The modern-day power grid aims at providing reliable and quality power, which requires careful monitoring of the power grid against catastrophic faults. Therefore one promising way is to provide the system a wide protection and control named as “Wide Area Measurement and Control System” /PMU is required.

1. “A review on WAMS/PMU”
By: Rahul Singh
M.Tech Power System

2. INTRODUCTION
The modern-day power grid aims at providing reliable and quality
power, which requires careful monitoring of the power grid against
catastrophic faults.
 As power grid is moving from the traditional to smart grid, the
operation of grid becomes more complex
 Renewable Energy Resources ,Electric-Vehicles increasing rapidly
therefore synchronization of grid become more complex
problem.
 Also present power system is operating near to its stability limits
if sudden increase/decrease in demand happens , will result in
grid failure/collapse.

3. TO PROTECT POWER SYSTEM FROM
COLLAPSE?
 One promising way is to provide the system a wide protection
and control named as “Wide Area Measurement and Control
System”.
 The WAMS consists of several sensors known as the phasor
measurement units (PMUs) that collect the real information
pertaining to the health of the power grid
 PMUs are the most accurate and advanced synchronized
measurement technology available.

4. WIDE AREA MONITORING SYSTEM (WAMS)
It is a collective
technology to monitor
power system dynamics in
real time and also to
identify system stability
related weakness and
helps to design and
implement counter
measures.(IEEE)
 WAMS uses a GPS satellite
signals to time-synchronize
from phasor measurement
units at important nodes in
the Power System, sends real
time phasors data to a
Control Centre.
 The acquired phasor data
provide dyanamic information
on power systems, which help
operators to initiate
corrective actions to enhance
the power system reliability.

5. TYPICAL WAMS SYSTEM

6.  PHASOR MEASUREMENT UNIT
(PMU)
 PHASOR DATA CONCENTRATOR
(PDC)
 SYNCHROPHASOR
COMMUNICATION CHANNEL.
WAMS COMPONENTS

7. The heart of the
WAMS technology is
are Phasor
Measurement Unit i.e.
a PMU

8. WHAT IS PHASOR?
 Phasor is a quantity with
magnitude and phase (with
respect to a reference) that is
used to represent a sinusoidal
signal.
 Here the phase or phase angle
is the distance between the
signal’s sinusoidal peak and a
specified reference and is
expressed using an angular
measure.
 Here, the reference is a fixed
point in time (such as time = 0).
 The phasor magnitude is
related to the amplitude of the
sinusoidal signal

9. SYNCHROPHASOR
 A synchrophasor is a phasor
measurement with respect
to an absolute time
reference.
 With this measurement we
can determine the absolute
phase relationship between
phase quantities at different
locations on the power
system.

10. WHAT IS PHASOR MEASUREMENT UNIT?
 IEEE Defination
“Phasor measurement unit (PMU): A device that produces synchronized
phasor ,frequency, and rate of change of frequency (ROCOF) estimates from
voltage and/or current signals and a time synchronizing signal”.
 Time synchronization is usually provided by GPS and allows synchronized
real-time measurements of multiple remote points on the grid.
 PMUs are capable of capturing samples from a wave form 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 synchrophasor. These time
synchronized measurements are important because if the grids supply and
demand are not perfectly matched, frequency imbalances can cause stress on
the grid, which is a potential cause for power outages.

11. CONTINUE...
 PMUs can also be used to measure the frequency in the power
grid.
 A typical commercial PMU can report measurements with very
high temporal resolution in the order of 30-60 measurements
per second. This helps engineers in analyzing dynamic events in
the grid which is not possible with traditional SCADA
measurements that generate one measurement every 2 or 4
seconds.
 Therefore, PMUs equip utilities with enhanced monitoring and
control capabilities and are considered to be one of the most
important measuring devices in the future of power systems.
 A PMU can be a dedicated device,or the PMU function can be in
corporated in to a protective relay or other device.

12. THE MAIN COMPONENTS OF PMU
 Analog Inputs
 GPS receiver
 Phase locked oscillator
 A/D converter
 Anti-aliasing filters
 Phasor micro-processor
 Modem

13. FUNCTIONAL BLOCKS IN PMU

14. ANALOG INPUT
 Current and potential transformers are employed at substation
for measurement of voltages and current.
 The analog inputs to the PMU are the voltages and currents
obtained from the secondary winding of potential and current
transformers.

15. ANTI-ALIASING FILTER
 Anti-aliasing filter is an analog low pass filter which is used to
filter out those components from the actual signal whose
frequencies are greater than or equal to half of nyquist rate to
get the sampled waveform.
 Nyquist rate is equal to twice the highest frequency component
of input analog signal.
 If antialiasing filters are not used, error will be introduced in the
estimated phasor

16. PHASE LOCK OSCILLATOR
 Phase lock oscillator along with Global Positioning System
reference source provides the needed high speed synchronized
sampling.
 Global Positioning System (GPS) is a satellite-based system for
providing position and time.

17. A/D CONVERTER
 It converts the analog signal to the digital signal.
 Quantization of the input involves in ADC that introduces a small
amount of error.
 The output of ADC is a sequence of digital values that convert a
continuous time and amplitude analog signal to a discrete time
and discrete amplitude signal.
 It is therefore required to define the rate at which new digital
values are sampled from the analog signal.
 The rate of new values at which digital values are sampled is
called the sampling rate of the converter.

18. GLOBAL POSITIONING SYSTEM
 The synchronized time is given by GPS uses the high accuracy
clock from satellite technology.
 Without GPS providing the synchronized time, it is hard to
monitor whole grid at the same time.
 The GPS satellites provide a very accurate time synchronization
signal ,available,via an antenna input, throughout the power
system.This means that that voltage and current recordings from
different substations can be directly displayed on the same time
axis and in the same phasor diagram.

19. PROCESSOR
 The microprocessor calculates positive-sequence estimates of
all the current and voltage signals using the DFT techniques.
 Certain other estimates of interest are frequency and rate of
change of frequency measured locally, and these also are
included in the output of the PMU.
 The time stamp is created from two of the signals derived from
the GPS receiver.
 The time-stamp identifies the identity of the “universal time
coordinated (UTC) second and the instant defining the boundary
of one of the power frequency periods.

20. MODEM
 A device that modulates an analog carrier signal and encodes
digital information from the signal and can also demodulate
the signal to decode the transmitted information from signal is
called modem.
 The objective of modem is to produce a signal that can be
transmitted and decoded to make a replica of the original
digital data.
 Modem can be used with no means of transmitting analog
signals

21. APPLICATION OF PMU IN POWER SYSTEM
 Adaptive relaying
 Instability prediction
 State estimation
 Improved control
 Fault recording
 Disturbance recording
 Transmission and generation modeling verification
 Wide area Protection
 Fault location

22. PHASOR DATA CONCENTRATOR (PDC)
 A PDC works as a node in a communication network
 The main function of this PDC are to gather data from several PMUs,
PDC will receive the voltage current phasor information along with the
frequency also from the PMUs, to reject the bad data.
 The PDC can exchange the data and commands with PMUs and also
with other PDCs. It receives data from multiple PMUs, performs a
check on the received data, time aligns the data and creates an output
stream.
 The communication links are basically bidirectional, most of the data
flows upward in hierarchy , although there are some tasks which
require communication capability in reverse direction.
 Usually these commands for configuring the downstream components,
requesting data in a particular form, etc

25. SYNCHROPHASOR COMMUNICATION
TECHNOLOGIES
 As the signal is time stamped, it is transmitted from the PMU to
the PDC through the synchrophasor communication network.
 The key communication technologies , for synchrophasor data
transfer, can be broadly classified into two categories:
1. Wired
2. Wireless.

26.  The wired communication technology offers high
reliability, huge bandwidth and protection against
interference.
 On the other hand, wireless technology enjoys
superiority in terms of rapid deployment, low
installation and maintenance costs, access to remote
geographic locations, etc.

27. SYNCHROPHASOR
COMMUNICATION
TECHNOLOGIES in PMUs
Wired
Communication
Channel
Power Line
Communication
Fibre Optic
Communication
Wireless
Communication
Channel
Microwave
Communication
Cellular
communication
Satellite
Communication

28. Wired Communication Channel

29. POWER LINE COMMUNICATION

30. Power Line Communication (PLC) uses the existing power line cables for the
transfer of synchrophasor data, this technology provides the fastest and
economical means for the deployment of communication networks. There are
two types of PLC technologies:
1. Narrow Band PLC (NB-PLC) ,used for low bandwidth applications
2. Broad Band PLC (BB-PLC) , used for applications requiring higher
bandwidth.
As the synchrophasor application is mission critical, BB-PLC would be the
preferred choice. Typical data rates ranging from 2 to 3 Mbps can be achieved
using this technology.
In spite of having several advantages, the technology suffers from many
disadvantages such as the difficulty in modeling the communication channel due
to the noisy background in the power cables. Moreover, the PLC is not meant for
high bandwidth applications due to fading and interference. The signal to noise
ratio (SNR) is low and this technology is usually combined with other
communication technologies, such as cellular communication, to provide a
hybrid solution for power grid communications.

31. FIBRE OPTIC COMMUNICATION
This communication channel used for long-distance
communication The high data rates, low attenuation, high
reliability and negligible interference made them a widely used
synchrophasor communication technology

32. The data received from the PMU is converted into an optical
signal by the optical transmitter, which is basically a light
emitting diode or a laser. These optical signals are then
carried via the optical fibers to the PDC. At the PDC, the
optical signal is converted back into electrical signals using a
photodiode. Between the PMU and the PDC, optical
repeaters are placed at regular intervals to boost the signal
strength and to maintain the signal quality.

33. Wireless Communication Channel

34. MICROWAVE COMMUNICATION

35. With the growth of wireless technology, the transfer of data in
Gbps are being achieved. Thus, this technology provides a viable
alternative to the optical fiber SPCS.
In the microwave communication, the synchrophasor data
generated by the PMU is fed to a PMU radio terminal that
converts the electrical signal into radio frequency (RF) signal. The
RF signal is then fed to a microwave antenna that converts the RF
signal into an electromagnetic signal. This electromagnetic signal
propagates in free space and is received by the microwave
antenna at the PDC. The PDC radio terminal converts the RF signal
back into the electrical signal, which is sent to the PDC for
analysis.
Intermediate repeaters are required to maintain the signal
strength and to ensure communication feasibility in the case of
non-line of sight propagation.

36. CELLULAR COMMUNICATION
 It is one of the fastest growing technologies in the world.
 The research is already in progress to achieve data rates of 100
Gbps per user.
 Even though this technology can cater to the demands of the
synchrophasor application in terms of the data rate
requirements, the shared nature of this technology makes it
unacceptable for mission-critical applications that require
uninterrupted communication services.

38. Technology Data Rates
General Packet Radio Service
(GPRS)
Up to 114 Kbps
Enhanced Data rates for GSM
Evolution
(EDGE)
Up to 384 Kbps
Universal Mobile
Telecommunications
System (UMTS)
Upto 2 Mbps
High-Speed Packet Access (HSPA) 600 Kbps – 10 Mbps
Long Term Evolution-Advanced
(LTE-A)
Up to 100 Mbps
Cellular Technologies for Synchrophasor
Applications

39. SATELLITE COMMUNICATION
 In this technology communication equipment is located in space. Thus, this
technology is unaffected by natural disasters such as floods, earthquakes, etc.
 It consists of two different segments:
I. Earth segment
II. Space segment
 The space segment consists of the satellites and the ground facilities that are
responsible for Tracking Telemetry and Control (TT&C).
 The earth segment consists of transmitting and receiving earth stations.
 This technology can be used for the transfer of synchrophasor data when the
end equipment is separated by several hundred kilometers.
 However, the major disadvantage for synchrophasor application is that
communication delay is higher compared to any other technology and is
seldom used.

41. SYNCHROPHASOR MESSAGE FRAMEWORK
 Four message types are defined here:
1. Data
2. Configuration
3. Header
4. Command
 The first three message types are transmitted from the
PMU/PDC that serves as the data source
 The last (command) is received by the PMU/PDC.

42. IEEE C37.118.2-2011 MESSAGE FRAMES
 Data frame
This contains the real-time synchrophasor data measured by the PMU. It
includes an identification header, the length of the message, message
source ID, a time stamp, detailed status information regarding the data
and its source and quality, frequency, ROCOF and analog and digital
quantities messages are the measurements made by a PMU.
 Configuration frame
There are three configuration frames. The first configuration frame config1 indicates
the data reporting capability of the PMU. The config2 and config3 indicate the current
measurements that are being reported in the data frame.
 Header frame
The header frame is sent from the PMU to the PDC to help the PDC identify the
sender.
 Command frame
These frames are sent by the data receiving device to the data transmitting device
requesting it to start or stop the transmission, to transmit the configuration frame or
the header frame.
 Each data stream shall have its own IDCODE so that the data, configuration,
header, and command messages can be appropriately identified.

43. MESSAGE FORMAT
 All message frames start with 2-byte SYNC word
followed by a 2-byte FRAMESIZE word, a 2-byte
IDCODE, a time stamp consisting of a 4-byte second-of-
century (SOC) and 4-byte
 FRACSEC, which includes a 24-bit FRACSEC integer and
an 8-bit Time Quality flag.

44. WORD DEFINITIONS
COMMON TO ALL FRAME
TYPES

45. Field Size(bytes) Comments
SYNC 2 Frame synchronization word.
Leading byte: AA hex
Second byte: Frame type and version, divided as follows:
Bit 7: Reserved for future definition, must be 0 for this standard version.
Bits 6–4: 000: Data Frame
001: Header Frame
010: Configuration Frame 1
011: Configuration Frame 2
101: Configuration Frame 3
100: Command Frame (received message)
Bits 3–0: Version number, in binary (1–15)
Version 1 (0001) for messages defined in IEEE Std C37.118-2005 [B6].
Version 2 (0010) for messages added in this revision,
IEEE Std C37.118.2-2011.
FRAMESIZE 2 Total number of bytes in the frame, including CHK.
16-bit unsigned number. Range = maximum 65535
IDCODE 2 Data stream ID number, 16-bit integer, assigned by user, 1–65534 (0 and 65535 are reserved). Identifies destination data stream
for commands and source data stream for other messages. A stream will be hosted by a device that can be physical or virtual. If a
device only hosts one data stream, the IDCODE identifies the device as well as the stream. If the device hosts more than one data
stream, there shall be a different IDCODE for each stream.
SOC 4 Time stamp, 32-bit unsigned number, SOC count starting at midnight
01-Jan-1970 (UNIX time base).
Range is 136 years, rolls over 2106 AD.
Leap seconds are not included in count, so each year has the same number of seconds except leap years, which have an extra day
(86 400 s).
FRACSEC 4 Fraction of second and Time Quality, time of measurement for data frames or time of frame transmission for non-data frames.
Bits 31–24: Message Time Quality
Bits 23–00: FRACSEC, 24-bit integer number. When divided by TIME_BASE
yields the actual fractional second. FRACSEC used in all messages to and from a given PMU shall use the same TIME_BASE that
is provided in the configuration message from that PMU.
CHK 2 CRC-CCITT, 16-bit unsigned integer.

46. References:
1. Bhargav Appasani and Dusmanta Kumar Mohanta (2018) “A review on synchrophasor
communication system: communication technologies, standards and applications”(SpringerOpen)
2. Dr. Premalata Jena ,Department of Electrical Engineering ,Indian Institute of Technology, Roorkee
(Lecture 11,12) Online lecture “Introduction to Smart Grid”.
Weblink:http://www.infocobuild.com/education/audio-video-courses/electronics/introduction-to-
smart-grid-iit-roorkee.html
3. IEEE Standard for Synchrophasor Measurements for Power Systems
C37.118.1-2011, C37.118.2-2011
4. Prof. (Dr.) Pravat Kumar Rout Department of EEE ITER Siksha‘O’ Anusandhan (Deemed to be
University), Bhubaneswar, Odisha, India “Distribution Generation and Smart Grid”, (Slideshare)