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Left – Vacuum Contactor 6kV 400A; Right – 12 kV, 40 kA Indoor Vacuum Circuit Breaker
Mohan
MV Circuit Breaker Or Vacuum Contactor? (Part 1)
Application considerations
To compare the application of medium-voltage circuit breakers and of f used contactors, we must
understand the basic characteristics of each switching technology.
Comparison presented here shows the major characteristics of medium-voltage circuit breakers and
medium-voltage f used contactors that inf luence the application. Of course, the table entries are
generalized, and the inf ormation varies by the voltage and current ratings of the equipment.
However, the comparison is valid for an overall understanding.
Medium Voltage circuit breakers are favored when:
1. Typical loads include transf ormers, capacitors, larger motors, generators or distribution f eeders.
(Ratings required exceed those of vacuum contactors 400A or 720 Aat up to 7.2 kV)
2. Continuous load current is high (e.g., larger transf ormers, larger motors)
3. Switching is not very f requent (e.g., weekly or monthly);high endurance (1,000s of operations) is
satisf actory
4. Process continuity is critical (e.g., no time f or f use replacement).
5. Reduced-voltage (RV) starting is not needed (RV starting complicates switchgear bus
arrangements).

2. Medium-voltage NEMA Class E2 controllers (fused contactors) are favored when:
1. Typical loads include motors or smaller transf ormers.
2. Continuous load current is low or moderate (e.g., smaller motors or transf ormer.
3. Switching is very f requent (e.g., daily or several times per day); very high endurance (100,000s of
operations) is needed.
4. Process continuity is compatible with f use replacement time.
5. Reduced-voltage starting is needed to reduce starting duty (and voltage f luctuation) on system.
Historically, circuit breakers have been used f or medium-voltage motors in certain industries, especially in
utility generating stations.
As these stations have aged, and station operation has changed f rom base-load to peaking service, many
of these motor-starting circuit breakers have experienced total operations well in excess of the endurance
required by the ANSI/IEEE standards. As a result, these applications have had higher maintenance costs
than if medium-voltage f used contactors had been used originally.
In contrast, users in the process industries have long f avored the use of f used Contactors f or such
applications, and have enjoyed long service with lower maintenance costs.
Will be continued…
Reference: SIEMENS Tech articles