A Flexible GPS based system for synchronised phasor measurement in electric distribution networks
Sreejith Mohan
S7 applied electronics
College Of Engineering, Trivandrum
2007-11 batch

CONTENTS
Need for this system
Synchrophasors
Hardware
General block diagram
Synchronized phasor evaluation
Advantages & Applications
Challenges & future works
Conclusion
Reference

Need for this system
This system can be used to develop automatic systems that are aimed at optimizing energy production and distribution

This method is used for simultaneous measurement of electrical parameters at various nodes

Synchronized measurements collected and processed are used for estimation of network state

This system is flexible

SYNCHROPHASORS
It is defined as a phasor calculated from data samples using a standard time signal as the reference for the measurement

The time reference signal is the coordinated universal time (UTC) which has a repetition of 1 pulse per second

A sinusoidal signal represented by x(t)=Xm cos(2πft+ø) can be represented as phasor as

The absolute phase of synchrophasor is given by (2π∆ft+ø)
∆f=f-fn. Fn-nominal frequency

HARDWARE COMPONENTS
Global Positioning System (GPS)

Phasor Measurement Unit (PMU)
or

Data Acquisition Boards (DAQ)

Phasor Data Concentrator

PHASOR MEASUREMENT UNIT
(PMU)
These are devices which use synchronization signals from the global positioning system satellites and provide the phasor voltages and currents measured at a given substation.

Even though PMU has greater accuracy due to its synchronization with UTC it has lesser sampling rates

It is not flexible

GLOBAL POSITIONING SYSTEM
(GPS)
GPS provides the coordinated universal time for evaluation of Synchrophasors

By synchronizing the sampling processes for different signals it is possible to put phasors in same phasor diagram

GPS furnishes a timing pulse accurate to within 1 microsecond at any location on earth
DATA ACQUISITION BOARD
(DAQ)
DAQ is used to interface general purpose computers and software packages for measurement applications
DAQ is provided with monitored & GPS signal, it provides sampled outputs

GENERAL BLOCK DIAGRAM
REALLOCATION OF SAMPLES
NEED FOR REALLOCATION OF SAMPLES
The internal clock of DAQ has only a limited accuracy

This makes the accuracy of time reference provided by GPS useless

This limited accuracy affects time positioning of samples

SYNCHRONIZED PHASOR EVALUATION
There will be harmonic content in distribution systems
Due to harmonic content DFT is used to extrapolate the components at the fundamental frequency
The amplitude and absolute phase of harmonic components are measured at different nodes
Two different measurement techniques are used,
Fixed length window method
Adjustable length window

FIXED LENGTH WINDOW
PHASE COMPENSATION
Let us consider a periodic signal u(t) composed of M
Harmonic components. Its generic sample k can be expressed as



where

CONTINUATION
ADJUSTABLE LENGTH WINDOW
ADVANTAGES
Adaptive relaying

Instability prediction

State estimation

Improved control


APPLICATIONS
Fault recording

Disturbance recording

Transmission and generation modeling verification

Wide area Protection

Fault location
CONCLUSION
A flexible measurement system for measuring synchronous phasors were developed

This system can be modified for specific measurement needs

Proposed measurement system can be improved by using more sophisticated acquisition hardware

Two methods for absolute phase measurement were discussed

REFERENCES
A. G. Phadke, “Synchronized phasor measurements in power systems,”IEEE Comput. Appl. Power, vol. 6, no. 2, pp. 10–15, Apr. 1993.
A. Carta, N. Locci, C. Muscas, and S. Sulis, “A flexible GPS-based system for synchronized phasor measurement in electric distribution networks,”in Proc. IEEE IMTC, Sorrento, Italy, Apr. 24–27, 2006, pp. 1547–1552
C. Mensah-Bonsu, U. Fernández Krekeler, G. T. Heydt, Y. Hoverson, J.Schilleci, and B. Agrawal, “Application of the global positioning system to the measurement of overhead power transmission conductor sag,” IEEE Trans. Power Delivery, vol. 17, pp. 273–278, Jan. 2002.

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