Ground-Fault Protection In The Case Of 3Rb21 / 3Rb31 - Siemens SIRIUS 3RU Manual

Functions

5.2 Ground-fault protection in the case of 3RB21 / 3RB31

5.2 Ground-fault protection in the case of 3RB21 / 3RB31
Introduction
In addition to the current-dependent protection of loads against impermissibly high
temperature rise resulting from overload, 3RB21 / 3RB31 electronic 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 electronic
overload relays in conjunction with star-delta
(wye-delta) assemblies
54
Ground-fault detection
SIRIUS 3RU thermal overload relays / SIRIUS 3RB electronic overload relays
Application
For motors with three-wire connection for the
detection of fault currents ≥ 75 % of the current
setting I in operation
e
can be found in the Chapter ...
Contactor assembly for star-delta (wye-delta) start
(Page 63)
Manual, 09/2016, A5E03656507420A/RS-AB/003