GE D90 Plus Instruction Manual page 484

AUTOMATION LOGIC
474
Figure 405: UR
The states of all digital signals used in the D90
logic operands, 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 an automation logic 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 required, 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 automation
logic. For example, if it is required to have the closed state of contact input H7a and the
operated state of the phase undervoltage element block the operation of the breaker
control element, the two control input states are programmed in an automation logic
equation. This equation ANDs the two control inputs to produce a virtual digital output,
which then is selected when programming the phase time overcurrent to be used as a
blocking input. Virtual digital outputs can only be created by automation logic 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. Automation logic minimizes the requirement for auxiliary components
and wiring while making more complex schemes possible.
Plus
-series architecture overview
Plus
are represented by flags (or automation
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 8: AUTOMATION