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Instructional Literature
Page
148
Effective: May 2008
Instructions for the FP-6000 Protective Relay
For more information visit: www.eaton.com
IB02602004E
8 Application and Settings
8.1Overall Measuring Principles of the FP-6000
8.1.1Analog Input Sample Processing
The four current (IA, IB, IC, IX) and four voltage (VA, VB, VC, VX)
inputs are sampled 32 times per cycle. The residual current, IR, is
computed from the phase currents during each update. The
definition of IR is dependent upon the System Configuration
setting for the CT Connection. Diagrams of the system
configurations and definitions of IR are included in Section 8.2 -
CT Connection Options.
For most protection purposes, the values of voltage and current
are updated every frequency cycle. In the case of instantaneous
overcurrent protection (50X and 50P) the values are updated
every half cycle.
For the monitoring function, values are the sums of one cycle
rms values averaged over 32 cycles. The averaged rms quantities
provide stable values of current and voltage for display on the
front panel. The phase angle for voltages and currents is
computed from the one-cycle voltage and current phasor values
every 32 cycles for updating the current phasor angle displays.
8.1.2 Frequency Measurement
The line frequency is obtained through the measurement of the
period of the phase A voltage. The frequency measurement is
used to determine the dynamic sampling rate of all other voltage
and current inputs. A system configuration setting is used to
declare the nominal frequency as 50 or 60 Hz, and this frequency
will be used for sampling in the case where phase A voltage is
unavailable.
8.1.3 Discrete Input Sampling
The eight discrete contact inputs Cin1 – Cin8 and the zone
interlocking input states are declared every cycle.
8.2 CT Connection Options
The Current Transformers may be connected in several ways, and
the specified configuration affects the way system
measurements are made and results computed.
The computation of the residual current IR, is dependent on the
System Configuration setting for the CT Connection. The
configurations resulting from the three setting options are shown
as well as the calculated IR residual current.
Figure 42. Three-Wire CT Connection.
Figure 43. Four-Wire with IN CT.
Figure 44. Four-Wire with IG CT.