Phasor data concentrator

1. Introduction
1.1 Power Grid
1.2 WAMS
2.Components of WAMS
2.1 PMU
2.2 PDC
3. Standards for PMU
3.1 IEEE C37.118
4. Communication between PMU & PDC
4.1 UDP Communication
4.1 TCP Communication
5. WAMS Implementations
6. Possible Approach
7. Conclusion
8. References

10/18/10 Wide Area Measurement 2

Introduction
Power Grid
High voltage electric transmission is the bulk transfer of electric energy, from
generating power plants to substations located nearer.

Transmission lines, when interconnected with each other, become high voltage
transmission networks these are typically referred to as power grids.


Wide Area Measurement System (WAMS)
Advanced measurement technology to collect information.


The WAMS technologies are comprised of two major functions:


 obtaining the data

 extracting value from it

Getting the data is accomplished with a new generation of data recording hardware
that produces high quality and high volume recordings.

Data is extracted and analyzed using several signal analysis tools and algorithms.



Need Of WAMS

In order to avoid major regional blackouts such as those occurred in North America and
Canada in 2003.

When constant monitoring applications are available immediate action can be taken if
some failures are detected.


Comparison of SCADA & WAMS

SCADA can only provides steady, low sampling density, and non synchronous
information of the network.

Controlling centre cannot know the dynamic operation states of the system.


Instant action cannot be taken in case of failures.


WAMS enables us to observe the power system synchronously in more elaborate time
scale.

WAMS requires data to be sent and captured at very fast rate.



Components of WAMS

Phasor Measurement Unit (PMU)


Phasor Data Concentrator (PDC)



PMU
They are devices which use synchronization signals from the global positioning
system (GPS) satellites and provide the phasor voltages and currents measured at a
given substation.

A phasor is a complex number that represents both the magnitude and phase angle of
the sine waves found in electricity.

PMU can have different Data Rate i.e. 60, 30, 10 frame per second.


Input Output
PMU
Secondary Corresponding
sides of the Voltage or
3Φ P.T. or Current
C.T. phasors


Advantage of using GPS

 It is accurate to within 1 microsecond at any location on earth.

A 1-microsecond error translates into 0.021° for a 60 Hz system and 0.018 ° for a 50


Hz system and is certainly more accurate than any other application.


PDC
It is a node in a system where phasor data from a number of PMUs or PDCs is
correlated and fed out as a single stream to other applications.

PDC would performs the Real time monitoring , alarming , event triggering.


It performs local archiving.

It performs various quality checks on the phasor data.



Operations inside PDC

Receive data from PMU's/PDC's


Align the data as per the time tag and then perform sorting


Combine all data from multiple PMU's having same time stamp t into a single frame


Perform Local archival and also send the combined frame to other applications.


PDCs are available as Hardware and Software.



Time Based Aligning of Data

Algorithm 1
An array of time stamped buffers is maintained.
PDC will group together measurements from the same time stamp in to a
single buffer.
 In some cases the measurements may be delayed so there will be more than

one time stamped buffer.
When the buffer is full the PDC will forward it to the applications consuming

it.

Drawbacks
PDC has to wait for the buffer to be full before forwarding it to the

applications.


Algorithm 2

Add a time-out per time stamped buffer.


The PDC assigns this newly arrived measurement to a new buffer.


The countdown to the time-out is initiated when the first phasor measurement of a
certain time stamp arrives at the PDC.

When the time-out is up the PDC will forward the set without waiting for the rest of
the phasor measurements to arrive


Continue…


Standards for PMU

IEEE Std 1344
IEEE C37.118

OPC-DA / OPC-HDA - A Microsoft Windows based interface protocol that is

currently being generalized to use XML and run on non Windows computers.

IEC 61850 a standard for electrical substation automation.


BPA PDCStream - a variant of IEEE 1344 used by the Bonneville Power


Administration (BPA) PDCs and user interface software.


IEEE C37.118

Four message/frame types

1)Command (Binary)
2)Configuration (Binary)

3)Data (Binary)

4)Header (ASCII)

Frame Transmission Order

SYNC FRAMESIZE IDCODE SOC FRACSEC
2B 2B 2B 4B 4B

DATA 1 DATA 2 DATA n CHK


1) Command Frame is received by PMU in order to take a particular action.
Example “turn ON the transmission of data”.

1) Header frame is human readable/ASCII information about the PMU, the data
sources, scaling, algorithms, analog filters used, or other related information.

1) Configuration frame contains the information and processing parameters of the
PMU. Like it contains phasor, analog, frequency and digital value of PMU.


Configuratio
n Frame
Organizatio
n


3) Data frame provides information regarding phasor data and the state of the digital
inputs on each channel. It also defines the frequency, angle, over-current, under-voltage
and rate of frequency change.


Communication between PMU & PDC

1) UDP Communication

2) TCP Communication


PDC PMU
CMD Frame - Send CFG frame

UDP CFG Frame
Communication
CMD Frame - Send data frame

Data Frame

Data Frame

Data Frame

Conf change
bit (0->1)
CMD Frame - Send New CFG frame

CFG Frame

CMD Frame - Send data frame

Data Frame

Data Frame

CMD Frame -data transmission off

PDC
PMU
SYN , Seq=0
TCP
Seq=0, Ack=1
Communicatio
n Seq=1,Ack=1

CMD Frame - Send CFG frame

Ack = YY

CFG Frame : Seq 22

Ack = 22

CMD Frame - Send Data frame Seq :23

Ack = 23

DATA Frame : Seq 24

CMD Frame - Stop Data frame Seq :xx

FIN


WAMS Implementations

OpenPDC

The openPDC is a complete set of applications for processing streaming time-
series data in real-time.

The openPDC is based on the SuperPDC which was developed by the Tennesse
Valley Authority starting in 2004.


Wide Area Frequency Monitoring Network (FNET)

It is a GPS-synchronized wide-area frequency measurement network.


Currently, FNET collects data from over 80 FDRs, most of which are installed in the


North American power grid.

Applications provided by FNET include


event detection and location,

oscillation detection

visualization.


Wide Area Frequency Monitoring by IIT Bombay

It is a continuous data archiving system.


It provides Web display of of the archived data.


Work on generating triggers, alarms in case some unusual events occur is in progress.


Currently, frequency measuring sensors are located at Mumbai, Kharagpur and


Ahmedabad.

http://www.wafms.co.cc/



Other Implementations

ePDC


SEL


TNB


KalkiTech



PDC Product Comparison Chart


Possible Approach

We have considered TCP/UDP as network communication protocol.


Client Server Architecture.


State Diagram :

PDC :
CMD FRM - send CFG Frame Process 1

PMU
Simulator CFG FRM

DATA FRM
CMD FRM - send DATA
PDC :
Process 2


PDC Process 2 Details
Receive data/cnf frames
Shared Memory

CFG frames

Pass_ to_ upper_
Layer()

Match

Create
data nodes Sort()
Maintains Buffer List

Archive()

History


Conclusion

Synchronized phasor measurement technologies have proliferated in many countries
all over the world.

With the spread and advancement in this technology real time monitoring and decision


making is going to be much easier.

Development of free and open source PDC software will certainly boost more
contributions from all over the world.


References

Ken Martin, “IEEE Standard for Synchrophasors for Power Systems”, IEEE Std C37.118 -2005 (Revision of
IEEE Std 1344-1995).

“Real Time Wide-Area Monitoring, Control and Protection”, EIPP Real Time Task Team, White Paper DRAFT
3: Wide Area Monitoring-Control Phasor Data Requirements.

Andrew Armenia, “A Flexible Phasor Data Concentrator Design Leveraging Existing Software
Technologies”, IEEE TRANSACTIONS ON SMART GRID, VOL. 1, NO. 1, JUNE 2010.

Biju Naduvathuparambil, Matthew C. Valenti and Ali FeXiachi, “Communication Delays in Wide Area


Measurement Systems”, Lane Dept. of Comp. Sci. & Elect. Eng., West Virginia University, WV.

Basics of Electric Power Transmission and Grid technology
http://en.wikipedia.org/wiki/Electric_power_transmission.

http://www.phasor-rtdms.com/phaserconcepts/phasor_adv_faq.html#Question9.



Thank you


Phasor data concentrator

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