GRZ100
6
PSBZ
PSBZ
PSBZ
0
PSBZ
PSBIN
PSBOUT
R
X
PSBZ: Impedance setting of PSB element
Figure 5 Characteristics of power swing blocking element
Out-of-step Trip Protection
The out-of-step tripping function is used to execute power
system separation at the optimum point when an out-of-step
occurs.
An out-of-step is detected by using two distance measuring
elements with quadrilateral characteristics as shown in
Figure 5. The element operates when the out-of-step locus
passes from Zone A
Æ
Zone B
Æ
Zone C (or Zone C
Æ
Zone B
Æ
Zone A) and remains in Zones A and C for the
detection time (TOST).
X
Impedance
locus
OSTXF
Zone A
OSTR2 OSTR1
OSTXB
Zone B
Zone C
R
Figure 6 Characteristics of out of step trip element
Breaker Failure Protection
When an overcurrent element remains in operation longer
than a pre-determined length of time following the output of
a trip signal the associated circuit breaker is judged to have
failed and adjacent circuit breakers can be tripped as a
back-up measure.
Two independent timers are available, one of which can be
used to control the RETRIP of the original circuit breaker(s). The
second timer is used to control the backtripping of adjacent
circuit breakers.
For high-speed protection, an overcurrent element with
high-speed reset time is used to prevent a spurious re-trip
or backtrip following a successful trip or re-trip action.
Overcurrent Backup Protection
The IDMT(inverse definite minimum time) overcurrent
element is provided for non-directional inverse time
overcurrent protection. The IDMT element is available in
conformity with either of three IEC Standard characteristics
(Standard inverse, Very inverse, Extremely inverse) or a
Long-time inverse.
The characteristics of each IDMT are shown in Figure 8.
The IDMT element has a reset feature with definite time reset.
If the reset time is set to instantaneous, then no intentional
delay is added. As soon as the energising current falls
below the reset threshold, the element returns to its reset
condition.
If the reset time is set to some value in seconds, then an
intentional delay is added to the reset period. If the
energising current exceeds the setting for a transient period
without causing tripping, then resetting is delayed for a
user-definable period. When the energising current falls
below the reset threshold, the integral state (the point
towards operation that it has travelled) of the timing function
(IDMT) is held for that period.
This does not apply following a trip operation, in which case
resetting is always instantaneous.
Definite time overcurrent protection
Definite time overcurrent protection is enabled by the
instantaneous overcurrent element and pick-up delay timer.
Broken Conductor Detection
The unbalance condition caused by an open circuited
conductor is detected by the broken conductor
detection function. An unbalance threshold with
programmable definite time delay is provided.
High-resistance Earth Fault Protection
This protection provides high-resistance earth fault protection
using the directional earth fault (DEF) element and the earth
fault overcurrent element as follows.
Directional Earth Fault Protection
DEF element is used for time-delayed backup protection for
high-resistance faults.
Directional Earth Fault Protection using
Telecommunication
High-speed DEF protection using telecommunications is
provided by using a forward looking DEF element and a
reverse looking DEF element. POP, UOP, and BOP
schemes can be selected with DEF protection using
telecommunications.
To enable single phase tripping for a high impedance earth
fault, GRZ100, when equipped with the optional integral
communication channels, is provided with phase selection
logic to obtain phase segregated trip permission signals.
The characteristics of the forward and reverse looking DEF
elements are as shown in Figure 7.
-3V
0
Backward DEF
Forward DEF
3I
0
Figure 7 Characteristics of directional earth fault element
