Also known as Continental Synchronous area, UCTE is the second largest synchronous electrical grid in the world. It supplies over 400 million customers in 24 countries including most EU countries – and as of March 2022 – Ukraine and Moldova. Managing this grid is the European Network of Transmission System Operators for Electricity (ENTSO-E).
The Baltics’ integration into the EU electricity grid has been a priority for the European Commission (EC) for many years, receiving substantial EU funding. Joining the European grid will strengthen the region’s energy security and support the implementation of the Green Deal by ensuring secure, clean and affordable power for the Eastern Baltic Sea region and the Union as a whole.
This successful integration story is even more remarkable if we consider the complexities synchronising to the power grid entails. So, how does grid synchronisation work and why is it important?
What is grid synchronisation?
Grid synchronisation is the process of connecting a power-generating source, such as a solar PV, a wind turbine, a hydropower plant to the main electricity power grid. Even decentralised assets like electric vehicles (EVs) can be integrated to the electricity infrastructure via smart charging and power-to-grid technology). Before any connection, several parameters of the generated power must match with the grid in order to prevent disturbances and damages to the equipment.
Why is grid synchronisation important?
If the electricity source and the grid do not match these three parameters, it could cause damage to infrastructure and power black outs. Therefore, it is important that the system is able to detect any anomality before connecting to a new power source.
Ensuring security of supply
Making sure that the power grid works seamlessly is key to ensuring the supply of clean and reliable electricity across Europe. This means that grid synchronisation is a crucial step in the energy security picture, as it ensures the technical feasibility of connections and it offers a way out from energy dependency from unreliable partners as we’ve seen in the case of the Baltics, Ukraine and Moldova.
Disconnecting from unreliable energy partners
The de-synchronisation of Lithuania, Latvia and Estonia from the IPS/UPS transmission system largely managed by Russia, became an urgent priority after Russia’s invasion of Ukraine. Joining the European grid will allow the three Republics to regain control of their electricity networks and ensure their energy security. The EC granted the initiative the Project of Common Interest status and unlocked €1.2 billion to fund the project from the Connecting European Facility (CEF) fund.
Although the project was already agreed among the EC, Poland and the three Baltic states in 2018 and reinforced in 2019, it will be finalised ahead of the initial deadline, set at the end of 2025, in response to Russia’s weaponisation of energy. For the same reason, following the invasion of Ukraine in February 2022, ENTSO-E and the EC completed the synchronisation of the Ukrainian and Moldovan grids in less than 3 weeks!
How does grid synchronisation work?
When talking about electricity, we often tend to focus only on its quantity which is expressed in watt-hour (Wh). The quality of this electricity also matters and is expressed through parameters like voltage, frequency, phase angle and phase sequence. All of them need to be considered when connecting a power source to the main electricity grid.
The parameters for grid synchronisation
Voltage:
The two points to synchronise, the generator and the grid, might have a different electric potential, namely they might need a different amount of work per unit of electric charge to move the charge from one point to another. Such a difference in electric potential between two points is called voltage, and its unit is the volt (V).
Frequency:
When electricity is generated from a power plant, it is then carried to the point of use through wires. In alternating current (AC), this flow of electricity can switch directions across individual wires. Frequency is the rate of this switch and is calculated with Hertz (Hz) per second. 1 Hertz is the same as 1 cycle per second. Grid frequency is determined by how fast generators spin.
In the Continental Synchronous area, distribution system run at 50 Hertz, meaning that the electricity flow switches 50 times per second.
Grid frequency is a good indicator of the grid’s ability to balance supply and demand. When supply exceed demand grid frequency increase and vice versa. Network operators are therefore tasked with maintaining the grid frequency around the same value (50 Hz for Europe) to assure grid stability. When a new generator or distributed asset connects to the grid, the supply increase and will therefore impact frequency. It is therefore key to carefully assess the impact of a grid connection, especially on the system frequency.
Phase angle:
Phase angle is a way of describing the “timing difference”, or lag, between voltage and current in an electrical circuit. It helps us understand how these two things line up (or don’t) when alternating current (AC) is flowing.
Think of voltage and current like two dancers moving to the same rhythm. Ideally, they step in perfect sync, with no delays. But sometimes, one dancer (voltage) takes a step before the other (current) catches up. This “step difference” is the phase angle, measured in degrees (like angles in a circle, 0 to 360).
However, these two dancers need to move in sync to perform smoothly but sometimes, voltage and current can fall out of sync. For instance, when connecting electronic components like solar PV inverters, some components can make current move slightly ahead of voltage. This “timing difference” is the phase angle. It is therefore essential that when connecting a solar PV system to the power grid, the voltage and current from the solar asset match those of the grid – not just in size (voltage level) and speed (frequency) but also in timing (phase angle). If they’re not perfectly aligned:
- The power flow becomes unstable
- It can lead to energy losses or even damage the grid and the solar asset itself.
By understanding and managing the phase angle, engineers ensure that electrical systems work safely and efficiently for your home appliances as for broader power grid.
Phase sequence:
A fourth parameter is the phase sequence, namely the order in which the three phases of a three-phase system reach their peak values. For example, if phase A reaches its peak before phase B, and phase B reaches its peak before phase C, then the phase sequence is ABC. If phase C reaches its peak before phase B, and phase B reaches its peak before phase A, then the phase sequence is CBA.
It basically means that you connect the red wire to the red wire, yellow to yellow and blue to blue. And that both the grid and the generator run either clockwise or anticlockwise.
By minimising the difference in these parameters between the generated power and the grid supply, grid operators can monitor and act to prevent voltage and frequency disruptions. Beyond operators, a key element of grid stability is the so-called inertia.
What is inertia?
In conventional power systems, large turbines in power plants, such as coal, gas, nuclearor hydropower spin synchronously with the grid’s frequency (50 Hertz). These turbines have mechanical inertia, meaning they store kinetic energy in their rotating mass.
When there’s a disturbance, such as a sudden loss of generation or a spike in demand, the turbines can release or absorb some of this energy to help stabilise the grid frequency temporarily. In a more extreme case, where a generator completely stops supplying energy, the energy released from the spinning turbine gives the operators or the automated systems enough time (seconds) to react and restore frequency.
As previously explained, large frequency deviations can damage equipment or cause blackouts. Inertia provides a buffer to maintain stability during sudden disruptions. However, with the transition to renewable energy sources like wind and solar, grid inertia is decreasing because wind turbines and solar panels use power electronics to connect to the grid, which don’t inherently provide mechanical inertia. Solutions to compensate for low inertia are: synthetic inertia, utility-scale batteries and fast frequency response systems.
Moving forward
Stabilising the grid will be increasingly complex as more renewables enter the EU energy mix. Last year, 48% of the power generated in the EU came from renewables, followed by nuclear generation at 24%. As we progress in our decarbonisation journey, grid synchronisation will become ever more relevant to run Europe’s energy infrastructure smoothly at any time.
Beyond the energy sector, synchronising grids represents a crucial step in the EU integration process at times when external actors are threatening the block’s security. With energy security topping the agenda of the Polish Presidency of the EU Council, member states should strive to stay united even in their power transmission and distribution systems. The Baltics case showcases how grid synchronisation can offer a way out from depending on unreliable trade partners.
Disclaimer: This article is for informative purposes only and may not entirely reflect Eurelectric official positions. For formal positions, please consult our position papers here.