An overhead substation is a key part of the power distribution system, forming the final stage in the journey of electrical energy from power plants through the transmission grid to end users. Within this electrical system, substations transform medium voltage (typically 6–30 kV) to low voltage (400 V and below), making it suitable for safe electricity supply to customers. From there, electric power is distributed via distribution lines, overhead power lines, or underground cables, depending on local infrastructure and development conditions.
As of the end of 2024, Poland had over 275,000 electricity substations, with more than 60% categorized as overhead or pole-mounted installations. Their widespread use highlights their importance in maintaining the reliability, efficiency, and capacity of the national grid.
In this article, we explore how these substations are built, how they operate within the broader transmission system and distribution system, and how to effectively protect them from faults such as power surges and short circuits.
Free consultationHow are medium-voltage pole-mounted substations constructed?
First, I would like to mention that there are two main types of medium-voltage substations:
- MV/LV substations – used in power distribution, stepping voltage down to levels suitable for end users.
- MV/MV substations – used within the transmission grid to adjust voltage levels between different medium-voltage ranges.
Both types operate under high voltages and require similar substation equipment, particularly for surge protection and safety.
Overhead substations are typically installed at a substation site using a concrete or steel pole structure that supports essential electrical equipment. This includes surge arresters and transformers, which are the central unit that defines the output, capacity, and function of the station. Usually these are rated between 25 and 630 kVA, although higher-capacity units are also used depending on demand and grid requirements.
These installations are also directly connected to overhead lines or sub transmission lines, forming part of a wider network designed for electricity transmission over long distances.
NOTE: The transformer is highly sensitive to electric and magnetic fields, overvoltage, and environmental conditions. Its selection must be aligned with grounding methods, voltage levels, and surge protection strategy.
Reclosers – Additional substation equipment
Modern overhead substations often include automated electrical devices such as reclosers. These play a critical role in improving system reliability by detecting faults on overhead power lines, interrupting current during short circuits, and automatically restoring power after temporary disturbances. In short: they are used to automate grid operations.
This enhances the resilience of the distribution system, especially in rural areas where overhead power infrastructure is exposed to weather conditions. Our product range also includes such solutions from Arteche.
Pole-mounted or indoor substations? Other types of transformer substations
While overhead substations are common, other configurations exist within the power distribution and transmission system, depending on construction, location, and maintenance cost considerations.
- Indoor substations – as the name suggests, these types of stations are located inside buildings, these are used where access, safety, and space constraints require enclosed electrical equipment, often within a metal enclosure.
- Container substations – these are complete, pre-assembled units that integrate all substation equipment into a compact structure. These are categorized based on accessibility and operation type.
- Mobile stations – these are the portable versions of container units, designed for temporary use or emergency supply during outages.
The choice of substation type depends on site conditions, required voltage levels, and the structure of the electrical network.
How do you choose the right surge arresters for a substation?
The proper selection of surge arresters is one of the key elements of any substation design. Both pole-mounted substations and other types of substations require the installation of surge arresters on the medium-voltage (MV) side – they are mounted on each phase, between the power line and the transformer windings. Their purpose is to protect the transformer and other equipment from the effects of atmospheric and switching surges.
The primary criterion for selecting a surge arrester is the voltage of the network in which it will be installed. In Poland, overhead substations most often operate in 15 kV or 20 kV networks. Another factor is the transformer’s rated power – the rated current that the surge arrester must withstand without damage depends on this. Depending on the project requirements and the specific characteristics of the network, surge arresters with the appropriate rated voltage, continuous operating voltage, and protection level are selected.
Another important aspect in selecting equipment is the availability of rapid service support. Pole-mounted stations, due to their overhead design and exposure to the elements, require regular inspections. Surge arresters should be highly resistant to external conditions, such as moisture or extreme temperatures, and their installation should be as simple and safe as possible.
It is worth noting that, due to safety requirements, stations of this type are located at a minimum distance of 3–5 m from buildings, which affects access to components requiring maintenance.
PROXAR medium-voltage surge arresters for transformer substations
PROXAR surge arresters are solutions designed specifically to protect MV overhead substations. They are manufactured for a wide range of rated voltages, making them suitable for use in both 15 kV and 20 kV networks, which are common in Poland. Customers can select a variant that matches the specific operating conditions of the network and the requirements of the distribution system operator (DSO).
The use of PROXAR surge arresters is not limited to new projects – they can also be successfully installed as part of the modernization of existing substations. If you would like to learn more and see our full product range, please contact our team.
FAQ
What are the different types of transformer stations?
There are four basic types of transformer stations: pole-mounted (overhead), indoor, containerized, and mobile. Pole-mounted stations are the least expensive and are most common in rural and suburban areas. Indoor stations are used in cities and industrial-service zones where there is no space for overhead solutions.
What is an overhead transformer?
An overhead transformer is a device installed outdoors, most often at the top of an E-type spinning pole or on a concrete support structure, without an additional protective enclosure.
