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Course organization and introduction
Bertrand Cornélusse
[email protected]
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<iframe src="https://giphy.com/embed/FQyQEYd0KlYQ" width="480" height="266" frameBorder="0" class="giphy-embed" allowFullScreen></iframe> # Welcome to ELEC0447- A few words about the organization
- Show the overall structure of an electric power system
- Highlight a few important features of power system operation
- Illustrate those on the Belgian and European systems
- Present some orders of magnitude it is important to have in mind
- Introduce some terminology
Adapted from ELEC0014 introduction by Thierry Van Cutsem
- Course organization
- Components and structure of an electrical power and energy system
- Energy outlook for Belgium
- Insight on renewable and dispersed generation
- The power balance problem
- From DC to AC, large interconnections and the come-back of DC
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- Theory lectures (maximum 2 hours)
- Practice sessions (remainder of the session)
$\rightarrow$ bring your laptop - Project 1:
- Model a simple distribution system in PandaPower and make some simple analyses.
- Oral presentation
- Project 2:
- Analyze a system using power flow analyzes (power flow solver provided)
- Oral presentation
- Oral exam in January
- Theory (list of questions available) and one exercise
- Bertrand Cornélusse: main contact
- Geoffrey Bailly: exercise sessions + project 1
- Antonin Colot: last 2 lectures + project 2
Main reference book:
- Mohan, Ned. Electric power systems: a first course. John Wiley & Sons, 2012.
Other references:
- Course notes of ELEC0014 by Pr. Thierry Van Cutsem. (In french)
- Weedy, Birron Mathew, et al. Electric power systems. John Wiley & Sons, 2012.
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In modern society, electricity has become a “commodity”:
.center[“Commodity: marketable good or service whose instances are treated by the market as equivalent with no regard to who produced them”]
But “Behind the power outlet” there is a complex industrial process!
Electric energy systems are the largest systems ever built by man:
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Source: https://www.hydroquebec.com/safety/transmission-lines/understand-transmission-lines.html
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Source: https://www.bbntimes.com/society/common-reasons-for-use-power-transformers-in-residential-areas
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Source: Wikipedia
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Source: https://www.greentechmedia.com/articles/read/another-major-oil-company-invests-in-clean-energy1
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Source: https://www.osha.gov/etools/electric-power/illustrated-glossary/sub-station
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Source: https://www.exa-ecs.com/courant-fort-quels-sont-les-composants-dune-armoire-electrique/
Real-time measurements : active and reactive power flows, voltage magnitudes, current magnitudes, energy meters, phasor measurement units
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Source: https://eliagrid-int.com/egi_projects/elia-national-control-centre-support/
Unlike most other complex systems built by man, power systems are exposed to external “aggressions” (rain, wind, ice, storm, lightning, etc.)
.center[<iframe width="600" height="480" src="https://www.youtube.com/embed/bSSO5XT1k1I" title="touching a power line with a tree branch" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>]
In spite of those disturbances, modern electric power systems are very reliable. Assume a duration of power supply interruption of 0.5 hour / year .center[availability = (8760−0.5)/8760= 99.994 % !]
However, the cost of unserved energy is high
- average cost used by CREG (Belgian regulator) to estimate the impact of forced load curtailment: 8.3 k€/MWh (source: Bureau fédéral du plan)
- varies with time of the day : between 6 and 9 k€/MWh
- varies with type of consumer : 2.3 k€/MWh for domestic, much higher for industrial
- even higher average cost considered elsewhere (e.g. 26 k€/MWh in France !)
Large-scale failures (blackouts) have tremendous societal consequences
- next two slides: examples of blackouts and their impacts
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- 50 million people disconnected initially
- 61 800 MW of load cut in USA & Canada
- cost in USA : 4 to 10 billion US $
- in Canada : 18.9 million working hours lost
- 265 power plants shut down
- restoration : from a few hours to 4 days
.footnote[Source : North American Electric Reliability Council (NERC)]
- Cascade tripping of interconnection lines
$\rightarrow$ separation of Italy from rest of UCTE system .center.width-50[
] - Deficit of 6.7 GW imported in Italian system
$\rightarrow$ frequency to collapse in Italy - 340 power plants shut down, 55 million people disconnected initially - 27 GW lost (blackout occurred during night)
- Estimated cost of disruption
$\approx$ 139 million US $ - Restoration time: 15 hours
.footnote[Source : Union for the Co-ordination of Transmission of Electricity (UCTE) which is now part of ENTSOe]
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.footnote[In Belgium there are 30 and 36 kV underground cable networks, in Brussels and Antwerp areas. These are meshed and play the role of sub-transmission.]
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.footnote[source : SYNERGRID, as of December 2008]
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Transporting and distributing electrical energy is an industrial process with a relatively high efficiency
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Exercise: let's update this table together.
.footnote[source : ENTSOE]
- “Nuclear generation capacity” involves all units, even those temporarily shut down for technical reasons, or waiting for the decision to extend their lifetime
- Gas power plants includes small CHP (Combined Heat Power) units
- Same for biomass plants
- Purposes of pumping storage :
- pumping : convert electrical energy into mechanical (potential) energy when demand is low compared to available generation (e.g. during night)
- turbining : reverse operation when demand is high (e.g. at day peak)$\rightarrow$ “peak shaving” and “valley filling” of daily load curve
- efficiency of whole cycle
$\approx$ 85 % - usually profitable since cost of electricity higher when demand is high
- fast reserve : a hydro unit can be started (resp. pumping stopped) quickly to replace a generation unit that is taken out of service
- allows keeping base units (e.g. nuclear) in operation when load is very low
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- Capacity Factor:
$\frac{\text{energy produced in 1 year (MWh)}}{\text{generation capacity (MW)} \times 365 \times 24 (h)}$ - usually close to 90 % for nuclear, but some Belgian units have high unavailability
- note the low value for solar energy!
- Early retirement of gas power plants not enough competitive on electricity market, too expensive to maintain
- political decision to keep a “strategic reserve” !
- Angleur
- Biomass plant of "Les Awirs" just decommissioned.
- Natural hydro resources saturated in Belgium
- there are plans to expand the pumping storage
- Coo power plant : currently
$(3 \times 158 + 3 \times 230 =)$ 1164 MW installed capacity - Wind energy :
- public opposition to new on-shore wind farms (densely populated country !)
- NIMBY attitude : Not In My BackYard
- off-shore wind farms have a higher capacity factor than on-shore ones: wind is more steady in the sea
- Belgian off-shore wind farms in 2018 :
- 5 wind parks with an installed capacity of 1186 MW have produced 3,408 TWh
- Capacity Factor =
$(3,408 \times 10^6)/(1186 \times 365 \times24)$ = 32 % - still a great potential for new off-shore wind farms :
- 3 under construction (+ 1076 MW)
$\rightarrow$ 8 TWh production expected in 2020
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https://re.jrc.ec.europa.eu/pvg_download/map_index_c.html#!
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.center[Hour of the year 2013]
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Conservation of Energy over an infinitesimal time
Introducing the corresponding powers at time
- this demand fluctuates at any time
- kept as small as possible, not really controllable
- In sinusoidal steady state, the power in an inductor (or a capacitor) reverts every quarter of a period, and is zero on the average
- in balanced three-phase operation, the sum of the powers in the inductors/capacitors of the three phases is zero at any time !
- hence, electrical energy cannot be stored in the AC network
- to be stored, electrical energy has to be converted into another form of energy
- mechanical: e.g. potential energy of water in the upper reservoir of a pumping station, flywheels, etc.
- chemical: batteries, but amounts of stored energy are still very small !! Really?
- Hornsdale Power Reserve
- NGK's batteries
The variations of load power have to be compensated by the generators but the conversion (primary energy
- example: changing the flow of steam or water in a turbine takes a few seconds Hence, an “energy buffer” is needed to quickly compensate power imbalances
- this is provided by the rotating masses of synchronous generators
- a deficit (resp. excess) of generation wrt load results in a decrease (resp. increase) of speed of rotation speeds (and hence, frequency)
- in a synchronous generator and its turbine, kinetic energy
$\approx$ nominal power of the generator produced during 2 to 5 seconds - controlling the power balance in a power system without rotating machines (only power electronic interfaces) would be a challenge (still at research level) ! Larger variations in load (e.g. during the day) require starting up/shutting down power plants ahead of time
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End of 19th century : Gramme, Edison devised the first generators, that produced Direct Current (DC) under relatively low voltages
Impossibility to transmit large powers with direct current:
$\text{power} = \text{voltage}\times \text{current}$ - if the voltage cannot be increased, the current must be
- but
$\text{power lost} = \text{resistance} \times \text{current}^2$ $\rightarrow$ big waste of energy - and large sections of conductors required
$\rightarrow$ expensive and heavy - Hard to interrupt a large DC current (no zero crossing), for instance after a short-circuit
Changing for Alternating Current (AC)
- voltage increased and lowered thanks to the transformer
- standardized values of frequency : 50 and 60 Hz (other values used at a few places)
Larger nominal voltages have been used progressively
- up to 400 kV in Western Europe
- up to 765 kV in North America
- experimental lines at 1100 kV or 1200 kV (Kazakhstan, Japan, etc.)
- Mutual support between partners to face the loss of generation units
- Each partner would have to set up a larger “reserve” if it would operate isolated
- Larger diversity of energy sources available within the interconnection
- Allows exploiting complementarity of nuclear, hydro and wind power plants
- Allows partners to sell/buy energy, to create a large electricity market.
- If one partner is unable to properly “contain” a major incident, the effects may propagate to the other partners’ networks
- A transaction from one point to another cannot be forced to follow a “contractual” path; it distributes over parallel paths (“wheeling”) : see example on another slide.
- Partners not involved in the transaction undergo the effects of the power flow.
- In large AC interconnections, there may be emergence of badly damped interarea electromechanical oscillations (frequency in the range 0.1 - 0.5 Hz)
- Rotors of synchronous generators in one area oscillate against the rotors of generators located in another area
- It may not be possible to connect two networks with different power quality standards
.grid[ .kol-1-2[ENTSOe : European Network of Transmission System Operators for electricity
41 Transmission System Operators (TSOs) from 34 countries
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Energy flows in 2018 (in GWh)]]
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.footnote[Source: ENTSOE]
Paths taken by a production increment of 100 MW in Belgium covered by a load increase of 100 MW in Italy (variation of losses neglected):
Advances in power electronics
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- DC more attractive than AC for distances above >= 50 km : owing to capacitive effects of AC cables
- Existing links in Europe : see a previous slide
- Projects involving Belgium: Nemo with England, Alegro with Germany : see a previous slide
.grid[
.kol-1-2[Connection of off-shore wind parks (source: ENTSOE, AC and DC connections of off-shore wind parks in North Sea to the grid of the Tennet German TSO, links under construction shown with dotted lines):]
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.grid[ .kol-1-2[Two networks with different nominal frequencies
- connection of 50 and 60 Hz systems in Japan
- connection of Brazil at 60 Hz with Argentina at 50 Hz
- two networks that have the same nominal frequency but cannot be merged into a single C network, e.g. for stability reasons
- UCTE and Russian (IPS/UPS) system
- Eastern - Western interconnections in North-America
- Western Europe (see previous slides)]
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The end.