD) file, and is therefore extremely efficient at runtime. It is shown here how a model-centric tool, such as the open-source Eclipse Modeling Framework, can be used to manage the complexity of the IEC 61850 standard, by providing a framework for validating SCD files and by automating parts of the code generation process. The flexibility and convenience of the platform are demonstrated through a prototype of a real-time, fast-acting load-shedding scheme for a low-voltage microgrid network. The platform is the first open-source implementation of IEC 61850 which is suitable for real-time applications, such as protection, and is therefore readily available for research and education

Peak-ratio analysis method for enhancement of LOM protection using M class PMUs

A novel technique for loss of mains (LOM) detection, using Phasor Measurement Unit (PMU) data, is described in this paper. The technique, known as the Peak Ratio Analysis Method (PRAM), improves both sensitivity and stability of LOM protection when compared to prevailing techniques. The technique is based on a Rate of Change of Frequency (ROCOF) measurement from M-class PMUs, but the key novelty of the method lies in the fact that it employs a new “peak-ratio” analysis of the measured ROCOF waveform during any frequency disturbance to determine whether the potentially-islanded element of the network is grid connected or not. The proposed technique is described and several examples of its operation are compared with three competing LOM protection methods that have all been widely used by industry and/or reported in the literature: standard ROCOF, Phase Offset Relay (POR) and Phase Angle Difference (PAD) methods. It is shown that the PRAM technique exhibits comparable performance to the others, and in many cases improves upon their abilities, in particular for systems where the inertia of the main power system is reduced, which may arise in future systems with increased penetrations of renewable generation and HVDC infeed

Application of MPLS-TP for transporting power system protection data

Power utilities are increasingly dependent on the use of communications networks. These networks are evolving to be packet-based, rather than using conventional Time-Division Multiplexing (TDM) technologies. Transporting current differential protection traffic over a packet network is especially challenging, due to the safety-critical nature of protection, the strict requirements for low delay and low asymmetrical delay, and the extensive use of legacy TDM-based protocols. This paper highlights the key technical characteristics of Multi-Protocol Label Switching-Transport Profile (MPLS-TP), and demonstrates its application for transporting current differential protection traffic. A real-time hardware-in-the-loop testing approach has been used to thoroughly validate the technologies in various configurations. It is demonstrated that MPLS-TP technologies can meet the requirements of current differential protection and other, less critical applications. In particular, it is shown that delay and asymmetrical delay can be controlled through the inherent use of bi-directional paths---even when “hitless” link redundancy is configured. The importance of appropriate traffic engineering, clocking schemes, circuit emulation methods is also demonstrated

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

Automatically detecting and correcting errors in power quality monitoring data

Dependable power quality (PQ) monitoring is crucial for evaluating the impact of smart grid developments. Monitoring schemes may need to cover a relatively large network area, yet must be conducted in a cost-effective manner. Real-time communications may not be available to observe the status of a monitoring scheme or to provide time synchronization, and therefore undetected errors may be present in the data collected. This paper describes a process for automatically detecting and correcting errors in PQ monitoring data, which has been applied in an actual smart grid project. It is demonstrated how to: unambiguously recover from various device installation errors; enforce time synchronization between multiple monitoring devices and other events by correlation of measured frequency trends; and efficiently visualize PQ data without causing visual distortion, even when some data values are missing. This process is designed to be applied retrospectively to maximize the useful data obtained from a network PQ monitoring scheme, before quantitative analysis is performed. This work therefore ensures that insights gained from the analysis of the data - and subsequent network operation or planning decisions - are also valid. A case study of a UK smart grid project, involving wide-scale distribution system PQ monitoring, demonstrates the effectiveness of these contributions. All source code used for the paper is available for reuse

Modelling and analysis of asymmetrical latency in packet-based networks for current differential protection application

Current differential protection typically requires symmetrical communications channels—with equal latency in each direction—for correct operation. Conventionally, this has been delivered using protocols such as IEEE C37.94 over a Time-Division Multiplexing (TDM) wide-area network (WAN). Modern packet-based WANs offer improvements in efficiency, flexibility, and cost-effectiveness for utility applications. However, jitter is unavoidable in packet-based networks and, in extreme cases, jitter inevitably results in substantial asymmetrical latency in communications paths. This paper clearly defines how a new source of asymmetry arises due to the use of "de-jitter" buffers, which can jeopardize critical protection services. This is demonstrated using an analytical modelling approach, which precisely quantifies the degree of risk, and through real-time demonstration with actual devices, involving current differential protection over an IP/MPLS WAN. Using a novel method of real-time manipulation of Ethernet traffic to emulate large WANs, the modelling approach has been validated. It is shown how the sensitivity of relays to asymmetry depends on the protection settings and the magnitude of the measured load current. To address the risk of protection maloperation, a new approach for compensating for asymmetrical latency has been comprehensively validated. These developments will be of immediate interest to utilities operating, or migrating to, a packet-based infrastructure

Current-only directional protection of distribution networks using low-cost communication

Conventional distribution protection schemes may not be suitable for evolving and future networks due to the rapid increase in distributed energy resources. This paper presents a review of selected novel protection principles for distribution networks and proposes a new and effective protection technique using only current measurements, based upon comparison between pre- and during-fault current phasors. This comparison process only requires low-cost communication systems for intermittent data transmission between measurement points. An overview of potential communication solutions is also contained in the paper. The operation of the method is tested and validated using simulated case studies of different scenarios, which demonstrate that the proposed scheme is highly effective in detecting and isolating faults, thus presenting a promising solution for protection of future active distribution networks

Detailed analysis of the future distribution network protection issues

This study will present the results of several simulation-based analyses investigating the performance of distribution network protection under a range of future scenarios. It is widely accepted that the integration of a significant amount of distributed generation, often from renewable energy sources and interfaced to the main network via power electronics converters, will be commonplace in the future. Furthermore, at the transmission level, the interconnection of different countries through HVDC links and the decommissioning of many large-scale conventional synchronous generators will result in the power systems becoming progressively weaker in terms of reduced faults level and lower system inertia. This study will, therefore, illustrate and emphasise the challenges and issues that arise in future distribution networks protection due to reduced system strength, fault level and the changing nature of the contribution (both in terms of magnitude and possibly delay in provision) to fault levels and the possible impact this may have on traditional overcurrent based protection schemes by building a simple model of distribution network in Simulink, MATLAB. In addition to that, the paper will also discuss some potential solutions as novel schemes to tackle the arising protection related problems

Adaptive distance protection for multi-terminal lines connecting converter-interfaced renewable energy sources

Variation in infeed current challenges the distance relay performance significantly for protection of multi-terminal lines. Underreach issue with such a line configuration becomes more prominent for a relay at the substation when connected to renewable sources, due to generation variability and converter control operation. This may result in an incorrect decision by the distance relay, especially with a fixed zone-1 setting. In this paper an adaptive distance relaying method is proposed for such line configurations. The method obtains the remote end data during pre-fault and calculates the fault distance to derive accurate protection decision. Performance of the proposed method is tested for a three-terminal line using PSCAD/EMTDC. Comparative assessment with conventional distance relaying demonstrates the superiority of the proposed method

Enabling efficient engineering processes and automated analysis for power protection systems

The reliable operation of power networks depends on the correct configuration of protection systems. These systems involve the coordination of devices across a wide area, each with numerous setting parameters. Presently, protection settings data are typically stored in various vendor-specific proprietary formats, which are difficult to access, interchange, and manipulate automatically. Consequently, the engineering processes for implementing modern protection systems are extremely complex, involving multiple software tools from different vendors. This paper presents a novel solution to these challenges, through the use of the data model provided by the IEC 61850 standard, with the System Configuration description Language (SCL) format to represent protection settings data. The design of a Protection Setting data Conversion Tool (PSCT) that can automatically convert existing settings data between proprietary formats and the SCL-based format is presented. A case study of its implementation demonstrates the benefits of the common representation of protection settings for network operators and other stakeholders. The paper also addresses the challenges that network operators face in migrating to the new approach from existing legacy protection devices and data formats. Adoption of these recommendations and design approaches would shift protection systems from being largely single-vendor solutions to becoming efficient and truly open platforms, capable of supporting future intelligent applications and tools such as automated protection settings validation, diagnostics, and system simulation