2.4 METERING & MONITORING FUNCTIONS
2.4 METERING & MONITORING FUNCTIONS
The relay measures all input currents and calculates both phasors and symmetrical components. When AC potential is
applied to the relay via the optional voltage inputs, metering data includes phase and neutral current, phase voltage, three
phase and per phase W, VA, and var, and power factor. Frequency is measured on either current or voltage inputs. They
may be called onto the local display or accessed via a computer. All terminal current phasors and differential currents are
also displayed at all relays, allowing the user opportunity to analyze correct polarization of currents at all terminals.
The relay has a 'sequence of events' recorder which combines the recording of snapshot data and oscillography data.
Events consist of a broad range of change of state occurrences, including input contact changes, measuring-element
pickup and operation, FlexLogic™ equation changes, and self-test status. The relay stores up to 1024 events with the date
and time stamped to the nearest microsecond. This provides the information needed to determine a sequence of events,
which can reduce troubleshooting time and simplify report generation after system events.
The relay stores oscillography data at a sampling rate of 64 times per cycle. The relay can store from 1 to 64 records. Each
oscillography file includes a sampled data report consisting of:
Instantaneous sample of the selected currents and voltages (if AC potential is used),
The status of each selected contact input,
The status of each selected contact output,
The status of each selected measuring function,
The status of various selected logic signals, including virtual inputs and outputs.
The captured oscillography data files can be accessed via the remote communications ports on the relay.
The relay has current unbalance alarm logic. The unbalance alarm may be supervised by a zero sequence voltage detec-
tor. The user may block the relay from tripping when the current unbalance alarm operates.
On those outputs designed for trip duty, a trip voltage monitor will continuously measure the DC voltage across output con-
tacts to determine if the associated trip circuit is intact. If the voltage dips below the minimum voltage or the breaker fails to
open or close after a trip command, an alarm can be activated.
The most comprehensive self testing of the relay is performed during a power-up. Because the system is not performing
any protection activities at power-up, tests that would be disruptive to protection processing may be performed.
The processors in the CPU and all DSP modules participate in startup self-testing. Self-testing checks approximately 85-
90% of the hardware, and CRC/check-sum verification of all PROMs is performed. The processors communicate their
results to each other so that if any failures are detected, they can be reported to the user. Each processor must successfully
complete its self tests before the relay begins protection activities.
During both startup and normal operation, the CPU polls all plug-in modules and checks that every one answers the poll.
The CPU compares the module types that identify themselves to the relay order code stored in memory and declares an
alarm if a module is either non-responding or the wrong type for the specific slot.
When running under normal power system conditions, the relay processors will have "idle" time. During this time, each pro-
cessor performs "background" self-tests that are not disruptive to the foreground processing.
2.4.4 CT FAILURE / CURRENT UNBALANCE ALARM
L90 Line Differential Relay
2 PRODUCT DESCRIPTION
2.4.2 EVENT RECORDS
2.4.5 TRIP CIRCUIT MONITOR
2.4.6 SELF TEST
GE Power Management