Page 141 - SACE Tmax XT - Catalogue

SOLUTIONS 6/7

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Adaptive Protections

The Tmax XT adds a dual setting capability to the
switching device to ensure continuous coordination

Purpose Application example
User’s plants can work as an LV Microgrid thanks A plant is connected to the MV utility by means of
to the energy produced by renewable and local an MV/LV transformer. If the utility shuts down,
power sources, in particular as a consequence of the plant will become a microgrid supplied by a
the lack of a utility power supply, e.g. due to a local generator G, which will feed priority loads by
fault on the MV voltage side. In order to still guar- using the load shedding feature of the Tmax XT.
antee a high level of selectivity and continuity of In a grid-connected condition, the generator G is
service, it is important to take into account the disconnected. With reference to Fig. 1:
variation of the short-circuit power when moving • Circuit-breaker A is closed
from on-grid to off-grid operation. • Circuit-breaker B is open
Indeed, during grid connected conditions the • Circuit-breakers at position C are closed. The
fault current on a microgrid feeder is also sup- protection of the circuit-breaker at C that sup-
plied by the utility, thus resulting higher than the plies the feeders at D are adjusted using "Set A"
one supplied only by local generation during is- of the Tmax XT unit.
landed conditions. As a result, it is desirable that • Circuit-breakers at position D are closed
several protection thresholds of the units can be • Circuit-breaker E is closed
automatically changed during the transition to is- • Switch-disconnector QS1 is closed
landing conditions. • All loads are supplied.
The circuit-breakers at position C are selectively 06
coordinated with the upstream main cir-
cuit-breaker A, supplied by the utility, and the
downstream load circuit-breakers at position D
(see Fig. 2 at the following page).
U

G

A B

E C C C

non priority loads
QS1

D D D

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Fig. 1