Ground Fault Protection In The Case Of The 3Rb31 - Siemens SIRIUS 3RU2 Manual

5.2

Ground fault protection in the case of the 3RB31

Introduction
In addition to the current-dependent protection of loads against impermissibly high
temperature rise resulting from overload, 3RB31 solid-state overload relays offer ground-
fault protection.
Ground-fault protection
A ground fault can arise as a result of insulation damage or ingress of moisture or
condensate. This results in displacement of the neutral point voltage of the power network,
and in an unbalance. The neutral point voltage is simulated virtually in the device and when
a neutral point displacement voltage arises, the overload relay switches the contactor off
instantaneously. This prevents thermal follow-on damage and a resulting, and significantly
more critical, double ground fault.
Note
Contactor assembly for star-delta (wye-delta) start
Internal ground-fault detection is not possible with contactor assemblies star-delta (wye-
delta) start.
Table 5- 3
Type of ground-fault detection
Internal ground-fault detection
Reference
More information ...
about ground-fault protection of the solid-state
overload relays in conjunction with star-delta
(wye-delta) assemblies
SIRIUS Innovations - SIRIUS 3RU2 thermal overload relays / SIRIUS 3RB3 solid-state overload relays
Manual, 09/2014, A5E03656507420A/RS-AA/002
Ground-fault detection
Application
For motors with three-wire connection for the detection of fault
currents ≥ 75 % of the current setting I
5.2 Ground fault protection in the case of the 3RB31
can be found in the Chapter ...
Contactor assembly for star-delta (wye-delta)
start (Page 53)
Functions
in operation
e
43