Siemens SICAM Manual page 48

Device Functions
4.1 Description
[dw_sfcm-pulse_pattern-overcomp, 1, en_US]
Figure 4-16
For the faulty feeder, the ground-current pulse pattern is as follows:
•
When the clocking pulse is on, the capacitor is switched on, the ground current in the faulty feeder is
reduced, and the corresponding current pulse pattern is off.
•
When the clocking pulse is off, the capacitor is switched off, the ground current in the faulty feeder is
increased, and the current pulse pattern is on.
Table 4-10
Clocking Pulse
On
Off
With the Pulse-on duration and Pulse-off duration parameters, you can define the switch-on and
switch-off duration of the capacitor. These values must be set according to the operation of the clocking
device that determines the switch-on and switch-off duration of the capacitor. If you set these 2 parameters to
the same value or to similar values, there is a risk of failure. This is the case because the stage cannot distin-
guish the healthy and faulty feeders by only evaluating the ground current during a high-impedance ground
fault.
Number of Pulses for Operate (PulseTh Op.) is defined as the number of pulses to be detected
within the pulse monitoring time.
Number of Pulses for Monitoring (PulseTh Mon.) is defined as the number of pulses to be
considered for calculating the pulse monitoring time.
The pulse monitoring time is calculated via the following formula:
Pulse monitoring time = Number of Pulses for Monitoring (PulseTh Mon.) ⋅ (TPulse ON +
TPulse OFF)
If the measured Pulse-on duration and Pulse-off duration is equal to the configured TPulse ON
and TPulse OFF, then a valid pulse is detected. If the number of detected pulses within the pulse monitoring
time reaches the setting of the Number of Pulses for Operate (PulseTh Op.), then the ground
fault is detected.
48
Ground-Current Pulse Pattern in an Overcompensated System
Current Pulse Pattern in a Faulty Feeder
Capacitor Ground Current in the
Faulty Feeder
On Reduced
Off Increased
Current Pulse Pattern of the Faulty
Feeder
Off
On
SICAM, Feeder Condition Monitor, Manual
E50417-H8940-C580-A4, Edition 03.2019