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Planning high voltage switchgear

The following three criteria must be considered when planning high voltage switchgear installations:

Consider this when planning high voltage switchgear installations
Consider this when planning high voltage switchgear installations (photo credit: ABB)
  1. Voltage levels
  2. Plant concept and configuration
  3. Dimensioning

1. Voltage levels

High voltage installations are primarily for power transmission, but they are also used for distribution and for coupling power supplies in three-phase and HVDC systems. Factors determining their use include: network configuration, voltage, power, distance, environmental considerations and type of consumer:

HV InstallationsVoltage level
Distribution and urban networks> 52 – 245 kV
Industrial centres> 52 – 245 kV
Power plants and transformer stations> 52 – 800 kV
Transmission and grid networks245 – 800 kV
HVDC transmission and system interties> 300 kV
Railway substations123 – 245 kV

Go back to criteria list ↑


2. Plant concept and configuration

The circuitry of an installation is specified in the single-phase block diagram as the basis for all further planning stages. Table 1 shows the advantages and disadvantages of some major station concepts.

The availability of a switching station is determined mainly by:

  1. Circuit configuration, i. e. the number of possibilities of linking the network nodes via circuit breakers and isolators, in other words the amount of current path redundancy,
  2. Reliability/failure rate of the principal components such as circuit breakers, isolators and busbars,
  3. Maintenance intervals and repair times for the principal components.

Table 1 – Choice of plant concept and measures taken in relation to given boundary conditions

Concept configurationAdvantagesDisadvantages
Single busbar
  1. least cost
  1. BB fault causes complete station outage
  2. maintenance difficult
  3. no station extensions without disconnecting the installation
  4. for use only where loads can be disconnected or supplied from elsewhere
Single busbar with bypass
  1. low cost
  2. each breaker accessible for maintenance without disconnecting
  1. extra breaker for bypass tie
  2. BB fault or any breaker fault causes complete station outage
Double busbar with one circuit breaker per branch
  1. high changeover flexibility with two busbars of equal merit
  2. each busbar can be isolated for maintenance
  3. each branch can be connected to each bus with tie breaker and BB isolator without interruption
  1. extra breaker for coupling
  2. BB protection disconnects all branches connected with the faulty bus
  3. fault at branch breaker disconnects all branches on the affected busbar
  4. fault at tie breaker causes complete station outage
2-breaker system
  1. each branch has two circuit breakers
  2. connection possible to either busbar
  3. each breaker can be serviced without disconnecting the branch
  4. high availability
  1. most expensive method
  2. breaker defect causes half the branches to drop out if they are not connected to both bus bars
  3. branch circuits to be considered in protection system (applies also to other multiple-breaker concepts)
Ring bus
  1. low cost
  2. each breaker can be maintained without disconnecting load
  3. only one breaker needed per branch
  4. no main busbar required
  5. each branch connected to network by two breakers
  6. all changeover switching done with circuit breakers
  1. breaker maintenance and any faults interrupt the ring
  2. potential draw-off necessary in all branches
  3. little scope for changeover switching
1½-breaker system
  1. great operational flexibility
  2. high availability
  3. breaker fault on the busbar side disconnects only one branch
  4. each bus can be isolated at any time
  5. all switching operations executed with circuit breakers
  6. changeover switching is easy, without using isolators
  7. BB fault does not lead to branch disconnections
  1. three circuit breakers required for two branches
  2. greater outlay for protection and auto-reclosure, as the middle breaker must respond independently in the direction of both feeders

Go back to criteria list ↑


3. Dimensioning

On the basis of the selected voltage level and station concept, the distribution of power and current is checked and the currents occurring in the various parts of the station under normal and short-circuit conditions are determined.

The basis for dimensioning the station and its components is defined in respect of:

  1. insulation coordination
  2. clearances, safety measures
  3. protection scheme
  4. thermal and mechanical stresses

The basic designs available for switching stations and equipment together with different forms of construction offer a wide range of possibilities, see Table 2 below. The choice depends on environmental conditions and also constructional, operational and economic considerations.

Table 2 – The principal types of design for high voltage switchgear installations and their location

Basic designInsulation mediumUsed mainly for voltage level (kV)Location
OutdoorIndoor
ConventionalAir>52 – 123××
ConventionalAir123 – 800×
GISSF6>52 – 800× (1)×
Hybrid (2)Air/SF6245 – 500×
  1. GIS used outdoors in special cases
  2. Hybrid principle offers economical solutions for station conversion, expansion or upgrading.

There are various layouts for optimizing the operation and space use of conventional outdoor switchgear installations (switchyards), with different arrangement schemes of busbars and disconnectors.

Go back to criteria list ↑


North-East Agra – the world’s first multi-terminal UHVDC transmission link

The 800 kV North-East Agra UHVDC (ultra high voltage direct current) link will have a record 8,000 MW converter capacity, transmitting clean hydroelectric power, equivalent to the generation of 8 large power plants, from India’s northeast region to the city of Agra, a distance of 1,728 km.

The North-East Agra project was ABB’s fifth HVDC transmission link in India at that time.


Reference // Switchgear manual by ABB (Order PDF or hardcover directly from ABB)

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About Author

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Edvard Csanyi

Edvard -

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry fascilities. Professional in AutoCAD programming. Present on

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