Functions
2.11 Measures for Weak and Zero Infeed
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
277
2.11.2.2 Setting Notes
General
It is a prerequisite for the operation of the weak infeed function that this function is enabled during the config-
uration of the device at address 125 Weak Infeed = Enabled.
With the parameter FCT Weak Infeed (address 2501), it is determined whether the device shall trip during
a weak infeed condition or not. With the settings ECHO and TRIP and Echo &Trip(I=0), both the echo
function and the weak infeed tripping function are activated. With the setting ECHO only, the echo function for
provision of the release signal at the infeeding line end is activated. There is, however, no tripping at the line
end with missing or weak infeed condition. As the weak-infeed measures are dependent on the signal reception
from the opposite line end, they only make sense if the protection is coordinated with teleprotection (refer to
Section 2.7 and/or 2.9).
The receive signal is a functional component of the trip condition. Accordingly, the weak infeed tripping function
must not be used with the blocking schemes. It is only permissible with the permissive schemes and the
comparison schemes with release signals! In all other cases it should be switched OFF at address 2501. In
such cases it is better to disable this function from the onset by setting address 125 to Disabled during the
device configuration. The associated parameters are then not accessible.
The undervoltage setting value UNDERVOLTAGE (address 2505) must in any event be set below the minimum
expected operational phase-earth voltage. The lower limit for this setting is given by the maximum expected
voltage drop at the relay location on the weak-infeed side during a short-circuit on the protected feeder for
which the distance protection may no longer pick up.
Echo function
For line ends with weak infeed, it is useful to set the echo function in conjunction with the release schemes, so
that the feeding line end is released as well. The parameters for weak infeed are listed in Section 2.11.3.2. The
echo function can be enabled (ECHO only) or disabled (OFF) under address 2501 FCT Weak Infeed. By
means of this „switch“, the weak infeed tripping function can also be activated (ECHO and TRIPand Echo
&Trip(I=0)).
If no circuit breaker auxiliary contacts are routed and if no current flows over the line, a tripping during weak
infeed is only possible with the setting Echo &Trip(I=0). With this setting, the function is not blocked by
checking the residual current. If the circuit breaker auxiliary contacts are routed, a tripping during weak infeed
is further blocked if the auxiliary contacts signal that the circuit breaker is opened.
Tripping during weak infeed via ECHO and TRIP is only possible if either the circuit breaker auxiliary contacts
signal that the circuit breaker is closed or current flows in the corresponding phase which exceeds the preset
residual current (address 1130 PoleOpenCurrent).
Please do not fail to observe the notes on the setting of the distance protection stages at margin heading „Dis-
tance Protection Prerequisites“ in Section 2.7, and the notes on earth fault protection regarding the setting of
the earth current stage 3IoMin Teleprot at margin heading „Earth Fault Protection Prerequisites“ in Section
2.9.
The echo delay time Trip/Echo DELAY (address 2502) must be set long enough to avoid incorrect echo
signals resulting from the difference in fault detection pick-up time of the distance protection functions or the
earth fault protection function at all line ends during external faults (through-fault current). Typical setting is
approx. 40ms (presetting). This parameter can only be altered with DIGSI under Additional Settings.
The echo pulse duration Trip EXTENSION (address 2503) can be adjusted to the configuration data of the
signal transmission equipment. It must be long enough to ensure that the receive signal is recognized even
with different pickup times by the protection devices at the line ends and different response times of the trans-
mission equipment. 50 ms (default) is usually sufficient. This setting can only be made in DIGSI under Display
Additional Settings.
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