2-2 L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
PRODUCT DESCRIPTION CHAPTER 2: PRODUCT DESCRIPTION
2
62439-3 (clause 4, 2012) when purchased as an option.
Secure Routable GOOSE (R-GOOSE) is supported with software options.
In addition to current differential protection, the relay provides multiple backup protection for phase and ground faults. For
overcurrent protection, the time overcurrent curves can be selected from a selection of standard curve shapes or a
custom FlexCurveâ„¢ for optimum co-ordination. Additionally, five zones of phase and ground distance protection with
power swing blocking, out-of-step tripping, line pickup, load encroachment, and six pilot schemes are included.
The L90 incorporates charging current compensation for applications on very long transmission lines without loss of
sensitivity. The line capacitive current is removed from the terminal phasors.
For breaker-and-a-half or ring applications, the L90 design provides secure operation during external faults with possible
current transformation (CT) saturation.
Voltage, current, and power metering are built in as standard features. Current parameters are available as total
waveform RMS magnitude, or as fundamental frequency only root mean square (RMS) magnitude and angle (phasor).
Settings and actual values can be accessed from the front panel or EnerVista software.
The L90 uses flash memory technology that allows field upgrading as new features are added. Firmware and software are
upgradable.
The following single-line diagram illustrates the relay functionality using American National Standards Institute (ANSI)
device numbers.
Table 2-1: ANSI device numbers and functions supported
Device number Function Device number Function
21G Ground distance 51_2 Negative-sequence time overcurrent
21P Phase distance 52 AC circuit breaker
24 Volts per hertz 59C Compensated overvoltage
25 Synchrocheck 59N Neutral overvoltage
27P Phase undervoltage 59P Phase overvoltage
27X Auxiliary undervoltage 59X Auxiliary overvoltage
32N Wattmetric zero-sequence directional 67N Neutral directional overcurrent
32R Sensitive reverse power 67P Phase directional overcurrent
49 Thermal overload protection 67_2 Negative-sequence directional overcurrent
50BF Breaker failure 68 Power swing blocking
50DD Adaptive fault detector
(sensitive current disturbance detector)
78 Out-of-step tripping
79 Automatic recloser
50G Ground instantaneous overcurrent 81O Overfrequency
50N Neutral instantaneous overcurrent 81R Rate of change of frequency
50P Phase instantaneous overcurrent 81U Underfrequency
50_2 Negative-sequence instantaneous overcurrent 87RGF Restricted ground fault
51G Ground time overcurrent 87L Segregated line current differential
51N Neutral time overcurrent 87LG Ground line current differential
51P Phase time overcurrent
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