Application Of PMU Based Information In Improving The .
Application of PMU Based Information in Improvingthe Performance of Indian Electricity GridV.K.AgrawalGeneral Manager , NLDCPower System Operation CorporationNew Delhi, IndiaP.K.AgarwalHarish RathourDy. General Manager , NLDCPower System Operation CorporationNew Delhi, IndiaManager, NLDCPower System Operation CorporationNew Delhi, IndiaAbstract—SCADA/EMS system has been the most commonlyused tool for real time power system operation and controlthroughout the world. This system has been found to be veryuseful in steady state analysis of the power system. The everincreasing dependence of human society and country’s economyon electrical energy calls for reliable power delivery. In order tomeet these expectations, engineers across the globe have beenexploring for new technologies that can improve upon thelimitations of SCADA and provide dynamic visibility of thepower system. A breakthrough has now been achieved in urements using PMU deployed over wide-area, facilitatedynamic state measurement and visualization of power systemwhich are useful in monitoring safety and security of the gridThe Power System Operation Corporation (POSOCO) has takenup initiative and implemented its first pilot project in NRwherein nine Phasor Measurement Units (PMUs) along with onePhasor Data Concentrator (PDC) were commissioned. Theprimary objective of this pilot project was to comprehend theSynchrophasor technology and its applications in Power Systemoperation. The data received and information derived from pilotproject have been found very useful and helped in improving theperformance of the grid operation in several ways. The pilotproject is operational since last 2 years. Meanwhile otherinitiatives have been taken up and pilot/demo projects are beingimplemented in other regions also by Power System OperationCorporation. This paper detailed out the utilization of datacollected from these pilot/demo projects and application of thedata towards improvement in operation of the Indian asors, Wide Area MonitoringOscillations, PSS Tuning.I.UnitsSystem(PMU),(WAMS),the same time, industrialization and automation is putting morepressure on secure, reliable and environment friendly deliveryof electrical energy. In order to meet these expectations underever increasing risk, new technologies that can improve uponthe limitations of SCADA are being explored. A breakthroughhas now been achieved in the form of Synchrophasortechnology which has capability to provide time synchronized,dynamic visibility of the power systemUtilities in several countries are experimenting withSynchrophasors and trying to utilize the data that would assistthe System Operators in real-time as well as post dispatch. ThePower System Corporation has implemented a pilot projectwherein nine PMUs have been deployed for acquiring phasordata from widely dispersed locations in Northern India. In theproject, time synchronized data is telemetered at high speedfrom phasor measurement units (PMUs) at high speed throughOptic Fiber communication and at Phasor data concentratorlocated at northern Region Load Despatch Center (NRLDC).The objective of the pilot project was to gain a first-handexperience of synchrophasors based Wide Area MeasurementSystems (WAMS) before its large scale deployment in India.Since the commissioning of this project, POSOCO is utilizingthe information acquired from synchrophasors data inimprovement of grid performance in several ways. Some ofthese are as mentioned below: INTRODUCTIONElectricity energy being the most basic raw material for anyactivity of human being and its ever increasing role incountry’s economy must be delivered with security and highreliability.Until now, Supervisory Control and DataAcquisition system is very humbly discharging the duty ofmanaging power grid efficiently by providing the static view ofthe grid to the grid operators. But integration of widelydissimilar generating resources, increases in demand of morepower flow on limited transmission resource have resulted inexponential increase in the complicity of the grid operation. AtV.K.Agrawal is General Manager with National Load Despatch Center of thePower System Operation Corporation Ltd, B-9, Qutub Institutional Area, Katwaria Sarai,New Delhi, India ( e-mail: vkagrawal@ieee.org).P.K.Agarwal is Dy General Manager with National Load Despatch Center of thePower System Operation Corporation Ltd, B-9, Qutub Institutional Area, Katwaria Sarai,New Delhi, India ( e-mail: pkagarwal@ieee.org).Harish Rathour is Manager with National Load Despatch Center of the PowerSystem Operation Corporation Ltd, B-9, Qutub Institutional Area, Katwaria Sarai, NewDelhi, India ( e-mail: harish.rathour@gmail.com). Enhancing situational awareness in real-time.Setting of df/dt relays.Forensic analysis of faults/Disturbance analysis /determining the exact instant of fault and faultclearing time.Detection and analysis of oscillations in the powersystem.Angular separation value observed through the PMUalso helps in validating the network model in theSCADA as well as offline simulation packages.Validation and determining the need of SpecialProtection SchemesIt has been found that that synchrophasors can dramaticallyimprove the performance of grid operation and monitoring inseveral ways. Several other initiatives have also been taken upby POSOCO in the form of pilot projects in other regions i.e
Western Region, Southern Region, Eastern Region andSouthern Region. All the pilot projects will finally beintegrated in National Level pilot project underimplementation as extension of NR pilot project. By the end ofDecember 2012, a National Level pilot project will beavailable with about 53 PMUs located all over of India. Thispaper deals with experiences and improvements carried out toIndian power grid from the real time as well as historical dataobtained from synchrophasors pilot projects. The paperelaborates upon the details of the pilot project implemented inNorthern Region and also includes the case studies detailingthe applications of the information obtained from the pilotproject.II.time phasor data to SCADA visualization for displaying theload angle values between various points of the Northern Grid.PILOT PROJECT IN NORTHERN REGIONThe NR project comprised of Phasor Measurement Unit(PMU) along with GPS clock at strategically selected ninesubstations in the Northern Region. Phasor Data Concentrator(PDC) and other associated equipment have been installed atNorthern Regional Load Despatch Center (NRLDC), NewDelhi [1].The primary objective of the WAMS pilot project in NorthernRegion (NR) was to comprehend the WAMS technology andits applications for Power System Operation. Further, it wasalso understood that the PMU commissioned at a substationcould be relocated very quickly in case the earlier selection oflocation was not found appropriate. Therefore, a heuristicapproach was adopted for faster implementation. Since, thenumber of PMUs were small in comparison to the totalnumber of buses in Northern Region, PMU locations wereselected strategically rather than optimally. Figure-1 showsthe locations existing Phasor Measurement Units in NorthernRegion The broad criteria used for selection of PMU locationsin Northern Region are: Locations separated by large geographical distance. Locations with large load angle separation. Locations near large Generating Stations / CriticalNodes. Locations having fiber optic communication link withthe control center Locations important from point of view of operationand prospective power system augmentation.In order to implement the project in minimum possible time,initially only 4 PMUs and one data concentrator were installedin May 2010. Facility of data storage along with easy dataexchange with other system was also provided, in order toanalyze the data in commercially off the self (COTS) availablesoftware like Microsoft Excel, Matlab etc. After gaining theexperience and realizing the significance of phasormeasurement, subsequently, five more PMUs were added tothe project in Jan 2011. The phasor LAN of the project wasalso integrated with the existing SCADA LAN to transfer realFigure 1As on date Fourteen (14) PMUs have been installed underdifferent pilot projects out which nine are installed in NorthernRegion, two in Western region and three in Southern region.The three Phasor Data Concentrators (PDC) have also beeninstalled at the respective Regional Load Despatch Centers(RLDCs) located in New Delhi, Mumbai and Bengaluru.Placement of PMUs/PDCs at few more locations in India hasbeen envisaged under the pilot projects taken up by theRLDCs. The existing WAMS in Western and Southern Regionare demonstration projects, while in the Northern Region it iswas a pilot project. Figure-2 shows the locations existingPhasor Measurement Units in India.Figure 2
III.SYNCHROPHASORS APPLICATION WORLDWIDEWorldwide many utilities from North America, Europe,China, Russia and Brazil have started using/developing thenew PMU applications to harness the potential benefits of thisemerging technology in operating very large electrical grids.In 2006, China's Wide Area Monitoring Systems (WAMS) forits six (6) grids had 300 PMUs installed mainly at 500kV and330kV substations and power plants. Presently China hasinstalled more than 1000 PMUs in their Grid. By 2012, Chinaplans to have PMUs at all 500kV substations and all powerplants of 300MW and above. In U.S there are ten(10)synchrophasor projects underway involving 57 utilities andgrid operators across the country and installing about 850networked PMUs. By 2013, the devices will be operating innearly all regions of the country. The Eastern InterconnectPhasor Project (EIPP) (now known as the North AmericanSynchrophasor Initiative, or NASPI www.naspi.org/), has over40 connected phasor measurement units collecting data into a"Super Phasor Data Concentrator" system centered atTennessee Valley Authority (TVA). Southern nment)issuccessfully using synchrophasors today to trigger someautomated grid protection functions on their System. e.com) uses synchrophasor technology as apractical tool to locate and solve real-world operatingproblems. The utility has added more than 100 PMUs to thesystem, which provided monitoring almost 30% of itstransmission grid. From the synchrophasor data, OG&E candetermine if a disturbance is cleared by high-speed or stepdistance (delayed) tripping. The data is being used to locatethe source of event disturbance and proceed with aninvestigation. Another valuable use of synchrophasor data isthe detection of equipment failure, most of which is notdetectable by SCADA system. System stability assessment isbeing carried out using synchrophasor data especiallycapturing the intricacies of an interconnected system like lowfrequency oscillations due to generation control problem orother reasons. The benefit of PMU measurements at the pointof wind farm interconnection facilitates customer to receiveclean power (in terms of voltage fluctuation/flicker) whilemaintaining the level of system stability necessary for reliablepower system operation. Apart from above nations, othercountries like South Africa, Brazil, USSR, Western ElectricityCoordinating Council (WECC)(http://www.wecc.biz) whoseservice territory extends from Canada to Mexico and someEuropean countries have deployed/ planning to deploy a largeno. of PMUs in their system [3].IV.APPLICATIONS OF SYNCHROPHASORS DATAWhen the first commercial PMUs became available, postevent monitoring was the only application due to the lowavailability and high cost of communications channelsrequired for real-time monitoring, control, and protectionapplications [4]. New information and communicationtechnologies enabled synchrophasors to be processed in realtime [5]. Utilities and vendors in several countries are strivinghard to utilize phasor measurement data in real timeapplications from early warning and improving operator’ssituational awareness to wide area control and protection.Since, pilot project in NR, was implemented with a minimalistapproach, no real time applications was acquired with theproject. PMU data from the project is being utilized forforensic analysis of faults; post-dispatch analysis of gridperformance and; detection and analysis of oscillations in thepower system. During the period of last 2 years, several eventanalysis were carried out successfully with the help of datafrom the PMU. Information from the project were founduseful in taking decisions at various instant of time at thecontrol center by increasing the visualization depth to the gridoperators which helped in improving the performance of theIndian electric grid. Rest of the section of this paper willdescribes some of the such applications of PMU data andinformation used in different regions. However, an overviewof the applications of synchrophasors data used in differentregions in real-time and offline have also been summarized.V.UTILIZATION OF SYNCHROPHASORS IN REAL TIMEThe synchrophasor data is currently being used in differentregions for the following applications in grid operation:i). Improving Situational awareness through real timemonitoring of frequency, df/dt, angular separation.ii). Occurrence of transmission line tripping/ revivalwithin a flowgate by observing Step change in angular separation. Step change in line current (MW & MVAR)iii). Occurrence of generator tripping by observing: Frequency decline Increase in df/dt Change in angular separation Decrease in voltage magnitudeiv). Occurrence of auto reclosure by change in df/dt.v). Occurrence of load crash/ load throw off by observing Sustained High frequency Sustained abnormal phase angle separation Sustained High voltagevi). Help in subsystem synchronization during restorationby using standing phase angle separation and phasesequenceVI.UTILISATION OF SYNCHROPHASORS DATA IN OFFLINESynchrophasors data is being used in grid operation at variousinstances of off line applications as listed below: Visualization of power system dynamics with thehelp of State measurements. Visualization of phasors, sequence components,angular separation, inter area oscillations, df/dt,voltage dip during fault, voltage recovery afterclearance of fault, synchro-check etc.
Extensive utilization for post event (forensic)analysis. It helped in detection of type of fault(phases involved), Identification of the phase inwhich fault has occurred, Fault clearing timeProtection mis-operation detection.Detection of various modes in low frequencyoscillation using techniques like Prony Analysis, FastFourier Transform etc.Detection of inter area/local mode oscillationsValidation of operation of under frequency and df/dtrelays due to availability of high resolution frequencydata at the control center.Used in computation of Frequency ResponseCharacteristicDelay of 8 cycles was introduced in the df/dt relaysin Northern Region to reduce spurious operations.Identification of coherent group of generators duringgrid eventObserving SVC response during grid eventsValidation of operation time of SPS used for intertripping generating units at Karchan Wangtoo aftertripping of evacuation linesValidation of Transfer Capability for evacuation ofKarcham Wangtoo generation; Oscillations werevisible when the actual power flow crossed theprescribed limitsValidation of Steady state network model inSCADA/EMSValidation of fault level as reported by DisturbanceRecorder and as computed from offline studies.VII. CASE STUDIES OF APPLIACTIONS OF SYNCHROPHASORSDATASynchrophasors data from the pilot projects implemented byPOSOCO, have been utilized in several ways like incidenceanalysis, detection of oscillations, validation of operations ofspecial protection scheme (SPS), fine turning of SPS etc.POSOCO has published a report titled “SynchrophasorsInitiative in India” comprising about 38 case studies. Thereport can be downloaded from the website of NLDC andRLDCs. Important case studies have been analyzed here.A. Incedence AnalysisFirst encounter of significance of information fromsynchrophasors were very exciting and revealing. Initialproject was completed in the month of May 2010. In June2010, a event took place at Rihand Super Thermal PowerStation (Rihand STPS) (Stage 1 with 2x500 MW and Stage IIwith 2x500 MW units) located in the lower right part of theNorthern Region. Rihand STPS switchyard has one & halfbreaker scheme. One of the tie circuit breaker, at RihandSTPS switch yard, went under lockout due to low air pressurein the breaker. While carrying out the switching operation toisolate the locked out breaker, Rihand STPS stage-I unitstripped on pole slipping. And after 7 seconds Rihand Stage-IIunit 3 tripped on FD Fan off and Unit-4 tripped on loss of fuelsupply.The event sequence could not be ascertained in NRLDCcontrol room only with SCADA data. However, when datafrom the pilot project’s historian was analyzed and a veryclear analysis of the event could be achieved. It was found thatthe cause of tripping was occurrence of some fault and not theswitching operation and envisaged initially. During thisanalysis, we could gain the experience of actual visualizationof df/dt and oscillations in the power system. During the lossof complete power station a decrease of 10 degree in theangular separation between Vindhyachal and Moga was alsoobserved. The comprehensive plot of the measurements fromPMU located in the vicinity of Rihand STPS has been shownin figure-3 which is self-explanatory.Figure 3B. Improved Grid Stress IndicationMost significance measurement from a Phasor MeasurementUnit is angular separation. The angular separation betweentwo nodes within a synchronous system is primarily a functionof the voltage at the two nodes; Impedance between the twonodes and the power flow between the nodes. Therefore theangular separation between the two nodes is sensitive to thevariation in one or more of these variables. The difference ofthe phase angles between any two buses in the power girdgives accurate indication of the grid stress. Higher the value ofthis angle, higher the stress of the grid. This phenomena hasbeen used in Indian power grid very successfully even muchbefore the implementation of WAMS pilot project. The phaseangle difference across different nodes is a measure of staticstress across the grid and its proximity to instability andtherefore can be monitored with respect to predeterminedstability threshold limits. These threshold limits are being putbased on the past experiences of the system separation andoffline simulations [6].On 22nd October 2006, Northern Region, NortheasternRegion, Bhutan system and parts of Eastern Region separatedfrom rest of the N-E-W (synchronized North, Easy and Westgrid) grid due to the tripping of a transmission line. Both thesystems survived and they were quickly synchronized back. Itwas observed that the export from Northern Region to rest ofthe grid continued to increase along with the angular
separation between Vindhyachal North bus and West bus tillThe oscillation were observed in the system as visualized fromthe plots of frequency from the data collected from PMUsinstalled under the pilot project as shown in figure-6. It wasobserved that magnitude of oscillations are more at Moga substation, which is nearest to the Tehri. Hence it was concludedthat source of oscillation is Tehri power station. Subsequently,PSS tuning of Tehri power station was carried out and afterthis no oscillations had been observed again. By this issue ofline loadability / transfer capability could be resolved with thehelp of synchrophasors.Figure 5the tripping point was reached [6]. The phase anglemeasurement was being done by phase angel transducer ininstalled at Vindhyachal. Figure-4 depicts the w
wherein nine Phasor Measurement Units (PMUs) along with one Phasor Data Concentrator (PDC) were commissioned. The primary objective of this pilot project was to comprehend the Synchrophasor technology and its applications in Power System operation. The data received and information derived from pilot
(PMU) in development. 2002 Electronic relays with built-in PMU functions. 2005. 2. nd. Standard IEEE C37.118. SEL standardized many relays with built-in PMU . 2011. 1,110 standalone PMUs, with tens of thousands of built - in PMU in relays. 2017. PXiSE uses PMU for control in all areas of the grid . 1982 - Standalone PMU. Very few used for .
quality" [9], PMU timing accuracy [11], real-time supervisory assessment of multiple PMU data streams [12], and latency [13]. The importance of rigorous testing of PMU-based systems is strongly emphasised in [14]. Utilities are already using PMU data as tools for visualisation and stability monitoring [15], but closed-loop control, i.e. where .
Phase measurement units (PMU) provide synchronized phasor measurements at the sampling rate of 30 or 60 sample per second; More than 2000 PMU are installed in the North America. PMU are generating large-scale of datasets in the power grid; Data-driven methods based on PMU data are promising to automatically locate and identify abnormal
quality" [9], PMU timing accuracy [11], real-time supervisory assessment of multiple PMU data streams [12], and latency [13]. The importance of rigorous testing of PMU-based systems is strongly emphasised in [14]. Utilities are already using PMU data as tools for visualisation and stability monitoring [15], but closed-loop control, i.e. where .
frequency stability based on PMU data [15-17]. Ref. [15] estimated the system active vacancy by using the pre-disturbance PMU data to realize the steady-state frequency prediction. Based on Ref. [15], according to the PMU information, Ref. [16] considers the variation of load and transmission loss
Figure 1 illustrates a typical structure of a PMU-based WAMS in a smart grid. Indeed, the wide-area measurements from PMUs, which is coherent and time-synchronized, can help increase real-time situational awareness for system operators to carry out time-critical tasks under critical conditions. This indicates that the PMU-based WAMS serves great
method and linear estimation that utilizes PMU measurements. In [12], a real-time fault detection and faulted line identifi-cation functionality is proposed based on computing parallel synchrophasor-based state estimators. In addition to new techniques based on graph and PMU data analyses, power system security has been extensively
program at TNB which explores the potential benefits of PMU -Several real-time PMU-based applications have been successfully developed . voltage and stability violations Future work will involve integration with production SCADA/EMS system and PMUs, and exploring other potential applications that will benefit from .
