How to stabilize the low voltage grid?

The increase in connection points causing imbalances makes it crucial to stabilize the low voltage grid for its proper functioning

If the electrical grid was complex a few years ago, when the points of generation, transmission, distribution, and consumption were clearly drawn on the map, the current electrical grid, where connection points of different kinds have skyrocketed, has turned it into a complex infrastructure whose management poses an unprecedented technological challenge. The various types of consumers and generators, as well as the fluctuations in energy demand and supply, are causing voltage drop variations in the grid, jeopardizing its stability and thus affecting customers and operators. This is where we identify the great technological challenge: to stabilize the low voltage grid. But how can we achieve this?

Until now, there has been a traditional solution that, in the previous scenario, could serve to minimize the impact of these solutions. Thus, when designing installations, the voltage drop was limited; but this caused a reduction in the grid’s capacity to connect new elements. This situation makes it unfeasible, given the incorporation of multipoints such as renewable generation, both domestic and large-scale, or the electric vehicle charging grid.

Another solution has been to manually disconnect, as they are detected, those points where there are stability problems. In other words, cut to the chase. However, the high service standards and current needs make this solution unfeasible in the 21st-century electrical grid, which points towards more dynamic and flexible solutions to exploit the true capabilities that electricity can offer society.

So, which is the best solution for the grid?

The great revolution that the energy world is experiencing has caused the electrical equipment industry to respond technologically to the new needs of the grids. In this context, our protagonists today are born: the on-load tap changers. But what are these elements? They are revolutionary devices installed in medium voltage transformers, key nodes in the transformation of electricity from medium to low voltage, and they allow adjusting the transformer’s output voltage according to the grid’s conditions. In this way, these on-load tap changers allow optimal utilization of the total capacity of the low voltage grid.

But how do they achieve this in a grid where, as we have explained before, conditions change practically every moment? Thanks to two theoretical principles on which their operation is based:

• Undervoltages are mainly caused by large simultaneous consumptions or by imbalances of single-phase connections such as electric vehicles or heat pumps. If we increase the number of taps in the transformer, we increase its output voltage and, therefore, the voltage of the entire low voltage grid. Thus, we avoid these situations.

• Overvoltages are mainly generated by self-consumption injections and/or phase voltage imbalances due to single-phase connections. An example is photovoltaic panels. If we decrease the number of taps in the transformer, we reduce the output voltage and solve the problem.

Digitalization, key to adjust voltage values and stabilize the low voltage grid

If we can understand their operation theoretically, it is the technology of the tap changers that must respond, practically, to the problem of overvoltages and undervoltages.

These guardians of the low voltage grid use a digitized control system that measures the transformer’s output voltage in real-time and compares it with a setpoint value. If the voltage between both scenarios deviates, the system corrects the situation. For this, two main dynamic regulation techniques are used, which obtain an optimal setpoint value:

• Static automatic: Establishes a fixed output voltage value, suitable for absorbing voltage variations.
• Dynamic automatic: Sets an output voltage value that varies according to load fluctuations at the moment. Thus, the algorithm calculates the information in real-time, maximizing the grid’s capabilities.

In this way, both grid operators and end consumers have a more flexible, stable, and secure low voltage grid, complying with regulations and being prepared for today’s and tomorrow’s needs.

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