Appendix A

TeSys GV6PB devices incorporate the exclusive reflex-tripping system.

This system breaks very high fault currents.

The device is mechanically tripped via a “piston” actuated directly by the short-circuit.

For high short-circuits, this system provides a faster break, thereby ensuring discrimination

Reflex-tripping curves are exclusively a function of the device rating.

The limiting capacity of a device is its aptitude to let through a current, during a short-circuit, that is less than the prospective short-circuit current.

The exceptional limiting capacity of TeSys GV5PB / GV6PB devices is due to the rotating double-break technique (very rapid natural repulsion of contacts and the appearance of two arc voltages in-series with a very steep wave front). GV5/GV6 devices reduce current limit, but are not listed as current limiting devices.

The moving contact has the shape of an elongated “S” and rotates around a floating axis. The shape of the fixed and moving contacts is such that the repelling forces appear as soon as the circuit reaches approximately 15 times In.

Due to the rotating movement, repulsion is rapid and the device greatly limits short-circuit currents, whatever the interrupting level of the unit. The short-circuit current is extinguished before it can fully develop. Lower let-through currents provide less peak energy, reducing the required bus bar bracing, lowering enclosure pressure, and delivering improved series or combination ratings.

Current-limiting devices greatly reduce the negative effects of short-circuits on installations.

• Thermal effects: Reduced temperature rise in conductors, therefore longer service life for cables.

• Mechanical effects: Reduces electrodynamic forces, therefore less risk of electrical contacts, or busbar being deformed or broken.

• Electromagnetic effects: Reduction in disturbances for measuring devices located near electric circuits.

Cascading is a technique directly derived from current limiting.

Devices with breaking capacities less than the prospective short-circuit current may be installed downstream of a limiting device.

The breaking capacity is reinforced by the limiting capacity of the upstream device.

It follows that substantial savings can be made on downstream equipment and enclosures.

The limiting capacity of a device is expressed by two curves which are a function of the prospective short-circuit current (the current which would flow if no protection devices were installed):

• The actual peak current (limited current)

• Thermal stress (A?s), that is, the energy dissipated by the short-circuit in a condition with a resistance of 1 Ω.

The following figures show TeSys GV5PB / GV6PB current-limiting curves.

The following figures show TeSys GV5PB / GV6PB energy-limiting curves.