Merging Unit Research Articles

Backup subscription scheme for differential protection using IEC61850-9-2 sampled values

In IEC-61850-based digital substations, the protection IED’s performance is dependent on merging unit’s vendor implementation, communication networks, and measurement circuit’s health conditions. As the process bus Sampled Value(SV) enables the availability of all sensor data on a communication network, this paper proposes a Backup Subscription scheme (BSS) for a transformer differential protection (87T, PDIF) function. BSS utilizes sensor data in digital substations to achieve a flexible protection scheme using a dynamic subscription feature. Thus, in case of failure of one sensor, differential protection would be maintained. The paper presents the implementation and verification of a prototyped scheme using a Hardware-in-the-loop simulation test bed. The main result is that BSS integration into differential protection ensures its dependability and security. Moreover, delay compensation and seamless switching feature increases the availability of differential protection.

Research on the Technology of Improving the Compatibility of DC Measurement Devices Based on the Operation Experience of Siemens Hardware Solutions

The aim of this study was to manufacture alternative Siemens DC measurement system equipment to solve the problems of increased failure rates of foreign DC measurement equipment and the stopped production of key parts. In this paper, the overall structure and common faults of the Siemens DC measurement system are introduced, the difference between TDM signal frame structure and FT3 frame structure is detailed, and the related functional structure, chip type, and function of the Siemens distal module and merging unit (including laser function) are studied. The remote module, merging unit (including laser function), and related hardware design and software design to replace the Siemens DC measurement system were developed, and the test environment and control protection, fault recording wave for communication, and other functional tests were built. The test results show that the domestic remote module, merging unit (laser function), and other technologies communicate normally with the existing Siemens and the domestic mainstream manufacturers, and the accuracy meets the requirements of the 0.2 level.

A review of current practice in the design and analysis of extremely small stepped-wedge cluster randomized trials.

Stepped-wedge cluster randomized trials tend to require fewer clusters than standard parallel-arm designs due to the switches between control and intervention conditions, but there are no recommendations for the minimum number of clusters. Trials randomizing an extremely small number of clusters are not uncommon, but the justification for small numbers of clusters is often unclear and appropriate analysis is often lacking. In addition, stepped-wedge cluster randomized trials are methodologically more complex due to their longitudinal correlation structure, and ignoring the distinct within- and between-period intracluster correlations can underestimate the sample size in small stepped-wedge cluster randomized trials. We conducted a review of published small stepped-wedge cluster randomized trials to understand how and why they are used, and to characterize approaches used in their design and analysis. Electronic searches were used to identify primary reports of full-scale stepped-wedge cluster randomized trials published during the period 2016-2022; the subset that randomized two to six clusters was identified. Two reviewers independently extracted information from each report and any available protocol. Disagreements were resolved through discussion. We identified 61 stepped-wedge cluster randomized trials that randomized two to six clusters: median sample size (Q1-Q3) 1426 (420-7553) participants. Twelve (19.7%) gave some indication that the evaluation was considered a "preliminary" evaluation and 16 (26.2%) recognized the small number of clusters as a limitation. Sixteen (26.2%) provided an explanation for the limited number of clusters: the need to minimize contamination (e.g. by merging adjacent units), limited availability of clusters, and logistical considerations were common explanations. Majority (51, 83.6%) presented sample size or power calculations, but only one assumed distinct within- and between-period intracluster correlations. Few (10, 16.4%) utilized restricted randomization methods; more than half (34, 55.7%) identified baseline imbalances. The most common statistical method for analysis was the generalized linear mixed model (44, 72.1%). Only four trials (6.6%) reported statistical analyses considering small numbers of clusters: one used generalized estimating equations with small-sample correction, two used generalized linear mixed model with small-sample correction, and one used Bayesian analysis. Another eight (13.1%) used fixed-effects regression, the performance of which requires further evaluation under stepped-wedge cluster randomized trials with small numbers of clusters. None used permutation tests or cluster-period level analysis. Methods appropriate for the design and analysis of small stepped-wedge cluster randomized trials have not been widely adopted in practice. Greater awareness is required that the use of standard sample size calculation methods can provide spuriously low numbers of required clusters. Methods such as generalized estimating equations or generalized linear mixed models with small-sample corrections, Bayesian approaches, and permutation tests may be more appropriate for the analysis of small stepped-wedge cluster randomized trials. Future research is needed to establish best practices for stepped-wedge cluster randomized trials with a small number of clusters.

Implementing Organizational Change Strategies in US City Governments: Comparing Change Strategies and Influential Factors

ABSTRACT This study examines the implementation of organizational change strategies in city governments across the United States. Organizational change strategies include involving employees, merging units, and introducing bottom-up changes. Based on the analysis of data from a national survey, the study compares the implementation scores of the change strategies and tests the influence of financial conditions managerial factors, and organizational characteristics to the implementation. The findings reveal that merging agency units is the top change strategy and managerial attitudes affect the strategy of involving employees and merging units. The findings contribute to the research of public organizational change and government reforms.

What determines citizens’ attitudes to municipal mergers?

ABSTRACT To what extent can citizens’ attitudes to municipal mergers be explained by costs and benefits incurred by merging with a specific consortium of neighbouring units? To answer this question, we analyse data taken from a survey to citizens of 119 Norwegian local governments in the fall of 2019, merely a few months before the merger of their own unit with one or more neighbouring units was to be implemented as the result of a national local government reform decided over two years in advance. In line with previous studies, we find that citizens tend to prefer merging with wealthier neighbours rather than poorer ones. Moreover, we find that this preference is only observable among respondents in smaller units merging with one or more larger units. Furthermore, differentials in private wealth among the merging units appear to affect preferences more than public wealth. However, we did not find support for the theoretical assumption that citizens prefer mergers with units that are similar in terms of political and societal characteristics. Overall, our study suggests that concerns over local redistributive losses may impede support for mergers and, hence, increase the political costs of implementing comprehensive structural reforms.

Trends in Measuring Instrument Transformers for Gas-Insulated Switchgears: A Review

Voltage and current measurements in high-voltage substations are fundamental for stable operation. Conventional instrument transformers (ITs) face challenges in gas-insulated switchgears (GISs), such as size, weight, accuracy limitations, and behavioral instability at abnormal voltages and currents. Non-conventional instrument transformers (NCITs) have emerged to address these issues, complying with International Electrotechnical Commission (IEC) standards and providing millivolt-level signals, enabling downsizing of GIS bays. The transition to digital substations, as mandated by IEC 61850-9-2, requires a shift from the conventional 110 V/5 A outputs to levels ranging from millivolts to volts. Electronic instrument transformers (EITs), compliant with the IEC 60044-7 and 8 standards, offer alternatives to conventional ITs with smaller sizes and wider frequency ranges. However, issues remain with EITs, including limited adoption, the necessity of separate power sources, and susceptibility to electromagnetic interference. Recent standards, transitioning to IEC 61869, focus on low-power instrument transformers (LPITs). Low-power voltage transformers (LPVTs) and low-power current transformers (LPCTs), designed with passive components, present potential solutions by directly connecting to merging units (MUs) for digital signal transmission. This review outlines the current status of various IT standards, covering conventional ITs, EITs based on IEC 60044-7 and 8, and LPITs based on IEC 61869-10 and 11. Advancements in sensor technology relevant to these standards are also explored. The paper provides insights into the evolving landscape of instrument transformers, addressing challenges and offering potential pathways for future developments in digital substations.

Исследование точности определения места повреждения воздушных линий по данным от устройств синхронизированных векторных измерений различных классов и производителей

The technology of synchronized phasor measurements has been widely used in the Russian power system to analyze the parameters of steady-state electrical power modes and to record electro-mechanical transient processes. Issues on fault location based on synchronized phasor measurements have mainly been discussed in foreign publications. A significant drawback of most research papers on this issue is simplified modeling of both overhead lines and current and voltage measurement channel as well as digital filters of phasor measurement units (PMUs). The goal of this research is to develop a fault location algorithm based on synchrophasor measurements and to study its accuracy by using specialized equipment including a real-time digital simulator (RTDS), PONOVO current and voltage amplifiers and production-grade PMUs. A PMU-based double-ended fault location algorithm is developed using long-line equations and well-known electromagnetic transient theory concepts. Currents and voltage oscillograms of both overhead transmission line ends are modelled in the MATLAB/Simulink software package. These oscillograms are saved as COMTRADE files and played back using the RTDS hardware and all-in-one software package RSCAD. In addition, the study uses two production-grade PMUs, the first one is TPA-02, and the second one is a merging unit ENMU acting as a PMU, thus imitating PMUs at the line terminals. To time-align all the measurements and to aggregate PMU data frames, various auxiliary software such as PMU Connection Tester, and hardware is used. A double-ended fault location (FL) method utilizing synchrophasors under a fault has been developed. The method is based on an overdetermined system of nonlinear equations that describes physical processes in an overhead power line and can be applied under various fault types. An integrated study of the efficiency of the developed FL method has been conducted. FL errors have been computed using production-grade PMUs ENMU and TPA-02, along with the RTDS and other equipment. The authors have considered the case of configuring PMUs of different classes at the overhead line terminals, and different phasor reporting rates as well. The conducted experiments make it possible to reveal that the fault location errors do not exceed the thresholds imposed by the standard STO 56947007-29.120.70.241-2017 in 88 % of all the analyzed fault scenarios. The developed FL method makes it possible to achieve the accuracy required by regulatory guide in calculating the distance to the short circuit point in most of the cases examined. Based on the results of numerical experiments for various types of fault cases, it can be concluded that the PMU class and phasor reporting rate do not have a significant impact on the FL accuracy, provided that the fault duration is enough for the PMU filter to approach a steady output.

Applying Work Redesign Strategies in Chinese Government Reforms: Lessons for the Government Reform Study

This study examines the application of work redesign strategies in Chinese government agencies to understand their contributions to the field of government reform. Work redesign strategies that improve the performance of government include redesigning jobs and positions, combining agency functions, merging units, and eliminating different layers of hierarchy. The study first provides a review of the background of Chinese government reforms and related issues about work redesign studies. The study then explains the research data and analytical techniques used to examine the importance and implementation measure of the four work redesign strategies, while also testing influential personal and organizational factors that impact the work redesign strategy. The study concludes with discussions about lessons derived from the Chinese government reform and implications for future studies on government reforms.

Reliability analysis for vertical integration of protection, measurement, merge unit, and intelligent terminal device

The reliability analysis of vertically integrated protection devices is crucial for designing International Electrotechnical Commission (IEC) 61850-based substations. This paper presents the hardware architecture of a four-in- one vertically integrated device and the information transmission path of each function based on the functional information transmission chain of protection devices, measurement and control devices, merging units, and intelligent terminals. Additionally, a reliability analysis model of the protection device and its protection system is constructed using the fault tree analysis method while considering the characteristics of each module of the vertically integrated device. The stability probability of the protection system in each state is analyzed by combining the state-transfer equations of line and busbar protection with a Markov chain. Finally, the failure rate and availability of the protection device and its protection system are calculated under different ambient temperatures using a 110 kV intelligent substation as an example. The sensitivity of each device module is analyzed.

Testing Rogowski Coils with Merging Units for Smart Grids

As smart grids incorporate renewable energy sources and advanced power electronics, ensuring accurate measurement systems becomes paramount due to the increased complexity and potential sources of disturbances. This article focuses on the laboratory calibration of Rogowski coils (RCs) and merging units (MUs), which are fundamental for measuring, controlling, and monitoring digital power systems. A comprehensive digital calibration system is introduced, utilizing precise, commercially available components such as a fluxgate current transducer and a National Instrument. The system assesses magnitude and phase displacement errors under various operating conditions, including abnormal scenarios. Additionally, the impact of uncertainty sources on the measurement chain analysis is discussed, with test results conforming to established standards. This research contributes to enhancing the accuracy and reliability of measurement systems in the context of evolving smart grids.

Dual-dispersive spectral linear polarization imager based on coded-aperture

Spectral and polarization detections can increase the dimension of data acquisition and enhance the capabilities of target detection systems under complicated circumstances. A spectral linear polarization imager that combines double-disperser coded aperture imaging technology with a division of focal plane polarization detector is proposed in this paper to acquire spectral and polarization information simultaneously. First, the principles and mathematical model of the system are presented, where the proposed mathematical model considers the transformations among different coordinate systems and signal transmission processes, which is realistic and provides guidance for the calibration process. Then, targeting the detection and reconstruction methods based on the Hadamard transform, the loading approach of the coded aperture and the necessity of merging micro-mirror units are analyzed. Finally, according to the actual detection demands, the proposed system can achieve measurements and reconstructions at different spectral resolutions by loading 7th- and 15th-order cyclic S-matrix templates in real-time at the coded template. The results show the Pearson correlation coefficient and the root-mean-square error between the degree of linear polarization values acquired through proposed and reference systems are 0.9975 and 0.0238, respectively. Experimental results also demonstrate that although 15th-order cyclic S-matrix template can result a higher spectral resolution compared with 7th-order cyclic S-matrix template, it decreases the accuracy of the reconstructed results, indicating a trade-off between spectral resolution and accuracy in actual detections.

Prioritizing protection communication in a 5G slice: Evaluating HTB traffic shaping and UL bitrate adaptation for enhanced reliability

Abstract5G network slicing is promising in prioritizing time‐critical protection communication in wireless networks of smart grids. However, network slicing offered by telecommunication providers encompasses all smart grid applications, lacking granularity. Smart grid automation standards provide recommendations on prioritization of protection communication to improve reliability but only for wired connections. Therefore, this paper investigates hierarchical token bucket (HTB) traffic shaping and uplink (UL) bitrate adaptation of a live video stream for prioritizing protection communication within a 5G slice. An experimental setup combines controller‐hardware‐in‐the‐loop (CHIL) with a quality of service (QoS) measurement system for validation. The system under test consists of commercial 5G networks, intelligent electronic devices (IEDs), and merging units for validation with three smart grid applications: fault location, line differential, and intertrip protection. HTB traffic shaping improves protected faults by 47.57% in congested and 1.16% in non‐congested scenarios. UL bitrate of the video stream adaptation by 2 Mbps increases protected faults by 3.69%. HTB traffic shaping even improves prioritization with a wired connection without introducing additional delays. HTB traffic shaping must be deployed in routers to maintain good QoS for critical applications. Collaboration between utilities and telecommunication providers is essential to effectively deploy 5G network slicing on smart grids.

Performance Analysis of Overcurrent Protection under Corrupted Sampled Value Frames: A Hardware-in-the-Loop Approach

The IEC 61850 standard aims at digitization substations and provides interoperability between various Intelligent Electronic Device vendors. The digitization process is accompanied by several challenges related to data transmission on the ethernet network and the protection behavior under these conditions. Among the challenges, we can mention packet loss, delay, and duplicate frame, which occurs when the merging units (publisher) transmit the sampled values and, for some reason, these packets do not reach the subscriber or are duplicated. Nowadays, most Intelligent Electronic Device manufacturers block the protection function when some sampled value packets are corrupted. The effects of blocking protection when packet loss occurs under normal operating conditions do not cause significant problems. However, when a fault occurs, the corrupted packets can cause a delay in fault clearance, causing even more damage to the grid. The purpose of this article is to present the effects of corrupted sampled values on the performance of overcurrent protection. All the evaluations were performed in real time using the hardware-in-loop simulation approach with a commercial Intelligent Electronic Device. The OP5700 hardware platform from OPAL-RT, with the library “IEC 61850 Data Integrity Manipulation”, was used. The results show that corrupted sampled value frames affect the functioning of the protections.

Coherence of digital processing of current and voltage signals at decimation for power systems with a large share of renewable power stations

The high energy and environmental performance of renewable power stations (RPS) contributes to their widespread introduction in many countries. A trend towards decentralization of generating capacities and an increase in the share of RPS in their structure brings about the multifactorial features that affect the reliability of power systems. These factors can result in a failure and unnecessary or false operation of intelligent digital devices and systems that perform the protection and automatic control functions. Digital substations using the IEC 61850 protocol to exchange instantaneous values of analog signals employ merging units (MUs) for digital processing of current and voltage. MUs use down-sampling, i.e., decimation, to reduce the number of calculations and meet other purposes. The paper presents findings of an analysis of the digital processing effects associated with the disturbance of coherence of current and voltage signals during decimation. Failure to comply with the coherence requirements during decimation leads to significant errors in the estimates of signal parameters. The extent to which the sinusoidality of signals is distorted due to incoherence can be determined using a normalized cross-correlation coefficient. Simulation results have shown that incoherent sampling enhances the distorting effect for the signals containing high-frequency harmonics and interharmonics. Coherence of digital signal processing after decimation can be ensured by preliminary digital filtering. Superposition of noise components does not affect much the estimations of signal amplitudes during decimation, which are within the allowable error. Coherence of digital processing of current and voltage signals during decimation contributes to the reliable operation of power systems with a large share of RPS, first of all solar photovoltaic and wind power stations.

Centralized Multiple Back-Up Protection Scheme with Sharing Data between Adjacent Substations Based on IEC 61850

A centralized multiple back-up protection scheme with sharing data between adjacent substations based on IEC 61850 is suggested in this paper to overcome the inherent defects of a conventional back-up protection scheme such as uncertainty of a remote end condition, especially for a distance relay, long operating time delay, and IED/CT fails. A current differential protection element, a distance-based directional protection element, local back-up, and remote back-up protection elements are applied for the multiple back-up protection scheme suggested in this paper. The phasor voltage/current data of the IMU are transferred to a CPCU. In this paper, the IMU has two functions, which are local protection IED and merging unit, as well. The CPCU performs the back-up protection functions by using the phasor voltage/current data collected from other CPCUs located at the adjacent substations. IMU/CT fails are also considered. To verify the back-up protection scheme proposed, a testbed was composed of IMUs (implemented with ADS8688 and TMDSIDK572X), grand-master-clocks (LANTIME M1000-IMS), network switches (Syn 1588 Gbit switch), RTDS, and CPCUs. A target power system was modelled with RSCAD. The results of this research can be expected to provide a practical guide to constructing the future centralized protection for a digital substation.

GNSS Time Signal Spoofing Detector for Electrical Substations

This paper introduces a novel method of GNSS spoofing detection with applications in electrical substations. Time sensitive applications in electricity substations, including Phasor Measurement Units (PMU) and Merging Units (MU), rely on Global Navigation Satellite Signals (GNSS), often GPS, for time transfer. Recently, sophisticated ‘spoofing’ attacks have become feasible due to the availability of low cost Software Defined Radio (SDR) systems. The proposed method uses multiple GNSS receive antennas placed in close proximity at the electricity substation, such that it is not possible for an attacker to target a unique spoofing signal towards each antenna. In a system employing three or more receive antennas, during a spoofing attack two or more of the GNSS receive antennas will return an estimated position in impossible locations. This is sufficient to raise alarm that time sensitive applications should use an alternative time source or holdover clock. The contributions of this paper include a detailed description of the proposed method, an experimental assessment of GNSS receiver and substation clock position estimation variance to establish the minimum separation required between receive antennas, and a validation of the method by experimental demonstration. A further benefit of the authors’ method is that it may be put into practice immediately using commercial-off-the-shelf (COTS) substation clock equipment.

Nonparametric measurement of potential gains from mergers: an additive decomposition and application to Indian bank mergers

In this paper, we derive conditions under which merger between a number of firms within the same industry would induce a more cost efficient production of the aggregate output bundle, especially in the short-run, and show that potential cost economies from a merger can be attributed to three factors: convexity of the technology, sub-additivity of the ray short-run total cost curve, and a trade-off between reduction in the variable cost and increase in fixed cost arising from an aggregation of the fixed inputs of the merging units. We use this proposed analytical framework to evaluate the gains from various recent bank mergers in India. We employ the nonparametric method of Data Envelopment Analysis for retrospectively quantifying the potential gain from specific mergers and its components both in the short-run and in the long-run.

Phasor Measurement Unit With Digital Inputs: Synchronization and Interoperability Issues

In recent years, the electrical substations are experiencing a rapid transition towards a fully digital measurement infrastructure, in terms of data acquisition, storage and processing. The IEC Std 61850-9-2 defines the data format, also known as Sampled Value (SV), to be employed by instrument transformers, merging units, and controller devices. In this scenario, it is reasonable to expect that also Phasor Measurement Units (PMUs) will be directly connected with digital instrument transformers and will be required to process directly the SV data stream. In this paper, we present the design and development of a stand-alone PMU based on digital inputs. The prototype has been characterized in terms of estimation accuracy and enriched with a novel functionality that allows for monitoring the time quality of the SV data stream. In this way, the device truly becomes an Intelligent Electronic Device (IED) that guarantees higher interoperability as well as a more robust management of sporadic synchronization issues. The proposed results confirm the potential of SV-based PMUs, and highlight the possibility of further enhancement for synchrophasor measurements based on digital inputs only.

A Computer-Based IEC 61850 Sampled Values Analyzer for Parallel Power Quality Analysis

This paper introduces a system capable of characterizing on-site digital instrument transformers from the analysis of the IEC 61850/IEC 61869-9 frames injected by the Stand Alone Merging Units (SAMU) located in digital substations. Besides, the second objective of this work is to implement a suitable computation architecture to monitor distributed Power Quality (PQ) nodes. For that aim, capacity of calculating PQ from the information sent by the SAMU will be leveraged. In a first step, this approach relies on the implementation of an IEC 61000-4-30 class-A PQ library on an industrial-based computer. Concerning the first objective, several experimental tests were driven for a solid timestamping characterization of the received data. After that, different PQ tests were carried out to verify the suitability of the proposed solution by comparing the system against one traceable generator. The calculation of normalized error indexes (En) revealed that the developed system is compatible with respect to the reference generator. In this regard, the system can be used to calibrate digital instrument transformers (via SAMUs) against one analogue reference transformer. Later, the library is migrated to a more constrained hardware to identify the maximum number of parallel nodes that the analyzer can process. On this basis, several tests were conducted to stress the low-cost platform until reaching the thermal limit on CPU. In light of the results, the maximum number of nodes was 20. This fact indicates that the proposed low-cost analyzer meets the stringent class-A requirements of IEC 61000-4-30 for real-time parallel evaluations.

Real-Time B-Spline Interpolation for Harmonic Phasor Estimation in Power Systems

The fundamental component synchrophasors are widely used nowadays, based on the use of Phasor Measurement Units (PMU), in several applications in electrical power systems. For the advancement of monitoring technology, harmonic synchrophasor estimation is still a challenge. To make it possible, it is necessary to correctly estimate the harmonic phasor (magnitude and phase of each harmonic component), mainly in scenarios with frequency deviations and noise. In this context, the present paper proposes the use of B-Spline based interpolation as a preprocessing algorithm for the Discrete Fourier Transform (DFT). The performance is evaluated in terms of Total Vector Error (TVE) considering the tests proposed by the IEEE C37.118.1 and IEC 60255-118-1 standards and compared with four different harmonic phasor estimation methods, the HPE, SIFE, TFT and FT FIR. The proposed method can provide a TVE below 1% for all harmonic phasors, from the first to the fiftieth order, under significant frequency deviation. Also, for real time validation, the proposed method was implemented in an industrial computer as a software routine capable of processing the signals in real time. The signals are acquired by a commercial Merging Unit (MU) and the samples are published using the IEC 61850 Sampled Values (SV) protocol.