Page 74 - E24 Electrical Notebook

70 - Roto-Active Breaking (Using Compact NSX)

Introduction

In order to enhance limitation and discrimination performance, Compact NSX 100 to 630A MCCB
has been developed using “revolutionary” breaking technique: “roto-active” breaking. Compact
NSX provides an exceptional limiting capacity even on high short-circuits in order to drastically
reduce stresses on intermediate distribution.

Principle Short-circuit Breaking chamber
current Ua
Fixed
contact

Arc Arc chute Piston
Magnetic U
Breaking Moving
enclosure contact U-shaped
Arc current loop
Arc chute
Fixed
contact

Arc chute

Roto-active breaking: repulsion of contacts Roto-active breaking: tripping
by pressure

This high current limiting technique uses a new tripping energy, pressure, resulting from arc energy. Its operation is described below:
• Each circuit-breaker pole is housed within a “Breaking Unit” in which a rotating contact generates, by electromagnetic repulsion, two serial arcs on

occurrence of the short-circuit current
• A piston & spring device uses the pressure from arc energy to cause – beyond a certain threshold (roughly 25 ln) – reflex tripping, roughly 3ms after

contact repulsion
• Up to this threshold pressure is not sufficient to cause tripping & arc impedance limits the short-circuit current
• Beyond this threshold breaking is very quick (1ms) & limits still further the short-circuit current

The “Breaking Units” are sized to match circuit-breaker size. Consequently, limitation is greatest when rating is smallest. This technique provides Compact
NSX with an outstanding limiting capacity and thus with increased discrimination possibilities. This technique is also very useful for limiting stresses on
electrical power distribution.

Customer Benefits

Thanks to the use of breaking gas pressure speeding up tripping and implementation of energy discrimination, the Compact NSX circuit breaker ensures:
• Natural discrimination as standard, that is to say require no special trip units

Thanks to rotary breaking, the Compact NSX circuit breakers are ultra-quick and limiting. Cascading performance is thus excellent:
• With roto-active COMPACT NSX MCCB ensures Total Discrimination up to full breaking capacity of the device
• Continuity of the supply is optimum
• High breaking capacity: 150kA / 2ms
• Reflex tripping ensures that stresses on system are reduced to the minimal

Why not attend our CPD approved sessions on Cascading & Discrimination by contacting sam.sylvester@schneider-electric.com

Schneider Electric Ltd Customer Support Centre
Stafford Park 5 Tel : 0870 608 8 608
Telford Fax : 0870 608 8 606
Shropshire
TF3 3BL Website : www.schneider-electric.com/uk