Lesson 10 - Distribution Grid and Distributed Generation
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Transcript of Lesson 10 - Distribution Grid and Distributed Generation
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Radial network
Energy supplied top-downfrom feeder
Traditional distribution grid:
From feeder to meter
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Distribution grid Flanders:
Facts and figures
3,075 feeders
29,546 km of medium-voltage lines
29,331 distribution transformers 24,820 distribution cabins
6,203 switching posts 52,473 km of low-voltage lines
1,796,083 connections 2,580,279 meters
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3 technological drivers Power electronics (PE) becomes ubiquitous in loads, generators
and grids
More power produced (and stored) near consumers: DistributedEnergy Resources (DER)
Increased importance of Power Quality (PQ): more disturbancesand more sensitive devices
3 socio-economic tendencies Liberalization of energy markets
More sustainable energy (renewable and high-quality) Non-guaranteed security of supply
Evolution in electrical energy
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DER technologies
Distributed Generation: Reciprocating engines
Gas turbines
Micro-turbines Fuel cells
Photovoltaic panels
Wind turbines
CHP configuration
Energy Storage Batteries
Flywheels
Supercapacitors
Rev. fuel cells
Superconducting coils
Powder IronToroids
ArmatureWinding
Holders
Housing
Endcap
FieldWinding
& Bobbin
Rotor
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Power electronic dominated grids
Source: KEMA
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Microgrid ?
Grids may even separate from central supply No net power exchange: total autonomy
Important aspect, characterizing a Microgrid
o Ancillary Services are all delivered internally
Balancing the active and reactive power
Stabilizing the grid: frequency, voltage
Providing quality and reliability: unbalance, harmonics,
Is a Microgrid new ? It all started that way, before interconnection
In fact, no: the grid behind certain UPS systems isdriven like a microgrid with one generator
H h l l
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DG%
t
How much local sources can
a distribution grid accept ?
Distribution grid was neverbuilt for local powerinjection, only top-down power delivery
Electrical power balance, anytime, in any grid:
Electricity produced - systemlosses= electricity consumed storage
Barriers to overcome: Power quality & reliability Control, or the lack of
Safety
Societal issues
Economic aspects
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Power quality & reliability
Problem: Bidirectional power flows
Distorted voltage profile
Vanishing stabilizing inertia
More harmonic distortion
More unbalance
Technological solution: Power electronics may be configured
to enhance PQ
DG units can be used as backupsupply
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Example: MV cable grid
Substation
connecting
to HV-grid
Location:Leuven-
Haasrode,
Brabanthal +
SME-zone
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Impact of wind turbine
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Control, or the lack of
Problem: Generators are NOT
dispatched in principle
o Weather-driven (manyrenewables)
o Heat-demand driven (CHP)
o Stabilising and balancing incable-dominated
distribution grids is not as
easy as in HV grids
reactive power voltage
active power frequency
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Networked system operations
Solutions: Higher level of control required to coordinate balancing, grid
parameters ?
Advande control technologies
Future technologies, under investigation Distributed stability control
o Contribution of power electronic front-ends
Market-based controlo Scheduling local load and production, by setting up a micro-
exchange (see example)
Management of power quality
o Customize quality and reliabili ty level Alternative networks
o E.g. stick to 50 Hz frequency ? Go DC (again) ?
Rely heavily on intensified communication: interdependency
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Example: tertiary control on local market
DG units locally share loads dynamically based on marginal costfunctions, cleared on market
P P
MC MC
MC
P
P1old P1new P
2oldP
2new
equal marginal cost
translated
translated & mirrored
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Example: tertiary control on local market
Prices are set by marginal cost functions of generators: Real-time pricing
Real-time measurements
Network limitations introduce price-differences between nodes Safety and PQ issues similar to congestion in transmission grid
Demand side management Optimizing consumption
Load reacts to external signals as prices
Overall need for advanced metering
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Safety
Problem: Power system is designed for top-down
power flow
Local source contributes to the short-
circuit current in case of faulto Fault effects more severe
o Difficult to isolate fault location
Bidirectional flows
o Selectivity principle in danger: nobackup higher in the grid for failingprotection device
Conservative approach on unintentional
islanding Solution:
New active protection system necessary
G
G
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Societal issues
Problems: Environmental effects
o Global: more emissions due to
non-optimal operation oftraditional power plants
o Local effects as power isproduced on-the-spot, e.g.
visual pollution Making power locally often
requires transportinfrastructure for (more)primary energy
o Problem is shifted fromelectrical distribution grid to,for instance, gas distributiongrid!
Solution:
Multi-energyvectorapproach
Open debate onsecurity of supply
E i i
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Economic issues
Problems: Pay-back uncertain in liberalized
marketo Chaotic green and efficient power
productiono Reliability or PQ enhancement
difficult to quantify
System costso More complicated system operationo Local units offer ancillary services
System losses generally increase
Who pays for technologicaladaptations in the grid ? Who willfinance the backbone powersystem?
o Too much socialization causespublic resistance
Solution: Interdisciplinary
regulation, notonly legal
Need some realderegulation
S t l l
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System losses example
DG introductiondoes not mean
lowered losses
Optimum is 2/3power at 2/3distance
Other injections
generally causehigher system
losses
HV subst.
Load distributed along feeder cable
DG
Zero point
Af ter DG
Before DG
Power flow along cable
B l i ti i
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Balancing question, again
Fundamental electrical power balance,at all times is the boundary condition:
Electricity produced - system losses= electricity consumed storage
All sorts of reserves will decrease in the future
Role of storage? Storage also means cycle losses! Next step in enabling technologies
Usable storage
Activated intelligent loads (DSM technology), also playing
on a market as mentioned in example? Boundary condition: minimize losses
H f ?
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How far can we go?
Large optimization exercise, considering thedifferent technical barriers:
Optimal proliferation, taking into account localenergetic opportunities, e.g. renewables options
Unit behavior towards grid: technology choice
control paradigm
Is the same level of reliability still desired ?
Level of introduction of new additionaltechnologies (storage, activated loads)
Optima are different, depending on stakeholder E.g. grid operator vs. client
O ti i ti l
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Optimization example
Total problem yields a huge mixed integer-continuous optimization problem Optimization goals: voltage quality penalty, minimum
losses, minimum costs Complexity: sample grid yields 240 siting options for
simple domestic CHP and PV scenario need
advanced maths Results are different hourly and vary with time of year,
e.g. during day: PV opportunities in peak hours: CHP helpful
Conclusion
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Current grid: Interconnection
Higher PQ level required
DER looking around the corner
History repeats: after 100 years the idea of locally supplied,independent grids is back
Microgrids, being responsible for own ancillary services
Maximum (optimal?) level of penetration of DER= difficult optimization exercise Special (technological) measures are necessary
E.g. in system control, mainly balancing
Not only technology push, but also customer pull
Conclusion
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