GE D90 Plus Instruction Manual page 422

AUTOMATION INPUTS AND OUTPUTS
414
Seal-In
Range: any automation logic operand or shared operand
Default: OFF
This setting selects an operand (virtual output, element state, contact input, or virtual
input) that will seal-in the contact output when asserted.
Voltage Threshold
Range: 20 to 250 volts in steps of 1
Default: 20
This setting specifies determines the level at which the Contact Op 1 VOn and Contact
Op 1 VOff operands function. It is only shown for contact outputs that have monitoring.
Events
Range: Enabled, Disabled
Default: Enabled
If this setting is "Enabled", every change in the contact output state will trigger an event
in the sequence of events recorder.
For example, consider a trip circuit current being monitored by providing a current
threshold detector in series with some form-A contacts as shown below.
Figure 336: Trip circuit monitoring example
The name of the automation logic operand set by the monitor consists of the contact
output identifier followed by the name of the flag. For example, using the default
identifiers, we could have
Cont Op 1 Ion
In most breaker control circuits, the trip coil is connected in series with a breaker auxiliary
contact used to interrupt current flow after the breaker has tripped, to prevent damage to
the less robust initiating contact. This can be done by monitoring an auxiliary contact on
the breaker which opens when the breaker has tripped. However, this scheme is subject to
incorrect operation caused by differences in timing between breaker auxiliary contact
change-of-state and interruption of current in the trip circuit. The most dependable
protection of the initiating contact is provided by directly measuring current in the tripping
circuit, and using this parameter to control resetting of the initiating relay. This scheme is
often referred to as a trip seal-in scheme.
This trip seal-in scheme can be realized in the D90
logic operand to seal-in the contact output as follows.
and
Cont Op 1 Von.
Plus
by using the
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 8: AUTOMATION
automation
Cont Op 1 Ion