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.