PFTL101B-5.0KN/20KN 3BSE004203R1 ABB Supply of spare parts for tension controller system

PFTL101B-5.0KN/20KN 3BSE004203R1 ABB Supply of spare parts for tension controller system

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Considering a circuit-breaker type E1B1250 fitted with a PR111/P LSI release

and with TA of 1000 A, it is supposed that for the system requirements, the

protection functions are regulated according to the following settings:

The trip curve of the release is represented in the following figure (continuous

lines): it can be seen that:

• for function L, the curve is represented by the mean value between the

tolerances given by the Standard (the overload protection function must not

trip for current values lower than 1.05·ln, and must trip within 1.3·ln), therefore

corresponding to 1.175·ln (around 700 A);

• graphically, point 1 is obtained at the intersection of the vertical part of function

L and the horizontal segment (C0.4In-C1In) which connects the points relevant

to the same t1, taken from the curves with setting 0.4·ln and 1·ln;

• corresponding to point 2 (4000 A), the function S takes the place of function

L, as the trip time of function S is lower than the trip time of function L;

• in the same way as for point 2, for point 3 (8000 A) and beyond, function S is

substituted by function I.

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. To reduce these stresses,

current-limiting circuit-breakers have been designed (see Chapter 2.2 “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.