Determination Of Direction - Siemens SIPROTEC 7SJ62 Instruction Manual

Dropout For IEC
Curves
Dropout For ANSI
Curves
User Specified
Curves
6.3.1.3

Determination of Direction

Methods of
Determining
Direction
7SJ62 Manual
C53000-G1140-C121-1
pickup, the time delay of the trip signal is calculated using an integrated measurement
process. The calculated time delay is dependent on the actual fault current flowing and
the selected time-current characteristic curve. Once the time delay elapses, a trip sig-
nal is issued.
If the inrush restraint feature is enabled (see Section 6.5), and an inrush condition ex-
ist, no tripping takes place, but a message is recorded and displayed indicating when
the overcurrent element time delay elapses.
The characteristic curves of the 67-TOC and 67N-TOC relay elements may be select-
ed independently of each other. In addition, pickup, time multipliers, and time dials for
the 67-TOC and 67N-TOC elements may be individually set.
Dropout of an element using an IEC curve occurs when the current decreases to about
95% of the pickup value. When an element using an IEC curve drops out, the relay
element immediately resets.
Dropout of an element using an ANSI curve occurs when the current decreases to
about 95 % of the pickup value if instantaneous reset is selected, or 90 % of the pickup
value if disk emulation is selected. When instantaneous reset is selected, reset of the
element occurs without delay. When disk emulation is selected, reset occurs just as it
would for an electromechanical relay utilizing an induction disk.
For disk emulation, the reset process begins after fault current is interrupted. Reset
corresponds to the unwinding of an induction disk. A subsequent pickup of the relay
element prior to full reset will result in a reduced tripping time delay. The reduced trip-
ping time delay will be based on the degree to which the relay had reset when the sub-
sequent pickup occurred. When the current in the relay element is between 90 % and
95 % of the pickup value following dropout, neither disk movement in the tripping or
reset direction is simulated. When the current in the relay elements falls below 5 % of
the pickup value, disk emulation is canceled and full reset takes place.
Disk emulation offers advantages when the inverse time, directional overcurrent relay
elements must be coordinated with conventional electromechanical overcurrent relays
located toward the source.
When user specified curves are utilized, the time-current characteristic curve may be
defined point by point. Up to 20 pairs of values (current, time) may be entered. The
relay element then approximates the curve using linear interpolation.
When utilizing user specified time-current curves, the reset curve may be user speci-
fied as well. This is advantageous when the inverse time, directional overcurrent pro-
tection must be coordinated with conventional electromechanical overcurrent relays
located toward the source. If user specified reset curves are not utilized, the relay el-
ement drops out when current decreases to about 95% of the relay element's pickup
value, and immediate reset takes place.
Determination of fault direction is performed independently for each phase element
and for the ground element.
For the a-phase directional elements, direction is determined by comparing I
at the relay location. For the b-phase and c-phase directional elements, direction is de-
termined by comparing I
b
with V and I with V at the relay location. For phase-to-
ca c ab
Functions
with V
a bc
6-45