PM511V08 PM511V16 3BSE011181R1 ABB Full series sales one year warranty

PM511V08 PM511V16 3BSE011181R1 ABB Full series sales one year warranty

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Energy coordination is a particular type of discrimination that exploits the currentlimiting characteristics of moulded-case circuit-breakers. It is important to

remember that a current-limiting circuit-breaker is “a circuit-breaker with a break

time short enough to prevent the short-circuit current reaching its otherwise

attainable peak value” (IEC 60947-2, def. 2.3).

In practice, ABB SACE moulded-case circuit-breakers of Isomax and Tmax

series, under short-circuit conditions, are extremely rapid (tripping times of about

some milliseconds) and therefore it is impossible to use the time-current curves

for the coordination studies.

The phenomena are mainly dynamic (and therefore proportional to the square

of the instantaneous current value) and can be described by using the specific

let-through energy curves.

In general, it is necessary to verify that the let-through energy of the circuitbreaker downstream is lower than the energy value needed to complete the

opening of the circuit-breaker upstream.

This type of discrimination is certainly more difficult to consider than the previous

ones because it depends largely on the interaction between the two devices

placed in series and demands access to data often unavailable to the end user.

Manufacturers provide tables, rules and calculation programs in which the

minimum discrimination limits are given between different combinations of circuitbreakers.

Advantages:

• fast breaking, with tripping times which reduce as the short-circuit current

increases;

• reduction of the damages caused by the fault (thermal and dynamic stresses),

of the disturbances to the power supply system, of the costs...;

• the discrimination level is no longer limited by the value of the short-time

withstand current Icw which the devices can withstand;

• large number of discrimination levels;

• possibility of coordination of different current-limiting devices (fuses, circuitbreakers,..) even if they are positioned in intermediate positions along the

chain.

Disadvantage:

• difficulty of coordination between circuit-breakers of similar sizes.

This type of coordination is used above all for secondary and final distribution

networks, with rated currents below 1600A.