ABB handbook protection and control devices by ABB SACE

By ABB SACE

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3 Limitation curves A circuit-breaker in which the opening of the contacts occurs after the passage of the peak of the short-circuit current, or in which the trip occurs with the natural passage to zero, allows the system components to be subjected to high stresses, of both thermal and dynamic type. 2 “Main definitions”), which are able to start the opening operation before the short-circuit current has reached its first peak, and to quickly extinguish the arc between the contacts; the following diagram shows the shape of the waves of both the prospective short-circuit current as well as of the limited short-circuit current.

2 Curve B 10 1 1 10 1 40 125A 10 100A 80A 40A÷63A 32A 20A-25A 10 2 16A Irms [kA] Considering that the electro-dynamic stresses and the consequent mechanical stresses are closely connected to the current peak, the use of current limiting circuit-breakers allows optimum dimensioning of the components in an electrical plant. Besides, current limitation may also be used to obtain back-up protection between two circuit-breakers in series. In addition to the advantages in terms of design, the use of current-limiting circuit-breakers allows, for the cases detailed by Standard IEC 60439-1, the avoidance of short-circuit withstand verifications for switchboards.

For all the CT sizes t1=18s, except with 320 A CT (T4) and 630 A (T5) where t1=12s. 00 In prevention at 8 In T5 10-1 10-2 10-3 10-1 1 10 x In 10 Iu [kA] 1SDC210003F0004 1SDC210002F0004 10-1 10-2 10-3 10-1 1 10 102 x In Note: The dotted curve of function L corresponds to the maximum delay (t1) which can be set at 6xl1, in the case where 320 A CTs are used for T4 and 630 A for T5. For all the CT sizes t1=18s, except with 320 A CT (T4) and 630 A (T5) where t1=12s. 2 Trip curves 3 General characteristics 3 General characteristics Trip curve electronic releases Trip curve electronic releases S6 - S7 PR211/P S6 - S7 - S8 PR212/P 104 L-I Functions 0,5 0,4 103 1,5 102 0,4 1,5 4 A 2 D C 102 B 1 103 t [s] 2 D C 0,4-0,5-0,55-0,6-0,65-0,7-0,75-0,80,85-0,875-0,9-0,925-0,95-0,975-1 L-S-I Functions, S inverse short delay (I2t = constant) 0,7 0,95 0,6 0,8 1 0,9 t [s] 104 B 4 1 A 6 6 8 D C 101 8 D 10 101 12 C D C 2 3 B B A A 1 1 10 12 B 4 6 A 8 10 10-2 10-2 10-1 1 1,05 101 Note: for PR211/P-I releases, consider the curves relevant to function I only.

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