Interaction With The Fuse Failure Monitor (Ffm); Dynamic Cold Load Pickup Function; Inrush Restraint; Determination Of Direction - Siemens siprotec SJ62 User Manual

2 Functions
2.3.5

Interaction with the Fuse Failure Monitor (FFM)

2.3.6

Dynamic Cold Load Pickup Function

2.3.7

Inrush Restraint

2.3.8

Determination of Direction

Method of Direc-
tional Measurement
97
Spurious tripping can be caused by failure of a measuring voltage due to short-circuit,
broken wire in the voltage transformer's secondary system or pickup of the voltage
transformer fuse. Failure of the measuring voltage in one or two poles can be detect-
ed, and the directional time overcurrent elements (Dir Phase and Dir Ground) can be
blocked (see logic diagrams). Undervoltage protection, sensitive ground fault detec-
tion and synchronization are equally blocked in this case.
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 thresholds 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. The alternative pickup values can be set individually for each
element of the directional and non-directional time overcurrent protection.
The 7SJ62/63/64 features an integrated inrush restraint function. It prevents the "nor-
mal" pickup of all directional and non-directional overcurrent relay elements in the
phases and ground path, but not the high-set elements. The same is true for the alter-
native pickup thresholds of the dynamic cold load pickup function. After detection of
inrush currents above a pickup value special inrush signals are generated. These
signals also initiate fault annunciations and start the associated trip delay time. If
inrush conditions are still present after the tripping time delay has elapsed, a corre-
sponding message ("....TimeOut ") is output, but the overcurrent tripping is blocked
(for further information see "Inrush Restraint" in Section 2.2).
Determination of fault direction is performed independently for each of the four direc-
tional elements (three phases, ground or summation current 3I0).
Basically, the direction determination is performed by determining the phase angle
between the fault current and a reference voltage.
For the directional phase elements the short-circuit current of the affected phase and
as reference voltage the unfaulted phase-to-phase voltage are used. The unfaulted
voltage also allows an unambiguous direction determination if the fault voltage has
collapsed severely (close-up fault). With phase-to-ground voltages connection, the
phase-to-phase voltages are calculated. With connection to two phase-to-phase volt-
ages and V , the third phase-to-phase voltage is also calculated.
N
With three-pole faults, stored voltage values are used to clearly determine the direc-
tion if the measurement voltages are not sufficient. After the expiration of the storage
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015