Dynamic Cold Load Pickup Function; Inrush Restraint; Determination Of Direction - Siemens SIPROTEC 4 Manual

Functions
2.3 Directional Overcurrent Protection 67, 67N

Dynamic Cold Load Pickup Function

2.3.6
It may be necessary to dynamically increase the pickup values of the directional time overcurrent protection if,
at starting, certain elements of the system show an increased power consumption after a long period of zero
voltage (e.g. air-conditioning systems, heating installations, motors). Thus, a general raise of pickup thresh-
olds can be avoided taking into consideration such starting conditions.
This dynamic pickup value changeover is common to all overcurrent elements and is described in Section
2.4 Dynamic Cold Load
directional and non-directional time overcurrent protection.
2.3.7

Inrush Restraint

7SJ80 features an integrated inrush restraint function. It prevents "normal" pickup of the 67-1 or 67-TOC
elements (not 67-2 and 67-3) in the phases and in the ground path of the non-directional and directional
overcurrent protection functions. The same is true for the alternative pickup thresholds of the dynamic cold
load pickup function. If inrush currents are detected, special inrush pickup signals are generated. These signals
also initiate fault recording and start the associated trip delay time. If inrush conditions are still present after
the tripping time delay has elapsed, a corresponding message ("....TimeOut ") is output, but tripping is
blocked (for further information see "Inrush Restraint" in Section
51N).
2.3.8

Determination of Direction

The determination of the fault direction for the phase directional element and the ground directional element
is performed independently.
Basically, the direction determination is performed by determining the phase angle between the fault current
and a reference voltage.
Method of Directional Measurement
For the phase directional element the fault current of the corresponding phase and the unfaulted phase-
tophase voltage are used as reference voltage. The unfaulted voltage also allows for a correct direction deter-
mination even if the fault voltage has collapsed entirely (short-line fault). In phase-to-ground voltage connec-
tions, the phase-to-phase voltages are calculated. In a connection of two phase-to-phase voltages and V
third phase-to-phase voltage is also calculated.
With three-phase short-line faults, memory voltage values are used to clearly determine the direction if the
measurement voltages are not sufficient.Upon the expiration of the storage time period (2 s), the detected
direction is saved, as long as no sufficient measuring voltage is available. When closing onto a fault, if no
memory voltage values exist in the buffer, the relay element will trip. In all other cases the voltage magnitude
will be sufficient for determining the direction.
For each directional ground element there are two possibilities of direction determination.
Direction Determination with Zero-sequence System or Ground Quantities
For the directional ground fault elements, the direction can be determined from the zero-sequence system
quantities. In the current path, the Ι
device. Otherwise, the device calculates the ground current from the sum of the three phase currents. In the
voltage path, the displacement voltage V
calculates as reference voltage the zero-sequence voltage 3 · V
the magnitude of V
directional ground element will not initiate a trip signal. The directional ground element cannot be applied
when only two current transformers are used.
90
Pickup. The alternative pickup values can be set individually for each element of the
current is valid, when the transformer neutral current is connected to the
N
is used as reference voltage if connected. Otherwise the device
N
or 3 · V is not sufficient to determine the direction, the direction is undefined. Then the
0 0
2.2 Overcurrent Protection 50, 51, 50N,
from the sum of the three phase voltages. If
0
SIPROTEC 4, 7SJ80, Manual
E50417-G1140-C343-A8, Edition 12.2017
, the
N