Siemens UL 489 Operating Instructions Manual page 116

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)
- the graphical display (ETU776)
- TD400 and the software "powerconfig"
- the COM modules with a PC with the software "powerconfig" installed
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
The trip units ETU776 and ETU745 can be set to perform long-time protection using either I
improve coordination with many types of fuses. The ETU745 can be switched between the two modes via a slide switch and the ETU776 via
a menu setting.
In this case, the setting options for the long delay time t
Setting values for t
R
ETU745 t
ETU776 t
9 – 14
 (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
 (page
29-2).
9-87), a short-circuit occurring in systems with several grading levels can be
)
R
2 4 4
t or I t. I t will yield faster tripping times and will