Siemens UL 489, Operating Instructions Manual, Page: 117 / 352

9 – 15
Short-time delayed short-circuit protection switchable to I
2
t
Trip units ETU745 - 776 make it possible to switch over from a constant delay time to an I
2
t-characteristic. In this way, the delay time
depends on the short-circuit current, but with a constant I
2
t
sd
-value, providing better coordination with downstream fuses.
In this case, the setting options for the short-time delay t
R
are as follows:
Switchover to the I
2
t
sd
characteristic can be made via:
- the t
sd
rotary coding switch (ETU745); this must be set to a value in the white area.

.
- the graphical display (ETU776)
- TD400 and the software "powerconfig"
- the COM modules with a PC with the software “powerconfig” installed

(page 29-2) .
Changeable parameter sets
The trip unit ETU776 contains two complete sets of protective parameters and can be switched between them locally or remotely.

This enables lowering instantaneous and short-time settings for arc flash mitigation as well as changing parameters when the source

of supply changes between utility and generator.
Switching between parameter sets can be made manually via:
- the graphical display (ETU776)
or remotely via:
- the
Cublicle BUS
with an input signal at the digital input module.
- the PROFIBUS DP
- the PROFINET IO, Modbus TCP and Modbus RTU.
Settings for t
sd
ETU745 t
sd
= 0.1 / 0.2 / 0.3 / 0.4 sec. (at 12 x I
n
)
ETU776 t
sd
= 0.1 - 0.4 sec. (at 12 x I
n
)