GE D90 Plus Instruction Manual page 354

PROTECTION FLEXLOGIC™
346
Figure 283: UR
The states of all digital signals used in the D90
operands, which are described later in this section). A logic 1 state is represented by a set
flag. Any external contact change-of-state can be used to block an element from
operating, as an input to a control feature in a FlexLogic™ equation, or to operate a
contact output. The state of the contact input can be displayed locally or viewed remotely
via the communications facilities provided. If a simple scheme where a contact input is
used to block an element is desired, this selection is made when programming the
element. This capability also applies to the other features that set flags: elements, virtual
inputs, remote inputs, schemes, and human operators.
If more complex logic than presented above is required, it is implemented via FlexLogic™.
For example, if it is desired to have the closed state of contact input H7a and the operated
state of the phase undervoltage element block the operation of the phase time
overcurrent element, the two control input states are programmed in a FlexLogic™
equation. This equation ANDs the two control inputs to produce a virtual output, which is
then selected when programming the phase time overcurrent to be used as a blocking
input. Virtual outputs can only be created by FlexLogic™ equations.
Traditionally, protective relay logic has been relatively limited. Any unusual applications
involving interlocks, blocking, or supervisory functions had to be hard-wired using contact
inputs and outputs. FlexLogic™ minimizes the requirement for auxiliary components and
wiring while making more complex schemes possible.
Plus
-series architecture overview
Plus
are represented by flags (or FlexLogic™
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 7: PROTECTION