Siemens SIPROTEC 7SS523 V3.2 Manual page 119

5.1.3 Bus Coupler Variants
5.1.3.1 Bus Couplers with One Current Transformer
1-bay coupler
5.1.3.2 Bus Couplers with Two Current Transformers
2-bay coupler
Most large busbar configurations are divided into different zones which constitute au-
tonomous subsystems− called zones or measuring systems − that can be selectively
protected. The subsystems are connected by bus couplers so that the configuration
can assume all required operating states. Depending on the number of current trans-
formers and the type of switching element, a bus coupler can have different design
variants. The bus coupler variants are automatically recognized by the DIGSI Plant
Configuration. The admissible types of bus couplers are shown below.
Figure 5-11 Examples of bus coupler variants
Bus couplers with circuit breaker and one current transformer (Figure 5-11, page 103)
are the most common variant. The low cost of this economical solution is offset by the
disadvantage of a delayed trip of the faulted subsystem if a fault occurs in the dead
zone with the coupler closed. The "dead zone" is understood to be the bus zone be-
tween the circuit breaker and the current transformer. With the coupler open, the de-
tection of the circuit breaker status ensures selective tripping without delay.
In the 7SS52 V4 protection system, one bay unit is needed for this type of bus coupler.
Bus couplers can also have two current transformers, one on each side of the circuit
breaker. The allocation of the currents to the subsystems overlaps in that case (Figure
5-11, page 103). The advantage of this design is that in case of a fault between the
two current transformers both subsystems are tripped promptly, if not selectively. With
the coupler open, the evaluation of the circuit breaker status ensures selective and un-
delayed tripping for this coupler variant as well.
In the 7SS52 V4 protection system, two bay units are needed for this type of bus cou-
pler. For the connection of the bay units, please refer to Chapter 7.1.3.1, page 248.
7SS52 V4 Manual
C53000-G1176-C182-1
Busbar Protection
103