Menu
Search
SF6 or Vacuum MV Circuit Breaker In Specific Switching Applications
SF6 or Vacuum MV Circuit Breaker In Specific Switching Applications (on photo: ABB retrofit solution)

Matching the MV circuit breaker to the task

Many years of experience in developing both SF6 and vacuum medium-voltage circuit breakers has yielded up ample evidence that neither of the two technologies is generally better than the other, and especially that they are complementary from the application point of view.

Economical factors, user preferences, national ‘traditions’, competence and special switching requirements are the decision-drivers that favor one or the other technology.

Typical of such special applications is the switching of //

  1. Overhead lines and cables
  2. Dry-type transformers
  3. Small-size motors
  4. Capacitors
  5. Arc furnaces,
  6. Shunt reactors and
  7. Railway traction systems.

The need for ‘frequent switching’ or ‘soft switching’ can be an additional element influencing the choice. In such cases, a comprehensive study of the planned installation may be needed to find the best answer.


1. Overhead lines and cables

When applied to the onerous duty of switching and protecting overhead line distribution networks, in which the fault currents are distributed over the whole current range, both technologies provide adequate margins over and above the maximum required by the relevant standards and in normal service practice.

Medium voltage recloser
Medium voltage recloser

Go back to Special Applications ↑


2. Transformers

Modern vacuum MV circuit breakers as well as SF6 circuit breakers are suitable for switching the magnetizing currents of unloaded transformers with overvoltages lower than 3.0 pu. In special cases, for instance when vacuum circuit-breakers are used for switching dry-type transformers in industrial installations, the use of surge arresters is to be recommended.

MV cubicle with SF6 circuit breaker - Transformer function
MV cubicle with SF6 circuit breaker – Transformer function (photo credit: demitas.com.tr)

Go back to Special Applications ↑


3. Small-Size Motors

When choosing MV circuit breaker for motor-switching duty, attention should be paid to the problems of overvoltages during operation.

The target limit for overvoltages of less than 2.5 pu is obtainable with both technologies. Where vacuum MV circuit breakers are used for switching small motors (starting currents less than 600 A), measures may be necessary to limit overvoltages due to multiple re-ignitions.

However, the probability of this phenomenon arising is low.

Reconditioned General Electric 5 KV LimitAmp Motor Control Center
Reconditioned General Electric 5 KV LimitAmp Motor Control Center with a PowerVac 1200 amp Main Vacuum Circuit Breaker, 4 each 400 amp FVNR Vacuum Starters and 1 each 700 amp Vacuum Circuit Breaker; Credit: atlaselectricinc.com

Go back to Special Applications ↑


4. Capacitor banks

Both technologies are suitable for restrike-free switching of capacitor banks. When capacitors must be switched back-to-back, reactors may be necessary to limit the inrush currents. The synchronous control of MV circuit breakers is an effective solution to this problem.

SF6 is specifically recommended for applications with rated voltages higher than 27 kV.

Metal enclosed medium-voltage capacitors and filters
Metal enclosed medium-voltage capacitors and filters (photo credit: ABB)

Go back to Special Applications ↑


5. Arc furnaces

Arc furnace switching is often characterized by frequent operation at high current values and short intervals. Vacuum circuit breakers are particularly suited to these service conditions.

Furnace switchgear SIMELTCIS SIVAC-X
Furnace switchgear SIMELTCIS SIVAC-X – Adapted to the extreme requirements of ultra high-power arc furnaces (credit: SIEMENS)

Go back to Special Applications ↑


6. Shunt reactors

SF6 circuit breakers are suitable for switching with overvoltages generally lower than 2.5 pu. Where vacuum circuit breakers are employed, it may be necessary under certain circumstances to take additional measures to limit overvoltages.

Shunt reactor
Shunt reactor (photo credit: TRENCH)

Go back to Special Applications ↑


7. Railway traction

In principle, both interrupting technologies are well suited for this duty. However, in the case of low-frequency applications (eg, 16.67 Hz), vacuum circuit breakers are to be recommended.

ABB's Unigear medium voltage switchgeara
ABB’s Unigear medium voltage switchgeara (photo credit: sahkopena.fi)

Go back to Special Applications ↑

Reference // SF6 or Vacuum MV Circuit Breaker? – Guenter Leonhardt, Mauro Marchi, Giandomenico Rivetti at ABB (Download)

About Author //

author-pic

Edvard Csanyi

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

2 Comments


  1. Chris
    Oct 14, 2015

    The Rise, Risks & Safe Detection Of SF6 Gas. 50 years ago ABB pioneered GIS technology. – See more at: http://www.cablejoints.co.uk/blog/article/sf6-gas-detector-crowcon-fgas#sthash.xIembbJL.dpuf


  2. busiku hankondo
    Sep 15, 2015

    Thank you so much for the updates. Learnt more

Leave a Comment

Tell us what you're thinking... we care about your opinion!

Time limit is exhausted. Please reload CAPTCHA.

Get PDF