Transitioning the Grid from 10 kV to 20 kV: What It Means for Your Equipment

For decades, Serbia’s distribution network has operated with two medium-voltage levels: 10 kV and 20 kV.
The strategic direction has been defined for a long time. The network is gradually transitioning to 20 kV because a higher voltage means lower losses and greater transmission capacity through the same power lines.
For the distribution system operator, this is a long-term programme. For companies with their own transformer substations, however, it raises a very practical question: what will happen to my equipment when the line supplying my facility is converted to 20 kV?

Doubling the voltage while maintaining the same current makes it possible to transmit twice as much power through the same cable.

In a network facing growing electricity consumption, heat pumps, EV chargers and the connection of renewable energy generation, this is the most cost-effective way to increase the capacity of the existing infrastructure.
For this reason, new network sections are built for 20 kV, while older sections are gradually converted as the necessary conditions are met.

The key concept is the insulation level.
Medium-voltage switchgear is now normally supplied with a rated voltage of 24 kV, allowing it to operate in both 10 kV and 20 kV networks.

For transformers, the solution is a dual voltage ratio. A transformer marked 10(20)/0.4 kV can simply be reconnected to the higher voltage when the network conversion takes place, without replacing the unit.
Cables are also selected with insulation suitable for 20 kV, even when they are initially installed in a network currently operating at 10 kV.

This is precisely why the distribution system operator generally requires new equipment to be ready for 20 kV as part of the grid connection conditions.
The problem arises with substations built several decades ago and designed exclusively for 10 kV operation.
When the network section to which they are connected is scheduled for conversion, equipment that cannot withstand 20 kV must be replaced. This may include the medium-voltage switchgear, the transformer and, in some cases, the cable connections.

When this is discovered too late, replacement must be carried out under the pressure of the operator’s deadlines and at emergency procurement prices.

When identified in time, however, the replacement can be properly planned and budgeted. It can also be used as an opportunity to modernise the substation, introduce remote monitoring and prepare the facility for solar generation or battery energy storage.
Three factors provide the answer.

The first is the equipment nameplate data: what is the rated voltage of the switchgear, and does the transformer have a dual voltage ratio?

The second is information from the distribution system operator regarding conversion plans for the specific area.
The third is the age and condition of the equipment. Equipment approaching the end of its service life should already be included in a replacement plan, making it reasonable for the new equipment to be 20 kV-ready regardless of the exact network conversion schedule.
For every new transformer substation, the rule is simple: equipment that is not ready for 20 kV should no longer be installed.

The difference in purchase price is relatively small, while the risk of technological obsolescence is certain.

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