GE 845 Instruction Manual page 462

FLEXLOGIC
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FlexLogic™ equation, or to operate an output relay. The state of the contact input can be
displayed locally or viewed remotely via the communications facilities provided. In a
simple scheme where a contact input is used to block an element is desired, this selection
is made within the menu of the element. This applies to other features that set flags:
elements, virtual inputs, remote inputs, schemes, and human operators.
When more complex logic than the one presented above is required, the FlexLogic™ tool
should be used. For example, if it is desired to block the operation of a Phase Time
Overcurrent element by the closed state of a contact input, and the operated state of a
Phase Undervoltage element, the two input states need be programmed in a FlexLogic™
equation. This equation ANDs the two inputs to produce a virtual output which then must
be programmed within the menu of the Phase Time Overcurrent as a blocking input.
Virtual outputs can be created only 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.
The logic that determines the interaction of inputs, elements, schemes and outputs is field
programmable through the use of logic equations that are sequentially processed. The use
of virtual inputs and outputs in addition to hardware is available internally and on the
communication ports for other relays to use (distributed FlexLogic™).
FlexLogic™ allows users to customize the relay through a series of equations that consist
of operators and operands. The operands are the states of inputs, elements, schemes and
outputs. The operators are logic gates, timers and latches (with set and reset inputs). A
system of sequential operations allows any combination of specified operands to be
assigned, as inputs to specified operators, to create an output. The final output of an
equation is a numbered register called a 'Virtual Output'. Virtual Outputs can be used as an
input operand in any equation, including the equation that generates the output, as a
seal-in or other type of feedback.
A FlexLogic™ equation consists of parameters that are either operands or operators.
Operands have a logic state of 1 or 0. Operators provide a defined function, such as an
AND gate or a Timer. Each equation defines the combinations of parameters to be used to
set a Virtual Output flag. Evaluation of an equation results in either a 1 (=ON, i.e. flag set) or
0 (=OFF, i.e. flag not set). Each equation is evaluated at least 4 times during every power
system cycle.
Some types of operands are present in the relay in multiple instances; e.g. contact and
remote inputs. These types of operands are grouped together (for presentation purposes
only) on the faceplate display. The characteristics of the different types of operands are
listed in the table below.
845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: SETPOINTS