GE N60 Instruction Manual page 318

5.7 CONTROL ELEMENTS 5 SETTINGS
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).
As long as the current through the voltage monitor is above a threshold (see technical specifications for form-A), the "Cont
Op 1 VOn" FlexLogic operand will be set (for contact input 1 – corresponding operands exist for each contact output). If the
output circuit has a high resistance or the DC current is interrupted, the trickle current will drop below the threshold and the
"Cont Op 1 VOff" FlexLogic operand will be set. Consequently, the state of these operands can be used as indicators of the
integrity of the 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 problems can be detected before a trip oper-
ation 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 resis-
tance, the trickle current will fall below the monitor threshold and an alarm would be declared.
In most breaker control circuits, the trip coil is connected in series with a breaker auxiliary contact which is open when the
breaker is open (see diagram below). To prevent unwanted alarms in this situation, the trip circuit monitoring logic must
include the breaker position.
5
Figure 5–81: TRIP CIRCUIT EXAMPLE 1
Assume the output contact H1 is a trip contact. Using the contact output settings, this output will be 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 will be given an ID name, for example, "Cont Ip 1", and will be set "On" when the
breaker is closed. The settings to use digital element 1 to monitor the breaker trip circuit are indicated below (EnerVista UR
Setup example shown):
5-200 N60 Network Stability and Synchrophasor Measurement System GE Multilin