Understanding Voltage Classes: LV, MV, HV and EHV Explained

Electricity flows through different voltages before reaching households, industries, or green energy stations. Choosing the proper voltage classes is necessary not only for safety but also in terms of minimising power losses, efficiency, and meeting engineering criteria of the world. Whether designing a distribution network or a large transmission system, engineers must understand how Low voltage (LV), Medium voltage (MV), High voltage (HV), and Extra high voltage (EHV) differ. 

In this article, the differences between LV, MV, HV, and EHV, their practical applications, and the importance of selecting the proper voltage level will be described. 

What Are Voltage Classes? 

Voltage classes are standard voltage ranges used to group electrical systems, equipment, and networks. These categories help engineers choose the right insulation, protection systems, transformers, switchgear, and cables, and make sure everything meets IEC, IEEE, and BS EN standards. 

The exact voltage ranges can vary by country, but these are the most accepted voltage classes: 

Voltage Class	Primary Application	Typical Users
Low voltage (LV)	Up to 1 kV	Homes, offices, commercial buildings
Medium voltage (MV)	1–36 kV	Distribution networks, industries, renewable plants
High voltage (HV)	36–245 kV	Transmission systems and utility substations
Extra high voltage (EHV)	Above 245 kV	National transmission networks

Understanding Low Voltage (LV) 

The low voltage (LV) system is responsible for supplying power to the end user. Standard voltages are 230 V for single-phase and 400 to 415 V for three-phase. 

Typical uses are: 

• Residential houses 

• Offices / business warehouses 

• Industrial Plants 

• Lighting, HVAC 

• Subsidiary systems in power plant layout 

Although LV systems operate at lower voltages, robust protection against overloads, short circuits, and electric shocks is also required to guarantee safety.  

Understanding Medium Voltage (MV) 

Medium voltage (MV) systems serve as the interface between distribution systems and both industrial and residential end users, as well as renewable energy projects. Standard MV voltages are 11 kV, 22 kV, and 33 kV. 

A well-designed MV substation layout consists of: 

• Right rating for the transformer 

• Switchgear selection 

• Protection and control 

• Cables layout 

• Good earthing design 

A good earthing system results in efficient fault current, the safety of the person, and enhanced plant reliability.  

Solar and wind farms typically employ MV collector networks prior to stepping up the voltage for grid transmission. 

Understanding High Voltage (HV) 

When electricity is transmitted over long distances, energy is lost. High voltage (HV) systems reduce the current, allowing more efficient and economical power transmission. 

Common HV voltage levels include: 

• 66 kV 

• 110 kV 

• 132 kV 

• 220 kV 
  

These systems are widely used in: 

• Utility transmission networks 

• Large industrial facilities 

• Grid-connected renewable energy projects 

• Major HV substation design 

• Large-scale power plant design 

HV substations that are properly designed operate under load with minimal outage and acceptable risk. 

Understanding Extra High Voltage (EHV) 

When electricity must travel hundreds of kilometres, Extra High Voltage (EHV) is usually the best choice. Using very high voltages reduces losses and allows for the transfer of large amounts of power. 

Typical EHV levels include: 

• 275 kV 

• 400 kV 

• 500 kV 

• 765 kV 
  

These networks are commonly used for: 

• National transmission grids 

• Cross-border interconnections 

• Large hydroelectric projects 

• Offshore wind farms 

• Utility-scale solar parks 

Due to high electrical stress in EHV systems, good insulation and earthing systems/results are essential for safety and performance. 

Difference between LV, MV, HV and EHV 

Low voltage (LV)	End-user supply	Homes, offices, industries
Medium voltage (MV)	Distribution	Industrial plants, renewable projects
High voltage (HV)	Regional transmission	Utilities, substations
Extra high voltage (EHV)	Long-distance transmission	National grid operators

Selecting the right voltage class depends on the transmission distance, load size, network configuration, and future expansion plans. 

Voltage Levels Used in Substations 

The voltage of substations depends on which part of the power system they belong to. 

A typical power flow is: 

Generation → Step-up Transformer → EHV/HV Transmission → HV Substation → MV Distribution → LV Consumer Supply 

Each stage performs a specific function: 

• LV supplies end users. 

• MV distributes electricity to industries and renewable plants. 

• HV transfers power between substations. 

• EHV enables efficient long-distance transmission across national grids. 

Industry Standards and Engineering Trends 

Modern substations comply with international standards such as IEC, IEEE and BS EN. These standards determine the selection of equipment, the level of protection, the degree of insulation, and the type of testing. 

Today's projects increasingly incorporate: 

• Digital substations 

• IEC 61850 communication 

• Smart protection relays 

• Online asset monitoring 

• Advanced earthing design for improved safety 

These technologies improve grid reliability and make it easier to add more renewable energy to the system. 

Quick Checklist: Choosing the Right Voltage Classes 

Before selecting a voltage level, evaluate: 

• Electrical load connected 

• Length of transmission  

• Future requirements for expansion 

• Applicable Voltage levels used in substations 

• Protection coordination 

• Earthing design requirements 

• Compliance with IEC, IEEE, and BS EN standards 

Adhering to the above-mentioned list will help to create an efficient and cost-effective system. 

Conclusion 

Proper selection of voltage classes is critical in the design of any electrical power system. Different voltage classes have various roles, such as enhancing energy efficiency and long-term safety and reliability of the system. Engineers who understand the differences between LV, MV, HV, and EHV can design efficient, standard-compliant, and scalable power systems. In light of the evolving nature of power systems with incorporation of renewable energies and smart grids, proper voltage selection forms the basis of efficient and reliable networks. 

If you are planning a new substation, industrial site, or renewable energy project, VSS Power can help you design reliable and future-ready electrical systems. Contact our team to discuss your project needs. 

5 Key Takeaways 

1. Voltage classes allow standardisation of electrical systems for operation under safe and efficient conditions. 

2. LV caters to consumers, MV to distribution, HV to transmission, and EHV to long-distance bulk power transfer. 

3. The difference between LV, MV, HV, and EHV depends on the voltage range, application, and transmission distance. 

4. Proper HV substation design, MV substation design, and earthing design improve reliability and safety. 

5. Selection of proper voltage levels in substations minimises the losses and facilitates future expansion of the grid. 

FAQs 

1. What are Voltage classes? 

They classify electrical systems into Low voltage (LV), Medium voltage (MV), High voltage (HV), and Extra high voltage (EHV) based on operating voltage. 

2. What is the Difference between LV, MV, HV and EHV? 

The difference is based on voltage range, application, transmission distance, and equipment requirements. 

3. Why is High Voltage (HV) used for transmission? 

It reduces current, hence power loss, and allows for more efficient transmission over long distances. 

4. Which Voltage levels used in substations are common? 

Common levels include 11 kV, 33 kV, 66 kV, 132 kV, 220 kV, and 400 kV, depending on the network. 

5. Why is earthing design important? 

It safely dissipates fault currents, protects personnel and equipment, and ensures compliance with international standards.