What is medium voltage and how does it work?

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

Like a road, electricity flows through the electrical grid to carry energy from generation points to consumption points such as our home, workplace, infrastructure, and public services. But this seemingly simple path is more like a tree with countless branches in the form of choices and nuances depending on where the electricity comes from, how it is generated, how close the electricity consumption areas are, if there are energy storage systems, or the type of voltage in which it is transported. Today we are going to explain one of the three main branches of electricity, medium voltage, and what characterizes it and sets it apart from the other two types of existing electrical voltage.

Before talking about medium voltage, it is necessary to understand what we mean by electrical voltage and what types exist. Electrical voltage is a measure (technically speaking, a physical magnitude) that allows us to calculate the difference in electrical potential between two points in a grid. This would be something like the flow – speaking in terms of rivers – that a wiring can support along its line; therefore, the more electrical potential (greater amount or electrical charge), the higher the voltage that the grid is capable of carrying and/or supporting in a controlled and efficient manner.

The voltage, usually represented in volts, kilovolts, or megavolts, shows the capacity of the grid at each point. To draw a parallel with road transportation, these figures show the number of kilometers – approximately – 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 line of 1,000 km. Interesting, isn’t it?

So, there are three main types of voltage: high voltage, medium voltage, and low voltage. We 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 initial phases of energy transportation, where greater electrical potential is needed to increase the “flow” and try to reduce losses.

The medium voltage grid and its characteristics

Medium voltage comes into play, usually, when it comes to distributing the energy that comes through the large high-voltage lines that we all know. At that moment, electricity passes through electrical substations – electricity treatment centers that function as energy distributors for consumers – where different components of the switchgear adapt the energy to continue its path. Normally, medium voltage is considered to be within a voltage range of between 1 and 36 kV; therefore, any element of the electrical switchgear that operates in these ranges is part of the medium voltage grid.

While high voltage is very recognizable to our eyes – mainly because of the towers and lines mentioned earlier – medium voltage is more subtle in our perception; once it leaves the substations, it flows – at least in Europe – through underground grids that are not visible to the naked eye until they reach the distribution and low-voltage distribution centers, near consumption points. The most identifiable element to know if there is a nearby medium voltage grid is the transformer station, whose appearance is very easy to distinguish as it is a prefabricated concrete building that equips the switchgear for 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 MV?

For this whole journey to work like clockwork, a set of elements and/or electrical machinery, also known as electrical switchgear, is necessary to act efficiently and coordinatedly to transform the voltage. These are located inside the transformer substation, which is a key actor for the energy to reach its destination. Let’s take a look at what they are:

• Electrical transformer: It is the main protagonist of the transformer substation and it is an electrical element that allows increasing or decreasing the voltage of an electrical circuit for its subsequent distribution.
• Distribution switchgears: The switchgear- which is the focus of complexity and technological development in the center – is used for different functions according to its type, but it would be a large switch that cuts off or allows the flow of electrical energy. For this, the technological development that has occurred is crucial, obtaining a solution that allows operating the grid at medium voltage values with total safety for the operator and the grid under the most adverse conditions.
• Protection, control, and automation units: These elements are one of the main revolutions of the medium voltage grid in recent years. Their functions, ranging from remote control of medium voltage transformers, through reports and diagnostics to automation, have allowed giving intelligence to the grid; making them a key ally in the smartization of the grid.
• Low voltage board: 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 low voltage board distributes and protects energy to our homes.