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Retrofitting MV switchgears is one of the most current subjects in the power engineering industry. Every year, groups of users face the problem of using old switchgears, making the decision about replacement or purchase of a new switchgear.
We are certain that our proposal will expand the current alternative of solutions, so that everyone could better customise the solution to specific technical and economic conditions.

New retrofitting idea for MV switchgears

Any modern bay in a two-section switchgear in air insulation is an example of a new solution. The number of the operating elements is reduced (only two: the breaker switch or the switch disconnector and the earthing switch), and the whole system is supervised by the mechanical and electrical locks to prevent the employee from forbidden operations (e.g. closing the earthing switch when the switch disconnector is in the ‘on’ position).
Using a withdrawable unit with a disconnector or a contactor, instead of a fixed unit, is highly practical. Offer of various producers include the so-called fixed units for withdrawable switch disconnectors. The units are provided in two versions:

  • A fully enclosed cassette with a locked front door
  • A support frame (which consists only of the back panel with insulation grommets and bottom guides for the withdrawable unit)

Advantages of the new solution

Apart from increasing reliability of the bay, cassette or support frame offer additional benefits:

  • Preventing the personnel from execution of a wrong operation (withdrawable in or out of the bay with a closed switch is not possible, switching of the withdrawable unit from ‘on’ to ‘test’ to the item “the test” is not possible without first closing of the earthing switch, the earthing switch cannot be closed before opening of the switch disconnector
  • The structures are fitted with insulation pass curtains, i.e. the contacts in the passes cannot be touched after closing and locking.
  • Withdrawable the unit to the “test” position and closing the insulation passes with curtains allows the personnel to see the insulation break in the circuit on the incoming and outgoing sides; withdrawable out the unit performs the role of two disconnector switches in the old system.
  • Any necessary element may be installed in the withdrawable unit: a vacuum breaker switch, an SF gas breaker switch or a contactor.
  • When the user decides in the future to buy a modern two-stage switchgear, the withdrawable units may be reused without modifications.
  • The additional advantage of cassettes and support frames is quick installation in the bay. It significantly shortens the time to be assigned for operation in one bay in case of replacement of all fixed elements traditionally, one by one.


  • Nominal voltage 7,2; 12; 17,5 kV
  • Nominal current 630; 1250; 1600; 2000; 2500; 3150
  • Rated frequency50 Hz
  • Rated short-time withstand current 20; 31,5 kA/3s
  • Rated peak withstand current 51 kA
  • Insulation typeair
  • Circuit breakerVB-17 (PRE); VD4 (ABB)
  • Surge arresterem>3EK (Siemens); MWK (ABB)