Siemens UL 1066, Operating Instructions Manual

Page: 94 / 334

9 – 14
Neutral conductor protection – N-tripping
Trip units ETU745 - 776 also make it possible to protect the neutral conductor against overload. This requires a current transformer for the
neutral conductor, which can be retrofitted if necessary.

(page 9-91)
For tripping, the same long-time delay t
R
applies as for overload tripping.
9.1.6.2 Additional functions
Load monitoring (load restore / load shedding)
Trip units ETU745 - ETU776 offer the possibility of additional load monitoring. Two current values, "load shedding" and "load restore", as
well as a delay time t
x
, can be set.
If the setting value "load restore" is undershot, and the lower limit value for current transmission is exceeded at the same time, a signal is
output by the
Cublicle BUS
after the set delay time t
x
has elapsed. If the setting value "load shedding" is exceeded, a signal is output by the
Cublicle BUS
after the set delay time t
x
has elapsed. These signals can be used to connect or disconnect loads, thereby preventing an over-
load tripping of incoming circuit breakers.
Load monitoring can be adjusted via:
- the alphanumeric display (ETU745 - 748)
- the graphical display (ETU776)
- the BDA
- the PROFIBUS-DP
- the MODBUS.
Leading signal for L-tripping
Trip units ETU745 - 776 provide a leading signal for "L-tripping", which is transmitted via the
Cublicle BUS
100 milliseconds before overload
tripping. In this way it is possible e.g. to disconnect thyristor controllers.
Phase failure protection
Trip units ETU776, the phase failure protection can also be activated when the motor protection is not activated.
If the phase failure protection is activated and the operating current of the lowest loaded phase is 50% lower than the operating current of
the highest loaded phase, the setting value I
R
is automatically reduced to 80%. If the values of the three phase currents differ by less than
50%, the setting I
R
applies again.
Setting values for I
N
ETU745 - 748 I
N
= (0.5 / 1.0) × I
n
; OFF
ETU776 I
N
= (0.2 - 2.0) × I
n
; OFF
NOTICE
Neutral Conductor Overheating.
Neutral conductor or insulation may be damaged.
Settings I
N
> 1 x I
n
should only be used if the neutral conductor has been properly sized.
Setting values for load monitoring
"Load shedding" and "load restore" 40 A - 1.5 x I
n
Delay time
t
x
= 1 - 15 sec.