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Implementation of Synchrophasor Technology for Better System Utilization & Reliability WAMS-WIDE AREA MEASUREMENT SYSTEMPMU-PHASOR MEASUREMENT UNITNeed for Synchrophasor Technology1. Visualisation of dynamic behaviour 2. Stability aspects3. Operate the system at its limits 4. Protections backup & adaptive + adaptive islanding5. State determination6. Empower system operatorsPhasor Representation 2Acos(2 f t +) or Aej or A A phasor is the complex form of the AC waveformPHASOR REPRESENTATIONStandards The original standard for PMUs, C37.1344, was released in 1995 and was reaffirmed in 2001. The new standard IEEE PC37.118 “Standard for Synchrophasors for Power Systems” has now replaced the earlier one. There are no IEC standards at the moment and it is most likely that the IEEE will become IEC standard as was in the case of the COMTRADE standard.MACRODYNE 1690 PMUPhasor Measurement UnitsA PMU by our convention measures bus voltage (phase or sequence) and all 3-phase line currents on all branches (transmission lines and transformers) emanating from the substation alongwith the phasor anglesFEATURES OF A PMUTIME TAGGED AC PHASORS +VE SEQUENCE VOLTAGES AND CURRENTS AS REAL & IMAGINERY QUANTITIES OR OUPUT AS MAGNITUDE & PHASE ANGLE FOR LOCAL & REMOTE APPLICATIONSFREQUENCY & RATE OF CHANGE OF FREQUENCYVARIABLE DATA TRANSFER RATES 1 PER CYCLE, 1 PER 2CYCLES OR 1 PER 4CYCLESSYNCHRONISED SAMPLING BY USE OF GPS- TIME TAGGING ACCURACY UPTO 50 SECOND(GPS ACCURACY OF 1 SECOND)ACCURATE PHASE ANGLE CALCULATION WITH ACCURACY OF UPTO 1 DEGREE OR LESSFEATURES OF A PMU-CONTINUEDCAN HANDLE 6 ANALOG CUURENT INPUTS WITH 3 ANALOG VOLTAGE INPUTS WITH OPTIONAL EXTENSION BY 100% 2 SETTABLE LEVELS FOR FREQUENCY AND RATE OF CHANGE OF FREQUENCY SETTABLE LEVELS FOR UNDER VOLTAGE & OVERCURRENT PICKUPONE NO CONTACT FOR ABNORMAL FREQUENCY, RATE OF CHANGE OF FREQUENCY, UNDERVOLTAGE & OVERCURRENT PICKUP LOSS OF DC AND OTHER INTERNAL SELF MONITORINGFEATURES OF A PMU-CONTINUED REMOTE COMMUNICATION PORT FOR TCP/IP AND STREAMING DATA IN IEEE1344 OR PC 37.118 SYNCHROPHASOR FORMAT OPTIONALLY ADDITIONAL OPTICAL COMMUNICATION PORT FOR TCP/IP AND STREAMING DATA IN IEEE1344 OR PC 37.118 SYNCHROPHASOR FORMAT FRONT MOUNTED MENU DRIVEN DISPLAY FOR DISPLAYING +VE SEQUENCE VOLTAGE AND CURRENT AS AMPLITUDE AND PHASE ANGLEPower P = V I cos() Reactive Power Q = V I sin() Compute MW & MVAR Synchronized MeasurementsLocation 1Location 2Phase angular difference between the two can be determined if the two local clocks are synchronized.Synchronizing pulses obtained from GPS satellites.Role of GPSConstellation of 24 satellites orbiting at 20,200 km Developed by US dept of defenseAvailable for free for civilian useBeyond navigation use, it provides time reference: Protection systems derive usage of GPS from the timing signal 4 satellites are needed for knowing timing and location position Satellites have atomic clocks Provides coordinated universal time (UTC) which is international atomic time compensated for leap seconds for slowing of earths rotations can obtain accurate timing pulse every second with an accuracy of 1 microsecondPMU Facts PMU uses discrete Fourier transform (DFT) to obtain the fundamental frequency components of voltage / current(Half cycle or Full cycle) Data samples are taken over one cycle / multiple cycles. Currently, sampling is done at 12 samples/cycle (IEEE C37.111 Std.). Resolution of the A / D converter is 16 bits.Communication Options Telephone lines Fiber-optic cables Satellites Power lines Microwave linksDelay Calculations Fixed delay Delay due to processing, DFT, multiplexing and data concentration Independent of communication medium used Estimated to be around 75 ms Propagation delay Function of the communication link and physical separation Ranges from 25 ms in case of fiber-optic cables to 200 ms in case of low earth orbiting (LEO) satellitesDelay Calculation TableCommunication linkAssociated delay one way (milliseconds)Fiber-optic cables 100-150Microwave links 100-150Power line (PLC) 150-350Telephone lines 200-300Satellite link 500-700Standards: Key Items Time reference = UTC (Universal Time Coordinated) Reporting rates = (10,25 phasors/sec for 50Hz system; 10,12,15,20,30 phasors/second for 60Hz system starting at the top of a second) Optional reporting rates 50/100 phasors/sec for 50Hz and 60/120 phasors/sec for 60Hz. Angle reference = cosine (0 deg at positive waveform peak) Communication model (standard frames and data types, interoperability)Integration of PMU dataHardware Requirements Phasor Measurement Units (PMU) placed at strategic substations Communication Links, including networking equipment at substations as well as at control centers Phasor Data Concentrator (PDC) Computer systems located at the central control centers, consisting of servers, storage, workstations and printing facilities.Software Requirements Phasor data collector software, for preprocessing of PMU data Basic monitoring applications Ergonomic graphical user interface, with results visualization facilities Core power system application software; Analytics Communications Though many communication media is possible, fiber optic provides, by and large, the most secure and fast communication medium. PMU placementIt is not at all necessary to place PMUs at all busses in the power system to make it observable. When a PMU is placed at a bus, then its neighbouring busses also become observable. In general, a system can be made observable by placement of PMUs on approximately 25% to 33% of the busses in the system Optimal PMU placement problem i.e., minimum PMU placement problem for system observability, can be formulated as an Integer Linear Programming (ILP) problem.PMU placement57 bus systemPMU Applications SCADA Displays State estimation Control (WAMS)/SPS Measurement based controls for: Voltage Stability Angle Stability Frequency Stability Event and system analysis Improved operational observability Dynamic System Stability Probe & Control - Power system damping-PSS PMU data trends can detect CB/switch status changes in the network, which will improve the topology estimationWAMSWAM Design ConstraintComputation time+Communication timeResponse time of the system dynamics trigger control actions like gen/load tripping or dynamic brake to prevent loss of synchronism.OR Allow graceful system separation and do intelligent load/gen tripping to stabilize frequency and voltage in islandFormer is preferable - no resynchronization of systems required BUT how does onea) Predict out of step in real time b) Determine quantum of control actionsFor controlled system separation :Adaptive choice of separation points conceivable NON-LOCAL measurements may helpSPS: How can WAMS help ? Frequency stability :Present day problems: Local frequency contaminated due to swings (1 -2 Hz). df/dt should not trigger on swings but on “common” motion of generator speeds. Solution: filter, but filtering will involve delay. Setting of df/dt relay should reflect actual power deficiency. Need to know total inertia (will need to know whether islanded or not, which generators in island)Conclusion : NON LOCAL signals will help!WAMS for Transmission Protection Systems Current Differential Protection can be implemented with ease: Most accurate Provides crisp zone of protection Free of non-idealities like tripping on power swings, non-tripping on voltage or current inversion, etc. Can be applied to series compensated lines Current Differential Scheme can be used to suitably block Zone-3 trips WAM based Z3 BlockingAs Line BC is quite long in comparison to AB, Zone-3 on AB at A can trip on power swingIf Current Differential Protection was implemented on line BC, it could be used to block Zone-3 of relay AB if no fault is detected by it on BCSince Z2 and Z3 timer setting are of the order of 15-30 cycles and 90 cycles respectively, communication delays will not be very criticalBlocking scheme will not impair but only improve the performance of the systemA Transmission System with a short line terminating into a long lineABCWAM Applications Islanding Detection Loss of Synchronism detection Average line temperature can be estimated from true line impedance: picture of thermal overloading if it exists Power System RestorationBetter picture better confidence level better decisions.More remote actionsRoadmap on improving existing transmission system utilization Provide better analytics to ISO/TSO to estimate line and system loadability Use WAMS to improve performance of system protection schemes WAMS based Out of step protection schemes WAMS based islanding schemes (smart islanding) Use WAMS to improve security of the existing transmission system protection schemes (smart protection)Initiative in WR Project under New Millennium India Technology Leadership Initiative Along with POWERGRID, other members of the consortium are TCS IIT Bombay Tata PowerImplementation of WR Project Part-I : Installation of PMUs and PDCs Data collection at PDC level and visualisation Part-II : Optimal placment of PMUs State Estimator based on PMU data System wide protection schemes Supervised Zone-3 blocking schemes Emergency control schemes Parameter validation Implementation of WR Project (contd) Project duration: 3 years 2 years for implementation and 1 year for testing Expert guidance from Prof. A.G. Phadke of Virginia Tech Total cost : 16.75 Cr + 2.21 Cr for making data available at SLDCs Project Initiatives for NR Number of PMUs 4 ; with PDC at NRLDC PMUs to be installed at Vindhyachal, Kanpur, Dadri and Moga Total project cost : 3 Cr. Implementation period : 3 months Order placed on SEL THANK YOU
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