Transcript Slide 1

Technical Paper : D2-1-33
Out-of-step Detection
using Wide Area Measurements
Under the supervision of
Srinu Babu. Matta
Dr. Seethalekshmi K.
Research Scholar
Babu Banarasi Das University,
Lucknow, Uttar Pradesh, India
Professor
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Out-of-detection (OOS) using WAMS
Contents
 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
Power System - A Snap-shot
Indian Power Scenario
The power system – Structure
Generation – Transmission - Distribution
Generation
The power demand in 1947 was 1670 MW and
today it is 224,907 MW.
(Source: GOI site,CEA, Studygalaxy.com )
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 - Challenges
Indian Power System Perspective
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Power System - Challenges
Peculiarities of Regional Grids in India
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Smart Grid - An Emerging Technology
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
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Wide Area Measurement Systems (WAMS)
Synchrophasors
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Wide Area Measurement Systems (WAMS)
Phasor Monitoring Unit (PMU)
‘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.
PMU
Hardware
Block Diagram
Analog
Inputs
Anti-aliasing
filters
GPS
receiver
Phase-locked
oscillator
16-bit
A/D
converter
Modems
Phasor
microprocessor
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Wide Area Measurement Systems (WAMS)
Synchrophasor :: Applications & Benefits
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
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Protection system – Need & Schemes
Various Schemes
Classification of Transmission lines on the basis of
Source-to-line impedance ratio (SIR).
Typical Protection scheme followed wrt the type of
transmission line.
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Protection system – Need & Schemes
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.
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Out-of-step detection techniques
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-ofstep 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.
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Out-of-step detection techniques
Classification
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Out-of-step detection techniques
Comparison of various techniques
• Concentric Distance Relay Characteristics.
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 the
higher impedance zones.
• Blinders scheme
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.
Two blinder scheme.
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Out-of-step detection techniques
Comparison of various techniques
S. No.
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Technique
Continuous impedance
measurements
Merits
+A delta impedance setting is not required
anymore.
Demerits
- For security reasons additional predictive
calculations may be required.
+dynamic calculation of the delta impedance - very precise & faster calculation cycles of the
and an automatic adaptation to the change of algorithm is required.
the power swing impedance.
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Swing center voltage and + Independent of the system source and line - The technique also requires offline system
impedances
stability studies to set the threshold value (rate of
its rate of change
change of SCV),
+ The magnitude of the SCV relates directly - System specific.
to d, the angle difference of two sources.
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Neural networks based
Fuzzy logics based
Energy function based
- 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.
- 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. With
some 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.
+ Quick decisions
- Enormous trainging effort required to train for all
possible swing scenarios.
+ self adaptive
- Complexity increases as the system
interconnections increase.
+ Quick decisions
- Enormous trainging effort required to train for all - Proper weighing factors needs to be assigned for
possible swing scenarios.
right logical our put from the assigned rules.
- Complexity increases as the system
interconnections increase.
+ Burdensome heuristic setting process of
the fuzzy system are avoided and a kind of
optimization is realized.
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Potential application
+ Accurate
- 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.
- The method requires computation of power flow
+ Useful in initiating emergency control measures
and phase angle across lines belonging to the critical such as controlled system separation.
cutset.
+ no assumptions are made regarding the
- To implement as an out-of-step algorithm,
power-angle relationship in a line, nor are any measurements across all series elements are required
data on the system equivalents necessary
to find the cutset. This technique is difficult to
in implementing the detection scheme.
implement as a protection algorithm because it is
based on wide area information.
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Proposed Out-of-step detection techniques
Resistance based scheme
The 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 techniques
Resistance based scheme
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 subelements 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.
Algorithm of Swing Detection Element
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Proposed Out-of-step detection techniques
Impedance based scheme
The 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 techniques
Impedance based scheme
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 subelements 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.
Algorithm of Swing Detection Element
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Case studies & Results
Case 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.
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Case studies & Results
Results – Resistance based scheme
Magnitude change detection element
Magnitude change detection element
Differential magnitude change detection element
Differential magnitude change detection element
Differential rate of change detection element
Differential rate of change detection element
Voltage Signal
Voltage Signal
Swing Detection Element – Out put signal
Swing Detection Element – Out put signal
No Trip signal
Trip signal
Stable swing- Created a disturbance at 2 Sec and Unstable swing- Created a major disturbance at 3
removed after 0.5 Sec. between line 1-7 of WSCC Sec and removed after 0.5 Sec. between line 1-7
9-bus system
of WSCC 9-bus system
Case studies & Results
Results – Impedance based scheme
Magnitude change detection element
Magnitude change detection element
Differential magnitude change detection element
Differential magnitude change detection element
Differential rate of change detection element
Differential rate of change detection element
Voltage Signal
Voltage Signal
Swing Detection Element – Out put signal
Swing Detection Element – Out put signal
No Trip signal
Trip signal
Stable swing- Created a disturbance at 2 Sec and Unstable swing- Created a major disturbance at 2
removed after 0.5 Sec. between line B1-B2 of Sec and removed after 0.5 Sec. between line B1-B2
SMIB system
of SMIB system
Out of step detection using WAMS
Concluding Observations
Case
Power
swing
Amount of
loading
(MW)
Proposed scheme:
Amount of Operating time (sec) loading
WAM based schemes
(MVAR) Resistance Impedance
based
based
Other OOS detection schemes
Operating time (Sec)
R- Rdot
Double
blinder
Impe
difference
SCV
Resi
difference
N Ope
0.83
N Ope
1.11
N Ope
0.84
N Ope
N Ope
0.66
0.91
N Ope : Not operated
N Ope
0.66
SMIB
SMIB
Stable
Unstable
4000
9000
2300
4450
N Ope
0.51
N Ope
0.499
N Ope
0.61
N Ope
0.68
WSCC
WSCC
Stable
Unstable
4000
20000
2300
7450
N Ope
0.112
N Ope
0.110
N Ope
0.41
N Ope
0.50
 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.
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Out of step detection using WAMS
Future scope
 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.
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Out of step detection using WAMS
References
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[3]
[4]
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Out of step detection using WAMS
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