MV Distribution System: Components, Types, Design & Applicati

An MV distribution system is a medium-voltage electrical network used to distribute power from substations or supply points to transformers, industrial facilities, commercial buildings, infrastructure, renewable-energy projects, and other electrical loads.

A typical MV distribution system can include MV switchgear, circuit breakers, transformers, feeders, cables, busbars, protection relays, metering equipment, and monitoring systems. Depending on the application, the network may use a radial, ring, or interconnected configuration.

The correct design depends on the system voltage, load requirements, fault level, reliability objectives, environmental conditions, applicable standards, and future expansion plans.

What Is an MV Distribution System?

An MV distribution system is the part of an electrical power network that distributes electricity at medium voltage.

There is no single worldwide voltage that defines every MV network. Different countries, utilities, and standards use different voltage classifications and rated values. Common project voltages include systems around 11 kV, 12 kV, 20 kV, 22 kV, 24 kV, 33 kV, and 36 kV, although the actual equipment rating must be selected according to the specific electrical system.

A simplified distribution path is:

Substation → MV switchgear → MV feeder → Distribution transformer → LV distribution → Electrical loads

In larger installations, several substations, feeders, transformers, and switching points may be interconnected.

The purpose is not simply to transport electricity. An effective MV distribution system must also provide protection, isolation, switching, control, monitoring, and operational flexibility.

How Does an MV Distribution System Work?

An MV distribution system receives electrical power from a substation or another supply source and distributes it through one or more medium-voltage feeders.

A typical sequence is:

1. Power enters the distribution substation.
2. The required voltage is established through the relevant transformer arrangement.
3. MV switchgear controls the incoming and outgoing circuits.
4. MV feeders transport electricity to distribution points.
5. Protection devices detect abnormal electrical conditions.
6. Circuit breakers or switches isolate affected sections when required.
7. Distribution transformers reduce voltage for downstream utilization.
8. Low-voltage equipment supplies the final loads.

The network configuration determines how power flows during normal operation and what happens when a fault occurs.

For example, a radial system generally has one primary supply path, while a ring arrangement can provide alternative supply paths or facilitate sectionalization depending on its operating configuration.

Main Components of an MV Distribution System

MV Switchgear

MV switchgear is a core component of medium-voltage distribution infrastructure.

It provides a controlled location for switching, protection, isolation, and—in suitable configurations—earthing and measurement.

Depending on the design, an MV switchgear assembly may include:

• Vacuum circuit breakers
• Load switches
• Disconnectors
• Earthing switches
• Busbars
• Current transformers
• Voltage transformers or sensors
• Protection relays
• Control equipment
• Cable compartments

Different switchgear technologies are available for different voltage, environmental, safety, space, and operational requirements.

Explore Degatech switchgear products for examples of medium-voltage switchgear and related equipment.

MV Circuit Breakers

Circuit breakers interrupt electrical current when a fault or other switching condition requires circuit interruption.

Vacuum circuit breakers are commonly used in MV distribution applications. Their vacuum interrupter performs the current-interruption function, while the complete circuit breaker includes the operating mechanism, insulation system, contacts, and associated components.

Circuit-breaker selection should consider:

• Rated voltage
• Rated current
• Short-circuit breaking capacity
• Short-time withstand current
• Operating sequence
• Mechanical endurance
• Protection requirements
• Installation conditions

Distribution Transformers

Distribution transformers transfer electrical energy between voltage levels.

In many MV networks, transformers reduce medium voltage to a lower voltage suitable for facility or consumer loads.

Selection factors can include:

• Rated capacity
• Primary and secondary voltage
• Frequency
• Impedance
• Cooling method
• Insulation
• Installation environment
• Load profile
• Efficiency requirements

MV Feeders and Cables

MV feeders distribute electrical power from switchgear toward transformers, substations, or other loads.

Underground cables are common in many installations, while overhead lines may be used in suitable utility distribution networks.

Cable selection should account for:

• Continuous current
• Voltage rating
• Insulation
• Installation method
• Ambient conditions
• Short-circuit withstand
• Voltage drop
• Mechanical requirements

Busbars

Busbars provide a conductive connection between incoming and outgoing circuits within switchgear and substations.

Their design must consider continuous current, short-circuit stresses, temperature rise, insulation, physical configuration, and enclosure requirements.

Protection and Monitoring Equipment

Protection relays, current transformers, voltage transformers, sensors, meters, and digital monitoring equipment provide the information required to operate and protect an MV network.

Depending on the system, protection functions can include:

• Overcurrent
• Earth fault
• Overvoltage
• Undervoltage
• Directional protection
• Transformer protection
• Feeder protection

MV Distribution System Types

Radial MV Distribution System

A radial MV distribution system supplies loads through a single primary electrical path.

Its relatively simple architecture can make it straightforward to design, operate, and protect.

The trade-off is that a fault or outage along the supply path may interrupt downstream loads unless an alternative supply or restoration strategy is available.

Radial networks are therefore commonly considered where the required reliability can be achieved with a relatively simple arrangement.

Ring MV Distribution System

A ring distribution system forms a loop between distribution points.

Depending on the operating arrangement, sections of the ring can be isolated while the remaining network continues to receive power through another path.

Ring configurations are frequently associated with ring main units (RMUs) in medium-voltage distribution.

Interconnected MV Distribution System

An interconnected system contains multiple electrical connections between sources, feeders, and loads.

This can provide increased operational flexibility and potentially greater supply resilience, but protection coordination and network management become more complex.

The appropriate architecture depends on the criticality of the load, network size, operating philosophy, and cost requirements.

MV Switchgear in Distribution Networks

MV switchgear provides one of the main control points in an MV distribution system.

A typical lineup can contain:

• Incoming feeder
• Busbar
• Outgoing feeders
• Circuit breakers
• Current transformers
• Voltage measurement devices
• Protection relays
• Earthing switches
• Cable termination compartments
• Local control and indication

For systems using vacuum circuit breakers, the vacuum interrupter is responsible for interrupting current, while the overall switchgear provides the necessary isolation, connection, protection, and control functions.

Understanding circuit-breaker terminology can help when comparing equipment. See this guide to VCB model letters and designations.

MV Circuit Breakers and Protection

Protection is essential because an MV distribution network can experience short circuits, earth faults, overloads, insulation failures, and equipment faults.

Overcurrent Protection

Overcurrent protection detects current above a configured threshold and can initiate circuit-breaker operation.

Earth-Fault Protection

Earth-fault protection identifies current associated with an unintended connection between an energized conductor and ground.

Feeder Protection

Individual feeders can have dedicated protection schemes designed to isolate faults while keeping unaffected feeders energized.

Protection Coordination

Protection coordination aims to ensure that the protective device closest to a fault operates appropriately while unnecessary upstream interruptions are minimized.

A coordination study can consider:

• Fault current
• Relay curves
• Breaker operating times
• Transformer impedance
• Cable characteristics
• Upstream protection
• Downstream protection

The actual settings must be determined from the project-specific electrical study rather than copied from a generic example.

MV Distribution System Design Considerations

Designing an MV distribution system requires more than choosing equipment with the correct voltage rating.

Load Analysis

Engineers should establish the current and expected future load.

Important factors include:

• Connected load
• Maximum demand
• Load diversity
• Motor loads
• Power factor
• Harmonics
• Critical loads
• Future expansion

System Voltage

The selected MV voltage should correspond to the utility connection, project requirements, network architecture, and applicable standards.

Equipment must have suitable insulation and withstand characteristics for the selected system.

Short-Circuit Analysis

Short-circuit calculations determine prospective fault currents at important points in the network.

These results are used to evaluate switchgear, circuit-breaker, busbar, transformer, and cable requirements.

Voltage Drop

Voltage-drop calculations help determine whether feeders and cables are adequately sized.

Long feeders and high-power loads deserve particular attention because their impedance can have a significant effect on voltage performance.

Protection Coordination

Protection devices should be coordinated across feeders, transformers, switchgear, and upstream sources.

A well-designed protection system helps isolate faults without unnecessarily disconnecting healthy portions of the network.

Equipment Layout

MV equipment needs sufficient space for installation, cable termination, operation, inspection, and maintenance.

For withdrawable switchgear, the physical breaker withdrawal path should be included in the layout.

Clearances should not be selected from a generic rule of thumb. Manufacturer requirements, applicable regulations, standards, and project conditions should determine the final layout.

MV Distribution for Industrial Applications

Industrial facilities often require MV distribution because their electrical demand can exceed what is practical for a low-voltage-only architecture.

An industrial MV system may supply:

• Motors
• Production equipment
• Large HVAC systems
• Pumps
• Compressors
• Process equipment
• Plant substations
• Auxiliary systems

Industrial distribution networks may use multiple MV feeders to separate major load groups.

This can simplify fault isolation and operational management, provided that the protection and switching architecture is properly designed.

Critical industrial facilities may also require redundant or alternative supply arrangements.

MV Distribution for Solar, Wind and BESS

The expansion of renewable generation and energy storage is increasing the importance of MV distribution equipment.

Solar Power

Utility-scale and commercial solar installations often use MV collection networks.

A simplified architecture is:

Solar arrays → Inverters → Step-up transformers → MV collection system → Substation → Grid

MV switchgear provides switching and protection at collection and grid-interconnection points.

Wind Power

Wind farms can use MV collector systems to connect multiple turbine transformers or collection points to a central substation.

The design needs to consider feeder length, cable characteristics, fault levels, protection coordination, and grid-connection requirements.

Battery Energy Storage Systems

BESS installations can include MV switchgear between power conversion systems, transformers, and the grid or facility network.

Unlike a simple load, a BESS can operate with bidirectional power flow. Consequently, protection and control requirements must be designed around the specific system architecture and operating modes.

Smart MV Distribution Systems

Traditional MV distribution systems increasingly incorporate digital technologies.

A smart MV distribution network can include:

• Digital protection relays
• Sensors
• Intelligent electronic devices
• Remote switching
• Condition monitoring
• Communication networks
• SCADA integration
• Distribution automation

These technologies can improve visibility into network conditions and equipment status.

For utilities and large industrial facilities, remote monitoring can also support faster fault analysis and more informed maintenance and operational decisions.

However, digitalization introduces additional considerations, including communications reliability, interoperability, cybersecurity, data management, and system integration.

SF6-Free MV Distribution

Environmental considerations have increased interest in medium-voltage equipment that avoids SF6 where appropriate.

Alternative technologies can include vacuum interruption combined with solid insulation and other insulation approaches.

Solid-insulated switchgear can integrate insulating materials into the equipment architecture instead of using SF6 gas as the primary insulation medium.

See Degatech’s solid-insulated switchgear information for additional technical context.

The choice between technologies should consider voltage, current, fault level, insulation requirements, environmental conditions, maintenance strategy, applicable standards, and project specifications.

How to Select MV Distribution Equipment

When selecting equipment for an MV distribution system, buyers and engineers should evaluate the complete application rather than focusing on a single specification.

1. Rated Voltage

Verify the nominal system voltage and the equipment’s rated voltage.

2. Rated Current

Determine the maximum continuous current and consider planned load growth.

3. Short-Circuit Capability

Confirm the required breaking and withstand ratings using the project’s short-circuit study.

4. Insulation Technology

Evaluate air-insulated, solid-insulated, gas-insulated, and other appropriate technologies according to the application.

5. Protection

Confirm the required protection functions and compatibility with the overall protection-coordination scheme.

6. Environmental Conditions

Consider:

• Temperature
• Humidity
• Altitude
• Pollution
• Dust
• Corrosion
• Indoor or outdoor installation

7. Maintenance

Consider access, inspection, diagnostics, spare parts, switching mechanisms, and the desired maintenance strategy.

8. Digital Connectivity

For automated networks, evaluate communication protocols, sensors, remote control, monitoring, and protection-system integration.

9. Supplier Capability

For engineered MV projects, supplier evaluation can include technical documentation, customization capability, testing requirements, production capability, quality processes, delivery capacity, and technical support.

Common MV Distribution Challenges

Common issues that can affect MV system performance include:

• Incorrect equipment ratings
• Poor protection coordination
• Insufficient fault-current analysis
• Inadequate cable sizing
• Excessive voltage drop
• Poor equipment layout
• Insufficient maintenance access
• Inadequate environmental protection
• Limited monitoring
• Insufficient provision for future expansion
• Incompatible protection and control interfaces

Addressing these factors during the design stage is generally more effective than attempting to correct them after installation.

FAQs About MV Distribution Systems

What is an MV distribution system?

An MV distribution system is a medium-voltage electrical network that distributes power from substations or supply points to transformers, facilities, renewable-energy installations, and other electrical loads.

What does MV stand for in electrical distribution?

MV stands for medium voltage. The exact voltage range or classification depends on the applicable standard, country, utility, and electrical system.

What voltage is an MV distribution system?

There is no single global MV voltage. Common project system voltages include approximately 11 kV, 12 kV, 20 kV, 22 kV, 24 kV, 33 kV, and 36 kV, depending on the application and electrical network.

What are the main components of an MV distribution system?

Common components include MV switchgear, circuit breakers, transformers, feeders, cables, busbars, protection relays, instrument transformers or sensors, disconnectors, earthing equipment, meters, and control systems.

What is an MV feeder?

An MV feeder is an electrical circuit that distributes medium-voltage power from a substation or switchgear assembly to another distribution point, transformer, or load.

What is the difference between radial and ring MV distribution?

A radial system normally has one main supply path. A ring system forms a loop and may provide alternative supply paths or facilitate sectionalization, depending on its operating arrangement.

What is an RMU?

An RMU, or ring main unit, is a compact medium-voltage switchgear assembly commonly used in distribution networks, particularly for ring and compact-substation applications.

Why are vacuum circuit breakers used in MV systems?

Vacuum circuit breakers use a vacuum interrupter to interrupt current. They are commonly applied in MV systems because vacuum interruption is well suited to many medium-voltage switching and protection applications.

What is the role of protection relays in MV distribution?

Protection relays monitor electrical conditions and can issue trip commands to circuit breakers when configured fault or abnormal operating conditions are detected.

Can an MV distribution system connect solar power?

Yes. Solar installations can use MV collection systems, transformers, switchgear, and protection equipment to collect generated power and connect it to a substation or electrical grid.

Can BESS systems use MV distribution?

Yes. BESS installations can use MV switchgear, transformers, protection, and feeders to connect power conversion systems with the grid or facility network.

What is smart MV distribution?

Smart MV distribution combines conventional electrical equipment with digital protection, sensors, communications, monitoring, and automation to provide improved network visibility and control.

What is SF6-free MV switchgear?

SF6-free MV switchgear uses alternative insulation and/or interruption technologies without relying on SF6 gas for the relevant function. Depending on the design, this can include vacuum interruption with solid insulation.

Which IEC standard applies to MV switchgear?

Different parts of the IEC 62271 series apply to different types of medium- and high-voltage switchgear and controlgear. The specific applicable standard should be determined based on the equipment type and application.

Conclusion

An MV distribution system provides the infrastructure needed to distribute medium-voltage electrical power safely and efficiently between substations, transformers, industrial facilities, renewable-energy projects, and other loads.

The system typically combines MV switchgear, circuit breakers, transformers, feeders, cables, busbars, protection relays, monitoring equipment, and control systems. Its architecture may be radial, ring-based, or interconnected depending on reliability and operational requirements.

Modern MV distribution is evolving through digital protection, automation, remote monitoring, renewable-energy integration, BESS, compact equipment, and interest in SF6-free technologies.

For equipment procurement, the most important factors include voltage rating, current rating, short-circuit capability, insulation technology, protection, environmental conditions, maintenance, layout, digital integration, standards, and supplier capability.

A properly engineered MV distribution system should be designed around the complete electrical network rather than any individual component. This system-level approach helps ensure that switchgear, transformers, feeders, protection equipment, and controls work together as intended.