Fundamentals of the Electrical Grid
Cyber security considerations for the Electrical Grid
When we hear the term Electrical Grid, we likely picture large transmission towers, right? Whilst these are integral components of the Electrical Grid, there is a lot more to the grid than meets the eye. In this post, we will explore some of the fundamental concepts related to the Electrical Grid. Feel free to explore some of the other topics we have covered in this series including Substations, Open Cycle Gas Turbines, Coal Power Stations, and Process Control.
Security consideration: throughout this post you will find these security
considerations. These are used to highlight some of the important processes
that may be worth considering from a security perspective. This is not an
all-encompasing analysis, though, so try and keep the following questions
in mind when reading the post -
[1] Is this a critical process that may be worth protecting?
[2] What should we do to protect the system?
* Disclaimer: this information should not be used for nefarious or unauthorised
purposes but rather as an educational tool (see the Welcome post of this
blog).Introduction
Electricity is typically not generated close to consumers since the plants may be loud/dangerous or they simply need to be close to some form of a natural resource. This means that we need some form of network to connect the producers to the consumers. Subsequently, the grid is split up into three different components, namely, generation, transmission, and distribution. Figure 1, below, provides an overview of the three stages:
Let us explore each of these components separately:
Generation
Generation refers to the creation of electricity. In the generation process, we typically convert some form of potential energy (usually chemical) into kinetic energy (motion) to power a generator. This can occur through a number of processes, the most common of which we will briefly discuss below:
- Coal: coal is burned to heat water which turns to steam. The steam turns a turbine which is connected to a generator which produces electricity.
- Nuclear: nuclear power operates similarly to coal power except that nuclear fission is used to heat the water.
- Hydro: water is allowed to flow from a higher to a lower point using gravity to spin a turbine which, as in the other cases above, is connected to a generator.
- Renewable: there are various forms of renewable energies including solar (converting the sun’s potential energy to electrical energy) and wind (converting the wind’s kinetic energy to electricity by spinning a generator).
Supply and Demand
An important point to discuss when considering the generation component of the electrical grid is supply and demand. Electricity generation is a just-in-time process i.e. we do not typically have large batteries that we can use to store electricity (except for dams, yes). This means that electricity generation needs to adapt to the supply. The different generation methods described need different amounts of time to start up before they can be used on the grid. A coal power station, for example, can take days/weeks to reach full load while a hydropower plant, provided the water is available, can provide electricity within minutes. Subsequently, different generation methods are used for different stages of consumption.
Electrical load (power requirement) is generally divided into three categories: base, intermediate, and peak. The base load is what is used all of the time and is powered by large plants such as coal and nuclear which are rarely shut down. Intermediate and peak loads can vary depending on conditions such as time of day and season. At night, for example, the demand/load is typically higher resulting in the grid potentially having to respond quickly to manage this influx in demand. Plants such as hydropower, which can be started quickly, can be used to manage these peaks in electricity usage. When the peak dies down, the sluice gates are closed and the hydro plant is shut down — something which you cannot do with a coal plant. (Hint: ask any South African what happens when demand outstrips supply).
Security consideration: managing supply and demand is a crucial task for a
grid operator. Anything that may hamper their ability to perform this task,
e.g. being provided with incorrect information leading to incorrect actions,
could result in damage to equipment or effect one of the most important
parameters for a grid operator - availability.Likewise, renewable power such as wind and solar can be very unpredictable which means that their input into the grid needs to be managed as well. Needless to say, managing a grid is a very complex task.
Grid Frequency
The electrical grid operates on the principle of alternating current (AC) which means the voltage changes its magnitude in sinusoidal cycles (more on this later). The frequency of the grid (in most countries this is 50 Hz) is a (note the only) important indicator of the stability of the grid. As the load is increased, the generators slow down and as the load decreases, the generators speed up (supply and demand discussed above). Either condition can be detrimental to the equipment where in the first case, it may cause damage to equipment and potentially even stall the generation process. In the second case, the generators may spin up and exceed their operational limits. This is why the monitoring of the electrical grid, and specifically the frequency, is so important.
Since AC is used, it inherently implies that some form of synchronisation is required. This is important because if generators are supplying electricity at different frequencies/phase angles, an unstable power supply will be achieved (you will likely encounter spikes and drops in the voltage).
Transmission
As discussed above, power plants are typically not located within close proximity to the end consumers. This may be because they need to be close to a dam or a river/ocean. Hydropower plants, for example, need a dam and nuclear plants need large amounts of water for cooling purposes. Subsequently, we need a transmission system which can transmit the electricity to the consumer. These transmission lines can take various forms but are most commonly associated with high-voltage towers as the ones seen in Figure 2, below:
As seen in Figure 1, the electricity produced by the power plant is fed through a substation which steps up (increases) the voltage before it is transmitted over the transmission lines. The electricity is stepped up to minimise the losses. A further design decision, to increase efficiency and stability that is implemented, is to transmit the electricity in three phases. A power line may have three cables (one for each phase) and perhaps a fourth neutral wire.
Side Note: three-phase alternating current (AC) electricity refers to electricity that is transmitted as three alternating waves, each 120 degrees out of phase as seen in Figure 3, below. Furthermore, the system can either be configured in Y or Δ (Delta) configurations, however, these concepts are out of scope for this post. Residential homes typically receive one phase but heavy industry may make use of three phases because it increases the stability of the supply and allows for the driving of heavier loads.
Security consideration: if the phases of on the grid are not correct (e.g.
different order) equipment such as generators may be damaged. The reason for
this is that a generator coil may be excited when it should not be because
of the position of the rotor (the coil is expecting no voltage but due to the
incorrect phase, a voltage is present on the coil).Why are transmission lines not straight, you may ask? Since these lines are usually very large and heavy, tensioning them to be straight would exert too much strain on the towers. Furthermore, the sagging provides the lines with the ability to change shape during seasons. Transmission lines are made up of a combination of aluminium (for conductivity) and steel (for strength). Where the transmission lines connect to the towers, one will often see long ceramic insulators which ensure that that the electricity does not flow into the pylons inadvertently grounding them.
Side Note: The ceramic insulators are usually standardised. If you count the number of discs and multiply this by 15, you should have a pretty good estimate of the voltage of the line.
As mentioned above, the voltage is ‘stepped-up’ (increased) before being sent over the transmission lines. The voltage can vary between 69 kV and 795 kV. This voltage is too high for consumers to use and subsequently requires a ‘step-down’ when it reaches the distribution phase. This process is also performed at a substation by means of a transformer as seen in Figure 1.
Security consideration: overloading of transmission lines can result in a
very serious situation. A trip of a circuit breaker could cause the load
from one transmission line to be transferred to another. If this new
transmission line cannot handle the additional load, it will also trip
(this time because of protection mechanisms) transferring the load to yet
another transmission line (resulting in a cascading failure).
In the worst case, if this were to continue, a complete grid collapse may
occur. Distribution
The electricity has now reached the consumers and has to be distributed to the individual loads (users). There are various loads that need to be serviced including everything from heavy industry to houses and everything in between. Subsequently, substations and transformers are once again used to change the voltage to the correct value for the respective loads. Distribution systems typically operate between 4 kV and 46 kV, however, as you get closer to homes, this will be further stepped down to the 110 V/240V.
Side Note: your cellphone or laptop charger also includes a little transformer that steps the voltage down to 5V. The charger also utilises a rectifier circuit to convert the AC to DC.
An important concept that needs to be considered in the distribution network is redundancy and single points of failure. Since distribution networks are more likely to face physical interruptions (as opposed to the large transmission lines that are far away from humans and typically more resilient) they are designed in such a way that single points of failure are kept to a minimum.
Core Components
Alright, so we have discussed the three important components of the grid. However, we need many components in order to physically implement these. These systems will come up again and again in our discussions on power plants so let us cover them now (note that we might discuss them in more detail in later posts):
Transformer
A transformer is used to either step up (increase) or step down (decrease) the voltage. As described above, this is done for efficiency purposes. A transformer makes use of a common core and then two sets of windings/coils in order to change voltage. Figure 4, below, highlights this principle.
In this specific case, we have more primary windings than we have secondary windings which means we have a step-down transformer. The exact number of windings (more specifically the ratio between them) defines to what extent the voltage is manipulated.
Side Note: If we allow ourselves to quickly consider some maths, we can analyse transformers by their number of coils as follows:
Nₚ/Nₛ = Vₚ/Vₛ and so,
Vₛ= NₛVₚ/Nₚ,
where p and s refer to primary and secondary.
Transformers tend to generate heat and as such require a form of cooling. A common method is to use mineral oil along with a radiator in order to dissipate the heat. Figure 5 illustrates what one of these transformers may look like in real life.
Security consideration: overloading of a transformer, may cause overheating
which could damage a transformer. In a switched environment, such as a
substation, switching more loads onto the transformer than what it is rated for
could result in this overheating condition. Too much heat could cause a fire
or explosion.Substation
A substation is essentially an electrical switching station. Imagine an IT network switch that connects different networks together and determines where packets are allowed to go. Now imagine a switch that is 100s of times bigger and wants to kill you.
Side Note: High-voltage electricity is incredibly dangerous and requires specialised equipment and training in order to operate safely.
Figure 6, provides a high-level overview of some of the important components of a substation.
The first important role that a substation fulfills is that of switching. This function is used to isolate, transform and control the load. We may have electricity that comes from various sources and needs to be transmitted to various destinations (furthermore, the voltages between these may vary).
The different systems are connected by means of buses. Circuit breakers, in turn, are used in place of fuses to prevent overload conditions that may occur in the event of a short circuit. Circuit breakers are specialised pieces of equipment that are used to disrupt high voltages while attempting to minimise damage to equipment.
As shown in Figure 6, above, some circuit breakers may contain oil which limits the creation of an arc. A recloser, in turn, is a circuit breaker that resets by itself after a certain amount of time before determining whether it needs to break again. Substations are also built with large grounding meshes in the ground to sink as much current as possible, as quickly as possible in order to trip the breakers.
The topic of substations is covered in more detail in this post.
Security consideration: opening all circuit breakers would not only disrupt
electricity to clients but may, under certain conditions, cause a sudden
loss of load which could damage the generators.Electrical Generator
We briefly discussed 3-phase power in a previous section. You may have asked yourself the question, well, how do we generate this form of power? At a high level, we simply have a spinning magnet which is exciting 3 sets of coils (technically 6 but they are pairs of connected coils) as seen in Figure 7 below:
As the magnet is turned by some external force, electrons move within the conductors. The keen observer will also note where the sinusoidal waves come from i.e. the effect of the magnet on the conductor changes as the magnet moves. We make use of three phases instead of one (for systems with higher power requirements) because this reduces the magnitude of the troughs. Why not more phases? Well, it becomes expensive and we have just settled on 3 phases as a good compromise.
Grid Synchronisation
Now that we have covered some AC and generator theory, let us revisit the topic of grid synchronisation. In order to synchronise with the grid, four conditions need to be met:
- Phase sequence: the sequence of the phases from the generator needs to match the ones being used on the grid.
- Voltage magnitude: the sinusoidal voltage magnitude from the generator needs to match that of the grid. A higher voltage would lead to VARs (reactive power covered in more detail in the Substations post) being transmitted whilst a lower voltage would lead to VARs being absorbed.
- Frequency: the frequency of the sinusoidal signal from the generator needs to match that of the grid.
Security consideration: If the frequency is too low, the generator would
act like a motor with the grid attempting to speed it up. Similarly, the grid
will attempt to slow the generator down if the generator frequency is
too fast. Both cases would result in the stator and rotor slipping poles
which could result in damage.- Phase Angle: the phase angle of the generator needs to match that of the grid. An incorrect phase angle, when the breaker is closed could damage the generator.
The video below highlights what a synchronisation process may look like.
Side Note: a synchroscope (as seen in the video above) can be used to determine if two systems are synchronised.
Security consideration: closing the breaker before the generator has
synchronised could damage the generator (see scenarios above). A
manipulated sensor value could make it look like equipment is synchronised
when, in fact, it is not. When the circuit breaker is closed, the equipment
may be damaged.Conclusion
So we have covered quite a bit of information regarding the fundamentals of the Electrical Grid. There is a lot more associated with a grid such as the control surfaces but we will discuss that at a later stage. Important for now is that the grid is divided into three distinct sections, namely, generation, transmission, and distribution each of which contain its own attack surfaces. We will likely need to dive into more detail for some of these systems to determine how they may be vulnerable but it is important to understand the fundamentals.
Security consideration: we managed to identify several security
considerations throughout this post. Nevertheless, we may have missed
something. Feel free to leave a comment with additional considerations!