SF6 or MV vacuum circuit breaker in specific switching applications

Match the MV circuit breaker to the task
Many years of experience in the development of both SF6 and medium/mv voltage vacuum circuit breakers have provided ample evidence that neither technology is generally better than the other, and above all that they are complementary from the point of view. of the application.

SF6 or MV vacuum circuit breaker in specific switching applications.
Economic factors, user preferences, national ‘traditions’, skill and decision-making requirements favorable to one or the other technology.
Switching of:
Overhead lines and cables
Dry transformers
Small size motors
Capacitors
Arc furnaces,
Shunt reactors and
Railway traction systems.
The need for ‘ frequent switching ‘ or ‘ soft switching ‘ may be an additional factor influencing the choice. In such cases, a complete study of the planned installation may be necessary to find the best answer.

vacuum circuit breaker
MV vacuum circuit breaker
  1. Overhead lines and cables
    When applied to the duty of switching and protection of overhead line distribution networks, in which fault currents are distributed over the entire current range, both technologies offer sufficient margins beyond the maximum required by standards. applicable and under normal conditions of use
  2. Transformers
    Modern MV vacuum circuit breakers, as well as SF6 circuit breakers, are suitable for switching the magnetic currents of unloaded transformers with overvoltages below 3.0 pu. In special cases, for example, when vacuum circuit breakers are used to switch dry-type transformers in industrial installations, it is recommended to use surge arresters.
  3. Small size motors
    When choosing an MV circuit breaker for motor switching, it should be prone to overvoltage problems in operation.
    The target limit for surges below 2.5 pu is available with both technologies. When MV vacuum circuit breakers are used for switching small motors (starting currents less than 600 A), it may be necessary to take measures to limit overvoltages due to multiple re-ignitions.
    However, the likelihood of this happening is low.

LimitedAmp Limited General Electric 5 KVMotor control center with 1200 amp PowerVac main vacuum circuit breaker, 4 x 400 amp FVNR vacuum starters, and 1 700 amp vacuum circuit breaker; 

  1. Capacitor banks
    Both technologies are suitable for stress-free switching of capacitor banks. When capacitors need to be switched back to back, reactors may be needed to limit inrush currents. Synchronous control of MV circuit breakers is an effective solution to this problem.
    SF6 is specifically recommended for applications with nominal voltages above 27 kV.
  2. Arc furnaces
    Switching of the arc furnace is often characterized by frequent operation at high current values ​​and at short intervals. Vacuum circuit breakers are particularly suitable for these operating conditions.

Equipment for SIMELTCIS SIVAC-X furnace – Adapted to the extreme requirements of very high power arc furnaces (credit: SIEMENS)

  1. Shunt reactors
    SF6 circuit breakers are suitable for switching with overvoltages typically less than 2.5 pu. When vacuum circuit breakers are used, it may be necessary for certain circumstances to take additional measures to limit the surges.
  2. Rail traction
    In principle, both interrupt technologies are well suited for this task. However, in the case of low-frequency applications (eg 16.67 Hz), vacuum circuit breakers are recommended.

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