GPS in Power Systems

APPLICATIONS OF GPS IN POWER ENGINEERING

What is GPS?

GPS or Global Positioning Systems is a highly sophisticated navigation system developed by the United States Department of Defense. This system utilizes satellite technology with receivers and high accuracy clocks to determine the position of an object.

The Global Positioning System

A constellation of 24 high-altitude satellites

GPS is

A constellation of satellites, which orbit the earth twice a day, transmitting precise time and position (Latitude, Longitude and Altitude) Information.

A complete system of 21 satellites and 3 spares.

GPS at Work

1.Navigation - Where do I want to go?

2.Location - Where am I?

3. Tracking - Monitoring something as it moves

4. Mapping - Where is everything else?

5. Timing - When will it happen?

Why do we need GPS?

Safe Travel Traffic Control Resource Management Defense Mapping Utility Management Property Location Construction Layout

4 ‘birds’ (as we say) for 3-D fix

Global Positioning Systems (GPS) Applications

in Power Systems

Power companies and utilities have fundamental requirements for time and frequency to enable efficient power transmission and distribution.Repeated power blackouts have demonstrated to power companies the need for improved time synchronization throughout the power grid. Analyses of blackouts have led many companies to place GPS-based time synchronization devices in power plants and substations

Why GPS For power Eng

It furnishes a common-access timing pulse which 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

GPS time synchronization

By synchronizing the sampling processes for different signals –

which may be hundreds of kilometers apart – it is possible to put their phasors in the same

phasor diagram

V

VV1

V2

Substation 1

Substation 2 t1 t2 t3 t4 t5 t6 t7

GPS time synchronized pulses

V1

V2Ψ

FFT or any other technique gives:•Magnitude•Phase angleWith respect to GPS

GPS time synchronizationGPS time synchronization

Absolute Time Reference Across the Power System

Synchronized phasor measurements (SPM) have

become a practical proposition.

As such, their potential use in power system applications has not yet been fully realized by many of power system engineers.

Phasor Measurement Units PMUsPhasor Measurement Units PMUs

Phasor Measurement UnitsPhasor Measurement Units(PMU)(PMU)

[or SYNCHROPHASORS][or SYNCHROPHASORS]

Phasor Measurement UnitsPhasor Measurement Units))PMU)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.


Secondary sides of the 3Φ P.T. or

C.T.

Corresponding Voltage or

Current phasors

input outputPMU


Phasor Monitoring Unit (PMU) Hardware Block Diagram:

GPSreceiver

Phase-locked oscillator

16-bit A/D

converter

Phasor micro-

processor

Modems

Anti-aliasingfilters

Analog Inputs

Sampling at Fixed Time Intervals Using an Absolute Time Reference

The GPS receiver provides the 1 pulse-per-second (pps) signal, and a time tag, which consists of the year, day, hour, minute, and second. The time could be the local time, or the UTC (Universal Time Coordinated).

The l-pps signal is usually divided by a phase-locked oscillator into the required number of pulses per second for sampling of the analog signals. In most systems being used at present, this is 12 times per cycle of the fundamental frequency. The analog signals are derived from the voltage and current transformer secondary's.

The Birth of the PMUs Computer Relaying developments in Computer Relaying developments in

1960-70s.1960-70s.

NowNow

RES RES 521521

SEL-SEL-421421

Phasor Measurement Unit’s

central data collection


Data Concentrator (Central Data Collection)

Different applications of Different applications of PMUs in PMUs in

power systempower system

1. Adaptive relaying

2. Instability prediction

3. State estimation

4. Improved control

5. Fault recording

6. Disturbance recording

7. Transmission and generation modeling verification

8. Wide area Protection

9.Fault location

Applications of PMU in power Applications of PMU in power SystemSystem

1-Adaptive relaying1-Adaptive relaying

Adaptive relaying is a protection philosophy which permits and seeks to make adjustments in various protection functions in order to make them more tuned to prevailing power system conditions

Applications of PMU in power SystemApplications of PMU in power System

2-Instability prediction2-Instability prediction

• The instability prediction can be used to adapt load shedding and/or out of step relays.

• We can actually monitor the progress of the transient in real time, thanks to the technique of synchronized phasor measurements.


• The state estimator uses various measurements received from different substations, and, through an iterative nonlinear estimation procedure, calculates the power system state.

3-State estimation3-State estimation

• By maintaining a continuous stream of phasor data from the substations to the control center, a state vector that can follow the system dynamics can be constructed.• For the first time in history, synchronized phasor measurements have made possible the direct observation of system oscillations following system disturbances


• Power system control elements use local feedback to achieve the control objective.

4-Improved control4-Improved control

• The PMU was necessary to capture data during the staged testing and accurately display this data and provide comparisons to the system model.

• The shown figure shows a typical example of one of the output plots from the PMU data


• They can capture and display actual 60/50 Hz wave form and magnitude data on individual channels during power system fault conditions.

5-Fault Recording5-Fault Recording


• Loss of generation, loss of load, or loss of major transmission lines may lead to a power system disturbance, possibly affecting customers and power system operations.

6-Disturbance Recording6-Disturbance Recording


These figures are examples of long-term data used to analyze the effects of power system disturbances on critical transmission system buses.

Disturbance RecordingDisturbance Recording


• Computerized power system modeling and studies are now the normal and accepted ways of ensuring that power system parameters have been reviewed before large capital expenditures on major system changes.

7-Transmission and Generation 7-Transmission and Generation Modeling VerificationModeling Verification

• In years past, actual verification of computer models via field tests would have been either impractical or even impossible

• The PMU class of monitoring equipment can now provide the field verification required


• The shown figure compares a remote substation 500 kV bus voltage captured by the PMU to the stability program results

7-Transmission and 7-Transmission and Generation Modeling Generation Modeling

VerificationVerification


The introduction of the Phasor Measurement Unit (PMU) has greatly improved the observability of the power system dynamics. Based on PMUs, different kinds of wide area protection, emergency control and optimization systems can be designed

8-Wide – Area protection


A fault location algorithm based on synchronized sampling. A time domain model of a transmission line is used as a basis for the algorithm development. Samples of voltages and currents at the ends of a transmission line are taken simultaneously (synchronized) and used to calculate fault location.

9-Fault Location9-Fault Location


The Phasor measurement units are installed at both ends of the transmission line. The three phase voltages and three phase currents are measured by PMUs located at both ends of line simultaneously

Fault LocationFault LocationApplications of PMU in power SystemApplications of PMU in power System

PMU ASynchronized phasor

Modal Transform of synchronized

samples

PMU BSynchronized phasor

SPM-based applications in power systems

off-line studies

real-time monitoring and visualization

real-time control, protection and emergency control

42

SOME RESEARCH PROGECTS (I participated in)

Global Positioning System (GPS)-Based Synchronized Phasor

Measurement

By

Eng. Marwa M. Abo El-Nasr

Supervised by

Prof. Dr. Mohamed M. MansourDr. Said Fouad Mekhemer

CONCLUSIONS

The conclusions extracted form the present work can be summarized as follows:

1. A technique for estimating the fault location based on synchronized data for an interconnected network is developed and implemented using a modal transform

2. One-bus deployment strategy is more useful than tree search for fault location detection as it gives more system observability

3- The average value of mode 1 and 2 of Karrenbauer transformation is used for 3-phase and line-to-line faults, while the average value of the 3 modes is used for line-to-line-ground and line-to-ground faults

4- The results obtained from applying the developed technique applied to a system depicted from the Egyptian network show acceptable accuracy in detecting the fault and locations of different faults types.

ConclusionsConclusions

Essence:

This thesis is to address three issues:

1- Optimal allocation of Phasor Measurement Units (PMUs) using Discrete Particle Swarm Optimization (DPSO) technique.

2- Large scale power system state estimation utilizing the optimal allocation of PMUs based on Global Positioning Systems (GPS).

3- Power system voltage stability monitoring based on the allocated PMUs’ readings.

49

Prepared ByFahd Mohamed Adly Hashiesh

Under Supervision ofProf. Dr. M. M. Mansour

Dr. Hossam Eldin M. AtiaDr. Abdel-Rahman A. Khatib

Cairo – Egypt

2006

Research Objective

Propose a protection system (strategy) to counteract wide area disturbance (instability), through employing adaptive protection relays, and fast broadband communication through wide area measurement.

Configure and adapt the proposed system to be applied on Egypt wide power system network.

50

A Master Student is Trying to Implement a PMU Lab Prototype in Ain-Shams Univ.

CONCLUSIONS AND FUTURE WORKS

thanks to their multiple advantages, nowadays, the technologies based on synchronized phasor measurements have proliferated in many countries worldwide (USA, Canada, Europe, Brazil, China, Egypt !,..).

up to now most applications based on synchronized phasor measurements have concerned mainly off-line studies, on-line monitoring and visualization, and to a less extent the real-time control, Protection, and the emergency control.

the toughest challenge today is to pass from Wide Area Measurements Systems (WAMS) to Wide Area Control Systems (WACS) and WAP.

52

Off-line SPM-based applications

software simulation validation SPM-based technologies can be very useful to help the

validation of (dynamic) simulation software system parameter/model identification (e.g. for loads,

lines, generators, etc.) the identification of accurate model/parameter is a

very important and tough task for the power system analysis and control.

difficulty: large number of power system components having time-varying characteristics.

synchronized disturbances record and replay this task is like that of a digital fault recorder, which

can memorize triggered disturbances and replay the recorded data if required.

the use of SPM allows more flexibility and effectiveness. 54

Real-time monitoring SPM-based applications fault location monitoring

accurate fault location allows the time reduction of maintenance of the transmission lines under fault and help evaluating protection performance.

power system frequency and its rate of change monitoring the accurate dynamic wide-area measured frequency is highly desirable

especially in the context of disturbances, which may lead to significant frequency variation in time and space.

generators operation status monitoring this function allows the drawing of generator (P-Q) capability curve. Thus,

the generator MVAr reserve, can be supervised. transmission line temperature monitoring

the thermal limit of a line is generally set in very conservative criteria, which ignores the actual cooling possibilities. The use of SPM allows the higher loading of a line at very low risk.

on-line "hybrid" state estimation the SPM can be considered, in addition to those from the Remote

Terminal Units (RTU) of the traditional SCADA system, in an on-line "hybrid" state estimation.

SPM-based visualization tools used in control centers display: dynamic power flow, dynamic phase angle separation, dynamic

voltage magnitude evolution, real-time frequency and its rate of change, etc.

55

Real-time (emergency) control SPM-based applications

automatic (secondary and tertiary) voltage control aim: optimize the var distribution among generators, controllable ratio

transformers and shunt elements while keeping all bus voltage within limits.

in the context of WAMS application, the solution of this optimization problem can be used to update settings of those reactive power controllers, every few seconds.

damping of low frequency inter-area oscillations (small-signal angle instability) low frequency inter-area oscillations (in the range of 0.2 – 1 Hz) are a

serious concern in power systems with increasing their size and loadability.

In Europe, in particular, many research studies have been performed to reveal such oscillations as well as provide best remedial actions to damp them out.

transient angle instability since such instability form develops very quickly, nowadays, Special

Protection Systems (SPS), also known as Remedial Action Schemes (RAS), are designed to act against predefined contingencies identified in off-line studies while being less effective against unforeseen disturbances.

56

Real-time (emergency) control SPM-based applications (cont’d)

short- or long-term voltage instability a responde-based (feedback) Wide-Area stability and voltage Control

System (WACS) is presently in use by BPA. this control system uses powerful discontinuous actions (switching

on/off of shunt elements) for power system stabilization.

frequency instability the underfrequency load shedding has its thresholds set for worst

events and may lead to excessive load shedding. new predictive SPM-based approaches are proposed aiming to avoid the

drawbacks of the conventional protection.

57

Conclusions:

• A new modified DPSO technique is developed to determine the optimal number and locations for PMUs in power system network for different depths of unobservability. It gives the optimal PMUs' allocation for different depths of unobservability comparable to other techniques

• The developed DPSO is tested on both 14-bus and 57-bus IEEE standard systems.

• For small power systems, DPSO gives either equivalent or better results. However for large power systems, it gives almost better locations and sometimes less number of PMUs for large power systems.

• DPSO determines the optimal PMUs' allocation for complete observability of the large system depicted from the Egyptian unified electrical power network.

A- Discrete Particle Swarm Optimization Technique:

Conclusions (continued):

• The phasors readings of PMUs are taken into consideration in a new hybrid state estimation analysis to achieve a higher degree of accuracy of the solution.

• The effect of changing the locations and numbers of PMUs through the buses of the power network on the system state estimation is also studied with a new methodology.

• The hybrid state estimation technique is tested on both 14-bus and 57-bus IEEE standard systems. It is also applied to a large system depicted from the Egyptian unified electrical power network.

• PMUs' outputs affect the state estimation analysis in a precious way. It improves the response and the output of the traditional state estimation.

B- Hybrid State Estimation Technique:


• The locations of PMUs according to state estimation improvement do not need to be similar to those locations according to observability depth.

• The system parameters, system layout and power flow affect the PMUs' positioning for optimal state estimation.

• For each system there is a certain number of PMUs with certain connections that reduces the estimation error significantly. As the number of PMUs' increases over the optimal solution, the estimation analysis begins to magnify the measurements error of the other devices.


• The readings of the allocated PMUs are to be utilized using a newly developed technique for on-line voltage instability alarming predictor.

• The predictor gives two types of alarms, one for voltage limit violation (10% voltage decrease) and the other for voltage collapse prediction according to the maximum permissible angle difference between bus voltages for certain bus loading angle.

• The time taken by the alarming predictor is small, and is determined by the speed of PMUs and the used computational system.

• The voltage instability alarming predictor concept is tested on both 14-bus IEEE standard system. It gives effective results.

• The alarming predictor is applied to the large system depicted from the Egyptian unified electrical power network, with the aid of the voltage instability limits calculation of the system.

C- On-line Voltage Instability Alarming Predictor:

GPS in Power Systems

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