ABB VD4 Medium Voltage Vacuum Circuit Breakers Quenching Principle for Arc Extinguishing Chambers

ABB Arc Extinguishing Principle for Arc Extinguishing Chambers

In a vacuum arc extinguishing chamber, the arc starts at the moment of contact separation and is maintained until zero current is applied and may be affected by magnetic fields.

Vacuum Arc - Diffuse or contracted after contact separation, a single melting point is formed over the entire surface of the cathode, generating the metal vapour that supports the arc.

A diffuse vacuum arc is characterised by expansion of the contact surfaces and uniform distribution of thermal stresses across the contact surfaces.

At the rated current of the vacuum interrupter, the arc is always diffuse. Contact erosion is very limited and the number of current interruptions is very high.

As the value of the interrupting current increases (above the rated value), the arc changes from a diffuse to a contracting type due to the Hall effect.

Starting at the anode, the arc contracts and gradually becomes defined with further increases in current.

In the vicinity of the area in question, the temperature rises, which causes thermal stress on the contacts.

To prevent overheating and erosion of the contacts, the arc needs to remain rotating. As the arc rotates, it becomes similar to a moving conductor through which current passes.

Spiral geometry of ABB vacuum interrupter contacts

The special geometry of the helical contact generates a radial magnetic field in all areas of the arc column and concentrates it around the circumference of the contact.

Spontaneously generated electromagnetic forces acting in a tangential direction cause the arc to rotate rapidly around the contact axis.

This means that the arc is forced to rotate and involves a wider surface than a fixed contracting arc.

All this makes contact erosion negligible, except for minimising thermal stresses on the contacts.

Most importantly, the arc extinguishing process can be controlled even in the case of extremely high short circuits.

ABB vacuum interrupters are zero-current interrupters, which do not produce any re-strikes.

At zero current, the current charge is rapidly reduced and the metal vapour condenses, thus restoring the maximum dielectric strength between the interrupter contacts in microseconds.

VD4 circuit breakers have passed the following tests to ensure the safety and reliability of the equipment when used in any installation environment.

- Type tests: heating, industrial frequency withstand voltage insulation, lightning impulse withstand voltage insulation, short-time and peak withstand voltage current,

Mechanical life, short-circuit current generation and breaking capacity, no-load cable disconnection.

- Individual tests: main circuit insulation at working frequency voltage, insulation of auxiliary circuits and operating mechanisms, main circuit resistance measurement, mechanical and electrical operation.

Service safety

With a full range of mechanical and electrical locks (available on request), it is possible to build safe distribution switchgear with VD4 circuit breakers.

Locking devices have been studied to prevent incorrect operation and to check the device while maximising operator safety.

Keyed locking or padlocking devices enable switching and/or racking-in and racking-out operations.

Racking out with door closed devices allow the circuit breaker to be racked in or out of the switchgear only when the door is closed.

Anti-breaking locks prevent breaking in of circuit breakers with different current ratings, as well as breaking in operations when the breaker is closed.

ACCESSORIES

VD4 circuit breakers are available with a comprehensive range of accessories to meet all installation requirements.

The operating mechanism has a standardised range of accessories and spare parts which are easy to identify and order.

The accessories can be easily fitted from the front of the circuit breaker. Electrical connections are made using plug and socket connectors.

The equipment is simple to use, maintain and service with limited resource requirements.

Operating Mechanism

The operating mechanism of the VD4 circuit breaker is designed to be simple and easy to use, with a wide range of customised accessories for quick and easy installation.

This simplicity gives the equipment a higher degree of reliability.

The operating mechanism is of the energy storage type and is fitted as standard with an anti-pumping device with appropriate locks to prevent incorrect operation.

Each operating sequence can only be activated if all the conditions to ensure its correct execution are met.

All types of VD4 circuit breakers have the same accessories.

- Highly reliable operating mechanism thanks to low component count due to mass-produced system

- Extremely easy to maintain

- The accessories are common to the entire series and are the same for both AC and DC applications

- Quick and easy installation or replacement of electrical accessories, as the cables are already equipped with plug and socket connectors

- Mechanical anti-pumping device as standard

- Built-in closing spring-loaded charging lever

- Protective cover for the opening and closing buttons that can be operated with special tools

- Padlock device on the operating buttons