Ultra-rapid circuit breaker

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 additional feature (based on the Thomson effect technology for instance) provide an ultra rapid opening system on very high short circuit level (see Fig. H58). The breaking performance makes it possible to limit the prospective short-circuit current and energy, and consequently protect the electrical installation against the electrodynamic and thermal effects of short-circuit.

Fig. H58 – Example of ultra rapid power circuit breaker: Masterpact UR (Schneider Electric)

Example of limitation offered by Masterpact UR in decoupling bus bars in case of short circuit

(see Fig. H59).

When a short-circuit occurs downstream in the installation (A) with no tie breaker, the short-circuit level will be the result of the total generated power (illustrated by curve 1).

Fig. H59 – Diagram of the network

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)

Fig. H60 – Diagram of the network with Masterpact UR added as tie breaker

The resulting short circuit current is illustrated by curve 4 (see Fig. H61):

Fig. H61 – Resulting short-circuit current

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

Fig. H62 – Example of limitation by Masterpact UR for 690 V - 60 Hz network.

Source 2	Source 1
	50		55		60		65		70		75		80		85		90		95		100		110
50	169	207	183	229	193	240	203	251	213	262	224	273	234	284	244	295	254	306	264	317	274	327	295	349
55	176	229	189	240	199	251	210	262	220	273	230	284	240	295	250	306	260	317	270	327	281	338	301	360
60	178	240	191	251	201	262	211	273	220	284	230	295	240	306	249	317	259	327	269	338	278	349	298	371
65	181	251	194	262	204	273	214	284	223	295	233	306	242	317	252	327	262	338	272	349	281	360	301	382
70	185	262	198	273	207	284	217	295	226	306	236	317	246	327	255	338	265	349	275	360	284	371	304	393
75	189	273	201	284	211	295	220	306	230	317	240	327	249	338	259	349	268	360	278	371	288	382	307	404
80	192	284	205	295	214	306	224	317	233	327	243	338	252	349	262	360	272	371	281	382	291	393	310	415
85	196	295	208	306	218	317	227	327	237	338	246	349	256	360	265	371	275	382	284	393	294	404	313	426
90	199	306	212	317	221	327	231	338	240	349	249	360	259	371	268	382	278	393	288	404	297	415	316	437
95	204	317	216	327	225	338	235	349	244	360	253	371	263	382	272	393	282	404	291	415	301	426	320	448
100	209	327	221	338	230	349	239	360	249	371	258	382	268	393	277	404	287	415	296	426	306	437	325	458
110	218	349	230	360	239	371	248	382	258	393	267	404	276	415	286	426	295	437	305	448	314	458	333	480

	limited short-circuit current with Masterpact UR
	non limited short-circuit current