Siemens UL 1066 Operating Instructions Manual page 95

Thermal memory can be switched On/Off
Trip units ETU745 - 776 make it possible to continue with the internally calculated reproduction of the thermal processes in downstream
switchgear and consumers even if the circuit breaker is open and the electronic system has no external supply. In this way, an effective
protection against thermal overload can also be guaranteed for frequent closing and opening processes.
The thermal memory can be activated via:
- a slide switch (ETU745, ETU748)
- the graphical display (ETU776)
- the BDA (ETU776)
- the PROFIBUS-DP (ETU776)
- the MODBUS (ETU776).
Zone selective interlocking
If the circuit breaker is combined with a ZSI module
precisely localized.
For this purpose, all circuit breakers are interconnected through their ZSI-modules.
When a short-circuit occurs, each circuit breaker affected by the short-circuit current queries its downstream circuit breaker to determine
whether the short-circuit is also present in the next downstream grading level. In the direction of the energy flow, only the circuit breaker
nearest to the short-circuit is tripped. A delay time which may have been set for the short-circuit tripping is deactivated. However, tripping
takes place after 50 milliseconds at the earliest.
Overload protection switchable to I
Trip units ETU745 and ETU776 make it possible to switch over from the I
a slide switch. This improves the selectivity of the overload protection in combination with fuses.
In this case, the setting options for the long delay time t
Setting values for t
R
ETU745 - 748 t
ETU776 t
 (page
4
t
change as follows:
R
= 1 / 2 / 3 / 4 / 5 sec. (at 6 x I
R
= 1- 5 sec. (at 6 x I )
R R
9-82), a short-circuit occurring in systems with several grading levels can be
2 4
t to an I t inverse-time function for overload protection by means of
)
R
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