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Ultra-rapid circuit breaker

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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. H58Example 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. H59Diagram 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. H60Diagram of the network with Masterpact UR added as tie breaker

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

Fig. H61Resulting 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

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

Fig. H62Example of limitation by Masterpact UR for 690 V - 60 Hz network.

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