Key Bollen ContinuitySupply

7/28/2019 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)



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”)



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



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



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!



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.



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



A B

C D

E

Main

Grid

Wind

park

Small town

Existing approach

Operating reserve

Protecting the lines



Main

Grid

Curtailable

customer

Small town

Smart-grid approach

No operating reserve

Protecting the customers


http://slidepdf.com/reader/full/key-bollen-continuitysupply 10/21Current

T i m e

1

23

4

The protection curves

1. Maximum permanent load current2. Curtailment settings

3. Overcurrent protection

4. Actual thermal limit



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



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%



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



Emission from wind turbines



Impact on the grid



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



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



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



Risk-based operation

State of thepower system

Momentaryfailure rates

State, historyand forecast

of the weather

Calculate theoperational risk

Give warningto the

operational staff



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



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

Documents

Key Bollen ContinuitySupply