Phasor data concentrator

1. Introduction1.1 Power Grid

1.2 WAMS

2.Components of WAMS2.1 PMU

2.2 PDC

3. Standards for PMU3.1 IEEE C37.118

4. Communication between PMU & PDC4.1 UDP Communication

4.1 TCP Communication

5. WAMS Implementations

6. Possible Approach

7. Conclusion

8. References

10/18/10 2Wide Area Measurement

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Introduction

Power GridHigh 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.


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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.


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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.


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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.


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Components of WAMS

Phasor Measurement Unit (PMU)

Phasor Data Concentrator (PDC)


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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.

PMU

PMUInput

Secondary sides of the 3Φ P.T. or

C.T.

Corresponding Voltage or

Current phasors

Output


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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 50Hz system and is certainly more accurate than any other application.


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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.


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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.


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Time Based Aligning of Data

Algorithm 1An 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.


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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


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Continue…


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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.


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IEEE C37.118

Four message/frame types

1)Command (Binary)

2)Configuration (Binary)

3)Data (Binary)

4)Header (ASCII)

SYNC 2B

FRAMESIZE 2B

IDCODE 2B

SOC 4B

FRACSEC 4B

DATA 1 DATA 2 DATA n CHK

Frame Transmission Order


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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.


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Configuratio

n Frame

Organizatio

n


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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.


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Communication between PMU & PDC

1) UDP Communication

2) TCP Communication


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UDP

Communication

Data Frame

Data Frame

Data Frame

CMD Frame - Send New CFG frame

CFG Frame

Data Frame

Data Frame

CMD Frame -data transmission off

CMD Frame - Send CFG frame

CFG Frame

CMD Frame - Send data frame

Conf change bit (0->1)

CMD Frame - Send data frame

PDC PMU


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TCP

Communicatio

n

SYN , Seq=0

Seq=0, Ack=1

Seq=1,Ack=1

CMD Frame - Send CFG frame

Ack = YY

CFG Frame : Seq 22

DATA Frame : Seq 24

CMD Frame - Send Data frame Seq :23

Ack = 23

CMD Frame - Stop Data frame Seq :xx

Ack = 22

FIN

PDCPMU


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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.


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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 includeevent detection and location,oscillation detectionvisualization.


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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 andAhmedabad.

http://www.wafms.co.cc/


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Other Implementations

ePDC

SEL

TNB

KalkiTech


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PDC Product Comparison Chart


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Possible Approach

We have considered TCP/UDP as network communication protocol.

Client Server Architecture.

State Diagram :

PDC : Process 1

PDC : Process 2

PMU Simulator

CMD FRM - send CFG Frame

CFG FRM

CMD FRM - send DATADATA FRM


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PDC Process 2 Details

Shared Memory

CFG frames

Receive data/cnf frames

Match

Create data nodes Sort()

Maintains Buffer List

Pass_ to_ upper_ Layer()

Archive()

History


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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.


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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.


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http://en.wikipedia.org/wiki/Electric_power_transmission








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Phasor data concentrator

Technology

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