Ultra-rapid circuit breaker
From Electrical Installation Guide
As installed power increases, electrical distribution has to shift from a LV design to a HV design. Indeed, a high short-circuit level can be a threat to the installation and make impossible the selection of low voltage equipments (Switchboard and bus bars, circuit breaker…)
These situations could be met in the following applications:
Bus bars coupling onboard merchant vessels, off shore platform, loop networks (in industry), where the current and energy are important because of the installed power (several transformers or generators in parallel) and HV design not easy.
Two solutions could be used:
- Pyrotechnic interruption switching device
- Power circuit breaker based solution
Some power circuit breakers with additionnal feature (based on the Thomson effect technology for instance) provide an ultra
rapid opening system on very high short-circuit level. The breaking performance makes it possible to limit the
short-circuit current and prospective energy, and consequently protect the electrical installation against the electrodynamic and thermal effects of short-circuit.
Example of ultra rapid power circuit breaker: Masterpact UR
Example of limitation offered by Masterpact UR in decoupling bus bars in case of short circuit
When a short-circuit occurs downstream in the installation (A) with no tie breaker, the short-circuit level will be the total sum of all the generated power (illustrated by curve 1).
By inserting a tie breaker - Masterpact UR - to separate the sources under fault conditions, the short circuit at (A) will consist in:
- a limited short circuit coming from generator G1 and G2 interrupted by the Masterpact UR (see curve 2)
- a non limited short circuit from generators G3 and G4 (see curve 3)
The resulting short circuit level is illustrated by curve 4. 
The consequence of the strong limitation of the short circuit current and the prospective energy allows the design of a LV network instead of a MV design. This also prevents the network from being totally shutdown (black out) in case of short circuit in the main switchboard.
The following table give some example of limitation with MAsterpact UR as a tie breaker between source 1 & 2
