PM150V08 3BSE009598R1 ABB Industrial control automation controller in stock

PM150V08 3BSE009598R1 ABB Industrial control automation controller in stock

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 it enables the use of current-limiting circuit-breakers only at levels hierarchically

lower down the chain; the other circuit-breakers have to be capable of

withstanding the thermal and electro-dynamic stresses related to the passage

of the fault current for the intentional time delay. Selective circuit-breakers,

often air type, have to be used for the various levels to guarantee a sufficiently

high short-time withstand current;

• the duration of the disturbance induced by the short-circuit current on the

power supply voltages in the zones unaffected by the fault can cause problems

with electronic and electro-mechanical devices (voltage below the

electromagnetic releasing value);

• the number of discrimination levels is limited by the maximum time that the

network can stand without loss of stability.

The following example shows a typical application of time discrimination obtained

by setting differently the tripping times of the different protection devices.

his type of coordination is implemented by means of a dialogue between

current measuring devices that, when they ascertain that a setting threshold

has been exceeded, give the correct identification and disconnection only of

the zone affected by the fault.

It is available with the circuit-breakers of Emax series only.

In practice, it can be implemented in two ways:

• the releases send information on the preset current threshold that has been

exceeded to the supervisor system and the latter decides which protective

device has to trip;

• in the event of current values exceeding its setting threshold, each protective

device sends a blocking signal via a direct connection or bus to the protective

device higher in the hierarchy (i.e. upstream with respect to the direction of

the power flow) and, before it trips, it makes sure that a similar blocking signal

has not arrived from the protective device downstream; in this way, only the

protective device immediately upstream of the fault trips.