Page 12 - Sace Emax 2 Manual for design engineers

ABB | SACE Emax 2
3 - Selectivity between ABB SACE circuit-breakers

Foreword It is possible to obtain selectivity between ABB SACE circuit-breakers (including Emax 2).
There is selectivity in an installation when, in the event of an overload or short-circuit, it is possible to identify
and isolate the point of overload or fault by opening only some circuit-breakers to guarantee service continuity
to the installation.

NOTE: selectivity is recommended in all installations with multiple switchgears or circuit-
breakers connected, for example cascading or in a tree (with a main circuit-breaker on
the supply side, and other circuit-breakers downstream to protect areas on the other side).
Thus, only the circuit-breaker immediately upstream the overload or fault trips, and avoids
opening of the circuit-breakers further upstream.

Types of selectivity With ABB SACE electronic trip units selectivity can be:
• Current-based selectivity, activated in the event of over-current, and in which the protections of the
trip units are set with different current thresholds, based on the principle the closer the fault point is to the
power supply the greater the current will be.
• Time selectivity, activated in the event of a short-circuit in which the S protection normally trips, and in
which the protections of the trip units are set with different tripping times, so that with cascading circuit-
breakers the circuit-breakers further downstream open before those further upstream.
• Time-current selectivity, which is a combination of the previously mentioned types, and in which the
protections of the trip units are set so that the tripping times and current thresholds increase with proximity
to the power supply.
• Energy selectivity, which uses current-limiting circuit-breakers, characterized by extremely short tripping
times in the event of a short-circuit to avoid the current reaching the peak value (in the case of ABB SACE
circuit-breakers, for example, all the moulded-case circuit-breakers of the Tmax series and certain air
circuit-breakers of the Emax series are limiters).
• Zone Selectivity, which is an evolution of time selectivity, and in which is a dialog created between the
trip units by means of output and input blocking signals. For more information on Zone Selectivity with ABB
SACE circuit-breakers and in particular Emax 2, see the chapter “1 - Zone Selectivity" starting on page 135.

Further documents For each type of selectivity, the protections must be set so that only those circuit-breakers capable of isolating
the overload or fault open, without the rest of the installation being de-energized. Relevant definitions, operating
principles, areas of application, advantages and disadvantages, requirements, indications for setting the
protections and examples are provided in the Technical Application Paper QT1 1SDC007100G0205 "Low
voltage selectivity with ABB circuit-breakers".

10 | © 2020 ABB | 1SDH001330R1002 - ECN000134959 - Rev. A Circuit-breakers E1.2-E2.2-E4.2-E6.2 | 3 - Selectivity between ABB SACE circuit-breakers