10th Mediterranean Conference on
Power Generation, Transmission,
Distribution and Energy Conversion
6-9 November 2016
Belgrade, Serbia
Mitigation of Cascading Outages and Prevention of
Blackouts：System-Wide Corrective Control
Lei Ding
Shandong University
Cascading Outages and Blackouts
• Power System Blackout: the loss of supply to the load in the
entire power system, or parts of the system
• Cascading Outage: a sequence of events in which an initial
disturbance, or a set of disturbances, causes a sequence of one
or more dependent component outages
• Each blackout has its own specific nature
large number of scenarios and blackout paths
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Cascading Outages and Blackouts
• Electric power systems have become extremely complex and difficult to
operate and protect
• It is impractical and uneconomical to design power systems to be stable for
every possible disturbance
• To maximize profit and utilization of all available generation and transmission
assets, power systems operate relatively close to their stability limits
• There is always a risk that cascading outages or blackouts happen.
• The economic and social implications of blackouts can be disastrous and
difficult to quantify in advance
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
New Challenge 1—Integration of RES
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10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
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New Challenge 2—AC/DC Hybrid System
Modern power systems take more cascading risks in AC/DC
hybrid system due to:
• Tightly-coupled interaction between HVDC and AC systems
• Large global impact subject to failure in HVDC system
• HVDC delivers a large amount of active power to receiving AC system.
• Commutation failure and even cascading commutation failure may be caused
by faults in AC system.
• Once HVDC is blocked, the loss of large power transmitted will create a large
disturbance to AC systems connected.
• Such disturbance is huge for AC system to be withstood in a limited area.
Larger disturbance, low inertia system and weakened regulation ability
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
New Challenge 2—AC/DC Hybrid System
• Two risky accidences, which may
result in cascading events, were
recorded although no severe
blackout was triggered
• On Aug. 8, 2012 simultaneous
commutation failures in four
HVDCs
• On Jul. 5, 2013 simultaneous
commutation failures and forced
blocking in two HVDCs
• Power grids in China feature typical AC/DC
hybrid interconnections
• Central Grid transmits large power to East
Grid by five HVDCs
• one of which is Ultra HVDC with power of
6400MW
From Prof. Xiaoxin Zhou
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
New Challenge 2—AC/DC Hybrid System
Procedure during “7.5”(2013) event
• A 500kV AC line in East Grid was tripped by temporary single-phase fault
• Two HVDC i.e. Fulong-Fengxian and Tuanlin-Fengjing suffered commutation
failure successively
• AC faulted line was reclosed successfully
• Single pole at Fengjing inverter and bipolar at Fulong converter were blocked
• Power transmitted by HVDC reduced 4,530 MW
• Frequency of East Grid decreased to 49.82HZ
• Power through AC tie line from other grid increased to 700MW
From Prof. Xiaoxin Zhou
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Power System Collapse - Blackouts
• A generic path to a blackout:
Uncontrolled
System Separation
Initiating Event
Precondition
Restoration can
be very time
Restoration
consuming
Cascading Events
Partial or total blackouts
Steady-State Progression
High Speed
Cascade
Triggering Event
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Power System Collapse - Blackouts
• A generic path to a blackout:
Special System Protection
Initiating Event Emergency control
Uncontrolled
System Separation
Corrective control
Precondition
Cascading Events
Steady-State Progression
Restoration
High Speed
Cascade
Triggering Event
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Power System Collapse - Blackouts
• A generic path to a blackout (HVDC system, with RES integration):
Initiating Event
Precondition
Uncontrolled
System Separation
Cascading
Events
Restoration
High Speed Cascade
• Initiating event, such as HVDC blocking, will be a huge disturbance.
• System inertia and regulation ability are weakened.
• Whole cascading process will be highly accelerated.
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Power System Collapse - Blackouts
• A generic path to a blackout (HVDC system, with RES integration):
Initiating Event
Precondition
Uncontrolled
System Separation
Cascading
Events
Restoration
High Speed Cascade
System-wide emergency control: alleviate or limit the impacts of the large disturbance
using all possible system-wide measures: regulation capacity of RES, active load
control, storage, etc.
System-wide corrective control: mitigate the cascading outages and prevent blackouts:
controlled islanding, system-wide coordinated load shedding
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Role of Controlled Islanding
• Controlled islanding is a typical system-wide corrective control
measure
• Avoid uncontrolled system separation (blackout) by initiating a
controlled system separation
• Separation can prevent mechanisms that would, without
islanding, cause the system to collapse:
– e.g. unstable oscillations
– or voltage collapse
• Separate the system into isolated islands
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Role of Controlled Islanding
Initiating Remedial
Event
Actions
Taken
Healthy
System
Uncontrolled
System Separation
Remedial
Actions
Fail
Steady State
Progression
High Speed
Cascade
Restoration
Healthy
System
Verify Feasibility of
Islanding Solution
Triggering
Event
Pre-Islanding
Actions
Determine
Necessity
of Islanding
Blackout
Post-Islanding
Corrective
Actions
Plan
Separate Islands
Islanding
Stable
Islanded
Operation
Healthy
System
Resynchronise
Islands
Islanding can avoid a blackout: limiting the load unsupplied
and accelerating the return to healthy operation
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Supporting Infrastructure
• Successful Controlled Islanding will require extensive supporting
infrastructure
– Wide area monitoring
– Algorithms for detecting imminent collapse
– Algorithms for creating the islanding solution
– Centralised processing to implement algorithms
– Automated, wide area control of:
• Breakers for separation
• Control elements for pre/post islanding actions (e.g. shedding relays)
• Protection settings (settings must be changed post islanding)
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Supporting Infrastructure
System-wide Corrective Control
System state, dynamics
and events
Performed within centralised control centre
Transparent
database technique
Reliable, Fast
Communication
Network
Centralised Computing
Algorithm to
Detect
Imminent
Cascade
Algorithm to
Determine
Islanding
Solution
State estimation
Security Evaluation
Risk Pre-warning
Wide Area Monitoring
Centralised,
Automated
Decision Making
Power System
Automated, remote access
to protection settings
External
Inputs
Initiate Islanding
Reliable, Fast
Communication
Network
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
- Breaker opening
schedule
- Pre/Post control
actions
- New protection
settings
Role of Controlled Islanding
• Need an islanding solution to island the system
• Islanding solution must describe:
–
–
–
–
If or whether to split?
Where to split: splitting boundary?
When to split: timing
What order should the islands be created and should other
actions be taken before/after this, e.g. load reduction (HOW?)
• The answers to these may be interdependent and not
optimally determined in isolation
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Where to Split?--SCCI Description
• Stable islanded operation: Coherent generators and small
power-imbalance
• SCCI: Spectral Clustering based Controlled Islanding
• Two Steps
– Construct Dynamic Graph and cluster generator nodes
– Construct Static Graph and cluster all nodes
• Spectral Clustering
– Construct the Laplacian matrix of graphs (dynamic, static)
– Compute the first two eigenvectors (bisection case)
– Use K-medoids to cluster nodes
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
SCCI Description
First Step: Dynamic graph and generator grouping
Generator groups {1}, {2,3}
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
SCCI Description
Second Step: Static graph and splitting boundary
Splitting boundary {4-5;4-6} (red dash line)
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
19
When to Split?
Disturbance
pre-islanding process
Separation
post-islanding process
Pre-disturbance SEP
Post-islanding SEPs
• The post-islanding SEP is determined by the splitting boundary-island topology.
• Find a proper splitting boundary to make sure post-islanding SEP exists
• During the whole process, dynamic stability must be satisfied.
• Given a certain the splitting boundary, the post-islanding dynamic process is
determined mainly by the timing of controlled islanding.
•If the separation is undertaken at the right time, the transition will be smoothly.
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
When to Split?-right time to split
• Construct a transient energy function of each intended island
• If the island is separated when the energy is below the critical energy, then
the island will retain its stability
• If the island is separated when the energy of the island is greater than critical
energy then the island may lose its stability.
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
21
When to split?
22
• Consider two islands: Island 1 and Island 2
• The stability of each island (post separation) is
determined by the time the separation occurs at
A window for stable separation is created
Legend
stable
unstable
ISLAND 1
ISLAND 2
Time
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
22
Interdependency
23
No intersection time exists where the islands can be separated
and both remain stable?
Legend
stable
unstable
ISLAND 1
ISLAND 2
t1
•
•
•
•
t2
Time
change the splitting boundary produces a non-empty intersection;
take remedial control;
split in a sequential way.
So, by changing where the islands are created it is possible to
create a suitable When for separation
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
Controlled Islanding Example
1
Wind Speed >= Cut Out Speed
Disconnection of Wind Farms
Initiating Event
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
24
Controlled Islanding Example
2
Line trips due to
overload
2.16s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
25
Controlled Islanding Example
3
Line trips due to
overload
2.22 s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
26
Controlled Islanding Example
4
Line trips due to
overload
2.29 s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
27
Controlled Islanding Example
5
Generator trips
due to out of
step operation
2.64 s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
28
Controlled Islanding Example
6
Line trips due to
overload
6.01s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
29
Controlled Islanding Example
7
Line trips due to
overload
6.43s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
30
Controlled Islanding Example
7
6.43s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
31
Controlled Islanding Example
8
Generator trips
due to out of
step operation
7.10s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
32
Controlled Islanding Example
9
Generator trips
due to out of
step operation
8.03s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
33
Controlled Islanding Example
10
Generator trips
due to out of
step operation
9.55s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
34
Controlled Islanding Example
9.55s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
35
Controlled Islanding Example
1
Wind Speed >= Cut Out Speed
Disconnection of Wind Farms
Initiating Event
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
36
Controlled Islanding Example
2
Intentional
tripping of the
lines
0.60s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
37
Controlled Islanding Example
2
0.60s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
38
Controlled Islanding Example
3
Generator trips
due to out of
step
1.24s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
39
Controlled Islanding Example
3
1.24s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
40
Controlled Islanding Example
4
Line trips due to
overload
2s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
41
Controlled Islanding Example
Comparison
9.55s
Time(s)
0 1 2 3 4 5 6 7 8 9 10
Without Controlled
Islanding
With Controlled
Time(s)
Islanding
0
2s
1 2 3 4 5 6 7 8 9 10
Element
Assets Lost
Capacity Lost
(%)
Element
Assets Lost
Capacity Lost
(%)
Tripped Generators
1,8,9,10
33.9
Tripped Generators
1
13.2
6
18.1
Unsupplied
Unsupplied
1,3,4,6
42.0
Loads
Loads
Non-Energised
Lines
1,2,3,4,11,17,
22, 23, 24,
25, 26, 27, 28
28.5
Non-Energised
Lines
1, 2, 4, 9, 11
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
9.1
42
Conclusion
• System-wide corrective control could play a role in
mitigating cascading outage and preventing blackouts,
especially in AC/DC hybrid systems with large-scale RES
integration.
• Prevents an uncontrolled separation by performing a
controlled separation of the power system
• System-wide corrective control is very complex and
must be found online, during a system collapse
• Demands high level of confidence in automated, closed
loop control with widespread authority over breakers
and other control procedures
10TH MEDITERRANEAN CONFERENCE ON POWER GENERATION, TRANSMISSION, DISTRIBUTION AND ENERGY CONVERSION
6-9 November 2016, Belgrade, Serbia
10th Mediterranean Conference on
Power Generation, Transmission,
Distribution and Energy Conversion
6-9 November 2016
Belgrade, Serbia
Mitigation of Cascading Outages and Prevention of
Blackouts：System-Wide Corrective Control
Lei Ding
Shandong University
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