Siemens SIMOCODE pro Operating Manual page 123

External ground-fault monitoring
The external ground-fault monitoring is normally used in the following cases:
● in cases in which power systems are grounded with high impedance
● in cases, in which precise detection of the ground-fault current is necessary, for example,
for condition monitoring.
With ground-fault detection using the residual current transformer 3UL23, it is possible to
determine the precise residual current as a measured value to define freely selectable
warning and trip levels in a wide range 30 mA to 40 A.
Method of operation:
The main conductors and, if present, the neutral conductor to which the load is connected,
are routed through the opening of the residual current transformer 3UL23. Its secondary
winding is connected to the ground-fault module.
If an insulation fault occurs, for example, a residual current arises between the incoming and
the outgoing currents that the ground-fault module evaluates via the residual current
transformer.
For maximum plant availability, the ground-fault module 3UF7 510-1AA00-0 and the residual
current transformer 3UL23 were developed with the following design goals:
● High measuring accuracy: The ground-fault module in conjunction with the residual
current transformer 3UL23 achieves a measuring accuracy of ±7.5 %. This enables set
limit values to be monitored very precisely. Spurious tripping caused by measuring errors
is minimized. The combination of ground-fault module and residual current
transformer 3UL23 is designed so that a warning or alarm is triggered at the latest upon
exceeding the set limit values. To achieve this, slightly higher residual currents than those
actually measured are displayed and compared with the set limit values. The measuring
accuracy is -15 % to 0 % of the value displayed. This takes into account the measuring
accuracy of monitoring relay and residual current transformer.
● Settable prewarning and trip levels: The threshold levels for the residual current are
defined over a very wide range of 30 mA to 40 A. The response of SIMOCODE pro on
reaching a prewarning level or trip level can be freely parameterized, including a delay.
● Permanent self-monitoring: The permanent self-monitoring of the ground-fault
module 3UF7 510-1AA00-0 and the connected transformer ensures reliable monitoring of
the function. The connected 3UL23 residual current transformer is also permanently
monitored for open-circuit or short-circuit. This means cyclic manual tests to verify the
function are obsolete.
● Settable active status and delay times of the residual current protection. Depending on
the application, the monitoring function can be active permanently, only when the motor is
running, or only after the motor has started. This permits the suppression of residual
currents that are only measured during motor starting due to high starting currents. Short-
term residual currents or immitted interference can be easily suppressed by means of the
adjustable tripping delay time.
SIMOCODE pro - Parameterize
Operating Manual, 04/2017, A5E40507630002A/RS-AA/001
Parameters
4.3 Monitoring functions
123