GE D90 Plus - Page 222

212 D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
GROUPED PROTECTION ELEMENTS CHAPTER 7: PROTECTION
the timer specified by the Delay 1 Pickup setting 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 by the
Delay 2 Pickup setting, 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 the
Delay 3 Pickup setting,
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
Seal-In Delay setting. If the “Delayed” trip
mode is selected, the element waits until the impedance locus leaves the inner
characteristic, then times out for the
Pickup Delay 2 setting 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
Delay 2 Pickup 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.
Figure 188: Power swing detect mho operating characteristic
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