Program for 2015 IEEE International Workshop on Applied Measurements for Power Systems (AMPS)
Wednesday, September 23
Wednesday, September 23, 08:30 - 09:00
Wednesday, September 23, 09:00 - 09:30
Wednesday, September 23, 09:00 - 09:01
Wednesday, September 23, 09:30 - 10:30
Harmonics and Interharmonics
Chair: Mihaela Albu (Politehnica University of Bucharest, Romania)
- Impact of Operating Conditions on Harmonic and Interharmonic Emission of PV Inverters
- This paper presents the results of testing and analysis investigating impact of operating conditions on harmonic and interharmonic emission of PV inverters. Tests include typical supply voltage distortion and source impedances. Measurement procedures and metrics recommended by standards for evaluating harmonic and interharmonic distortion are discussed. Finally, it is investigated how the Maximum Power Point Tracking control might impact interharmonic distortion.
- A Discriminative Approach to Harmonic Emission Assessment
- With the onset of renewable power sources onto the network, such as Photovoltaic power plants contributing to Total Harmonic Distortion (THD) in voltage, a methodology to quantify their contribution to the THD in voltage at the point of common coupling is needed. This paper give an overview of existing theory on the quantification of harmonic emission and in particular the method proposed by the CIRED/CIGRE C4.109 working group. It is concluded that the application of this method by single-point measurements can be improved upon by using synchronized multiple-point measurements. Discrimination to identity the harmonic currents regarded as emission is attempted in the assessment of harmonic emission at a PV plant feeding into a 22 kV distribution network.
Wednesday, September 23, 10:30 - 11:00
Wednesday, September 23, 11:00 - 12:30
Voltage and Current Transducers
Chair: Lorenzo Peretto (University of Bologna, Italy)
- A Current Clamp based High Voltage Monitoring System
- The feasibility of accurate monitoring a high voltage is investigated, which based on measuring a current through a capacitor, which is already installed in the grid. A current clamp based measuring system with high-resolution digitizer was developed. In order to adapt the system for different capacitors, the current clamp sensor is designed for a.c. currents in the range of 150 µA to 12 A, while the achieved accuracy of the sensor is better than 0.1 %. An implemented high quality analogue a.c. integrator processes the measuring signal to get a proportional scaled high voltage waveform at the sensors output. This feature is helpful for calculating the harmonics distortion in the HV grid. If a high-quality and well-known HV capacitor is available, accurate measurements within 0.5 % for rms values and phase angles are possible in the HV grid under on-site conditions. Such accuracies are usually more than adequate for monitoring purposes.
- Investigation of the thermal drift of open-loop Hall Effect current sensor and its improvement
- Linear Hall Effect IC can be used for the low price open-loop Hall Effect current sensor thanks to its high sensitivity. However, according to the experimental results, its thermal performance is greatly related to the thermal drift coefficient of linear Hall Effect IC and the gain of the amplifying circuit. In this paper, the thermal drift of the zero offset will be improved by two methods. One is to use two Hall Effect ICs, the thermal drift coefficients of which are similar, to build up a differential amplifying circuit to compensate the common thermal drift of the two Hall ICs. Another one is to add a magnetic core for concentrating the magnetic flux. In this way the gain of the amplifying circuit is reduced by increasing the magnetic flux density passed through the Hall IC. Experimental results show that the thermal performance of the optimized current sensor is reasonably improved by the proposed methods.
- Increasing Sensitivity on Non-Contact Voltage Sensor Using Time-Varying Components: A numerical analysis for accuracy assessment
- In this paper we introduce a numeric method to resolve a non-contact voltage sensor equation and track the original voltage in the measured surface for medium and high alternated voltage systems. We introduce the non-contact sensor itself, its principle of operation and equations, and also the method we use to increase the sensitivity of the measurement. The numeric method is then presented in detail, as well as the simulation results and an assessment of accuracy. We were able to achieve very good results with the presented technique, with the best results falling under 1% of estimation error for the fundamental frequency, as well as for the 3rd, 5th and 7th harmonics.
Wednesday, September 23, 12:30 - 14:00
Wednesday, September 23, 14:00 - 15:30
Characterization of PMUs
Chair: Andrew Roscoe (University of Strathclyde, United Kingdom (Great Britain))
- Effect of PMU Analog Input Section Performance on Frequency and ROCOF Estimation Error
- Phasor measurement unit (PMU) performance depends on the performance of the PMU's analog input section and the limitations of its DSP algorithms. For the different PMU performance requirements established in the standards, the relative importance of these two factors varies significantly. For steady-state frequency and rate-of-change-of-frequency (ROCOF) measurements, this paper shows that estimation error is primarily dependent on noise mechanisms in the input section and the effective bandwidth of the signal processing algorithms. Estimation error may be predicted based on understanding these two factors, and optimum performance may be realized by careful design choices. When the PMU function is implemented with separate data acquisition and computation functions, this interaction must be carefully considered, so that the PMU results are equivalent to those from an integrated, conformant PMU - as users expect.
- Critical analysis of PMU testing procedures for step response evaluation
- The Phasor Measurement Units (PMUs) are becoming an important element for the measurement systems of the electrical grid. To assure the high penetration of these measurement devices, the interoperability of the PMUs from different vendors must be ensured. The IEEE Standard C37.118.1-2011, with its amendments of 2014, defines two accuracy classes, P and M, and provides the steady state and the dynamic tests to be passed to achieve compliance. This paper focuses on the dynamic compliance in presence of step changes in phase and magnitude. In particular, the approach proposed by the standard to evaluate the performance of a PMU when it is exposed to a step change signal input, is analyzed and compared with a complete sample by sample approach in a simulation environment. The measurement results, in terms of response time, delay time and undershoots/overshoots and their accuracies, for different reporting rate, are discussed.
- Impact of Wideband Noise on Synchrophasor, Frequency and ROCOF Estimation
- Next-generation Phasor Measurement Units (PMU) must exhibit superior performances in order to meet the accuracy requirements of active distribution grids. Till now most researchers have focused their efforts on mitigating the impact of intrinsic amplitude and phase fluctuations as well as harmonic and inter-harmonic disturbances, since they are usually the largest sources of intrinsic uncertainty. The effect of wideband noise, both in amplitude and in phase, is instead often regarded as negligible, provided that the resolution of the data acquisition stage is chosen properly and both sampling jitter and synchronization uncertainty are kept strictly below worst-case limits. This paper extends and complements the results already available in the literature, by providing a general framework to evaluate the effect of wideband noise on synchrophasor, frequency and Rate of Change of Frequency (ROCOF) estimation. The results of this analysis show that, when the influence of the other disturbances is reduced, the impact of noise can become not only significant, but even critical for compliance (especially on frequency and ROCOF estimates) with respect to the limits reported in the IEEE Standards C37.118.1-2011 and C37.118.1a-2014.
Wednesday, September 23, 15:30 - 16:00
Wednesday, September 23, 16:00 - 17:00
Measurement of Network Harmonic Impedance
Chair: Roberto Langella (Italy, Italy)
- Measurement of network harmonic impedance in presence of electronic equipment
- Harmonic levels and their propagation in the power system are mainly determined by the network harmonic impedance. It is also an essential parameter for the calculation of harmonic current emission limits. Different methods for measuring the network harmonic impedance have been developed in the last decades, but all of them assume that the network harmonic impedance is constant within a cycle at fundamental frequency, which is true in case of passive elements only. As nowadays most of the equipment in low voltage grids contains power electronics including rectifier circuits, network harmonic impedance will vary within a half cycle of power frequency. As more and more equipment operates with switching frequencies of several ten kHz, knowledge about the network harmonic impedance in the frequency range up to 150 kHz is also of significant importance. Based on a review of existing measurement methods, the paper presents an extended measurement method, which is able to address both, above mentioned issues. The application of the method is illustrated by two example measurements in different low voltage grids.
- Continuous Harmonic Impedance Assessment Using Online Measurements
- The quantification of harmonic emission requires an accurate representation of the network harmonic impedances. A number of techniques have been proposed to make the assessment of the network harmonic impedances practical and less invasive. Using actual event data, captured at a solar farm, this paper aims to utilize existing assessment techniques to develop an online network harmonic impedances assessment model. The harmonic impedances can then be updated per event and automatically be corrected as the network develops. This technique is noninvasive and will provide an accurate estimation of the network impedances enabling the continuous assessment of power quality emissions.
Thursday, September 24
Thursday, September 24, 09:00 - 11:00
Measurements on Power System Components
Chair: Antonello Monti (RWTH Aachen University & Institute for Automation of Complex Power Systems, Germany)
- HVDC Test Environment for Loss Measurements on Multilevel Converter Modules
- For the determination of power losses in high-voltage direct current (HVDC) modular multilevel converters (MMC) the standards IEC 62751-1 and IEC 62751-2 demand component measurements with a sufficient uncertainty. Transient loss measurements on multilevel converter modules - so called submodules (SM) - are challenging, especially if they have to be done precisely. Measurement methods and results are rarely discussed in publications and for loss relevant datasheet values of SM components no uncertainty is given. The current work presents a HVDC test environment including two newly constructed SMs. The SM switching waveforms are analyzed in order to determine conduction and switching losses. Moreover, analyses of the measurement chain in terms of uncertainty are conducted.
- Response of a Hybrid Supercapacitor - PEM Fuel Cell System to Fast Fuel Cell Energy Dips
- PEM fuel cell (FC) operation is likely to be characterized by voltage dips on time scales shorter than 1 s, arising from temporary flooding of gas channels or porous layers, particularly when the FC is operated at high humidity levels. If supercapacitors are employed together with the FC as energy storage systems, they can make up for the temporary lack of energy produced by the FC. However, the steep slopes of the voltage dips affect the energy that can be actually delivered by the supercapacitor because of the frequency dependence of its capacitance, and this should be taken into account in sizing the supercapacitor. In this paper, the supercapacitor response to a FC voltage dip is simulated and discussed, based on an experimentally identified supercapacitor model and a typical voltage dip measured on a single PEM FC.
- Monitoring of Power Transformer Bushings in High Voltage Substations
- Power transformer bushings are among the least reliable components in high voltage systems, therefore the knowledge of their wear condition is very important for a proper management of the network. The aim of this work is to study the limits of applicability of an on-line monitoring method for transformer bushings previously presented by the authors. The technique allows to continuously estimate the variation of the bushing capacitance and its dissipation factor, without requiring to disconnect the bushing itself from the network. The method is based on a high frequency analysis of the impedance at the bushing tap. It is clear that its value is not only related to the bushing, but it also depends on the other substation devices. For this reason, it is vital to discriminate the variations of the parameters due to the bushing from those due to the rest of the components. In order to understand these dependencies and to evaluate the applicability of the monitoring method, a high-frequency equivalent model of the substation is required. In this work, a typical substation has been modeled considering frequencies around 1 MHz. Through proper simulations, the applicability of the method has been investigated, in particular the impact of the high voltage transmission lines.
- On Mercury Vapor Lamps and Their Effect on the Smart-Grid PLC Channel
- The mercury vapor lamp is the oldest high intensity discharge technology lamp that uses an electric arc, and comes in different shapes and designs. It creates a very bright light by using an arc through vaporized mercury in a high pressure tube. This lamp can cause unwanted interference to the smart-grid network or power line communications channel when connected to the channel's wiring system. In this paper we investigate the negative effects that the mercury vapor lamps with electric ballast have on the smart-grid PLC channel. This can have a strong and negative effect when using the smart-grid PLC network to control the automatic switching of lamps in public places. The narrowband and broadband channels are investigated where the interference level from mercury vapor lamps is significantly below the allowed maximum PLC signal levels on the band: (3 kHz - 150 kHz), and competes with Electromagnetic Compatibility (EMC) levels on the 150 kHz - 30 MHz band. The mercury vapor lamp uses an electric ballast to connect to the powerline system. This connection is explained in detail.
Thursday, September 24, 11:00 - 11:30
Thursday, September 24, 11:30 - 12:50
Chair: David Macii (University of Trento, Italy)
- Frequency Tracking for Efficient Phasor Measurement Based on a CSTFM Model
- The paper presents a technique based on the use of single-variable Kalman filters (KFs) to track the frequency variation of signal components in multifrequency phasor analysis. KF-based tracking is employed for accurate frequency estimation of both harmonic and inter-harmonic components in a Compressive Sensing Taylor Fourier Multifrequency (CSTFM) algorithm. This novel approach improves robustness of the CSTFM method to the effects of spectral interference among harmonic and interharmonic components, allowing better estimates of each component and extending the range of application beyond pure phasor measurement unit (PMU) devices. Computational efficiency compared to a plain CSTFM algorithm is also enhanced. Significant case studies, with signals including time-varying harmonic and interharmonic components, are analyzed and discussed with regards, in particular, to frequency estimation. Moreover, it is shown that intermittent components can be handled without loss of accuracy by KF-based tracking features.
- Recursive Phasor Estimation Algorithm for Synchrophasor Measurement
- One of the enabling technologies for smart grid development are synchrophasor measurements typically performed by devices called phasor measurement unit (PMU), that produce synchronized subsecond high-resolution voltage and current measurements, so greatly augment the traditional response time of supervisory control and data acquisition measurements. In this paper we present an algorithm that measures amplitude, frequency and phase of voltage and current phasors with great accuracy. It is based on the recursive search of the solution of the maximum likelihood function and can track small variations of all phasor parameters. Preliminary results show that its performance is comparable to the Cramer-Rao Lower Bound.
Thursday, September 24, 12:50 - 14:15
Thursday, September 24, 14:15 - 15:45
Architectures for Monitoring of Modern Distribution Grids I
Chair: Ferdinanda Ponci (RWTH Aachen University, Germany)
- Experimental Evaluation of an Hybrid Communication System Architecture for Smart Grid Applications
- In this paper a new communication system architecture is proposed for the development of a SCADA system which can remotely monitor and control intelligent electronic devices (IEDs) connected to the low voltage distribution networks, i.e low voltage smart meter (SM), interface protection devises (IPS). New distributed metering systems and interface devices, together with a proper communication infrastructure (HiperLAN and narrowband power line communication (NB-PLC) on low voltage network), have been developed to allow monitoring the whole power system and controlling the distributed generators of a Smart Grid also in the presence of harmonic distortions. In this way, the electrical energy distribution operator (DSO) would be able to monitor the distribution network and to take decisions to maintain the stability and the power quality of the electrical system. Experimental tests have been carried out in the pilot smart grid of the island of Favignana.
- Design and test of a real time Monitoring System based on a Distribution System State Estimation
- The development of the smart grid requires new monitoring systems capable of supporting automation functionalities such as control of DER. One of the key elements in the monitoring system is the estimation of the state of the network. This work presents a real time distribution system state estimation (DSSE) integrated with bad data processor. The developed DSSE is suitable for the real time application because it features computational efficiency, numerical stability and robustness against measurements with large error. This DSSE is integrated in an automation architecture, from which the requirements from the output and the specifications of the input are derived. The features and performance of the real time DSSE is analyzed and discussed by means of simulations performed in a 16 bus distribution network.
- First Experimental Characterization of LTE for Automation of Smart Grid
- Smart Grids require a pervasive communication network to interconnect their intelligent devices (e.g. generators, protections, and meters) that are usually distributed over a wide area. Recently, the Long Term Evolution (LTE) wireless cellular network communication technology has been introduced and its diffusion is rapidly increasing. As a consequence, LTE may be considered as a viable opportunity for the communication in Smart Grid, too. The aim of the paper is to experimentally verify the LTE performance of a current public LTE network when it is used as backbone for a Smart Grid system. The results of the experimental characterization highlight that the LTE may be taken into consideration for the design of a communication infrastructure limited to secondary/assisting tasks related to Smart Grid automation; the Round Trip Time (RTT) is typically below 100 ms, fully compatible with the least demanding smart grid automation.
Thursday, September 24, 15:45 - 16:15
Thursday, September 24, 16:15 - 17:15
Architectures for Monitoring of Modern Distribution Grids II
Chair: Paolo Attilio Pegoraro (University of Cagliari, Italy)
- Design, Implementation and Real-Time Testing of an IEC 61850 based FLISR Algorithm for Smart Distribution Grids
- This paper presents a novel Distributed FLISR algorithm that uses Intelligent Electronic Devices (IEDs) configured to communicate the status changes and the measurements with one another using IEC 61850 GOOSE messages. Evaluation of the performance of the algorithm requires real-time simulation, therefore, a modular real time test platform using Real Time Digital Simulator (RTDS) and IEDs supporting IEC 61850 GOOSE is setup. A list of user-defined information including status changes and measurements that needs to be exchanged by the IEDs, required for implementing the proposed algorithm is presented. To validate the performance and showcase the flexibilities offered by the algorithm, like measurement-based selectivity in Service Restoration and covering of multiple faults, three case scenarios are simulated with a model of the real distribution grid, managed by A2A Reti Elettriche SpA in Brescia.
- Study for Assessing the Conformity of a Commercial Measurement System for Smart Grid Application
- The paper presents a novel distributed measurement system for monitoring the operation of MV power networks. It is made by Low Power Instrument Transformers featuring high accuracy, power quality bandwidth and allowing protection operation functions. The sensors are connected to a new Intelligent Electronic Device (IED), which implements many protection and measurement functions along with the most common communication capabilities. The presented system is going to be installed in A2A-Reti Elettriche SpA power network in Brescia, Italy. The measurement uncertainty has been experimentally evaluated and compared with that obtained through simulation analysis. Results confirm that this last procedure can be effectively used as preventive uncertainty analysis for allowing the choice of proper high accurate measurement and protection systems, according to the specified applications.
Thursday, September 24, 20:00 - 22:00
Friday, September 25
Friday, September 25, 09:00 - 11:00
Chair: Carlo Muscas (University of Cagliari, Italy)
- Assessment of rapid voltage changes using PMU data
- Recently the main IEC standard on measurements in the frame of power quality has been updated , and a new section has been added for rapid voltage changes [RVC] assessment. Also, in the standard it is acknowledged the variability of voltage signals and the need of validation of the "steady state" behavior of the system characterizing the measurement context. In this context it is proposed the 1s time interval within the voltage variability should relate to the dynamic behavior. This paper addresses the potential implications of the new standard on the measurement layer in LV grids and on the knowledge management process for various power systems applications. PMU data obtained with the highest reporting rate is used to identify a rapid voltage change event and to potentially discriminate it from voltage sags or swells.
- Improving the Accuracy of Synchrophasor-based Overhead Line Impedance Measurement
- Knowledge of real-time impedance parameters of overhead lines can significantly enhance power system monitoring and control applications such as dynamic line rating and fault location. To ensure high accuracy of the determined parameters, methods for error detection and correction are required. In this paper the impact and correction of systematic errors in the voltage phasors are considered and corrected using an optimization procedure. The effectiveness of the proposed method was demonstrated in a case study involving a laboratory-based overhead line model. In contrast to a least squares-based estimator, a significant improvement in the impedance parameter accuracy was achieved, even when only phasor measurements from similar loading conditions were used.
- Performance of Three-Phase WLS Distribution System State Estimation Approaches
- The roadmap towards the so-called Smart Grids calls for a clever and efficient management of the distribution systems. In this context, Distribution System State Estimation (DSSE) tools play a crucial role to acquire the knowledge about the effective operating conditions of the network and to enable the proper management and control functions operation. DSSE is usually performed by relying on a Weighted Least Squares (WLS) method. Different WLS formulations can be designed depending on the state variables used in the estimator. In this paper, an analysis concerning the two main classes of WLS approaches proposed for distribution systems is presented. Three- phase estimators with state variables based on both node-voltage and branch currents have been considered. The performances in terms of accuracy, efficiency and numerical properties are analyzed and discussed. Results obtained on the 123 IEEE distribution network are presented and discussed.
- Field Performance of Ambient Modal Estimation in Small Signal Stability
- Small signal stability is one focus of Wide Area Measurement Systems (WAMS). WAMS systems are becoming more widespread, driven by availability of synchrophasor data from Phasor Measurement Units (PMUs). In this paper, two methods capable of performing real-time small signal stability monitoring is evaluated by application to simulated data. Performance of the methods are tested to conditions likely to be found in practical use. The potential of both methods are further evaluated when applied to real-world data from a practical case study.
Friday, September 25, 11:00 - 11:30
Friday, September 25, 11:30 - 12:30
Characterization of Voltage and Current Transducers
Chair: Mihaela Albu (Politehnica University of Bucharest, Romania)
- Effects of Radiated Electromagnetic Fields on Measurements Performed by Air-Core Passive LPCTs
- The increasing interest versus the employment as measuring transformer of air-core current transformers, such as for example Rogowski coils, is mainly due a combination of factors: linearity, bandwidth, no saturation, small size, lightweight. International standard are therefore endorsing specific requirements and the performance of this kind of current sensors must be stressed under different working condition. In this paper, the effect of radiated electromagnetic fields on measurements performed by air-core current transformers are investigated with the aim of verifying if proper EMC tests are needed.
- Frequency calibration of voltage transformers by digital capacitance bridge
- In modern power systems, several conducted disturbances and power quality phenomena are commonly experienced also at medium voltage level. Therefore, voltage and current transducers, adopted to scale voltage/current waveforms down to levels compatible with the measuring instruments, are expected to accurately work over a proper range of amplitudes and frequencies, keeping the signal integrity needed to properly perform their measuring tasks such as energy billing, protection coordination and power quality monitoring. Thus, there is an increasing need of characterized and traceable methods s for the performance characterization of transducers in a wider frequency range. This paper focuses on a method for the calibration of medium voltage measurement transformers from power frequency to 2.5 kHz, which involves a two step procedure based on the use of a digital capacitance bridge. The system is designed for the characterization of VTs at rated primary voltage up to 20/√3 kV, by applying an harmonic frequency sweep, whose magnitude can be selected from 2 % to 10% of the primary voltage.