GE C30 Instruction Manual page 259

CHAPTER 5: SETTINGS CONTROL ELEMENTS
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.
Figure 5-64: Trip circuit example 1
5
Assume the output contact H1 is a trip contact. Using the contact output settings, this output is given an ID name; for
example, "Cont Op 1." Assume a 52a breaker auxiliary contact is connected to contact input H7a to monitor breaker status.
Using the contact input settings, this input is given an ID name, for example, "Cont Ip 1," and is set "On" when the breaker is
closed. The settings to use digital element 1 to monitor the breaker trip circuit are indicated (EnerVista example shown).
C30 CONTROLLER SYSTEM – INSTRUCTION MANUAL 5-141