CHAPTER 5: SETTINGS
GROUPED ELEMENTS
L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUAL
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5
View the operating characteristic and logic figures along with the following discussion to understand the operation of the
element.
The power swing detect element operates in three-step or two-step mode, as follows:
•
Three-step operation
— The power swing blocking sequence essentially times the passage of the locus of the
positive-sequence impedance between the outer and the middle characteristic boundaries. If the locus enters the
outer characteristic (indicated by the
POWER SWING OUTER
FlexLogic operand) but stays outside the middle
characteristic (indicated by the
POWER SWING MIDDLE
FlexLogic operand) for an interval longer than
POWER SWING
PICKUP DELAY 1
, the power swing blocking signal (
POWER SWING BLOCK
FlexLogic operand) is established and sealed-in.
The blocking signal resets when the locus leaves the outer characteristic, but not sooner than the
POWER SWING RESET
DELAY
1
time.
•
Two-step operation
— If the two-step mode is selected, the sequence is identical to the three-step operation, but it is
the outer and inner characteristics that are used to time the power swing locus.
The out-of-step tripping feature operates as follows for three-step and two-step power swing detection modes:
•
Three-step operation
— The out-of-step trip sequence identifies unstable power swings by determining if the
impedance locus spends a finite time between the outer and middle characteristics and then a finite time between
the middle and inner characteristics. The first step is similar to the power swing blocking sequence. After timer
POWER
SWING PICKUP DELAY 1
times out, latch 1 is set as long as the impedance stays within the outer characteristic.
If afterwards, at any time (given the impedance stays within the outer characteristic), the locus enters the middle
characteristic but stays outside the inner characteristic for a period of time defined as
POWER SWING PICKUP DELAY 2
,
latch 2 is set as long as the impedance stays inside the outer characteristic. If afterwards, at any time (given the
impedance stays within the outer characteristic), the locus enters the inner characteristic and stays there for a period
of time defined as
POWER SWING PICKUP DELAY 3
, latch 2 is set as long as the impedance stays inside the outer
characteristic; the element is now ready to trip.
If the "Early" trip mode is selected, the
POWER SWING TRIP
operand is set immediately and sealed-in for the interval set
by the
POWER SWING SEAL-IN DELAY
. If the "Delayed" trip mode is selected, the element waits until the impedance locus
leaves the inner characteristic, then times out for the
POWER SWING PICKUP DELAY 2
and sets latch 4; the element is
now ready to trip. The trip operand is set later, when the impedance locus leaves the outer characteristic.
•
Two-step operation
— Similar to the three-step mode with two exceptions. First, the initial stage monitors the time
spent by the impedance locus between the outer and inner characteristics. Second, the stage involving the
POWER
SWING PICKUP DELAY 2
timer is bypassed. It is up to the user to integrate the blocking (
POWER SWING BLOCK
) and tripping
(
POWER SWING TRIP
) FlexLogic operands with other protection functions and output contacts in order to make this
element fully operational.
The element can be set to use either lens (mho) or rectangular (quadrilateral) characteristics, as shown in the figure. When
set to “Mho,” the element applies the right and left blinders as well. If the blinders are not required, set their settings high
enough to effectively disable the blinders.
