GE D90 Plus Instruction Manual page 399

CHAPTER 7: PROTECTION
NOTE:
Contact input and output default assignment
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
state is recognized immediately. Statistically, a delay of half the protection pass is
expected. Owing to the 0.25 ms scan rate, the time resolution for the input contact is less
than 1 ms.
For example, 16 protection passes per cycle on a 60 Hz system correspond to a protection
pass every 1.04 ms. With a contact debounce time setting of 3.0 ms, the FlexLogic operand
assert time limits are: 3.0 + 0.0 = 3.0 ms and 3.0 + 1.04 = 4.04 ms. These time limits depend
on how soon the protection pass runs after the debouncing time.
Regardless of the contact debounce time setting, the contact input event is time-stamped
with a 1 ms accuracy using the time of the first scan corresponding to the new state.
Therefore, the time stamp reflects a change in the DC voltage across the contact input
terminals that was not accidental as it was subsequently validated using the debounce
timer. Keep in mind that the associated FlexLogic operand is asserted/de-asserted later,
after validating the change. The debounce algorithm is symmetrical: the same procedure
and debounce time are used to filter the OFF-ON and ON-OFF transitions.
The active impedance feature controls the input impedance presented to the system
according to the current state of the input. When the contact input circuitry initially detects
a voltage increase, it draws 10 mA of current. If the state change is due to a transient
coupled through the stray capacitance of the field wiring, then the high current sink
charges the capacitance causing the transient to rapidly decay. If voltage increase is due
to a state change of the field contact, then the increased current has no impact on the
input voltage, and the state change is validated. Once the input has been declared to be
on, the input circuitry reduces the current drawn to 1 mA to minimize the power dissipated
by the input.
The contact input update time is 1 ms. However, depending on where the contact input
status change is triggered within a one millisecond window, the worst-case contact input
recognition time is 2 ms.
When a new settings file is created, the available contacts are assigned automatically to
the protection or automation functions according to the following convention:
First I/O module → protection
•
All subsequent I/O modules → automation
•
Plus
For example, if a D90 is configured with contact input/output cards in slots E, F, and G,
then the inputs and outputs associated with slot E are assigned to protection and the
inputs and outputs associated with slots F and G are assigned to automation.
These default assignments can be changed to match the requirements of the application.
This is done by right-clicking the setting filename and choosing the Manage Settings File >
I/O Assignments item. The following window displays.
PROTECTION INPUTS AND OUTPUTS
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