GE B90 Instruction Manual page 322

CONTROL ELEMENTS CHAPTER 5: SETTINGS
— Sets the required time delay from element pickup to element operation. If a pickup delay
DIGITAL ELEMENT 1 PICKUP DELAY
is not required, set to "0," To avoid nuisance alarms, set the delay greater than the operating time of the breaker.
— Sets the time delay to reset. If a reset delay is not required, set to "0."
DIGITAL ELEMENT 1 RESET DELAY
— This setting enables or disabled the digital element pickup LED. When set to "Disabled," the
DIGITAL ELEMENT 1 PICKUP LED
operation of the pickup LED is blocked.
Figure 5-88: Digital element logic
Circuit monitoring applications
Some versions of the digital input modules include an active voltage monitor circuit connected across form-A contacts.
The voltage monitor circuit limits the trickle current through the output circuit (see technical specifications for form-A).
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As long as the current through the voltage monitor is above a threshold (see technical specifications for form-A), the
Cont
FlexLogic operand is set (for contact input 1—corresponding operands exist for each contact output). If the output
Op 1 VOn
circuit has a high resistance or the DC current is interrupted, the trickle current drops below the threshold and the
Cont Op 1
FlexLogic operand is set. Consequently, the state of these operands can be used as indicators of the integrity of the
VOff
circuits in which form-A contacts are inserted.
Example 1: Breaker trip circuit integrity monitoring
In many applications it is desired to monitor the breaker trip circuit integrity so that problems can be detected before a trip
operation is required. The circuit is considered to be healthy when the voltage monitor connected across the trip output
contact detects a low level of current, well below the operating current of the breaker trip coil. If the circuit presents a high
resistance, the trickle current falls below the monitor threshold, and an alarm is declared.
In most breaker control circuits, the trip coil is connected in series with a breaker auxiliary contact that is open when the
breaker is open (see figure). To prevent unwanted alarms in this situation, the trip circuit monitoring logic must include the
breaker position.
5-166 B90 LOW IMPEDANCE BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL