Phasor Representation

Document Sample
Phasor Representation Powered By Docstoc
					      Implementation of
Synchrophasor Technology for
  Better System Utilization &
          Reliability



WAMS-WIDE AREA MEASUREMENT SYSTEM
   PMU-PHASOR MEASUREMENT UNIT
      Need for Synchrophasor
            Technology
1. Visualisation of dynamic behaviour
2. Stability aspects
3. Operate the system at its limits
4. Protections backup & adaptive +
   adaptive islanding
5. State determination
6. Empower system operators
   Phasor Representation
   A phasor is the complex form of the AC waveform



√2Acos(2 πf t +ө) or Aejө or A< ө
PHASOR REPRESENTATION
                 Standards
• 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 PMU
Phasor Measurement Units
A 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
angles
         FEATURES OF A PMU
• TIME TAGGED AC PHASORS

• +VE SEQUENCE VOLTAGES AND CURRENTS AS REAL &
  IMAGINERY QUANTITIES OR OUPUT AS MAGNITUDE & PHASE
  ANGLE FOR LOCAL & REMOTE APPLICATIONS

• FREQUENCY & RATE OF CHANGE OF FREQUENCY

• VARIABLE DATA TRANSFER RATES– 1 PER CYCLE, 1 PER
  2CYCLES OR 1 PER 4CYCLES

• SYNCHRONISED SAMPLING BY USE OF GPS- TIME TAGGING
  ACCURACY UPTO 50 µSECOND(GPS ACCURACY OF 1
  µSECOND)

• ACCURATE PHASE ANGLE CALCULATION WITH ACCURACY OF
  UPTO 1 DEGREE OR LESS
     FEATURES OF A PMU-CONTINUED

• CAN 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
    PICKUP

• ONE ‘NO’ CONTACT FOR ABNORMAL FREQUENCY, RATE OF
  CHANGE OF FREQUENCY, UNDERVOLTAGE & OVERCURRENT
  PICKUP

• LOSS OF DC AND OTHER INTERNAL SELF MONITORING
   FEATURES 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
  ANGLE
    Compute MW & MVAR




Power P = V I cos(θ−φ)
Reactive Power Q = V I sin(θ−φ)
Synchronized Measurements

                                            Location 2



   Location 1




                Phase angular difference between the
                two can be determined if the two local
                      clocks are synchronized.
                 Synchronizing pulses obtained from
                           GPS satellites.
                           Role of GPS




• Constellation of 24 satellites orbiting at 20,200 km
• Developed by US dept of defense
• Available for free for civilian use
• Beyond 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
          microsecond
            PMU 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 links
        Delay 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) satellites
      Delay Calculation Table

Communication Associated delay – one
link               way (milliseconds)
Fiber-optic cables         ~ 100-150

Microwave links        ~ 100-150
Power line (PLC)       ~ 150-350

Telephone lines        ~ 200-300

Satellite link         ~ 500-700
           Standards: 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 data
     Hardware 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 placement
It 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 it's
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.
57 bus system
                PMU placement
            PMU 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 estimation
WAMS
WAM Design Constraint




                     <
 Computation time
                         Response time of the
       +
                           system dynamics
Communication time
 Opportunities Provided by WAMS
• On-line or real time monitoring and state
  estimation
        – We can realize 1 state estimator run per cycle
        – provides us an opportunity to peep into electromechanical
          system dynamics in real time
            » upgrade from local control to wide area controller e.g., for
              PSS & damping controllers etc
            » improve performance of the apparatus protection schemes
            » improve performance of the system protection schemes
• Accurate measurement of transmission system
  data in real time
           WAM applications
• Protection
     Power Swing blocking
     Improved back up protection
     Current Differential protection

• Continuous Closed Loop Control ???
      e.g., PSS using global signals
  Unfortunately: Require to accurately determine
  the communication latencies for continuous
  control
            WAM applications
Emergency Control (System Protection Schemes)

•   Controlled System Separation

•   Triggering of load shedding based on
    NON-LOCAL signals. Better df/dt relaying.

•   Triggering other schemes (generator shedding,
    dynamic brake, governor)           etc.


Some may require accurate loss of synchronism prediction
 SPS: How can WAMS help ?
• Angular instability :
   – Predict of out of step in real time -> 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
     island

   Former is preferable - no resynchronization of systems
     required BUT how does one
      a) Predict out of step in real time
      b) Determine quantum of control actions
   For controlled system separation :
     Adaptive choice of separation points conceivable
NON-LOCAL measurements may help
 SPS: 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 Blocking
•   As Line BC is quite long in comparison to AB, Zone-3 on AB at A can trip on power
    swing
•   If 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 BC
•   Since Z2 and Z3 timer setting are of the order of 15-30 cycles and 90 cycles
    respectively, communication delays will not be very critical
•   Blocking scheme will not impair but only improve the performance of the system




         A                       B                                                C


      A Transmission System with a short line terminating into a
      long line
          WAM 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 Restoration
    Better picture – better confidence level –
    better decisions.
    More remote actions
 Roadmap 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 Power
 Implementation 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

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:19
posted:9/10/2012
language:English
pages:41