ABB handbook protection and control devices by ABB SACE


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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.

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.

1 of the Standard “Circuits of ASSEMBLIES which are exempted from the verification of the short-circuit withstand strength” states that: 1 1 10 102 103 Irms [kA] “A verification of the short-circuit withstand strength is not required in the following cases. … For ASSEMBLIES protected by current-limiting devices having a cut-off current not exceeding 17 kA at the maximum allowable prospective short-circuit current at the terminals of the incoming circuit of the ASSEMBLY. ” The example above is included among those considered by the Standard: if the circuit-breaker was used as a main breaker in a switchboard to be installed in a point of the plant where the prospective short-circuit current is 40 kA, it would not be necessary to carry out the verification of short-circuit withstand.

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