UE 11 - Guest lecture: Modelling electricity grids Flashcards
True or false?
Drawbacks of an Island System
- In a stand-alone grid, the grid frequency is determined exclusively by the speed of a generator
- As the load P increases, it induces an additional resistance in the magnetic field of the generator, causing it to slow down, which results in a drop in frequency
True!
What is missing?
Network Designs of Interconnected Grids
“…”
- Preferable for small/medium networks
- Advantage: Shortest route length
- Disadvantage: Security of supply
“…”
- Enable the integration of several generators in different locations
- Advantage: higher security of supply and easy expandability
- Disadvantage: expensive due to longer track length and nominal diameter of the loops
“…”
- Used for large distribution and transmission grids
- Advantages: optimal supply security; better expansion options and redundancy
- Disadvantage: very high investment costs
Radial networks
- Preferable for small/medium networks
- Advantage: Shortest route length
- Disadvantage: security of supply
Ring networks
- Enable the integration of several generators in different locations
- Advantage: higher security of supply and easy expandability
- Disadvantage: expensive due to longer track length and nominal diameter of the loops
Mesh networks
- Used for large distribution and transmission grids
- Advantages: optimal supply security; better expansion options and redundancy
- Disadvantage: very high investment costs
Network Designs of Interconnected Grids
Explain the application of the (n-1)-criterion in the context of electricity grids.
(n-1)-criterion: Redundant network structure
If one important system component (out of N total) fails, the system will still function without a major interruption.
Example
- A region has 5 transmission lines (N = 5)
- If 1 line fails, the remaining 4 must carry the full load
- No overloads, no outages allowed –> must plan for it in advance
True or false?
Transmission losses decrease quadratically with increasing transmission voltage!
True!
What is missing?
- “…” are used to connect AC networks of different voltage levels.
- Large “…” achieve efficiencies of up to 99 % at full load, but they usually still require to be cooled by a liquid cooling medium.
“Transformers”
“transformers”
Name the system components of power grids.
Generator
Transformer
Line (AC: short distance or overhead line for long distance; DC/HVDC: connecting transmission grid with different frequencies)
Engine (Consumer)
Equipment (Change of transmission characteristics)
What is missing?
Electrical Substations
“…”
- A transmission substation connects two or more transmission lines.
- Cases
–> All transmission lines have the same voltage: High-voltage switches
–> Conversion between two transmission voltages: Transformers
“…”
- A distribution substation transfers power from the transmission system to the distribution system of an area.
- In addition to transforming voltage, distribution substations also isolate failures in either the transmission or distribution systems.
“Transmission substation”
“Distribution substation”
What is missing?
Substation
- The purpose of “…” is to connect (switch on), interrupt (switch off) or disconnect current paths.
- “…” are devices for the repeated switching on and off of current paths, in which movable switching pieces are mechanically guided.
- In contrast, “…” are switching devices in which the current paths are interrupted by the melting of certain parts under the effect of the heat of electricity at high currents.
“switchgear”
“Switches”
“fuses”
What is missing?
“…”
Applications
- Transmission of electrical energy over long distances (> 600 km).
- Transmission of electrical energy via submarine cables (> 30 km).
- Connection of offshore wind farms to the three-phase grid of the mainland. − Coupling of asynchronous grids.
“High-Voltage Direct-Current (HVDC) Transmission”
Name the ancillary services provided by TSOs and DSOs to ensure a proper operation of the power grid.
- Operational management (operation of the grids, e.g. Redispatch 2.0 (congestion and feed-in management), switching operations)
- Frequency control (FCR, aFRR, mFRR)
- Voltage control (e.g. reactive load management)
- Black start capability / island operation capability (supply restoration after blackout)
(Frequency measure
- Spinning reserve
- Balancing energy
- Shreddable loads
Voltage compensation
- Power factor correction
- Loss energy
Reconstruction of supply
- Black-start
Operational management
- Monitoring of the grid
- Redispatch 2.0)
True or false?
Power Frequency Control
- Frequency deviations occur due to momentary imbalances between generation and consumption
- Objective: Maintaining the nominal frequency of 50 Hz
− The permissible fluctuation range is ± 0,4 % = ± 0,2Hz - Power frequency control refers to a control method for maintaining the electrical parameters agreed between the TSOs at the limits of their control zones during normal operation and in particular in the event of a failure.
True!
What is missing?
- Primary reserve (FCR) is used by “…”
- Secondary and tertiary control is used by “…”
Primary reserve (FCR: Frequency Containment Reserve)
- Activation “…”
- Period to be covered per disturbance: “…”
–> Frequency is stabilized - Technologies: “…”
Secondary reserve (aFRR: Frequency Restoration Reserve with automatic activation) - Complete activation “…”
–> Frequency is increased/decreased - Technologies: “…”
Tertiary reserve/minute reserve (mFRR: Frequency Restoration Reserve with manual activation)
- Complete activation “…”
- Period to be covered per fault “…”
–> Frequency is increased/decreased - Technologies: “…”
- Primary reserve (FCR) is used by all TSOs across control areas
- Secondary and tertiary control is used by the TSO of the effected control area
Primary reserve (FCR: Frequency Containment Reserve)
- Activation within 30 seconds
- Period to be covered per disturbance: 0 < t < 15 min
–> Frequency is stabilized - Technologies: Batteries (+/-), Hydro storage plants (+/-), flexible loads (-)
Secondary reserve (aFRR: Frequency Restoration Reserve with automatic activation)
- Complete activation within max. 5 min
–> Frequency is increased/decreased - Technologies: Batteries (+/-), Hydro storage plants (+/-), flexible loads (-), wind turbines (curtailed)(-)
Tertiary reserve/minute reserve (mFRR: Frequency Restoration Reserve with manual activation)
- Complete activation within max. 15 minutes
- Period to be covered per fault 60 min > t > 15 min or up to several hours in the event of several faults
–> Frequency is increased/decreased - Technologies: Gas turbine (+), biogas/biomass plants (+), flexible loads (-), wind turbines (curtailed)(-)
What is missing?
Power Frequency Control
- Generation = Consumption –> Frequency “…”
- Generation > Consumption –> Frequency “…”
- Generation < Consumption –> Frequency “…”
Power Frequency Control
- Generation = Consumption –> Frequency = 50 Hz
- Generation > Consumption –> Frequency > 50 Hz
- Generation < Consumption –> Frequency < 50 Hz
What is redispatch?
Redispatch
- Short-term changes to dispatch planning of power plants due to bottlenecks in the grid
- Redispatch 2.0: feed-in and grid congestion management
- Counter-trading; interventions in the generation capacity of power plants by TSOs to protect line sections from overloading
- Example: Generation is reduced before a grid bottleneck and increased after a grid bottleneck
What is missing?
The term “…” describes the communicative connection of the players in the energy system to the energy supply network, from generation to transport, storage, distribution and consumption.
“smart grid”
