ARTICLE
2-breaker system
1. each branch has two circuit breakers 1. most expensive method
2. connection possible to either busbar 2. breaker defect causes half the branches to drop out if
they are not connected to both bus bars
3. each breaker can be serviced without
disconnecting the branch
Ring bus
4. high availability 3. branch circuits to be considered in protection system
(applies also to other multiple-breaker concepts)
1. low cost 1. breaker maintenance and any faults interrupt the ring
2. each breaker can be maintained without
disconnecting load 2. potential draw-off necessary in all branches
3. little scope for changeover switching
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
1½-breaker system
1. great operational flexibility 1. three circuit breakers required for two branches
2. high availability 2. greater outlay for protection and auto-reclosure, as the
middle breaker must respond independently in the direc-
tion of both feeders
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
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 design
Insulation Used mainly Location
medium for voltage
level (kV)
Outdoor Indoor
×
Conventional Air >52 – 123 ×
Conventional Air 123 – 800 ×
GIS SF6 >52 – 800 × (1)
Hybrid (2) Air/SF6 245 – 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.
may 2018 Global MDA Journal
23