Supply and demand Flashcards
What is a cascading blackout?
describes the phenomenon where a power station trips, putting further pressure on the remaining power stations, which then all trip in a domino fashion
What is grid stability?
Describes how well an electricity grid is able to cope with unexpected changes that are often caused by sudden fluctuations in supply and demand
What is mechanical inertia?
Can be thought of as ‘back-up’ power in the form of energy stored in rotating masses
What is low frequency demand disconnection?
A deliberate action taken by a grid operator to prevent power stations tripping one after the other
What is the inertia represented in a system by
HS = inertia constant x normalised apparent power
What are the two types of primary responses and how long are they expected to last?
- Mandatory frequency response -
- Fast frequency response - a commercial provider turning things on/off including engines, generators and large plants
10 seconds
What is an example of an enhanced frequency response and how quick is this?
Batteries
1 second
What are the two types of secondary responses?
- Spinning reserve (pumped storage or thermal power station)
30 seconds - 2 mins - Short Term Operating Reserve (STOR) (thermal power stations, generators not spinning) ~20mins
Proportion of the UK’s electricity generated by renewable resources in 2019
Hydropower - 2%
Solar PV - 4%
Biomass - 11%
Wind - 20%
What is power islanding?
When a section of distribution network has become disconnected from the utility supply but customers continue to be energised by an embedded generator
When does LFDD occur?
Below 48.8Hz
The more inertia in the grid
The slower the rate of change of frequency
What has no natural intertia?
asynchronous
- Wind
- Solar PV
- HVDC links
What are secondary response used more for?
Predicted changes in demand
What is the largest loss scenario
1GW of primary and enhanced reserve
