Switchgear Design Guide: Principles, Components & Best Practices

A switchgear design guide helps engineers and project teams understand how to develop electrical switching and protection equipment around the requirements of a particular power system. Good switchgear design must consider electrical ratings, fault conditions, insulation, thermal performance, mechanical strength, protection, control, safety, installation, maintenance, and applicable standards.

Switchgear is not simply an enclosure containing a circuit breaker. It is an integrated assembly in which primary conductors, switching devices, insulation systems, protection equipment, measurement devices, control circuits, and mechanical structures must work together.

This guide explains the major considerations involved in switchgear design and provides a practical framework for developing or evaluating a switchgear specification.

What Is Switchgear Design?

Switchgear design is the process of defining the electrical, mechanical, insulation, protection, control, and physical characteristics of switchgear for a specific application.

The design normally begins with the requirements of the electrical network.

Typical inputs include:

• System voltage
• Rated current
• Frequency
• Short-circuit level
• Load characteristics
• Earthing system
• Number of feeders
• Switching requirements
• Protection philosophy
• Installation environment
• Cable configuration
• Space limitations
• Maintenance requirements
• Applicable standards

The designer then translates these requirements into an appropriate switchgear configuration.

Depending on the application, this may involve medium-voltage or low-voltage switchgear, indoor or outdoor equipment, fixed or withdrawable designs, vacuum switching technology, gas-insulated equipment, solid insulation, or other configurations.

Key Requirements in Switchgear Design

Before selecting individual components, the system requirements should be clearly established.

Voltage

The switchgear’s voltage rating must be appropriate for the electrical system.

For medium-voltage applications, common system classes include 12 kV, 24 kV, and 36 kV, although actual rated values and applicable equipment classes depend on the project and standard being applied.

The insulation system must also be capable of handling the specified power-frequency and impulse withstand requirements.

Current

Rated current determines the continuous current that the switchgear is designed to carry under specified conditions.

Current requirements can be influenced by:

• Transformer capacity
• Feeder loading
• Motor loads
• Generation capacity
• Ambient temperature
• Installation arrangement
• Future expansion

The continuous-current rating should be coordinated with the system load and expected operating conditions.

Short-Circuit Current

Short-circuit performance is one of the most important switchgear design considerations.

During a fault, very high currents can produce substantial electromagnetic and thermal stresses.

The design therefore needs to consider appropriate short-circuit withstand and interruption capabilities for the selected equipment.

Frequency

The equipment must be suitable for the system frequency.

Electrical characteristics, testing requirements, and some equipment designs can depend on frequency.

Earthing System

The network earthing arrangement influences protection, fault-current behavior, insulation considerations, and equipment requirements.

The switchgear design should therefore be coordinated with the project’s overall earthing and protection philosophy.

Main Components of Switchgear

A switchgear assembly contains multiple components performing different functions.

Circuit Breakers

Circuit breakers are designed to make, carry, and interrupt electrical current under specified conditions.

In medium-voltage switchgear, vacuum circuit breakers are commonly used for switching and fault interruption.

A vacuum interrupter contains the switching contacts in a vacuum environment. The interrupter’s characteristics influence the circuit breaker’s electrical performance and application.

For product information and related switchgear technologies, see Degatech’s switchgear products.

Busbars

Busbars distribute electrical current between switchgear sections and feeders.

The busbar design must account for:

• Rated current
• Short-circuit forces
• Temperature rise
• Insulation
• Mechanical support
• Connections
• Clearances

Busbar configuration can also influence system reliability and operational flexibility.

Possible arrangements include single-bus systems, sectionalized busbars, and more complex configurations depending on the application.

Disconnectors and Earthing Switches

Disconnectors provide isolation where required by the system design.

Earthing switches provide a means of connecting designated conductors to earth under specified operating conditions.

Their mechanical interlocking and sequencing are important aspects of safe switchgear operation.

Instrument Transformers

Current transformers and voltage transformers can provide measurement and protection signals.

Current transformers may supply inputs to protective relays and metering equipment, while voltage transformers can provide voltage measurement and protection inputs.

The selection of instrument transformers needs to account for the intended protection and measurement functions.

Protection and Control Equipment

Protection relays monitor electrical conditions and can initiate circuit-breaker operation when specified fault conditions are detected.

Modern switchgear may also integrate:

• Digital protection relays
• Metering
• Local controls
• Communication interfaces
• Status indication
• Sensors
• Condition monitoring

The secondary system should be coordinated with the primary equipment and the facility’s overall automation architecture.

Switchgear Electrical Ratings

A switchgear specification normally contains several important ratings.

Rated Voltage

Defines the voltage class for which the equipment is designed.

Rated Current

Defines the continuous current capability under specified conditions.

Short-Time Withstand Current

Indicates the current the equipment can withstand for a specified short duration.

This rating is particularly important when evaluating the thermal and mechanical effects of short-circuit currents.

Peak Withstand Current

Fault currents can generate strong electromagnetic forces. Peak withstand capability addresses the mechanical stresses associated with high current peaks.

Short-Circuit Breaking Current

For circuit breakers, the interrupting capability must be suitable for the prospective fault conditions of the installation.

Insulation Levels

Insulation coordination involves characteristics such as power-frequency withstand and lightning impulse withstand, as applicable to the equipment and voltage class.

The required values should be established according to the applicable standard and system conditions.

Insulation and Dielectric Design

Insulation is fundamental to switchgear design.

The insulation system separates energized conductors from:

• Other phases
• Grounded structures
• Enclosures
• Adjacent components
• Personnel

Traditional switchgear designs may use air, gas, solid insulation, or combinations of technologies.

Air-Insulated Switchgear

Air serves as the primary external insulation medium around energized components.

This approach can require greater physical space but can offer accessibility advantages depending on the design.

Gas-Insulated Switchgear

Gas-insulated designs use an insulating gas within defined compartments.

Historically, SF6 has been widely associated with gas-insulated electrical equipment. However, environmental regulations and decarbonization initiatives are increasing interest in alternative insulation and switching technologies.

Solid-Insulated Switchgear

Solid-insulated designs use solid dielectric materials around selected energized components.

This can support compact equipment designs, although dielectric, thermal, manufacturing, and service requirements must all be considered.

The appropriate insulation technology depends on voltage class, environmental conditions, physical constraints, safety requirements, and project specifications.

Switchgear Mechanical and Thermal Design

Electrical performance alone is not sufficient.

Thermal Performance

Current flowing through conductors generates heat.

Switchgear design therefore needs to consider:

• Conductor resistance
• Connections
• Enclosure configuration
• Ventilation
• Ambient temperature
• Heat dissipation
• Temperature rise

Poor thermal design can negatively affect equipment life and reliability.

Mechanical Strength

Short-circuit currents can generate substantial electromagnetic forces.

Busbars, supports, connections, and insulating structures must be designed to withstand the mechanical stresses associated with specified fault conditions.

Operating Mechanisms

Circuit breakers and switches require mechanisms capable of performing their intended operations reliably.

The mechanism design may involve springs, motors, solenoids, linkages, and position indicators depending on the equipment.

Switchgear Layout and Installation

Physical layout is an important part of switchgear design.

A switchgear lineup should provide suitable space for:

• Normal operation
• Inspection
• Testing
• Maintenance
• Cable termination
• Equipment removal
• Ventilation
• Safety access

The actual manufacturer’s dimensional drawings should be used when developing the final installation layout.

This is particularly important for withdrawable switchgear, where circuit breakers and other components may need to move between positions or be removed for testing and maintenance.

Cable routing also needs to be considered early.

The design should account for cable:

• Quantity
• Size
• Bending radius
• Termination
• Entry direction
• Support
• Separation
• Installation access

Switchgear Protection and Safety

Protection and safety should be incorporated into the design rather than added after the primary equipment has been selected.

Interlocking

Mechanical and electrical interlocks can help prevent incorrect operating sequences.

The exact interlocking philosophy depends on the equipment configuration and application.

Earthing

Accessible conductive parts should be appropriately connected to the protective earthing system according to the applicable design requirements.

Fault Containment

Where required, switchgear may be designed and tested for specific fault-containment characteristics.

For applications where arc-resistant performance is required, the appropriate equipment classification and test requirements should be established during specification.

Access Control

The physical arrangement should help restrict access to hazardous energized areas and provide appropriate operating interfaces.

Safety requirements vary by jurisdiction and installation, so applicable local regulations must be incorporated into the final design.

Applicable Switchgear Standards

Standards provide a framework for equipment ratings, construction, testing, and performance.

The IEC 62271 series is particularly important for many high-voltage and medium-voltage switchgear and controlgear applications. However, the relevant part depends on the specific equipment.

Other standards may also apply depending on:

• Equipment voltage
• Installation type
• Market
• Product category
• Testing requirements
• Local regulations

The designer should identify the applicable standards before finalizing the equipment specification.

For official standards information, consult the International Electrotechnical Commission (IEC).

How to Develop a Switchgear Design

A practical switchgear design process can be organized into several stages.

Step 1: Define the System

Establish the electrical system’s:

• Voltage
• Current
• Frequency
• Short-circuit level
• Earthing arrangement
• Load profile
• Number of feeders

Step 2: Develop the Single-Line Diagram

The single-line diagram establishes the electrical architecture.

It should identify sources, transformers, busbars, circuit breakers, feeders, and other relevant equipment.

Step 3: Establish Protection Requirements

Define the required protection functions and coordinate them with upstream and downstream equipment.

Step 4: Select the Switchgear Configuration

Determine the appropriate:

• Switchgear type
• Insulation technology
• Circuit-breaker technology
• Busbar arrangement
• Fixed or withdrawable configuration
• Indoor or outdoor arrangement

Step 5: Define Mechanical Requirements

Establish enclosure dimensions, cable-entry requirements, operating mechanisms, access, maintenance provisions, and installation constraints.

Step 6: Perform Electrical and Thermal Checks

Verify that the proposed equipment meets the required electrical ratings and relevant thermal and short-circuit requirements.

Step 7: Develop the Physical Layout

Create the switchgear room, substation, or outdoor installation arrangement using actual equipment dimensions.

Step 8: Verify Testing and Compliance Requirements

Identify the applicable type, routine, and project-specific testing requirements according to the relevant standards and specifications.

Step 9: Review the Complete Design

Perform multidisciplinary coordination covering:

• Electrical systems
• Civil works
• Structural interfaces
• HVAC
• Fire protection
• Cable systems
• Automation
• Maintenance
• Safety

Common Switchgear Design Mistakes

Selecting Equipment Before Defining the System

Choosing a product before establishing voltage, current, fault level, and protection requirements can result in an unsuitable configuration.

Ignoring Short-Circuit Conditions

The normal load current is only part of the design problem. Fault-current conditions can impose much higher electrical, thermal, and mechanical stresses.

Treating Layout as an Afterthought

Cable access, maintenance areas, equipment removal, and ventilation can affect the feasibility of the complete installation.

Using Generic Dimensions

Final layouts should use actual manufacturer drawings wherever possible.

Underestimating Environmental Conditions

Temperature, altitude, humidity, pollution, dust, and corrosion can affect equipment selection and performance.

Overlooking Future Expansion

If additional feeders or higher loads are reasonably foreseeable, expansion requirements should be considered during the initial design.

Failing to Coordinate Protection

Protection settings and equipment characteristics should be considered as part of the overall electrical protection system rather than independently for each panel.

Frequently Asked Questions

What is a switchgear design guide?

A switchgear design guide explains the main electrical, mechanical, insulation, protection, safety, layout, and standards-related considerations involved in designing or specifying switchgear for a particular electrical system.

What are the most important switchgear design parameters?

Key parameters include rated voltage, rated current, frequency, short-circuit withstand capability, breaking capacity, insulation level, environmental conditions, installation type, protection requirements, and applicable standards.

How do you design medium-voltage switchgear?

Medium-voltage switchgear design starts with system requirements such as voltage, current, fault level, earthing arrangement, and feeder configuration. Designers then select appropriate switching, insulation, protection, busbar, cable, enclosure, and control arrangements and verify them against applicable standards.

What is the role of a circuit breaker in switchgear?

A circuit breaker can make, carry, and interrupt current under specified conditions. In a protection system, it can interrupt fault current when instructed by the associated protection and control system.

Why are vacuum circuit breakers used in MV switchgear?

Vacuum circuit breakers use vacuum interrupters to interrupt current. They are an important switching technology for many medium-voltage applications, subject to the requirements of the particular system and equipment.

What is insulation coordination in switchgear design?

Insulation coordination is the selection and coordination of insulation characteristics with expected overvoltages and system conditions so that the equipment can withstand specified electrical stresses.

What factors affect switchgear layout?

Equipment dimensions, working clearances, maintenance access, cable routing, cable bending radius, ventilation, equipment removal, building constraints, safety requirements, and future expansion can all affect the layout.

What standards apply to switchgear design?

The applicable standard depends on the equipment and application. Relevant parts of the IEC 62271 series apply to many high-voltage and medium-voltage switchgear and controlgear products, while additional standards and local regulations may apply.

What is the difference between fixed and withdrawable switchgear?

Fixed switchgear has equipment installed in a fixed position. Withdrawable designs allow designated components, such as circuit breakers, to be moved between defined positions according to the equipment design, which can support operational isolation and maintenance procedures.

How does short-circuit current affect switchgear design?

Short-circuit current can produce high thermal and mechanical stresses and requires the equipment to have suitable withstand and interruption capabilities. Fault levels are therefore fundamental inputs to switchgear selection and design.

What should be considered when designing switchgear for renewable energy?

Renewable projects may have variable generation, inverter-based interfaces, collection networks, transformers, protection requirements, and grid interconnection requirements. The switchgear must be selected and coordinated with the project’s complete electrical architecture.

Can switchgear be designed without SF6?

For some applications, yes. Technologies such as vacuum switching combined with solid insulation or other insulation systems can provide alternatives to SF6-based designs. Suitability depends on voltage class, equipment architecture, standards, and project requirements.

How important is maintenance in switchgear design?

Maintenance should be considered from the beginning. Access, removable components, testing provisions, spare parts, monitoring, cable termination access, and operating procedures can all affect lifecycle performance.

What makes a good switchgear design?

A good design meets the electrical requirements while providing appropriate protection, insulation, mechanical and thermal performance, safety, maintainability, installation practicality, and compliance with applicable standards.

Conclusion

A successful switchgear design starts with the electrical system and works outward to the equipment configuration, protection system, insulation, mechanical construction, physical layout, and installation environment.

The most important design inputs include voltage, current, fault level, frequency, earthing arrangement, protection requirements, environmental conditions, and applicable standards. These inputs determine many of the characteristics of the final switchgear assembly.

Modern switchgear design can also incorporate vacuum switching, solid insulation, digital monitoring, intelligent protection, modular configurations, and other technologies. The appropriate choice depends on the project’s technical and operational requirements rather than on a single technology being universally suitable.

For engineers and procurement teams, the key is to evaluate switchgear as an integrated electrical system. Proper coordination between circuit breakers, busbars, insulation, protection, control, cable systems, layout, and maintenance requirements helps create equipment that is practical to install, operate, and maintain throughout its intended service life.