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LET’S DISCOVER THE TYPES OF MEDIUM VOLTAGE SWITCHGEAR

TYPES OF MEDIUM VOLTAGE SWITCHGEAR

Medium voltage switchgears are divided into two large families, MV switchgears for primary distribution (Metal Clad – Normal Clad) and MV switchgears for secondary distribution (Metal Enclosed – ATR).

Types according to their use

The choice of type is related to its use: the primary distribution switchgear is used for the transformation of electricity from high voltage to medium voltage, while the secondary distribution switchgear is used for the transformation from medium to low-voltage energy.

The medium-voltage switchgear for primary distribution has the peculiarity of having the components withdrawable and of being divided into compartments metallically segregated from each other.

These are two important technical characteristics that permit the maintenance of the switchgear in total safety, and to allow the continuity of service of the switchgear during interventions. The withdrawable circuit-breaker can be easily replaced, and the safety is ensured by segregated compartments, which avoid any contact with bars still powered, in compliance with the IEC 62271-200 standard.

The medium-voltage switchgear for secondary distribution in some installations is suitable for electrical systems for primary distribution.

This switchgear can be equipped with SF6 (sulfur hexafluoride) gas-insulated disconnectors, or with air-insulated disconnectors for cubicles equipped with circuit-breakers. The safety of the operator is guaranteed by the fixed and mobile components connected to the earthing system, as the structure of the switchgear prevents the compartment from opening when the earthing switch is open.

A mechanical and/or visual indicator allows verifying of the presence of voltage in the incoming cables, the state of the circuit-breaker, the disconnector, and the earthing system.

Types according to component insulation

The second type of the two families of switchgears concerns the insulation of the internal components such as the circuit-breakers or disconnectors.

The circuit-breaker can be air-insulated or in SF6 gas-insulated. Air insulation requires larger dimensions than gas insulation, since the latter is a dielectric gas (capable of transmitting electricity without conductivity) and non-flammable and prevents the creation of the internal arc during the opening of the circuit-breaker, therefore the connection points inside the component can be remarkably close together.

SF6 gas, sulfur hexafluoride, is not harmful to humans and animals, if inhaled in very small doses, and it is a much more effective gas than carbon dioxide (CO2) in trapping heat. However, it is very harmful to the environment and it is a contributing factor to the greenhouse effect. For this reason, it has been included in the list of polluting gases in the Kyoto Protocol, and in many countries, it is not authorized for the use of SF6 insulated equipment.

Over the years, to prevent the dispersion of this gas into the environment, important changes have been made to the external structure of the switchgear. In the first prototypes it was made of electro-welded iron, but it was not completely hermetic, subsequently monobloc plastic containers were produced, in order to have weak points. These containers are equipped with pressure switches that detect the level of gas inside, any lowering of the level indicates a leak in the closed system.

METAL CLAD SWITCHGEAR – NORMAL CLAD

Our Normal Clad switchgear is air-insulated and designed for primary distribution grids. It can be supplied in a standard version or resistant to internal arc on all four sides. For outdoor applications (mines, Oil & Gas) it can be realized in its special version with protection degree up to IP65 and double level configuration and double busbar system.

Technical features:

  • Protection degree from IP4X for indoor applications, up to IP65 for outdoor applications
  • Simple or double busbar system, double top with two breakers and other customizable configurations available
  • Front access
  • Multi-brand air or SF6 gas-insulated breakers applicated on the withdrawable carriage
  • Withdrawable breakers and voltage transformers
  • Protection and control relay, and customized and settable digital counters
  • Standard or digital synoptic
  • Digital option to reduce wiring in order to maximize performance
  • SCADA system integration
  • Integration of thermal control system on bars and breakers, upon request
  • Integration of internal-arc protection systems, upon request
  • Integration of fast transfer systems, frequency and load-shedding control, upon request

Staff safety is guaranteed by:

  • Compliance with the IEC 62271-200 standard during operation and maintenance of the switchgear
  • Connection to the earth system of the entire structure and all its components
  • Presence of a voltage indicator relating to the incoming cables
  • Special locking technology that does not allow maneuvering errors by the personnel
  • Mechanical indicator, which verifies the state of the circuit-breaker (open or closed)
  • Visual display, which verifies the status of the earth circuit-breaker (open or closed)
  • Our products offer the possibility of a completely manual operation of the system, in case of emergency or lack of auxiliary power supply
  • Opening/closing of the circuit breaker, possible by means of a manual lever

METAL ENCLOSED SWITCHGEAR – ATR

ATR is an air-insulated, metal-enclosed medium voltage switchgear, mainly used for secondary distribution power systems. It is also used in special configurations for primary distribution power systems, and it is designed and standardized for indoor installations. The ATR switchgear complies with the international standard IEC 62271-200/11-2003.

Technical features:

  • Front or back access
  • Installation of multi-brand breakers, air-insulated (AIS), or SF6 gas-insulated (GIS)
  • Installation on base frame or on concrete basement
  • Operators’ safety during operations and maintenance, according to Leg. Decree no. 81/2008 and legislation IEC 62271-200
  • Removable breakers and current transformers
  • Protection and control relay, and customized and settable digital counters
  • Static or digital synoptics
  • Digital option to reduce wiring in order to maximize performance
  • SCADA system integration
  • Integration of the thermal control system on bars and breakers, upon request
  • Integration of internal-arc protection systems, upon request
  • Integration of fast transfer systems, frequency and load-shedding control, upon request

Staff safety is guaranteed by:

  • The entire structure and all its components, fixed and mobile, are connected to the earth system
  • It is equipped with a voltage presence indicator for the incoming cables
  • The primary components of the cubicle are all within the cubicle itself. Access to all primary components of each circuit (measuring and protection transformers, circuit-breaker) is allowed from the rear of the cubicle, if the earth switch is closed
  • Electrical and mechanical interlocks prevent operational errors, ensuring the safety of personnel
  • The state of the circuit-breaker (open or closed) can be checked by means of a mechanical indicator
  • The status of the earthing and line disconnector (open or closed) can be checked by a visual check and a mechanical indicator fixed on the drive shaft
  • Instructions for proper use, including the key number, are indicated on the front of the panel
  • In the event of an emergency or lack of auxiliary power supply, our products offer the possibility of manual operation complete with all the main components of the compartment
  • The auxiliary boxes are designed in such a way as to allow the doors to be fully opened without obstructing the passage and have a design that facilitates routine operations and allows safe and rapid leak in the event of an emergency