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Home / Technical Articles / Medium voltage circuit breaker operating sequence

Rated switching sequence according to IEC, O – t – CO – t’ – CO. (cf. opposite diagram):

O – Represents opening operation
CO – Represents closing operation followed immediately by an opening operation

Three rated operating sequences exist:

  • Slow: O – 3 min – CO – 3 min – CO
  • Fast 1: O – 0.3 s – CO – 3 min – CO
  • Fast 2: O – 0.3 s – CO – 15 s – CO

NOTE: Other sequences can be requested from manufacturer.

Close/Open cycle

Assumption: O order as soon as the circuit breaker is closed

Close/Open cycle of medium voltage circuit breaker
Close/Open cycle of medium voltage circuit breaker


Automatic reclosing cycle

Assumption: C order as soon as the circuit breaker is open, (with time delay to achieve 0.3 s or 15 s or 3 min).

Automatic reclosing cycle of medium voltage circuit breaker
Automatic reclosing cycle of medium voltage circuit breaker
SOURCE: Schneider Electric – Medium Voltage Technical Guide

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Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


    Oct 06, 2023

    Which on is better for 4000A ACB (Main LT Panel)

  2. Ihsan A. Oudah
    Aug 20, 2021

    Please can you share with me the short circuit calculation guide for the protection relays

    Thank you

  3. Muhammad Usman
    Mar 27, 2018

    Hello Sir!
    Please explain Auxiliary Contacts State (OW-OD-C) what mean by (OW, OD).
    Also help how ti analysis of timing graph of High voltage Breakers.

  4. Erl Von Abong
    Jun 25, 2014

    Hello Sir,

    We have this rated operating sequence O-0.3s-CO-3min-CO VCB but our available unit have this rated operating sequence O-0.3s-CO-15s-CO.

    Is it OK to use?

    Please help.

    Thank you.

    • Kamal
      Sep 04, 2014

      I suppose,
      Requirement is O-0.3s-CO-3min-CO. And available VCB is O-0.3s-CO-15s-CO.
      15s VCB is suitable for autoreclosing application while 3 min VCB can’t.
      Although 15s VCB can be used in place of 3 min VCB with suitable delay timer in circuit of breaker.

      I hope it is the answer of your question.


  5. sudamadhav
    Jan 07, 2013

    The article is quite not clear, i want a detailed explanation on this and where could i find articles or features or details about VCB’s. pls help

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