Phasor Data Concentrator Research Articles

PMU based adaptive zone settings of distance relays for protection of multi-terminal transmission lines

This paper proposes Phasor Measurement Unit (PMU) based adaptive zone settings of distance relays (PAZSD) methodology for protection of multi-terminal transmission lines (MTL). The PAZSD methodology employs current coefficients to adjust the zone settings of the relays during infeed situation. These coefficients are calculated in phasor data concentrator (PDC) at system protection center (SPC) using the current phasors obtained from PMUs. The functioning of the distance relays during infeed condition with and without the proposed methodology has been illustrated through a four-bus model implemented in PSCAD/EMTDC environment. Further, the performance of the proposed methodology has been validated in real-time, on a laboratory prototype of Extra High Voltage multi-terminal transmission lines (EHV MTL). The phasors are estimated in PMUs using NI cRIO-9063 chassis embedded with data acquisition sensors in conjunction with LabVIEW software. The simulation and hardware results prove the efficacy of the proposed methodology in enhancing the performance and reliability of conventional distance protection system in real-time EHV MTLs.

Inter‐area oscillation damping with non‐synchronised wide‐area power system stabiliser

One of the major issues in an interconnected power system is the low damping of inter-area oscillations which significantly reduces the power transfer capability. Advances in Wide-Area Measurement System (WAMS) makes it possible to use the information from geographical distant location to improve power system dynamics and performances. A speed deviation based Wide-Area Power System Stabilizer (WAPSS) is known to be effective in damping inter-area modes. However, the involvement of wide-area signals gives rise to the problem of time-delay, which may degrade the system performance. In general, time-stamped synchronized signals from Phasor Data Concentrator (PDC) are used for WAPSS, in which delays are introduced in both local and remote signals. One can opt for a feedback of remote signal only from PDC and uses the local signal as it is available, without time synchronization. This paper utilizes configurations of time-matched synchronized and nonsychronized feedback and provides the guidelines to design the controller. The controllers are synthesized using $H_\infty$ control with regional pole placement for ensuring adequate dynamic performance. To show the effectiveness of the proposed approach, two power system models have been used for the simulations. It is shown that the controllers designed based on the nonsynchronized signals are more robust to time time delay variations than the controllers using synchronized signal.

Co-Optimal Placement of PMUs and Their Communication Infrastructure for Minimization of Propagation Delay in the WAMS

The phasor measurement unit (PMU) has evolved as an indispensable tool for real-time monitoring and control of the power system, thereby leading to its large-scale deployment in a wide-area measurement system (WAMS). Communication system plays a significant role for transferring measured real-time PMU data to the phasor data concentrator (PDC) for monitoring and control purposes. The propagation delay depends on the spatial position of the PMUs with respect to the PDC and the communication network. This paper deals with the problem of co-optimal placement of PMUs and their communication infrastructure for minimization of propagation delay in a WAMS. The novelty of the work is to explore the feasibility of microwave communication technology as an alternative to the existing fiber-based communication infrastructure in the WAMS. The proposed approach takes the link reliability and the geographical topological variations into consideration for the placement of the microwave links so as to minimize the propagation delay. The merit of the microwave communication technology in the framework of the WAMS is evaluated in terms of its cost and reliability. Simulation results and the propagation delay evaluations for the Eastern power grid of India validate the efficacy of the proposed approach in practical field applications.

Robust fault analysis in transmission lines using Synchrophasor measurements

As more electric utilities and transmission system operators move toward the smart grid concept, robust fault analysis has become increasingly complex. This paper proposes a methodology for the detection, classification, and localization of transmission line faults using Synchrophasor measurements. The technique involves the extraction of phasors from the instantaneous three-phase voltages and currents at each bus in the system which are then decomposed into their symmetrical components. These components are sent to the phasor data concentrator (PDC) for real-time fault analysis, which is completed within 2–3 cycles after fault inception. The advantages of this technique are its accuracy and speed, so that fault information may be appropriately communicated to facilitate system restoration. The proposed algorithm is independent of the transmission system topology and displays high accuracy in its results, even with varying parameters such as fault distance, fault inception angle and fault impedance. The proposed algorithm is validated using a three-bus system as well as the Western System Coordinating Council (WSCC) nine bus system. The proposed algorithm is shown to accurately detect the faulted line and classify the fault in all the test cases presented.

Impact of GPS Signal Loss and Its Mitigation in Power System Synchronized Measurement Devices

With the aid of global positioning system (GPS), synchronized measurement devices (SMDs) are increasingly deployed across power systems to monitor the status of electric grids by providing accurate measurement data along with unified time stamps. Unfortunately, GPS receivers tend to lose signal lock when certain uncontrollable and unpredictable factors arise. In order to investigate the presence of GPS signal loss (GSL) issues on measurement devices, analysis is performed on historical data from both phasor data concentrators and FNET/GridEye servers. Meanwhile, the impact of GSL on field measurement accuracy has not been previously explored in depth. Through analysis and experimental tests, this paper discovers angle drift caused by GSL, which consequently leads to the total vector error exceeding the IEEE standard C37.118.1-2011. Furthermore, a compensation method is proposed to rectify the angle drift and laboratory experiments demonstrate that the proposed method does effectively reduce angle drift and mitigate the impact of GSL in SMDs.

Access Control Attacks on PLC Vulnerabilities

In Industrial Control Systems (ICS), security issues are getting more and more attention. The number of hacking attacks per year is endless, and the attacks on industrial control systems are numerous. Programmable Logic Controller (PLC) is one of the main controllers of industrial processes. Since the industrial control system network is isolated from the external network, many people think that PLC is a safety device. However, virus attacks in recent years, such as Stuxnet, have confirmed the erroneousness of this idea. In this paper, we use the vulnerability of Siemens PLC to carry out a series of attacks, such as S7-200, S7-300, S7-400, S7-1200 and so on. We read the data from the PLC output and then rewrite the data and write it to the PLC. We tamper with the writing of data to achieve communication chaos. When we attack the primary station, all slave devices connected to the primary station will be in a state of communication confusion. The attack methods of us can cause delay or even loss of data in the communications from the Phasor Data Concentrator (PMU) to the data concentrator. The most important thing is that our attack method generates small traffic and short attack time, which is difficult to be identified by traditional detection methods.

Optimal Placement of Synchrophasor Sensors for Risk Hedging in a Smart Grid

Modern power system with its numerous sophisticated technological integrant constituents and their intricate interconnections is materializing into a smart grid (SG). The phasor measurement units have become indispensable sensors for the real-time monitoring of the SG. In a typical SG, these sensors are deployed at several locations, on the electrical buses for the accurate measurement of time synchronized current and voltage phasors. The time tagged synchrophasor data are then communicated to the phasor data concentrator (PDC) through the synchrophasor sensor communication system (SSCS) for monitoring and control purposes. Risk analysis and the subsequent risk hedging of this system are quintessential to safeguard against cataclysmic botches pertaining to monitoring, control, and protection of the power system. The proposed research presents the framework for the risk assessment of the SSCS and the subsequent optimal placement of the synchrophasor sensors and their communication infrastructure for risk minimization. Another significant aspect of the proposed work is the use of microwave point-to-point links for the transfer of the data from the synchrophasor sensors to the PDC. Communication feasibility is assessed using the digital elevation model data, taking into account the line of sight and communication link availability constraints imposed by the microwave links. Simulation results for the practical power system of India validate the efficacy of the proposed work.

Design of an Advanced Phasor Data Concentrator for Monitoring of Distributed Energy Resources in Smart Microgrids

Synchrophasor networks are subject to communication delays and packet dropout that can compromise data integrity and, thus, jeopardize control and monitoring of smart microgrids. This paper proposes an advanced phasor data concentrators (APDC) capable of counteracting the communication impairments and improving the quality of monitoring of distributed energy resources (DERs) in microgrids. The proposed APDC utilizes an adaptive compensation scheme to achieve an effective estimate of missing data elements. Moreover, a monitoring unit is proposed to reliably detect frequency excursions and identify the DERs affected by islanding events. The performance of the proposed APDC is evaluated based on realistic phasor measurement unit data aligned and processed with real-time OpenPDC software. The experimental results confirm a high-level data integrity under both normal and disturbed conditions of microgrids. Moreover, fast and reliable detection of islanding events is achieved due to the significant improvement in detection time even under severe data losses.

Centralized Disturbance Detection in Smart Microgrids With Noisy and Intermittent Synchrophasor Data

Microgrids are prone to network-wide disturbances such as voltage and frequency deviations. Detection of disturbances by a microgrid central controller is therefore necessary for improving the network operation. Motivated by this application, this paper presents a new structure for the centralized detection of disturbances with noisy synchrophasor data and packet delay/dropouts. We build the proposed structure starting from the analysis of noise-delay tradeoff in synchrophasor networks and developing a new phasor data concentrator for compensation of data losses. The statistical performance metrics of the disturbance detector are numerically evaluated in the case of islanding detection, corroborating that the centralized detector counteracts the measurement noise and lowers the detection time. Numerical results show that the proposed structure significantly mitigates the probability of false detection. Moreover, it can achieve the lower bound of average detection time in a wide range of packet drop rates. This paper is useful to network designers who need to employ data acquisition systems for reliable and robust microgrid control applications.

A threshold free synchrophasor measurement based multi-terminal fault location algorithm

A new impedance based fault location algorithm is proposed for a generic multi-terminal transmission network consisting of a main line and tapped branches with no direct measurements available at the intermediate tapping nodes. The core of the algorithm is a threshold free faulted branch search algorithm that systematically compares the multiple estimates of voltages for the tapping nodes, computed using synchrophasor measurements at the terminals. Once the faulted branch is identified, multi-terminal fault location problem is reduced into a two-terminal fault location problem to determine the exact location of fault within the branch. The proposed algorithm is simple and does not involve resource intensive mathematical operations such as matrix inversion. The proposed algorithm was implemented as a module in an in-house developed real-time synchrophasor application software program, and its performance was evaluated using a test setup consisting of a real-time simulator, an actual synchrophasor network, and a phasor data concentrator. The tests showed that the proposed algorithm is capable of correctly determining the faulted branch, except for few faults that are very close to tapping nodes. When the algorithm is used with practical synchrophasor measurements, the fault location error was within a typical tower span for most cases.

A New Wide-Area Backup Protection Scheme for Series-Compensated Transmission System

This paper presents a new wide-area backup protection scheme based on the phase angle of positive-sequence integrated impedance (PAPSII). The proposed scheme uses phasor measurement units (PMUs) that comply with standard C37.118.1-2011 for retrieving the phasor information. The PMUs provide the positive-sequence phasor information of the voltage and current signals at each and every bus of a system to a phasor data concentrator (PDC). The positive-sequence integrated impedance of each line of the system is extracted, and the PAPSII of each line is continuously monitored at the PDC. The values of the PAPSII help in identifying the faulted line of the power transmission system. The proposed scheme is extensively tested for different types of fault scenarios on a three-machine nine-bus power transmission network on a real-time digital simulator platform. Critical issues such as voltage inversion, current inversion, load encroachment, and the power swing are addressed in the proposed scheme. The test results indicate that the proposed scheme can overcome the limitations of existing backup protection schemes and can provide a reliable protection measure.

A New Power System Restoration Technique based on WAMS Partitioning

An important feature of a Wide-Area Measurement System (WAMS) is the ability to recover data during a communication failure. This paper presents a novel scheme of partitioning a PMU installed power network into a number of WAMS regions in order to make the power system restoration process simpler. This algorithm also proposes the optimal placement of Phasor Data Concentrators (PDCs) in each region to record the data from PMUs. This paper considers the restoration constraints like transformer equivalent bus, generation-load balance and the observability of region for the partitioning of power system. The proposed scheme is demonstrated with an IEEE-30 bus system. It is then applied on IEEE-39, IEEE-118 bus systems and on a Northern Regional Grid of the Indian Power Grid.

Optimal cost wide area measurement system incorporating communication infrastructure

A wide area measurement system installation cost minimisation and observability maximisation using binary gravitational search algorithm have been reported. Various methods have been employed in the past to determine the optimal locations of devices to retain the observability of the system. However, the costs of communication infrastructure (CI) from phasor data concentrator to phasor measurement units (PMUs) have not been given proper attention. To address this issue, the PMU placement problem has been formulated incorporating the cost of CI also in this study. Contingency cases have also been included to improve the reliability of the system. Besides, the effects of the presence of preinstalled PMUs have been considered. The results obtained for IEEE 14-bus, 30-bus and 118-bus systems have been compared with other methods in the literature. The test results reveal that the proposed methodology produced the PMU locations with higher observability and lesser distance path of establishing communication link compared to an existing method.

Wide-area measurement system-based supervision of protection schemes with minimum number of phasor measurement units.

Cascade tripping of power lines triggered by maloperation of zone-3 relays during stressed system conditions, such as load encroachment, power swing and voltage instability, has led to many catastrophic power failures worldwide, including Indian blackouts in 2012. With the introduction of wide-area measurement systems (WAMS) into the grids, real-time monitoring of transmission network condition is possible. A phasor measurement unit (PMU) sends time-synchronized data to a phasor data concentrator, which can provide a control signal to substation devices. The latency associated with the communication system makes WAMS suitable for a slower form of protection. In this work, a method to identify the faulted line using synchronized data from strategic PMU locations is proposed. Subsequently, a supervisory signal is generated for specific relays in the system for any disturbance or stressed condition. For a given system, an approach to decide the strategic locations for PMU placement is developed, which can be used for determining the minimum number of PMUs required for application of the method. The accuracy of the scheme is tested for faults during normal and stressed conditions in a New England 39-bus system simulated using EMTDC/PSCAD software. With such a strategy, maloperation of relays can be averted in many situations and thereby blackouts/large-scale disturbances can be prevented.This article is part of the themed issue 'Energy management: flexibility, risk and optimization'.

An adaptive supervised wide-area backup protection scheme for transmission lines protection

Maloperation of conventional relays is becoming prevalent due to ever increase in complexity of conventional power grids. They are dominant during power system contingencies like power swing, load encroachment, voltage instability, unbalanced loading, etc. In these situations, adaptive supervised wide-area backup protection (ASWABP) plays a major role in enhancing the power system reliability. A balance between security and dependability of protection is essential to maintain the reliability. This paper proposes multi-phasor measurement units (MPMU) based ASWABP scheme that can function effectively during faults besides power system contingencies. MPMU is an extended version of Phasor Measurement Unit (PMU). It is an intelligent electronic device which estimates the synchronized predominant harmonic phasors (100Hz and 150Hz) along with the fundamental phasors (50Hz) of three phase voltages and currents with high precision. The proposed ASWABP scheme can detect the fault, identify the parent bus, determine the faulty branch and classify the faults using MPMU measurements at System Protection Center (SPC). Based on these MPMU measurements (received at phasor data concentrator (PDC) at SPC) the appropriate relays will be supervised to enhance the overall reliability of the power grid. Numerous case studies are conducted on WSCC-9 bus and IEEE-14 bus systems to illustrate the security and dependability attributes of proposed ASWABP scheme in MATLAB/Simulink environment. Also, comparative studies are performed with the existing conventional distance protection (Mho relays) for corroborating the superiority of the proposed scheme regarding security and dependability. Comparative studies have shown that the proposed scheme can be used as adaptive supervised wide-area backup protection of conventional distance protection.

GPS signal loss in the wide area monitoring system: Prevalence, impact, and solution

The phasor measurement unit (PMUs), equipped with Global Positioning System (GPS) receivers for precise time synchronization, provides measurements of voltage and current phasors at different nodes of the wide area monitoring system. However, GPS receivers are likely to lose satellite signals due to various unpredictable factors. The prevalence of GPS signal loss (GSL) on PMUs is first investigated using real PMU data. The historical GSL events are extracted from a phasor data concentrator (PDC) and FNET/GridEye server. The correlation between GSL and time, spatial location, solar activity are explored via comprehensive statistical analysis. Furthermore, the impact of GSL on phasor measurement accuracy has been studied via experiments. Finally, several potential solutions to mitigate the impact of GSL on PMUs are discussed and compared.

Phasor measurement unit based wide‐area monitoring and information sharing between micro‐grids

Micro-grid (MG) monitoring and information sharing between them through a central monitoring unit is required in the present day operational environment. The proposed research focuses on developing wide-area monitoring platform for multiple MGs running in parallel. This is achieved by using C37.118.1 complied phasor measurements units (PMUs) which provides accurate and reliable information monitoring at remote ends of the MGs and are further connected to the Phasor Data Concentrator which acts as the central monitoring unit. This process not only retrieves information at different nodes of the MGs equipped with PMUs, but the information can be exchanged between MGs for further action if required during contingencies. The PMUs are used to monitor phasors (amplitude and phases) and frequency of fundamentals which are further used to compute wide-area functions at different operating nodes of the MGs at grid connected and islanded modes of operation including different operating conditions. The proposed PMU and MG models are developed on MATLAB/SIMULINK platform. Extensive test results indicate that the proposed monitoring process is highly essential to retrieve the operational status of the multiple MGs observed at the central monitoring unit.

Design and Implementation of Security Gateway for Synchrophasor Based Real-Time Control and Monitoring in Smart Grid

Synchrophasor technology has numerous applications ranging from simple grid monitoring/visualization to real-time protection and control. Most legacy phasor measurement units (PMUs) and phasor data concentrators (PDCs) deployed in power grids support the IEEE C37.118.2 communication framework, which is highly vulnerable to cyber attacks due to lack of inherent security mechanisms. The IEC 61850-90-5 recently emerged as new communication framework with support for security features but its use in commercial devices is still very limited. The replacement of legacy PMUs/PDCs in power grids is a big challenge due to cost and deployment complexity. The concept of a gateway has recently been proposed in the literature to enable IEEE C37.118.2 compatible PMUs to send data in IEC 61850-90-5 format. However, the published gateway has limited features and also lacks security functionalities. This paper addresses security, interoperability, and integration issues between legacy and state-of-the-art phasor devices through the design of a security gateway. The security gateway is implemented with flexibility in mind and can be used for PMUs as well as PDCs under different configurations. It provides: 1) protocol conversion functionalities (from IEEE C37.118.2 to IEC 61850-90-5 and vice versa) and 2) security functionalities based on IEC recommended group domain of interpretation security mechanism. The security gateway is very compact in size, based on low-power ARM processor and inexpensive to be deployed in power systems. Through detailed experimental evaluation with real PMU data, this paper also validated the suitability of the security gateway for different types of synchrophasor applications with strict latency and data rate requirements.

Synchrophasor Assisted Adaptive Relaying Methodology to Prevent Zone-3 Mal-operation During Load Encroachment

Phasor measurement unit (PMU) has uniquely blended the contributions of modern information and communication technology in terms of time synchronization and fast data transmission to emerge as the smart sensor for advanced protection methodologies in smart power grids (SPG). The latency issue associated with the functionality of PMUs has made synchrophasors assisted protection algorithms suitable for backup protection, so as to efficiently prevent events, such as mal-operation of relays under load encroachment as well as other stressed situations. This paper proposes a novel methodology to prevent Zone-3 mal-operation of distance relays during load encroachment using the synchrophasor measurements obtained from PMUs installed in a widely-spread power system network. The proposed algorithm is to be implemented in transmission line protection center (TPC), where the synchronized three phase voltage and current phasors acquired from the PMUs are transferred to Phasor data concentrator (PDC) and are used to calculate the impedances seen by the relays in real time. A load encroachment situation and a faulty situation can be distinguished by comparing the impedances seen by primary and backup relays installed at different buses for protecting their respective transmission lines. Numerous case studies have been conducted in WSCC-9 bus system modeled in PSCAD/EMTDC environment to validate the proposed methodology.

A method exploiting direct communication between phasor measurement units for power system wide-area protection and control algorithms

Synchrophasor measurements from Phasor Measurement Units (PMUs) are the primary sensors used to deploy Wide-Area Monitoring, Protection and Control (WAMPAC) systems. PMUs stream out synchrophasor measurements through the IEEE C37.118.2 protocol using TCP/IP or UDP/IP. The proposed method establishes a direct communication between two PMUs, thus eliminating the requirement of an intermediate phasor data concentrator, data mediator and/or protocol parser and thereby ensuring minimum communication latency without considering communication link delays. This method allows utilizing synchrophasor measurements internally in a PMU to deploy custom protection and control algorithms. These algorithms are deployed using protection logic equations which are supported by all the PMU vendors. Moreover, this method reduces overall equipment cost as the algorithms execute internally in a PMU and therefore does not require any additional controller for their deployment. The proposed method can be utilized for fast prototyping of wide-area measurements based protection and control applications. The proposed method is tested by coupling commercial PMUs as Hardware-in-the-Loop (HIL) with Opal-RT’s eMEGAsim Real-Time Simulator (RTS). As illustrative example, anti-islanding protection application is deployed using proposed method and its performance is assessed. The essential points in the method are:•Bypassing intermediate phasor data concentrator or protocol parsers as the synchrophasors are communicated directly between the PMUs (minimizes communication delays).•Wide Area Protection and Control Algorithm is deployed using logic equations in the client PMU, therefore eliminating the requirement for an external hardware controller (cost curtailment)•Effortless means to exploit PMU measurements in an environment familiar to protection engineers.