ABB The VD4 medium voltage circuit-breakers

ABB The VD4 medium voltage circuit-breakers

General

The new VD4 are a synthesis of the renowned technology in designing and constructing vacuum  interrupters embedded in resin poles, and of  excellency in design, engineering and production of  circuit-breakers. The VD4 medium voltage circuit-breakers use vacuum  interrupters embedded in resin poles. Embedding the interrupter in resin makes the circuitbreaker poles particularly sturdy and protects the  interrupter against shocks, accumulation of dust and  humidity. The vacuum interrupter houses the contacts and  makes up the interrupting chamber.

Current interruption in vacuum

The vacuum circuit-breaker does not require an  interrupting and insulating medium. In fact, the  interrupters do not contain ionizable material. In any  case, on separation of the contacts an electric arc is  generated made up exclusively of melted and  vaporized contact material.The electric arc remains supported by the external  energy until the current is cancelled in the vicinity of  natural zero. At that instant, the rapid reduction in the  load density carried and the rapid condensation of the  metallic vapour, leads to extremely rapid recovery of  the dielectric characteristics. The vacuum interrupter  therefore recovers the insulating capacity and the  capacity to withstand the transient recovery voltage, definitively extinguishing the arc. Since high dielectric strength can be reached in the  vacuum, even with minimum distances, interruption  of the circuit is also guaranteed when separation of  the contacts takes place a few milliseconds before  passage of the current through natural zero.

EL type operating mechanism

The low speed of the contacts, together with the  reduced run and low mass, limit the energy required  for the operation and therefore guarantee extremely  limited wear of the system. The circuit breaker  therefore only requires limited maintenance. The VD4 circuit-breakers use a mechanical operating  mechanism, with stored energy and free trip. These  characteristics allow opening and closing operations  independent of the operator. The operating mechanism is of simple conception and  use and can be customised with a wide range of  accessories which are easy and rapid to install. This  simplicity converts into greater reliability of the  apparatus.

FEATURES

• Vacuum interruption technique 

• Vacuum contacts protected against oxidation and   contamination 

• Vacuum interrupter embedded in the resin poles 

• Interrupter protected against shocks, dust and   humidity 

• Sealed-for-life poles 

• Operation under different climatic conditions 

• Limited switching energy 

• Stored energy operating mechanism with anti-  pumping device supplied as standard 

• Simple customisation with a complete range of   accessories 

• Fixed and withdrawable version 

• Compact dimensions 

• Sturdiness and reliability 

• Limited maintenance 

• Circuit-breaker racking in and racking out with door   closed 

• Incorrect and hazardous operations are prevented   thanks to special locks in the operating mechanism   and in the truck 

• High environmental compatibility

Quenching principle of ABB interrupters

In a vacuum interrupter, the electric arc starts at the  moment of contact separation and is maintained until  zero current and can be influenced by magnetic fields. Vacuum arc - diffuse or contracted following contact  separation, single melting points form over the entire  surface of the cathode, producing metal vapours  which support the arc. The diffuse vacuum arc is characterised by expansion  over the contact surface and by an even distribution  of thermal stress on the contact surfaces. At the rated current of the vacuum interrupter, the  electric arc is always of the diffuse type. Contact  erosion is very limited and the number of current  interruptions very high. As the interrupted current value increases (above the  rated value), the electric arc tends to be transformed  from the diffuse into the contracted type, due to the  Hall effect.

The spiral geometry of ABB vacuum interrupter  contacts

The special geometry of the spiral contacts generates  a radial magnetic field in all areas of the arc column,  concentrated over the contact circumferences. An electromagnetic force is self-generated and this  acts tangentially, causing rapid arc rotation around  the contact axis. This means the arc is forced to rotate and to involve a  wider surface than that of a fixed contracted arc. Apart from minimising thermal stress on the contacts,  all this makes contact erosion negligible and, above  all, allows the interruption process to be controlled  even with very high short-circuits.

FUNCTIONS

• Highly reliable operating mechanisms thanks to a   low number of components which are manufactured   using production systems for large quantities 

• Extremely limited and simple maintenance 

• The accessories are common to the whole range and   are identical for either a.c. or d.c. applications 

• The electrical accessories can be installed or   replaced easily and rapidly thanks to the cabling   which is already prepared with its own plugsocket   connectors 

• Mechanical anti-pumping device is supplied as   standard 

• Built-in closing spring charging lever 

• Protective covering over the opening and closing   pushbuttons to be operated using a special tool 

• Padlock device on the operating pushbuttons