What is medium voltage and how does it work?

The medium voltage network is part of one of the three ranges of electrical voltage and has its own technical characteristics

Just like a road, electricity circulates through the electrical grid to conduct energy from the generation points to the consumption points such as our homes, our workplaces, infrastructures and public services… But this path, at first glance simple, is something more like a tree with countless branches in the form of dilemmas and nuances depending on where the electricity comes from and how it is generated, how close the areas of electrical consumption are, whether there are energy storage systems or the type of voltage at which it is transported. Today we are going to stop to explain one of the three main branches of electricity, medium voltage, and what characterizes it and differentiates it from the other two types of existing electrical voltage.

It is clear that, before talking about medium voltage, it is necessary to understand what we mean by electrical voltage and what types exist. Electrical voltage is a measurement (a physical magnitude, technically speaking) that allows us to calculate the difference in electrical potential between two points on a network. This would be something like the flow—in river terms—that a cable can withstand through its line; then the greater the electrical potential (greater quantity or electrical charge), the greater the voltage that the network is capable of transporting and/or supporting in a controlled and efficient manner.

Voltage, which is normally represented in volts, kilovolts, or megavolts, indicates the capacity of the grid at each point. Using a similar model as road transport, these figures show the approximate number of kilometers that electricity can travel from one point in the grid to another. Thus, if we say that an electrical grid has 1,000 kV (1 megavolt), it will have the capacity to transport electricity along a 1,000 km line. Curious, isn’t it?

Therefore, there are three main types of voltage: high voltage, medium voltage, and low voltage. We will differentiate them according to the amount of electricity they are capable of displacing and how close or far each of them is from the consumption points. Normally, the voltage is higher in the first phases of energy transport, where greater electrical potential is needed to increase the “flow” and try to reduce losses.   

The medium voltage network and its characteristics

Medium voltage normally appears on the scene when it comes to distributing the energy that arrives through the large high voltage lines that we all know. At that point, the electricity passes through electrical substations—electricity processing centers that function as energy distributors for consumers—where different components of the switchgear adapt the energy to continue its journey. Normally, medium voltage is considered to be that which is within a voltage range between 1 and 36 kV; therefore, any element of the electrical switchgear that operates in these ranges is an element of the medium-voltage network.

While high voltage is very recognizable to our eyes—mainly due to the towers and lines already mentioned—medium voltage is more subtle to our perception; once it leaves the substations, it runs—at least in Europe—through underground networks that are not visible to the naked eye until it reaches the low-voltage distribution and distribution centers, now close to the points of consumption. The most identifiable element to know if there is a nearby MV network is the transformation center, whose appearance is very easy to distinguish as it is a prefabricated concrete building that equips the switchgear for the electrical transformation from medium to low voltage and is located – either on the surface or underground – very close to the main consumption points.

Which elements of the electrical switchgear work in medium?

For this entire journey to work like clockwork, a set of elements and/or electrical machinery, also known as electrical switchgear, is necessary to act efficiently and in a coordinated manner to transform the voltage. These are located within the transformation center, which is a key player in ensuring that energy reaches its destination. Let’s take a look at what they are?

• Electrical transformer: It is the main protagonist of the CT and it is an electrical element that allows the voltage of an electrical circuit to be increased or decreased for subsequent distribution.
• Distribution cells: The cell –which is the center’s complexity and technological development– is used for different functions depending on its type, but it would be like a large switch that cuts off or lets the electrical power flow. To achieve this, the technological development that has taken place is essential, obtaining a solution that allows the network to operate at medium voltage values ​​with complete safety for the operator and the network in the most adverse conditions.
• Protection, control and automation units: These elements are one of the main revolutions in the medium voltage network in recent years. Their functions, which range from remote control of medium-voltage transformers to reporting and diagnostics and automation, have made it possible to provide intelligence to the grid, making them a key ally in smartening the grid.
• Low-voltage panel: Although technically this is an element that works at low voltage, it is responsible for dividing the current to be transported safely directly to the consumption points. In this way, the BT panel, distributes and protects energy to our homes.