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Srinu Babu. MattaSrinu Babu. MattaResearch Scholar

Under the supervision of Dr. Seethalekshmi K.Dr. Seethalekshmi K.

Professor

Technical Paper : D2-1-33

Out-of-step Detection Out-of-step Detection using Wide Area Measurements using Wide Area Measurements

Babu Banarasi Das University,Lucknow, Uttar Pradesh, India

Power System – Snap shot & Challenges

Smart Grid – An emerging Technology

Protection schemes – Distance Protection

Out-of-step detection techniques

Proposed OOS- detection methods

Case studies & Results

Concluding Observations

Future scope

References

ContentsOut-of-detection (OOS) using WAMS

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Power System - A Snap-shot

The power demand in 1947 was 1670 MW and today it is 224,907 MW.

(Source: GOI site,CEA, Studygalaxy.com )

Indian Power Scenario

Generation

The power system – StructureGeneration – Transmission - Distribution

Highest monthly power generation recorded, so far is 91.7Million Units in April’13.

(Source:Power Line, June’13)

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Power System - ChallengesIndian Power System Perspective

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Power System - ChallengesPeculiarities of Regional Grids in India

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Opportunity for existing  AGING systems to leapfrog by envisioning a futuristic power grid

Smart Grid Characteristics

Emerging technology Integrates new technologies to enable re-look at design &

operation of power system Detect & address emerging problems before they impact service

Respond to local & system-wide inputs

Incorporate measurements & Feedback controls that quickly return to stable system operation after disturbances

Automatically adapt protective systems to accommodate changing system conditions

Re-route power flows, improve voltage profiles, change load patterns etc. during contingencies

Enable loads & Distributed generation to participate in operations

Self-healing & adaptive

“ Smart Grid”, means different things to different people

Smart Grid - An Emerging Technology

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Wide Area Measurement Systems (WAMS)Synchrophasors

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PMUHardware Block Diagram

GPSreceiver

Phase-locked oscillator

16-bit A/D

converter

Phasor micro-

processor

Modems

Anti-aliasingfilters

Analog Inputs

‘PMU’, 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.

Phasor Monitoring Unit (PMU) Wide Area Measurement Systems (WAMS)

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Synchrophasor technology enables cost-effective solutions to

substantially improve transmission system planning, operation,

maintenance and energy trading.

Real-Time Monitoring & Control

State Estimation.

Real Time Congestion Management

Post-Disturbance Analysis.

Benchmarking & System Model Variation

Power System Restoration

Adaptive Protection

Synchrophasor :: Applications & Benefits Wide Area Measurement Systems (WAMS)

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Protection system – Need & SchemesVarious Schemes

Typical Protection scheme followed wrt the type of transmission line.

Classification of Transmission lines on the basis of Source-to-line impedance ratio (SIR).

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Distance Protection - A snap shot

Description: Distance relays are double actuating quantity relays

with one coil energized by voltage and the other coil by current. The

system impedance is seen by the relay for judging the fault condition.

Rationale: Distance protection is non unit type protection and very

simple to apply. The Power swing block signal protects the system

from stable power swings by extending a block operation on Distance

relay and allowing the trip signal incase of unstable power swing.

Benefits: These relays are used as primary and back-up protection.

They can be used in carrier/communication/pilot aided distance

schemes in Auto-reclosing schemes. Distance protection is widely

used in protection of transmission lines.

Protection system – Need & Schemes

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OOS protection – A snap shot

Description: To avoid tripping of any power system element during

stable swings. Protect the power system during unstable or out-of-

step conditions

Rationale: Protective relays prone to respond to stable or unstable

power swings and cause unwanted trippings of transmission lines or

other power system elements include OC, UV, distance, directional

OC, Out-of-step relay protects the power system from stable power

swings by generating a out-of-step block signal (OSB)

Benefits: A controlled tripping of certain power system elements

during the OOS condition is necessary in order to prevent equipment

damage, and wide spread power outages, and minimize the effects of

the disturbance.

Out-of-step detection techniques

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Out-of-step detection techniquesClassification

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Out-of-step detection techniques

Two blinder scheme.

• Concentric Distance Relay Characteristics.

• Blinders scheme

Merits : +Simple +The power swing condition is checked before one of the impedance tripping zones is entered allowing the tripping elements to be blocked : Demerits : - limited to a single delta impedance setting and a timer setting - Load encroachment or limit the reach of thehigher impedance zones.

Merits : + Used for power swing detection applications is that it can be used independent of the distance zone characteristics. + Single blinder can be used to restrict tripping of the distance relay for loads outside of the blinders.+ It can be used for load encroachment applications. Demerits : -To find the correct settings for the blinders is not always simple and requires a sophisticated grid analysis. - The single-blinder scheme cannot distinguish between a fault and an OOS condition until the fault has passed through the second blinder within a given time.

Comparison of various techniques

S. No. Technique Merits Demerits Potential application

1 Continuous impedance measurements

+A delta impedance setting is not required anymore.

- For security reasons additional predictive calculations may be required. - As long as the changing impedance vector is not

approaching a tripping zone faster than the relay can confirm the out-of-step condition (at least 3 calculations 10 ms) the detection will be successful.

+dynamic calculation of the delta impedance and an automatic adaptation to the change of the power swing impedance.

- very precise & faster calculation cycles of the algorithm is required.

2 Swing center voltage and its rate of change

+ Independent of the system source and line impedances

- The technique also requires offline systemstability studies to set the threshold value (rate of change of SCV),

- In this,monitors the rate of change of swing centre voltage (SCV) and compares it with a threshold value to discriminate between stable and out-of-step swings. Withsome approximations, the SCV is obtained locally from the voltage at the relay location, which consequently makes the SCV independent of power system parameters. However, the approximation is true only if the total system impedance angle is close to 90 . For a multimachine system, the voltage measured at relay location does not give an accurate approximation of SCV.

+ The magnitude of the SCV relates directly to , the angle difference of two sources.

- System specific.

3 Neural networks based + Quick decisions - Enormous trainging effort required to train for all possible swing scenarios. - Able to make the decisions quickly for a new

case, which has close resemblance to a known predefined case for which the algorithm is trained.

+ self adaptive - Complexity increases as the system interconnections increase.

4 Fuzzy logics based + Quick decisions - Enormous trainging effort required to train for all possible swing scenarios.

- Proper weighing factors needs to be assigned for right logical our put from the assigned rules.

+ Burdensome heuristic setting process of the fuzzy system are avoided and a kind of optimization is realized.

- Complexity increases as the system interconnections increase.

5 Energy function based + Accurate - The method requires computation of power flow and phase angle across lines belonging to the critical cutset.

+ Useful in initiating emergency control measures such as controlled system separation.

+ no assumptions are made regarding the power-angle relationship in a line, nor are any data on the system equivalents necessaryin implementing the detection scheme.

- To implement as an out-of-step algorithm, measurements across all series elements are required to find the cutset. This technique is difficult to implement as a protection algorithm because it is based on wide area information. 15

Out-of-step detection techniquesComparison of various techniques

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Proposed Out-of-step detection techniquesResistance based schemeThe system consists of two 400KV buses M and N connected to two generators EM and EN respectively and two parallel lines connecting the buses. The relay is placed at bus M. Phasor Measurement Units (PMU) are placed at the buses M and N. PMU’s placed at the buses calculate voltage and current of the three phases of the line at a sampling rate of 20 – 60 samples / cycle. A fault occurs on one of the lines and the line is tripped. As a result of which there is an imbalance of power in the other line and thus it experiences power swing. The data collected by the PMUs is then used in the Data Concentrator to calculate the positive sequence voltage and current phasor at fundamental frequency using Discrete Fourier Transform algorithm.

. PMU based schemes for SMIB system Flowchart for the resistance based scheme

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Proposed Out-of-step detection techniquesResistance based scheme

Algorithm of Swing Detection Element

This element acts as checking criteria to ascertain the out of step condition during stable or unstable power swings. The algorithm comprises of four types of sub-elements as shown here, namely “Magnitude of change detection element “, “Rate of change detection element”, “differential magnitude of change detection element” and “Differential rate of change detection element”.

All the parameters like T1 to T4, K1 to K4, R1set,

R2set, Tmax and T are precisely set after conducting thorough study of the system configuration & its transient analysis. If either of the “Magnitude of change detection element “and “Rate of change detection element” sets along with either of the “differential magnitude of change detection element” and “Differential rate of change detection element”, then only the Swing Detection Element gives a positive output, this signal can be used for controlled tripping or for any power shedding application etc.

Swing Detection Element

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Proposed Out-of-step detection techniquesImpedance based schemeThe system consists of two 400KV buses M and N connected to two generators EM and EN respectively and two parallel lines connecting the buses. The relay is placed at bus M. Phasor Measurement Units (PMU) are placed at the buses M and N. PMU’s placed at the buses calculate voltage and current of the three phases of the line at a sampling rate of 20 – 60 samples / cycle. A fault occurs on one of the lines and the line is tripped. As a result of which there is an imbalance of power in the other line and thus it experiences power swing. The data collected by the PMUs is then used in the Data Concentrator to calculate the positive sequence voltage and current phasor at fundamental frequency using Discrete Fourier Transform algorithm.

. PMU based schemes for SMIB system Flowchart for the impedance based scheme

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Proposed Out-of-step detection techniquesImpedance based scheme

Algorithm of Swing Detection Element

This element acts as checking criteria to ascertain the out of step condition during stable or unstable power swings. The algorithm comprises of four types of sub-elements as shown here, namely “Magnitude of change detection element “, “Rate of change detection element”, “differential magnitude of change detection element” and “Differential rate of change detection element”.

All the parameters like T1 to T4, K1 to K4, R1set,

R2set, Tmax and T are precisely set after conducting thorough study of the system configuration & its transient analysis. If either of the “Magnitude of change detection element “and “Rate of change detection element” sets along with either of the “differential magnitude of change detection element” and “Differential rate of change detection element”, then only the Swing Detection Element gives a positive output, this signal can be used for controlled tripping or for any power shedding application etc.

Swing Detection Element

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Case studies & ResultsCase studies

The Power Stability studies for both the proposed schemes have been carried for testing on a single machine infinite bus system (SMIB) [13] and the WSCC 9-bus system [14]. The single line diagram of the systems are shown in Fig.6 and Fig.7 respectively. Simulations are carried out on PSCAD & MATLAB.

A disturbance was created on one transmission line, where the performance of the distance relay to be studied, is connected. The disturbance was created by connecting load on same line for some duration. The load location and amount of loading on the line is varied to study the performance of the distance relay on stable and unstable swings. In these schemes, the system frequency is considered to be constant. For stable swings, the accuracy of the relay to classify a power swing as a stable swing is monitored. During unstable swing, the relays have been observed for speed of detection of OOS condition. Loading of the line has been limited near the margins of stability and unstability of the system depending upon the case of study.

Single line diagram of SMIB. Single line WSCC 9-bus system.

Magnitude change detection element

Differential magnitude change detection element

Differential rate of change detection element

Voltage Signal

Swing Detection Element – Out put signal

Trip signal

Magnitude change detection element

Differential magnitude change detection element

Differential rate of change detection element

Voltage Signal

Swing Detection Element – Out put signal

No Trip signal

Case studies & ResultsResults – Resistance based scheme

Stable swing- Created a disturbance at 2 Sec and removed after 0.5 Sec. between line 1-7 of WSCC 9-bus system

Unstable swing- Created a major disturbance at 3 Sec and removed after 0.5 Sec. between line 1-7 of WSCC 9-bus system

Magnitude change detection element

Differential magnitude change detection element

Differential rate of change detection element

Voltage Signal

Swing Detection Element – Out put signal

Trip signal

Magnitude change detection element

Differential magnitude change detection element

Differential rate of change detection element

Voltage Signal

Swing Detection Element – Out put signal

No Trip signal

Results – Impedance based schemeCase studies & Results

Stable swing- Created a disturbance at 2 Sec and removed after 0.5 Sec. between line B1-B2 of SMIB system

Unstable swing- Created a major disturbance at 2 Sec and removed after 0.5 Sec. between line B1-B2 of SMIB system

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Power swing detection schemes based on WAMS - synchronised time measurement is proposed in this paper. Schemes work on the swing detection algorithm for resistance or impedance, where in the resistance, rate of change of resistance and differential measurements made from two sides of the transmission line detects the OOS condition.

These methods use PMU data available at both ends of the transmission line.

It is observed that as the disturbance severity increases, operating time of both the schemes reduces and this technique can operate for faults during steady state as well.

Simulation results in SMIB case and WSCC 9 bus system case reveals that both the proposed schemes can detect and classify the power swing very precisely.

Out of step detection using WAMSConcluding Observations

CasePower swing

Amount of loading

(MW)

Amount of loading (MVAR)

Proposed scheme: Operating time (sec) - WAM based schemes

Other OOS detection schemesOperating time (Sec)

Resistance based

Impedance based

R- RdotDouble blinder

Impe difference

SCV

Resi difference

 SMIB Stable 4000 2300 N Ope N Ope N Ope N Ope N Ope N Ope N OpeSMIB Unstable 9000 4450 0.51 0.499 0.61 0.68 0.83 1.11 0.84

 WSCC Stable 4000 2300 N Ope N Ope N Ope N Ope N Ope N Ope N OpeWSCC Unstable 20000 7450 0.112 0.110 0.41 0.50 0.66 0.91 0.66

N Ope : Not operated

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Using Classifiers like SVM to detect the Out of step condition.

Extending the same approach for using stable islanding application.

Application of the same approach for higher bus configured system.

Out of step detection using WAMSFuture scope

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References Out of step detection using WAMS  [1] P.Kundur, “Power System Stability,” McGraw Hill.[2] Stanley H. Horowitz, Arun G. Phadke, “Power System Relaying,” John Wiley & Sons Ltd, Third edition, 2008. [3] Dr. Jürgen Holbach, Siemens AG, Raleigh, NC, USA: “New Out Of Step Blocking Algorithm for Detecting Fast Power Swing Frequencies,” 30thAnnual Western Protective Relay Conference, Washington StateUniversity, Spokane , Washington, October 21-23, 2003 [4] Y. Liu, “Aspects on power system islanding for preventing widespread blackout,” in Proc. IEEE Int. Conf. Networking, Sensing and Control, 2006[5] A. Mechraoui, “A new principle for high resistance earth fault detection during fast power swings for distance protection,” IEEE Trans. Power Delivery, 1997.[6] D. Tziouvaras and D. Hou, “Out-of-step protection fundamentals and advancements,” IEEE, presented at the 30th Annual. Western Protective Relay Conf., Spokane, 2003. [7] V. Centeno, “An adaptive out-of-step relay [for power system protection],” IEEE Trans. Power Delivery, 1997. [8] R. Padiyar and S. Krishna, “Online detection of loss of synchronism using energy function criterion,” IEEE Trans. Power Delivery, 2006.

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References Out of step detection using WAMS

  [9] S. Chakrabarti, E. Kyriakides, T. Bi, D. Cai and V. Terzija, "Measurements Get Together," IEEE Power & Energy Magazine, 2009.[10] Yan Li, Xiaoxin Zhou, and Jingyang Zhou, “A new algorithm for distributed power system state estimation based on PMUs,” IEEE, International Conference on Power System Technology,. 2006.[11] J. Mooney, P.E and N. Fisher, "Application guidelines for power swing detection on transmission systems," Schweitzer Eng. Lab. Inc,59th Annual Coriference for Protective Relay Engineers, 2006.[12] Pratim Kundu, J. Ganeswara Rao, P. K. Nayak, A. K. Pradhan, “Wide Area Measurement based Out-of-Step Detection Technique,” IEEE Trans. Power Delivery, 2011.[13] S.M.Brahma, “Distance Relay with Out-of-step Blocking Function using Wavelet Transform”, IEEE transactions on power delivery, vol. 22, no. 3, July 2007.[14] Seethalekshmi K., S. N. Singh, and S. C. Srivastava, “SVM Based Power Swing Identification Scheme for Distance Relays” IEEE PES,GM, July2010.

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