key bollen continuitysupply
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Continuity of supply and voltage quality
in the electricity network of the future
Math Bollen
Luleå University of Technology(Energy Markets Inspectorate)
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Terminology
• Continuity of supply (CoS)
– Absence of supply interruptions
• Voltage quality (VQ)
– All other deviations from ideal voltage magnitude
and waveform
– Rather technical and detailed, different types of
deviations (“disturbances”)
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General status
• Aim of the power system: guarantee an
acceptable continuity and quality for the
customers.
• Requirements have become stricter through the
years; some interruptions are no longer
acceptable.
• New types of consumption and production
introduce new challenges to CoS and VQ
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Enter the smart grid
• New technology to address new challenges
– Challenges include new production, new
consumption, markets, but also increasing
demands on CoS and VQ
• Solutions fall into three groups:
– Solutions fully in the grid
– Combined solutions: grid + customers
– Fully market-based solutions
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What matters to the customer ?
• Continuity of supply (all customers)
• Voltage quality (most customers, but not all at
the same time)
• Network tariffs (all customers)
• Price of electricity (all customers)
• ... the rest is engineering!
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Some of the solutions
• Curtailment to prevent interruptions due to
transformer tripping on overload due to
electric heating
• Voltage control in the distribution grid to
prevent overvoltages with rural domestic
customers due to solar power
• Setting limits on harmonic emission from
windparks to prevent high voltage distortion in
the grid.
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Overload protection
• Overload protection prevents damage to grid
components
– Adverse impact on grid users is prevented by
preventing overloads
– Limiting installed capacity at distribution
– Operating reserve at transmission
• Smart grid: Overload protection to preventinterruptions
– Tripping / curtailing the cause of the overload
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A B
C D
E
Main
Grid
Wind
park
Small town
Existing approach
Operating reserve
Protecting the lines
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Main
Grid
Curtailable
customer
Small town
Smart-grid approach
No operating reserve
Protecting the customers
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T i m e
1
23
4
The protection curves
1. Maximum permanent load current2. Curtailment settings
3. Overcurrent protection
4. Actual thermal limit
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Distribution voltage control
• Existing approach
– On-line and off-line tap changers
– Limit feeder length and loading
• Smart grid approaches
– Advanced voltage control (measurements and
control at different locations)
– Curtailing consumption and production
– Excepting the occasional over/under voltage
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0.0 0.5 1.0 1.5 2.0 2.5 3.098.0
98.5
99.0
99.5
100.0
100.5
101.0
101.5
102.0
Nominal wind ower MW
Voltage(%
)
Statistical approach
V
o l t a g e ( % o
f l i m i t )
100
102
1
Installed capacity (MW)
2 398
100%
99.9%
99%
99.99%
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Harmonic emission
• Power-electronics has a number of big
advantages, but a drawback is the resulting
waveform distortion.
• Existing approach: limit emission; planning
levels based on compatibility levels
• Smart-grid approach
– Filters in the grid
– Reconsidering planning / compatibility levels
– Reconsidering need for emission limits
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Emission from wind turbines
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Impact on the grid
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0
1
2
3
4
5
6
7
8
9
10
1 3 5 7 9 1 1
1 3
1 5
1 7
1 9
2 1
2 3
2 5
2 7
2 9
3 1
3 3
3 5
3 7
3 9
4 1
4 3
4 5
4 7
4 9
Ordning av överton
G r ä n s v ä r d
e ( % )
Kompatibilitetsnivå Immunitetsgräns
Compatibility and immunity
V o l t a g e l i m i t ( % )
Harmonic order
10
5 403020
Immunity limit –
harmonic 5
Compatibility level – harmonic 5
Immunity limit – harmonic 5.5
Compatibility level – harmonic 5.5
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Transmission-system operation
• Existing approach: single redundancy always
– Has served us very well
– Sets limits on market transactions
– Not enough during major storms
• Smart-grid approach: adjust the level of
redundancy to the actual risk
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Limit
Component failure rate
S y s t e m
f a i l u r e r a t e
Mild
weather
Severe
weather
Major
storm
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Risk-based operation
State of thepower system
Momentaryfailure rates
State, historyand forecast
of the weather
Calculate theoperational risk
Give warningto the
operational staff
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Performance indicators
• Existing indicators
– Average number and duration of interruptions
– Average voltage quality levels
• Future developments
– Indicators at customer level
– Indicators during operation (“alarms”)
• Future needs
– Reliability indicators for curtailment and demand
response
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Conclusions
• CoS and VQ is what matters to the customer,
the rest is engineering.
• Protection should ultimately protect the
customer
• Reconsider all planning levels, emission
requirements, connection agreements, to see if
they still fulfil their ultimate aim
• Performance indicators will play an even more
important role