The phasor measurement unit (PMU) which is actually a key tool in providing situational awareness, operation and reliability of the power system network.

2. CONTENTS
 Introduction
 Need of PMU
 What is PMU?
 Block diagram of PMU
 Components of PMU
 Operation of PMU
 Scada vs PMU
 PMUs in WAMS
 PMU implementation in India
 Applications and challenges
 Conclusion

3. INTRODUCTION
 The complex nature of the power system makes it necessary to regularly monitor the elements
that make up the power system in order to protect these elements and in the long run avoid major
contingencies in the power system.
 The concept of monitoring the power system network has become very important today as a
result of different power system contingencies that have occurred in past.
 Widespread power system outages in different parts of the world have made it necessary to
monitor power system parameters such as amplitude, phase angle, and frequency to ensure that
these parameters are constantly within statutory limits.
 Monitoring the power system simply involves taking readings or measurements from power
systems at specified time intervals while these systems are in service.
 The phasor measurement unit (PMU) which is actually a key tool in providing situational
awareness, operation and reliability of the power system network.

4. NEED OF PMU
 Existing systems in power grid such as Energy Management System
and Supervisory Control and Data Acquisition system (SCADA)
have the capability to provide only steady state view of power
system with high data flow latency.
 In Supervisory Control and Data Acquisition system (SCADA) it
was not possible to measure the phase angles of bus voltages of
power system network in real time, due to technical difficulties in
synchronizing measurements from distant locations.

5. WHAT IS PMU?
 A phasor measurement unit (PMU) is a device used to estimate the magnitude
and phase angle of an electrical phasor quantity (such as voltage or current) in
the electrical grid using a common time source for synchronization.
 PMUs are capable of capturing samples from a waveform in quick succession and
reconstructing the phasor quantity, made up of an angle measurement and a
magnitude measurement.
 The resulting measurement is known as a synchro phasor.
 PMUs can also be used to measure the frequency in the power grid.
 This helps engineers in analysing dynamic events in the grid which is not possible
with traditional SCADA measurements that generate one measurement every 2
or 4 seconds.

6. BLOCK DIAGRAM OF PMU

7. COMPONENTS OF PMU
 Anti-aliasing filter
 Global Positioning System (GPS)
 Phase locked oscillator
 A/D converter
 Phasor microprocessor
 Modem

8. ANTI-ALIASING FILTER
 Anti-aliasing filters ensure that all the analogue
signals have the same phase shift and
attenuation, thus assuring that the phase angle
differences, and relative magnitudes of the
different signals are unchanged.
 If lower sampling rates are used, then the
original signal’s information may not be
completely recoverable from the sampled signal
and they may appear as aliases.
 Anti-aliasing filter is used to restricts the
bandwidth of the signal to approximately satisfy
the sampling theorem, for the fixed sampling
frequency of the system.

9. GLOBAL POSITIONING SYSTEM (GPS)

10. PHASE LOCKED OSCILLATOR

11. A/D CONVERTER
 Analog inputs to device are currents and voltages
obtained from the secondary windings of the current and
voltage transformers located in substation.
 The Analog to digital converter digitizes the analog
signal, from the AAF, at sampling instants defined by the
sampling time signals from PLO.
 The most common types of ADCs are flash, successive
approximation, and sigma-delta.

12. Modem
 A modulator-demodulator, or simply a modem, is a hardware device that converts data from a
digital format, intended for communication directly between devices with specialized wiring,
into one suitable for a transmission medium such as telephone lines or radio.
 A modem modulates one or more carrier wave signals to encode digital information for
transmission, and demodulates signals to decode the transmitted information.
 The goal is to produce a signal that can be transmitted easily and decoded reliably to
reproduce the original digital data.
 modem is one that turns the digital data of a computer into a modulated electrical signal for
transmission over telephone lines, to be demodulated by another modem at the receiver side
to recover the digital data.

13. Operation of PMU
 PMU can measure 50/60 Hz AC waveforms (voltages and currents) typically at a rate of
48 samples per cycle making them effective at detecting fluctuations in voltage or current
at less than one cycle.
 The analogue AC waveforms detected by the PMU are digitized by an analogue -to-
digital converter for each phase.
 A phase-locked oscillator along with a Global Positioning System (GPS) reference source
provides the needed high-speed synchronized sampling with 1 microsecond accuracy.
 However, PMUs can take in multiple time sources including non-GPS references as long
as they are all calibrated and working synchronously.
 The resultant time-stamped phasors can be transmitted to a local or remote receiver at
rates up to 120 samples per second.

14. SCADA VS PMU
Attribute SCADA PMU
Measurement Analogue Digital
Resolution 2-4 samples /second 100 samples/second
Observability Steady state Dynamic/Transient
Monitoring Local Wide-Area
Phase Angle measurement
NO YES

15. PMUs in WAMS
 The concept of smart meters providing information about the grid has been present for
years, quality of measurements and reporting rates of these devices have proven to be
inadequate for maximizing utilization of transmission assets, as well as foreseeing
blackouts and brownouts.
 Synchro phasors introduce the concept of time-synchronized measurements, utilizing the
precise time signal from GPS (Global Positioning System) satellites.
 They significantly increase their sampling resolution compared to ordinary smart meters.
Instead of reporting electrical RMS values in one or more second intervals, synchro phasors
constantly measure voltage and current waveforms and report their vector values
(amplitude and angle position of the AC signal), or phasors as they are called, up to 60
times per seconds.
 GPS signals provides the values which are perfectly synchronized in time across all
devices and this proves valuable for predicting blackouts.

17. CONTINUED..
 PMUs Pilot Project in the Northern Grid A pilot project on WAMS has been taken up in
India. The project comprised of installation of Phasor Measurement Unit (PMU) along with
GPS clock at selected 08 substations in the Northern Region.
 Phasor Data Concentrator (PDC) and other associated equipment have been installed at
Northern Regional Load Despatch Centre (NRLDC), New Delhi.
 PMUs Installation in the Western Grid with four out of five regional grids interconnected
the Western Regional grid is strategically located, wheeling power between various
Regions.
 Introduction of WAMS technology in Western Region would help in ensuring grid security
and safety.
 In view of this, a wide area measurement system (WAMS) project based on Phasor
Measurement Units has been initiated by Power Grid Corporation.

18. Applications
 Power system automation, as in smart grids
 Load shedding and other load control techniques such as demand response mechanisms to
manage a power system. (i.e. Directing power where it is needed in real-time)
 Increase the reliability of the power grid by detecting faults early, allowing for isolation of
operative system, and the prevention of power outages.
 Increase power quality by precise analysis and automated correction of sources of system
degradation.
 Wide area measurement and control through state estimation, in very wide area super grids,
regional transmission networks, and local distribution grids.

19. Challenges
 WAMS present architecture is not suitable for large system
 High initial investment requirement acts as deterrent
 Clear roadmap is needed.
 Communication network establishment is very expensive.
 On line voltage instability prediction
 Higher computational requirement.
 Lack of system models.

20. Conclusion
 PMU is an advanced replacement of SCADA technology.
 In addition to the original intended applications on “Phasor Measurement”,
PMUs offer attractive options for improving protection and control actions
on modern power systems.
 Future power systems will have to face more stressful regimes, improved
protection and control offered by the wide area measurement systems
based on PMUs will become even more important.

21. References
 C37.118.1a-2014 - IEEE Standard for Synchro phasor Measurements for Power
Systems
 . Skok; D. Brnobic; V. Kirincic. "Croatian Academic Research Wide Area
Monitoring System — CARWAMS“
 Zhang; J. Chen; M. Shao (October 2007). "Phasor Measurement Unit (PMU)
Implementation and Applications (DOCID 1015511)“
 . LLoyd, P. J. Harding; A. Gillies, A. Varghese. "Implementation of a wide-area
monitoring scheme for the Indian power system"