essential tools for monitoring and control of dynamic phenomena occurring in power grids and for ensuring the electric network reliability and stability.
20 2013 Smart Grid Conference (SGC) December 17-18, 2013, Tehran, Iran
Practical Aspects of Phasor Measurement Unit (PMU) Installation in Power Grids Shohreh Rabiee, Hosein Ayoubzadeh, Davood Farrokhzad Deputy of Grid Planning and Security Supervision Iran Grid Management Company (IGMC) Tehran, Iran Abstract— Phasor measurement units (PMUs) are becoming essential tools for monitoring and control of dynamic phenomena occurring in power grids and for ensuring the electric network reliability and stability. This paper discusses some valuable experiences and viewpoints associated with the practical aspects of PMU installation. Among the points discussed here are the required substation infrastructure and facilities, installation requirements, communication system preparation, and monitoring center establishment. Additionally, lessons learned from the project are thoroughly discussed which could be worthy for practitioners involved in similar projects.
I. INTRODUCTION Measurement system, without any doubt, has been a crucial means for the power system operation for over several decades. The old-fashioned measurement systems were tailored for each individual component and were lacking any wide-area coverage. They conventionally included generator output powers, bus voltages and injection powers, and transmission line currents and powers. This information was being used in local operation functions such as a single generating unit monitoring and control. In the late 1960s, a new class of measurement system came into use known as supervisory control and data acquisition system (SCADA). This huge infrastructure is still in charge for the power systems monitoring, operation, and control. SCADA gathers all available data across the power system in a central control room and provides a quasi-static image of network situation with an updating rate about 1-10 seconds. Due to the errorprone processes and asynchronous measurements, the difference between the SCADA captured image and the real situation of network is inevitable. This attribute degrades performance and effectiveness of the control center energy management system (EMS) and yields some difficulties and even deficiencies for the network monitoring and control. In recent years, a new generation of monitoring infrastructure referred to as wide-area measurement system (WAMS) has been introduced. WAMS, increasingly, appealed a significant interest all over the world and many pilot and practical WAMS projects are presently under development and their number is on the rise. This infrastructure, with an
978-1-4799-3040-1/13/$31.00 ©2013 IEEE
Farrokh Aminifar School of Electrical and Computer Engineering College of Engineering, University of Tehran Tehran, Iran updating rate about 50 frames/second or higher, is capable to provide a live image of network situation disclosing the dynamic phenomena [1]. WAMS, enabled by broadly deployment of phasor measurement units (PMUs), produces an image that is near real-time and very close to the system actual situation. This unprecedented feature is realized by PMU’s precise and synchronous data and direct phase angle measurements. Because of frequency never-ending changes and their effect in phasor calculations, busbar phase angles can be compared to each other only when they are calculated with an identical time reference. This requirement is alleviated in PMUs by receiving GPS synchronous signals. WAMS information enhances the situational awareness for control center operators by offering a number of real-time means. The situational awareness along with computation tools for the assessment of power network security will improve the decision-making process and applying control instructions in order to increase the network reliability [2]. WAMS has a centralized computational structure for the whole system real-time and long-term applications. Additionally, some local and even component-level functions are realized with synchrophasor data. PMUs transmit phasor measurements, frequency, rate of change of frequency, and digital states toward the phasor data concentrator (PDC) server via communication links [3], [4]. As a result, PDC receives all PMU data, aligns them regarding their time stamps, removes repeated overhead data, and nourish applications [5], [6], [7]. Generally speaking, WAMS applications are categorized into three classes: (1) Applications associated with network real-time operation covering situational awareness, frequency monitoring, power oscillations observation and trending, voltage monitoring and voltage instability prediction, setting system operating limits and alarming, special protection schemes and intentional islanding, variable and intermittent resource integration, state estimation, dynamic transmission line rating and congestion management, and outage restoration; (2) Applications relevant to the planning and system study tasks such as event analysis, baselining power system performance, validation and calibration of static and dynamic
21 system and component models, load characterization, study of primary frequency (governor) response, system inertial constant estimation, and operational planning; and (3) Closed-loop/autonomous control applications mostly falling in research and pilot-implementation stages [8], [9]. The first class of applications necessitates an extremely fast data collection, analysis, and quick decisions. However, the second group of applications relies on archived data; thus, the speed of data analysis and study is much less important. Implementation of WAMS in power grids consists of PMU installation and commissioning in substations and establishment of monitoring center. This paper discusses the practical aspects of a typical WAMS implementation project consisting of generic specifications of the project, substations defects and their associated solutions, and monitoring center capabilities. Amongst are the lack of three CVTs in some substation busbars, missing communication active equipments in some cases, lack of connection to the optical fiber network associated with some substations, particular condition of distributed control system (DCS) substations, logic of line connectivity to busbar, and determining PMU locations in substations. These issues would be digested in the following. II. GENERAL SPECIFICATIONS OF PMU INSTALLATION PROJECT The necessity of equipping the power grids with PMUs was felt in the consequence of power oscillation observations and postmortem analysis of widespread blackouts. The major reason of this tendency was due to the fact that the deep event and power oscillation analyses were impossible through the available data recorder devices. One of the suggestions was the PMU installation for dynamic monitoring of the network and for early recognition of abnormal conditions. Building a monitoring room to collect all PMUs data in a central location was obviously in essence. In the following subsections, the PMU placement strategy along with technical specifications of PMUs and monitoring center equipments are discussed. A. PMU Placement Strategy It is neither economical nor essential to equip all buses of any given network with PMU devices. Fast communication infrastructure, mainly based on the fiber optic technology, is a key building block of the WAMS. If this infrastructure does not have a fully coverage over the substations, alleviating the deficit is extremely costly and requires very long-time projects. Also, substation preparations to install PMU devices and associated accessories are of high expenditure. In the opposite direction, PMU indirect measurements, which are calculated quantities corresponding to a bus adjacent to a PMU-equipped bus, considerably enhance the WAMS observability over the network. The complete observability of the whole network could be guaranteed just with a limited number of PMUs counted to a small fraction of network buses; however, they have to be located in strategic places. In countries intending to install a number of PMUs as a pilot WAMS project with local or distributed observability, but incomplete, PMU locations are usually determined according to a set of qualitative criteria. This approach adopts the following locations as PMU installation candidates [10]:
• Substations associated with large power plants which are effective in the network stability and frequency control; • Substations delivering bulk power or serving very strategic demands; • Substations of main power transmission corridors; • Substations located in an area with observed or suspected dynamic phenomena; • Substations of transmission lines linking neighbor systems. According to the abovementioned criteria, a number of substations should be selected for the PMU installations in the initial stage of WAMS development project. After that, extra PMUs are to be installed in the grid with the aim of complete observability of the network and subjected to the location of existing PMUs [11]. Probabilistic studies could also be employed for this purpose [12]. B. PMU Technical Specifications Typically, PMU devices have 32 analog inputs in eight isolated cards for current and voltage measurements, 16 digital inputs in two isolated cards, GPS receiver including GPS antenna connectivity for the time synchronization, and communication ports in front and rear. The sampling rate is 144 samples/cycle (or 7.2 kHz) and the reporting rate of data toward the monitoring center is 50 frames/second. The connection of PMU devices with PDC server in monitoring center is compatible with IEEE C37.118 standard. Each data packet includes frequency, rate of change of frequency, and phasor of three-phase bus voltage and line currents, and it is extendable as well to comprise line active, reactive, and apparent powers, and phasor sequence values. Two software packages are associated with PMU devices; one of which was deemed for PMU management and settings such as defining data reporting rate, setting fault recorder trigger thresholds, downloading the PMU recordings, and remote diagnostics. This software, furthermore, provides a real-time and direct access to PMU measurements with additional analyses such as harmonic content spectrum. The other software is to visualize and analyze PMU recordings and converting them to ordinary data files. This software is installed in the control center workstations. C. Monitoring Center Equipments The following equipment and settings were considered for the monitoring center: (1) Ten clients for monitoring center and offline study room; (2) Three sets of servers including main and backup sets for acquisition, archiving, and WAMS applications; and (3) Monitoring center software package tailored for the application server. The acquisition server (PDC) collects all PMU data, the archiving server periodically stores the collected data, and the application server uses the PDC data and executes the WAMS applications. In this project, WAMS functions incorporate: • Monitoring and trending of real-time PMU data such as magnitude and phase angle of voltages and currents, frequency and its rate of change, and power quantities; • Visualization and graphical presentation of PMU data, • State estimation and calculating indirect measurements;
22
for
all
Monitoring Center
Servers Cat 6 1 GB switch Server Room Fiber Optic
Cat 6
SDH
III. COMMUNICATION REQUIREMENTS The first and foremost challenge in the WAMS implementation project was the deficits of communication infrastructure for PMU data transfer toward the monitoring center. The communication system overall structure from substations to the monitoring center and in the substations are depicted in Figs. 1 and 2, respectively. Referring to Fig. 1, data transfer capability from substations to the monitoring center is feasible only when the substations are equipped with active communication devices. Hence, all PMU installation candidate substations are to be fall in the optical fiber network with 2 Mbs dedicated bandwidth plus an IP/PMU. The existence of a switch in the communication structure of substations, shown in Fig. 2, is to provide the possibility of adding one or more additional PMUs to the substation. If more than one PMU are installed in a substation, one IP and 2 Mbs bandwidth will be dedicated to each PMU. Also, the output of every PMU would be connected to the switch via a optical fiber, an optical convertor, and a Cat 6 cable. In such a case, PMUs’ data would be transferred to the monitoring center via an optical fiber with 2n Mbs dedicated bandwidth for the substation with n PMUs. It should be noted that Cat 6 is a standard cable for the gigabit Ethernet and has more precise characteristic against system noise and cross talk in comparison with Cat 5 cables. The main reason for the IP dedication to PMUs is to offer the possibility of direct connection to each PMU devices. The connection actualizes some critical options like downloading PMU recordings, substation real-time monitoring, distant diagnostics, and remote setting of parameters. From the communication system perspective, there were two major problems in the project: (1) some substations are not connected to the fiber optic network, and (2) some substations lack active communication equipment. These two issues are discussed in the following in detail. It is a prerequisite that all PMU installation candidate substations have to be connected to the optical fiber network; while, this condition did not hold in our project. These deficits were successfully alleviated by expanding the fiber optic network. However, the bad weather conditions, on one hand, and costly and time consuming process of procurement and installation of equipment, on the other hand, imposed an extra cost and delay beyond the project business plan. The other problem regards those substations missing active communication devices. In order to overcome this difficulty, the nearest substation equipped with active devices was selected and the communication path was completed using two switches and an optical fiber link. This solution is shown in Fig.3. The proposed scheme was successfully implemented.
Clients
• Monitoring of phase angle differences; • Alarming based on predefined margins measurement and calculated values; • Playback of pre- and post-fault instants; • Frequency-based islanding recognition; • Oscillation detection and analysis; • Voltage monitoring and instability prediction.
Private WAN Fiber Optic
2 Mbs dedicated bandwidth
S.S.2
S.S. 1 S.S. SDH
S.S.26
S.S. SDH
S.S. SDH
S.S.: Substation Fig. 1 Communication structure from substations to the monitoring center. SDH Rack Cat 6
Optical fiber
O.C. Cat 6 Switch
S.S. Communication Room O.C.: Optical Convertor
PMU Rack PMU
S.S. Control Room
Fig. 2 Communication structure from PMU rack to SDH rack. Substation 2
Substation 1
SDH Cat 6 Switch 2
Nearest S.S. with SDH
Optical fiber
PMU System Cat 6 Switch 1
PMU-equipped S.S.
Fig. 3 Communication system structure in substations lacking SDH
IV. SUBSTATIONS PREPARATION FOR PMU INSTALLATION In the preparation process of substations for the PMU installation, we encountered to two different challenges: (1) feeding three-phase busbar voltage signals to the PMU analog inputs, and (2) determining the appropriate location of PMU in substations, manufacturing and installation of a PMU host rack, and needed cabling and wiring. These two challenges and their related solutions are discussed in this section. A. Feeding Three-Phase Busbar Voltage Signals to the PMU PMU analog inputs are lines’ currents and busbar voltages acquired from the secondary side of instrumentation current and capacitor voltage transformers (CTs and CVTs). PMU in a given substation measures currents of several transmission lines originating from the substation and voltages belonging to the substation busbar. The positive sequence of voltages and currents is of a great value in its own right. These desired quantities of a network constitute its state vector and are key inputs for many steady-state analyses such as load flow. Recalling fundamentals of unbalanced system analysis, calculation of positive sequence quantities associated with currents and voltages requires three-phase values. Hence, in substations hosting PMUs, it is necessary to apply three-phase busbar voltages and line currents to the PMU analog inputs. This requirement was, however, not met in majority of substations since they had just one single CVT on one phase
23 of the busbar (usually on phase B). This attribute is a shortcoming for the PMU installation, although it was justifiable in the past because one busbar CVT was sufficient for the synchronization purpose and for the awareness of busbar live or dead status. The proposed solutions are:
new CVTs were not identical with the existing one, three CVTs were purchased and installed. (3) The remaining substations have four or less transmission lines. Thus, the third solution, i.e. feeding all transmission lines’ voltage data to the PMU analog inputs, was taken.
(1) Installation of two CVTs similar to the existing one: This is the best and most reliable solution; while it is costly. (2) Using three-phase voltage of a transmission line instead of the busbar voltage: Even though this can be a suitable suggestion in the normal operation condition, voltage data will not be available if the line goes out of service. In such conditions, the data loss would not be limited to the bus voltage and encompasses all relevant calculations such as frequency, total harmonic distortion (THD), and active and reactive powers of all transmission lines. (3) Using all transmission lines’ voltages as the PMU analog inputs: Technically, this alternative is absolutely reliable since at least one of the transmission lines is always connected to the bus. In this solution, the number of analog inputs for currents and voltages should be identical. Thus, knowing that the number of PMU analog inputs is limited to eight, only four transmission lines would be maximally observed and installation of two PMUs is inevitable to monitor seven transmission lines. Procurement of the additional PMU along with its subsidiary accessories such as more voltage cablings makes this solution very costly and uneconomical in most substations. However, it is a justifiable and technically sound solution for substations with four or less transmission lines. (4) Allocation of one PMU device and using a selection relay alongside PMU to select the PMU voltage input among several line voltage data: For this purpose, the voltage data of all transmission lines is applied to this relay and it selects only one set and passes it to the PMU analog input. The process of line selection will be relied on the breaker status and Under-Voltage relay condition. The disadvantage associated with this solution will appear when the breaker of line whose data is feeding to the PMU opens. In this situation, the selection relay should be able to verify the faulty condition and switch to another line with closed breaker. The required time for this replacement is about hundreds of milliseconds. At this time duration, voltage measurement, voltage phasor calculation, system frequency, and all transmission lines active and reactive powers will be invalid. Moreover, it should be emphasized that the line trip might be due to an event in the power system and the PMU data is evidently of an extreme importance in such a situation.
The other point regarding the bus voltage issue is that in some substations with 1.5 breakers or double-busbars configurations, there are two busbars. As it is probable that the busbar whose voltage is applied to the PMU becomes dead, the substation voltage data might be inaccessible for some whiles. The only solution for this difficulty is to equip two busbars with three CVTs and dedicate two analog channels to the voltages. However, as the probability of this situation is too low and the cases leading to the malfunction of PMU data reporting is not limited to this event, in this project, just one busbar was equipped with three CVTs.
In the project at hand, the following cases were encountered and resolved. (1) Some substations were already equipped with three CVTs and the bus voltage data was fed to the PMU analog input. (2) Some substations were already equipped with just two CVTs and some others had only one CVT on their busbars. For these substations, the first solution was taken and one or two CVTs were installed. Note that in substations where the
B. PMU Locationing and Other Installation Tasks Subsequent to overcoming the voltage measurement problem, the next stage was to determine the location of PMU in substations. The first and utmost factor of specifying PMU location is the necessity of PMU installation in the protection path. The reason for this decision is that PMU data are vital for faults analysis. As the saturation of CT measurement cores in faulty conditions is very likely, it is essential to use currents derived from the CT protection core in the PMU analog inputs. The other factor is the distance between PMU rack and the nearest window or free sky access for the GPS antenna installation. In order to avoid signal quality attenuation, the distance between GPS antenna and GPS card should not exceed 15 meters. Therefore, this limitation should also be satisfied in determining the location of PMU rack. Finally, all cablings associated with busbar or transmission lines voltage (based on solution taken), lines currents, and breaker and disconnect switches status were performed. Some information was required for PMU settings and their commissioning. The process of gathering this information was done in parallel with manufacturing of PMU rack and performing the cabling and wiring. This information includes the technical specifications of CTs and CVTs feeding the PMU, substation short circuit levels, GPS antenna locations, and the distances between PMU racks and SDH racks. V. LOGIC OF TRANSMISSION LINE CONNECTION TO BUSBAR In order to provide the awareness of transmission lines’ connectivity to the busbar, PMU digital inputs are employed. For this reason, the status of breakers and line disconnect switches were used. Depending on various configurations of these binary signals in 1.5 breaker and double-busbar substations, the implemented logic for them was different. These issues are covered in the flowing. A. 1.5 Breaker Substation In these substations, which their configuration is depicted in Fig. 4 (a), if one of the breakers and the line disconnect switch are closed, the associated line is connected to the busbar. Therefore, as shown in Fig. 4 (b), the implemented logic whose output is applied to the PMU digital input is an
24 "OR-AND" circuit. To do so, status of breakers are inputs of "OR" gate, and the status of line disconnect switch along with the output of the "OR" gate are the input of "AND" operation. It is obvious that if the logic output is 1, the relevant line is connected to the busbar; otherwise, the line is disconnected. Busbar 1
CB1
CB3
CB 1 CB 2
OR AND
Line DS
CB
AND
Line DS
PMU digital input
OR Bypass DS
PMU digital input
(a)
(b)
Fig. 6 A double-busbar substation with bypass disconnect switch a) substation schematic b) the implemented logic for PMU digital input Line DS CB
DS: Disconnect Switch CB: Circuit Breaker (a)
Some of 1.5 breaker substations do not have the line disconnect switch and is equipped with the earth disconnect switch, as illustrated in Fig. 5 (a). In these substations, the status of earth disconnect switch is used in the digital input logic. The logic designed for these systems is shown in Fig. 5 (b). As it can be seen, the logic is similar to that of ordinary 1.5 breakers substations, but the "NOT status of earth disconnect switch" is applied to the "AND" gate. At these substations, lines will be connected to busbar if at least one of the breakers is closed and the earth disconnect switch is open. CB 1 CB 1 CB 2
CB 2
OR
E DS NOT
AND
PMU digital input
CB 3 Busbar 2 EDS: Earth Disconnect Switch (a)
CB 1 Line DS
Busbar 1
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Fig. 4 A 1.5 breaker substation with line disconnect switch: a) substation schematic b) the implemented logic for the PMU digital input
EDS
Bypass DS
CB
Busbar 2
Busbar 2
Busbar 1
Line DS
Busbar 1
Line DS
CB2
of the breaker status with line disconnect switch is applied to the PMU digital input.
(b)
Fig. 5 A 1.5 breaker substation with earth disconnect switch a) substation schematic b) the implemented logic for PMU digital input
B. Double-Busbar Substation Double-busbar substations exist in different topologies. Therefore, the procedures of utilized logic for their PMU digital input are dissimilar. (1) In some double-busbar substations, there are bypass disconnect switches, as shown in Fig. 6 (a). Hence, to create PMU digital input signal, an "AND-OR" circuit was employed, shown in Fig. 6 (b). The breaker and line disconnect switch status are inputs of "AND" gate. The result of this gate together with the status of bypass disconnect switch are considered as "OR" gate inputs. The line is connected to the busbar either the bypass disconnect switch is closed or both breaker and line disconnect switch are closed. (2) Some other double-busbar substations have simple configurations with no bypass disconnect switch. Figs. 7 (a) and (b) demonstrate the substation schematic and the logic used for the PMU digital input, respectively. As seen, “AND”
PMU digital input
AND
Busbar 2 (a)
(b)
Fig. 7 A double-busbar substation without bypass disconnect switch a) substation schematic b) the implemented logic for PMU digital input
VI. DCS AND CONVENTIONAL SUBSTATIONS In comparison with conventional substations, in DCS substations, protection and control racks are not located in a room and racks related to each bay are distributed in bay control rooms (BCRs). Unlike conventional substations where all required signals including lines’ current, voltage, and breakers status are available in the control room, in DCS substations, the signals are distributed in BCRs which are usually far away from each other; thus, there is no central access to prescribed signals. There are two suggestions: (1) Allocation of one PMU for each BCR: This alternative proposes installation of one smaller PMU with fewer current inputs in each BCR. According to Fig. 9, the output of each PMU would be transmitted to a switch in the substation via optical fibers. In this solution, we have to assign 2 Mbs bandwidth for each PMU and consequently, we have to consider 2n Mbs bandwidth for a substation with n BCRs. Talking about the economical aspects, the installation and commissioning of n PMUs, procurement of several optical fibers, GPS antennas, and PMU software packages render this solution very costly and rather uneconomical. DCS substation with n BCR
BCR1
PMU1 4 V /12 C /16 dig. Inputs
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Fiber Optic V: Voltage C: Current dig: digital
PMU2 4 V /12 C /16 dig. Inputs
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Switch 2n Mbs dedicated Ethernet PDC
Monitoring Center
Fig. 9 Assigning one PMU for each BCR in DCS substation
(2) Allocation of one PMU for a BCR or control room and wiring from other BCRs: In this solution, as shown in Fig. 10, a PMU will be installed in one of BCRs or in the control room and all demanded signals will be transferred to the PMU location by cabling from other BCRs. In some
25 substations, since the distance between BCRs or between BCRs and the control room are too long, it is essential to calculate the cables’ cross section based on the available CT burden. This method is more economically viable. DCS substation with n BCR BCR 1
BCR 2
Control Room
BCR n
(1) Preparation of monitoring center building map. (2) Preparation of monitoring center wiring. (3) Preparation and implementation of monitoring center Ethernet network. This network is dedicated to this center. (4) Procurement of standard furniture (5) Installation of air conditioner units for all spaces. More powerful units were considered for the server room. (6) Installation of the video-wall for the monitoring room.
PMU Required cabling
4 V/ 28 C /16 dig. Inputs
2 Mbs dedicated Ethernet Monitoring Center
PDC
Fig. 10 PMU installation in one BCR or in the control room and performing required cabling from the other BCRs
In the current project, there are three DCS substations: (1) In one of substations, there are three BCRs for feeders and one BCR for the busbar protection scheme. Since all required signals are available in the busbar protection BCR, similar to conventional substations, only a single PMU device was installed in this BCR. However, all breakers’ status were unavailable in this BCR; hence, the required ones were transferred by additional wiring. (2) In another substation, there are two BCRs which are 100 meters away. Thus, a PMU was installed in the BCR which is nearer to the control room and all required cabling was performed from the other BCR. (3) The last DCS substation has three BCRs one of which is farther (600 meters) from the other BCRs and the control room. Taking the second solution and choosing the control room as the PMU location, required calculations such as CT burden and current cable cross sections were performed and existing current cables were replaced with proper ones. VII. MONITORING CENTER ESTABLISHMENT Along with substations’ infrastructure preparation, monitoring center was established according to the associated standards. This center encompasses the following spaces: (1) Monitoring room for real-time applications such as situational awareness through visualization of network states and trending PMUs’ output. Five clients are considered for this room and each has access to the WAMS software and to PMU devices. A video-wall for comprehensive monitoring and teamwork tasks and discussions is also equipped. (2) Offline study room for power system and component static and dynamic analyses based on WAMS archive and PMU recordings. This section includes four clients responsible for event analysis, system baselining, component and system model validation and correction, investigating new credible applications, etc. (3) Server room (4) Conference room. The following tasks were conducted for the establishment of the monitoring center:
VIII. CONCLUSION The rapidly increasing activities of advanced countries in development of WAMS infrastructures indicate the undeniable role of these systems for the enhancement of power system operation and security as well as for ensuring the electricity service reliability. In large power grids, the studies on large disturbances and observed oscillations revealed the unavoidable requirement for the PMU installation and WAMS development. This paper reviewed the reasons convincing us to initiate the WAMS development project, requirements of PMU installation and commissioning, communication infrastructure and substations defects and solutions, and WAMS monitoring center establishment process. All experiences and lessons learned in this project were discussed in detail which could be fruitful in similar projects. A group has now initiated the network analysis including offline studies and achievements would be gradually presented. REFERENCES F. Aminifar, D. Farrokhzad, and M. Fotuhi-Firuzabad, “Wide-area measurement system (WAMS): history, structure, current applications and future operations,” Smart Grid Conference, Tehran, Iran, Oct. 2010. [2] T. Bilke, “Phasor measurement impact for regional reliability awareness,” Power Energy Soc. Gen. Meeting, Jul. 2008, pp.1-2 [3] A. G. Phadke and J. S. Thorp, Synchronized Phasor Measurements and Their Applications. New York: Springer, 2008. [4] D. Karlsson, M. Hemmingsson, and S. Lindahl, “Wide area system monitoring and control - terminology, phenomena, and solution implementation strategies,” IEEE Power Energy, vol. 2, no. 5, pp. 6876, Sep./Oct. 2004. [5] A. G. Phadke, “System of choice,” IEEE Power Energy, vol. 6, no. 5, pp. 20-22, Sep./Oct. 2008. [6] K. Martin and J. Carroll, “Phasing in the technology,” IEEE Power Energy, vol. 6, no. 5, pp. 24-33, Sep./Oct. 2008. [7] S. Chakrabarti, E. Kyriakides, T. Bi, D. Cai, and V. Terzija, “Measurements get together,” IEEE Power Energy, vol. 7, no. 1, pp. 41-49, Jan./Feb. 2009. [8] NERC, “Real-time application of synchrophasor for improving reliability,” available at:www.nerc.com/docs/oc/rapirtf/RAPIR%20final %20101710.pdf [9] V. Terzija et al, "Wide-area monitoring, protection, and control of future electric power networks,” IEEE Proc., vol. 99, no. 1, pp. 80-93, Jan./Feb. 2010. [10] F. Aminifar, M. Fotuhi-Firuzabad, M. Shahidehpour, and A. Safdarian, "Impact of WAMS malfunction on power system reliability assessment," IEEE Trans. Smart Grid, vol. 3, no. 3, pp. 1302-1309, Sep. 2012. [11] F. Aminifar, M. Fotuhi-Firuzabad, M. Shahidehpour, and A. Khodaei, "Observability enhancement by optimal PMU placement considering random power system outages," Energy Syst., vol. 2, no. 1, pp. 45-65, Mar. 2011 [12] F. Aminifar, M. Fotuhi-Firuzabad, and A. Safdarian, "Optimal PMU placement based on probabilistic cost/benefit analysis," IEEE Trans. on Power Syst., vol. 28, no. 1, pp. 566-567, Feb. 2013 [1]
