IEEE Chapter Symposium
Possible Applications of PMUs for
Detecting Angle Instability in Power
Systems
Nima Farkhondeh Jahromi
Zongyu Liu
April 9, 2015
1
Outline
• Problem Formulation
• Angle Stability Classification
• First Proposed PMU-Based Algorithm
• Second Proposed PMU-Based Algorithm
• Conclusion and Remarks
April 9, 2015
2
Problem Formulation
• Centralized Power plants
• Popularity of renewable energy
Small number of large scale gen. units
Large number of small scale gen. units
• Traditional generator design/const.
Not so high efficiency
• Newer Technology in generator design
Higher efficiency
Power networks (due to power transfer capacity) get closer to their stability margin
Less tolerance
• Regulated electricity market
• Deregulated electricity market
Various power flow directions
More congestions
Contradictory combination
Stability control (instability detection) is (will be) the key challenge
April 9, 2015
3
Angle Stability Classification
[Real-time] Angle Stability Assessment in future Power Systems
Axis 1
Axis 2:
[Real-time] large disturbance
angle stability (transient stability)
assessment
[Real-time] small disturbance angle
stability assessment
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1st Proposed PMU-based Algorithm
Detection of transient instability based on the real-time COA
• Concept of Centre Of Angles (COA)
N
 COA 
 H
i 1
N
i
H
i 1
i
i
 i : Internal machine rotor angle
Difficult to directly measure
Difficult to access in real time. Number of
H i : Inertia time cte.
units being dispatched can vary
April 9, 2015
5
1st Proposed PMU-based Algorithm (1)
• Substitution of the internal angle with the phase angle of the
high side bus voltage
G
U  U 
T
Phase Measurement Unit (PMU)
• Substitution of the inertia time constant with the high side
active power injection
Phigh side injection  M mass
Approximation! (could be a source of error)
April 9, 2015
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1st Proposed PMU-based Algorithm (2)
• Illustration of substitution of the inertia time constant with
the high side active power injection
April 9, 2015
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1st Proposed PMU-based Algorithm (3)
• Real-time Centre of Inertia for area i
N
 ci 
i
i

P
 j j
j 1
N
i
P
 j
 gi (t )
j 1
• Real-time Centre of Inertia for the whole system
N
c 
i i

 cP
i 1
N
i
P

 g sys (t )
j 1
April 9, 2015
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1st Proposed PMU-based Algorithm (4)
Taking the appropriate remedial action(s) based on the value of  c
i
•
If
 ci > “pre-specified benchmark” (continuously)
speeding up
2) Suitable remedial action is to trip some generators
1) Area i (in a detailed analysis each gen. can be an area) is
• If
 ci
< “pre-specified benchmark” (continuously)
slowing down
2) Suitable remedial action is load shedding
1) Area i (in a detailed analysis each gen. can be an area) is
April 9, 2015
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1st Proposed PMU-based Algorithm (5)
Alarm mode based on comparing the real-time signals
• A real-time signal for area i
ci  c  gi (t )  gsys (t )  fi (t )
• A signal to be used as a reference: Critically-stable response
cicrt stab  ccrt stab  gi crt stab (t )  gsyscrt stab (t )  fi crt stab (t )
April 9, 2015
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1st Proposed PMU-based Algorithm (6)
• Rescue-time definition
Permanent decline
April 9, 2015
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1st Proposed PMU-based Algorithm (7)
• The method (the reference signal) is fault-location
(and also fault-type) dependent.
• The method is dependent on the inertia time constant
of the generators (Perhaps in future; lighter machines
have higher output)
April 9, 2015
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2nd Proposed PMU-based Algorithm
•
•
Principal idea is to have a real-time energy function (by means of PMUs) for a system divided
into two clusters.
The main question: Based on the real-time energy function, will the system split to more
clusters or not?
Area 1
M1
ω1
d (1   2 ) 2
1
1
2
EK  M eff eff  M eff (
)
2
2
dt
M 1M 2
eff  1  2 , M eff 
M1  M 2
Area 2
M2
ω2
New [temporary] steady-state
V ( ,  )  EK   ( Pline  Pline , steady  state )  d (1   2 )
April 9, 2015
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2nd Proposed PMU-based Algorithm (2)
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Conclusion and Remarks
• It might be possible to perform an on-line transient
instability detection and mitigation for a multi-area
power systems
• By improving (generalizing) the proposed algorithm, it
might be possible to avoid some blackouts happen due
to islanding
• Designing the appropriate remedial action, is very
much dependent on the system capabilities and is
difficult to be generalized
April 9, 2015
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Discussions
Suggestions
Questions
Criticisms
Ideas
Compliments
April 9, 2015
16