P and M class phasor measurement unit algorithms using adaptive cascaded filters

The new standard C37.118.1 lays down strict performance limits for phasor measurement units (PMUs) under steady-state and dynamic conditions. Reference algorithms are also presented for the P (performance) and M (measurement) class PMUs. In this paper, the performance of these algorithms is analysed during some key signal scenarios, particularly those of off-nominal frequency, frequency ramps, and harmonic contamination. While it is found that total vector error (TVE) accuracy is relatively easy to achieve, the reference algorithm is not able to achieve a useful ROCOF (rate of change of frequency) accuracy. Instead, this paper presents alternative algorithms for P and M class PMUs which use adaptive filtering techniques in real time at up to 10 kHz sample rates, allowing consistent accuracy to be maintained across a ±33% frequency range. ROCOF errors can be reduced by factors of >40 for P class and >100 for M class devices

Reachability analysis for the verification of adaptive protection setting selection logic

The testing of adaptive protection schemes is a problem that remains largely unaddressed. These schemes can be characterized by uncertainty in behavior due to the dynamic changes in their configuration to suit prevailing network conditions. This paper proposes a novel approach to formalizing this behavior using hybrid systems modeling. This unlocks the ability to verify the safety performance of the schemes using reachability analysis. In this paper, an adaptive setting selection logic for distance protection is verified for its safety, using reachability analysis, during changes in network conditions

Assessing the reliability of adaptive power system protection schemes

Adaptive power system protection can be used to improve the performance of existing protection schemes under certain network conditions. However, their deployment in the field is impeded by their perceived inferior reliability compared to existing protection arrangements. Moreover, their validation can be problematic due to the perceived high likelihood of the occurrence of failure modes or incorrect setting selection with variable network conditions. Reliability (including risk assessment) is one of the decisive measures that can be used in the process of verifying adaptive protection scheme performance. This paper proposes a generic methodology for assessing the reliability of adaptive protection. The method involves the identification of initiating events and scenarios that lead to protection failures and quantification of the probability of the occurrence of each failure. A numerical example of the methodology for an adaptive distance protection scheme is provided

Application of a MW-scale motor-generator set to establish power-hardware-in-the-loop capability

This paper presents a Power-Hardware-in-the-Loop (P-HiL) testbed coupled to a MW-scale Motor-Generator (MG) set. The P-HiL configuration interfaces an 11 kV physical distribution network with a transmission network modeled in a Real Time Digital Simulator (RTDS) through the MG set. Uniquely, and in contrast with other P-HiL arrangements, the MG set used is equipped with a proprietary frequency controller with an inherent response that does not provide the desired characteristics to cater for a P-HiL interface. The paper describes a methodology to tackle this problem associated with undesirable response of the MG set’s existing controller by introducing additional frequency and phase control loops. Experimental results are presented and show that the P-HiL testbed is capable of maintaining a high level of synchronization during disturbances and allows the power interaction between the model and physical network. The testbed offers a realistic and flexible testing environment for prototype systems connected to distribution networks with a specific focus on testing systems that control demand side resources for frequency response during loss of generation events

Switching Markov Gaussian models for dynamic power system inertia estimation

Future power systems could benefit considerably from having a continuous real-time estimate of system inertia. If realized, this could provide reference inputs to proactive control and protection systems which could enhance not only system stability but also operational economics through, for example, more informed ancillary reserve planning using knowledge of prevailing system conditions and stability margins. Performing these predictions in real time is a significant challenge owing to the complex stochastic and temporal relationships between available measurements. This paper proposes a statistical model capable of estimating system inertia in real time through observed steady-state and relatively small frequency variations; it is trained to learn the features that inter-relate steady-state averaged frequency variations and system inertia, using historical system data demonstrated over two consecutive years. The proposed algorithm is formulated as Gaussian Mixture Model with temporal dependence encoded as a Markov chains. Applied within a UK power system scenario, it produces an optimized mean squared error within 0.1s2 for 95% of the daily estimation if being calibrated on a half-hourly basis and maintains robustness through measurement interruptions of up to a period of three hours

International White Book on DER Protection : Review and Testing Procedures

This white book provides an insight into the issues surrounding the impact of increasing levels of DER on the generator and network protection and the resulting necessary improvements in protection testing practices. Particular focus is placed on ever increasing inverter-interfaced DER installations and the challenges of utility network integration. This white book should also serve as a starting point for specifying DER protection testing requirements and procedures. A comprehensive review of international DER protection practices, standards and recommendations is presented. This is accompanied by the identifi cation of the main performance challenges related to these protection schemes under varied network operational conditions and the nature of DER generator and interface technologies. Emphasis is placed on the importance of dynamic testing that can only be delivered through laboratory-based platforms such as real-time simulators, integrated substation automation infrastructure and fl exible, inverter-equipped testing microgrids. To this end, the combination of fl exible network operation and new DER technologies underlines the importance of utilising the laboratory testing facilities available within the DERlab Network of Excellence. This not only informs the shaping of new protection testing and network integration practices by end users but also enables the process of de-risking new DER protection technologies. In order to support the issues discussed in the white paper, a comparative case study between UK and German DER protection and scheme testing practices is presented. This also highlights the level of complexity associated with standardisation and approval mechanisms adopted by different countries

Assessment of low frequency demand disconnection impact on network operability

This paper presents an assessment of Low Frequency Demand Disconnection (LFDD) impact on network operability. One of the issues arising from LFDD relay operation is the disconnection of Distributed Generators (DGs) along with loads during disconnection of large numbers of Extra High Voltage (EHV) substations. This could compromise the effectiveness of LFDD schemes considering the increasing presence of DGs in distribution networks. Another issue is the loss of system earth (i.e. from 132/33 kV substations) from the point of view of connected DGs following LFDD operation that might occur in some areas within distribution grids due to back-feed current from 33/11 kV primary substations. A distribution network model experiencing the above issues has been used in the PowerFactory to simulate a number of operation and fault scenarios. Different types of DGs including Photovoltaic (PV), Battery Energy Storage System (BESS), Wind Generation (WG) and Synchronous Generation (SG) have been modelled. The results provide useful insights on the LFDD schemes impact on network operation with DGs interface protection based on ENA Engineering Recommendation G99 and how the LFDD schemes based on direction of current could influence the frequency response in the network. The results also show that the loss of system earth issue on the studied LFDD scenarios occurs when the network is operating in its minimum loading condition

Facilitating the validation of adaptive power system protection through formal scheme modelling and performance verification

There exists a critical mass in research related to adaptive protection approaches that address some of the shortcomings of conventional protection functions. This is in response to concerns in the reliability of conventional protection which manifested itself in some severe disturbances in more recent years. Despite the fact that adaptive protection offers a compelling technical solution to some of these performance problems, the industry has not widely adopted adaptive protection approaches as a de facto policy for future protection scheme implementations. This is attributed to the difficulties associated with the testing of such schemes where no significant work has been reported yet. Furthermore, the benefits vs. the risks associated with such a protection strategy are not well understood. This is coupled with the conservatism towards radical changes in the way the power system is operated. As such the work reported in this thesis complements the existing body of research in order to address some of the major technical and institutional challenges associated with adopting adaptive protection schemes for future networks, especially those networks that exhibit flexibility in operation to deal with uncertainty in generation and to maximise asset utilisation. These are network characteristics that adaptive protection approaches are seen to be an effective enabler of. This thesis focuses on formal structural and behavioural modelling of adaptive protection schemes as means to effectively validate their functional operation and verify their performance. Novel contributions have been made in formalising a user requirements driven architecture for these schemes. Furthermore, significant contributions have been made to conducting formal algorithm verification that complements inherently limited standard protection scheme validation techniques. The thesis makes thorough use of a proposed adaptive distance protection scheme for circuits with quadrature booster transformers to communicate the challenges, lessons learned and contributions in designing, implementing and testing adaptive protection schemes.There exists a critical mass in research related to adaptive protection approaches that address some of the shortcomings of conventional protection functions. This is in response to concerns in the reliability of conventional protection which manifested itself in some severe disturbances in more recent years. Despite the fact that adaptive protection offers a compelling technical solution to some of these performance problems, the industry has not widely adopted adaptive protection approaches as a de facto policy for future protection scheme implementations. This is attributed to the difficulties associated with the testing of such schemes where no significant work has been reported yet. Furthermore, the benefits vs. the risks associated with such a protection strategy are not well understood. This is coupled with the conservatism towards radical changes in the way the power system is operated. As such the work reported in this thesis complements the existing body of research in order to address some of the major technical and institutional challenges associated with adopting adaptive protection schemes for future networks, especially those networks that exhibit flexibility in operation to deal with uncertainty in generation and to maximise asset utilisation. These are network characteristics that adaptive protection approaches are seen to be an effective enabler of. This thesis focuses on formal structural and behavioural modelling of adaptive protection schemes as means to effectively validate their functional operation and verify their performance. Novel contributions have been made in formalising a user requirements driven architecture for these schemes. Furthermore, significant contributions have been made to conducting formal algorithm verification that complements inherently limited standard protection scheme validation techniques. The thesis makes thorough use of a proposed adaptive distance protection scheme for circuits with quadrature booster transformers to communicate the challenges, lessons learned and contributions in designing, implementing and testing adaptive protection schemes

Facilitating the Validation of Adaptive Power System Protection through Formal Scheme Modelling and Performance Verification

There exists a critical mass in research related to adaptive protection approaches that address some of the shortcomings of conventional protection functions. This is in response to concerns in the reliability of conventional protection which manifested itself in some severe disturbances in more recent years. Despite the fact that adaptive protection offers a compelling technical solution to some of these performance problems, the industry has not widely adopted adaptive protection approaches as a de facto policy for future protection scheme implementations. This is attributed to the difficulties associated with the testing of such schemes where no significant work has been reported yet. Furthermore, the benefits vs. the risks associated with such a protection strategy are not well understood. This is coupled with the conservatism towards radical changes in the way the power system is operated. As such the work reported in this thesis complements the existing body of research in order to address some of the major technical and institutional challenges associated with adopting adaptive protection schemes for future networks, especially those networks that exhibit flexibility in operation to deal with uncertainty in generation and to maximise asset utilisation. These are network characteristics that adaptive protection approaches are seen to be an effective enabler of. This thesis focuses on formal structural and behavioural modelling of adaptive protection schemes as means to effectively validate their functional operation and verify their performance. Novel contributions have been made in formalising a user requirements driven architecture for these schemes. Furthermore, significant contributions have been made to conducting formal algorithm verification that complements inherently limited standard protection scheme validation techniques. The thesis makes thorough use of a proposed adaptive distance protection scheme for circuits with quadrature booster transformers to communicate the challenges, lessons learned and contributions in designing, implementing and testing adaptive protection schemes

Lessons Learned from Deployed Smart Grid Protection and Control Strategies

This paper is a precursor to a number of HubNet position papers identifying research challenges and directions associated with developing a UK smart grid blueprint that effectively integrates smart control and protection functions with the aid of a robust communications infrastructure