Siemens 7SJ82, Manual

Page: 617 / 1638

Measured Value 3I0, Method of Measurement
The function usually evaluates the sensitively measured ground current 3I0 via a core balance current trans-
former. Since the linearity range of the sensitive measuring input ends at approx. 1.6 A, for larger secondary
ground currents, the function switches to the 3I0 current calculated from the phase currents. This results in a
very large linearity and settings range.
The method of measurement processes the sampled current values and filters out the fundamental compo-
nent numerically.
Depending on the connection type of the measuring point as well as the current terminal blocks used,
different linearity and setting ranges result. You can find more information in section
Measured Value 3I0,
Method of Measurement , Page 569 .
Y0
The fundamental-component values of V0 and 3I0 are used to calculate the admittance Y0 through the
formula Y0 = 3I0/V0. This stage uses Y0 as a condition to recognize the ground fault.
Minimum 3I0 Threshold
To start the Y0 calculation, the IN/3I0 value must exceed a minimum 3I0 threshold. For protection-class
current transformers, the threshold value is 30 mA (I
rated, sec
= 1 A) or 150 mA (I
rated, sec
= 5 A). For sensitive
current transformers, the threshold value is 1 mA (I
rated, sec
= 1 A) or 5 mA (I
rated, sec
= 5 A).
Ground-Fault Detection, Pickup
If the absolute value of the zero-sequence voltage V0 exceeds the threshold value
V0> threshold value
and Y0 exceeds the threshold value
Threshold Y0>
, the stage recognizes the ground fault. If the threshold
values remain exceeded during the
Pickup delay
, the stage picks up.
Blocking the Stage via Binary Input Signal
Blocking of the stage is possible externally or internally via the binary input signal
>Block stage
. In the
event of blocking, the picked up stage will be reset.
Blocking the Stage in Case of Measuring-Voltage Failure
The stage can be blocked if a measuring-voltage failure occurs. In the event of blocking, the picked up stage
will be reset.
The following blocking options are available for the stage:
•
From inside on pick up of the Measuring-voltage failure detection function
•
From an external source via the binary input signal
>open
of the function block Voltage-transformer
circuit breaker, which links in the tripping of the voltage-transformer circuit breaker.
The
Blk. by meas.-volt. failure
parameter can be set so that measuring-voltage failure detection
blocks the stage or does not block it.
Blocking of the Time Delay
You can use the binary input signal
>Block delay & op.
to prevent the start of the time delay and thus
also the operate indication. A running time delay is reset. The pickup is indicated and a fault record is opened.
Blocking of the Operate Indication via the Device-Internal Inrush-Current Detection Function
The
Blk. w. inrush curr. detect.
parameter allows you to define whether the operate indication of
the stage should be blocked by exceeding of the threshold values due to an inrush current. In case of a
blocking, the stage picks up. The start of the time delay and the operate indication are blocked. The function
indicates this through a corresponding indication. If the blocking drops out and the threshold value of the
stage is still exceeded, the time delay is started.
Protection and Automation Functions
6.15 Sensitive Ground-Fault Detection
SIPROTEC 5, Overcurrent Protection, Manual 617
C53000-G5040-C017-8, Edition 07.2017