Today’s MV/LV distribution transformers (DTs) maintain a design that has remained largely unchanged for nearly two centuries. The evolution of these transformers has primarily occurred in the areas of materials and efficiency, where the Eco-design directive has led to a significant reduction in losses. Over the past decade, the main innovation in this field has been in voltage regulation, where on-load tap changer (OLTC) systems have gained support among worldwide DSOs. In this context, a potential game-changer could be the energy transition and the need to connect and operate high volumes of photovoltaic (PV) generators and new loads such as heat pumps and electric vehicles (EVs). This could lead to more frequent voltage fluctuations, changes in current direction, and power quality (PQ) issues than DSOs currently experience.
Highlights
The evolution of DTs to solid-state smart DTs could leverage on power electronics with multiple-stage AC/DC active rectifiers, DC/DC converters, DC/AC grid-tied inverters and storage as an option. Required features might be voltage regulation, phase balancing, load balancing, power factor control, harmonics correction all together controlled by advanced artificial intelligence (AI) based on precise measurements. These functionalities are currently being developed in different designs and piloted in distribution grids. Traditional alternatives, such as reinforcing low voltage (LV) lines, may represent a significant investment, for which OLTC transformers may be, in some instances, an efficient and competitive solution to avoid voltage saturations in LV networks.
Opportunities for DSOs
- Solving multiple LV issues with one technical solution and in one location.
- Cost reduction compared to traditional network reinforcement solutions.
- Improvement in preventive maintenance strategies.
- Lower financial outlay compared to the need for grid modernisation.
- Faster response to voltage changes caused by large distributed energy resource (DER) fluctuations.
- Lower handling costs (no need to hire crews to change taps).
Challenges for DSOs
- Presumed price increase in comparison with traditional DTs.
- Lower lifetime (traditional DTs are expected to stay in the grid for 30-40 years).
- Lower reliability due to significant technical complexity.
- Possible additional technical losses in the electricity conversion which is strictly against EU policies.
E.DSO Considerations
E.DSO recommends to:
- Cooperate with universities, research organisations and start-ups on innovative solutions and test them in real grids.
- Embrace OLTC on DTs and voltage regulation by autonomous functions of smart inverters as a standard and thus solve the majority of LV grid voltage issues with existing technologies.
Potential use cases
- Quality of service. Grid monitoring and automation will allow better handling of contingencies and non-programmed tasks. If these are detected and located before customers notice them, the response time will improve significantly while possible customer complaints will be reduced.
- Technical losses reduction and lower grid saturation. Addressing phase or feeder unbalances will allow to improve high losses situations with efficient solutions.
- Non-technical losses reduction. The possibility to monitor the amount of energy delivered from a secondary substation compared with the consumed energy from the customers will simplify the detection of issues.
- Grid saturation improvement. The monitoring of all different feeders will allow balancing the grid and reducing the number of saturated cables.
- Maintenance and renovation. The prediction of unwanted situations (e.g., grid faults) together with a constant analysis of grid information will allow improving preventive maintenance strategies, reinforcement and renovation, prioritisation of on-site tasks to reduce mistakes and extend the expected life of assets expected. The final goal will be to implement automated maintenance schedules.
- Planning improvement. With new loads such as EVs and distributed generation connecting to the grid, it will be possible and necessary to analyse future grid saturations in advance through constant energy and power flow measurements.
Ongoing projects
- All Spanish DSOs are working on a flexible solution for monitoring and automating the LV network., while sharing experiences, use cases, technical information as well as lessons learned. In this context, i-DE is deploying smart DTs in an industrialised way, prioritising secondary substations with voltage problems. Furthermore, the dynamic setpoint method developed by i-DE’s Innovation Hub is used to improve automatic regulation algorithms, obtaining real-time data from smart meters and LV elements in the grid to improve que real-time regulation of the smart DTs.
- 50 OLTC will be tested in 2024 on ORES network in the most problematic LV circuits and for MV voltage management. These proofs of concept are only carried out on circuits where there is sufficient penetration of communicating meters.
- Several proof of concepts have been undertaken by Enedis to test MV/LV transformers equipped with OLTC. The results confirmed that this solution is effective to solve voltage issues but the cost, up to now, is still too high compared with the cost of other options.
- PGE Dystrybucja will install a 630 kVA OLTC transformer in combination with a power electronic voltage regulator installed in the area supplied by the OLTC transformer. The installation site will be matched to the conditions and needs of the grid in the area so to optimise the grid use of and solve the voltage problems that occur due to high PV saturation.
Last update: 4 October 2024