Basler BE1-CDS240, Instruction Manual

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3-2 BE1-CDS240 Input and Output Functions 9365200990 Rev F
BE1-CDS240 for any protective or metering function that accepts a circuit selection setting. Virtual circuits
are referred to as Circuits 5 and 6.
Voltage Measurement
Three-phase voltage inputs are reduced to internal signal levels by a precision resistor divider network.
Voltage Measurement Functions
The input waveforms are sampled by an analog-to-digital converter (ADC) at 144 samples per cycle and
digitally filtered in a DSP (digital signal processor) using an FIR (finite impulse response) anti-aliasing
filter algorithm. This high sampling rate allows the analog filter to have a high cutoff point, which virtually
eliminates errors from the analog filter elements. The output from the digital filter is sample data reduced
to 24 samples per cycle. The relay extracts the magnitude and angle of the fundamental components of
each three-phase voltage inputs.
VT Connections
When four-wire VT connections are used, the relay measures the AN, BN, and CN voltages and
calculates the phase voltage quantities. Overvoltage and undervoltage functions (27/59) can be set to
operate on either the phase-to-neutral (PN) or phase-to-phase (PP) quantities. Three-wire VT
connections limit 27/59 operation to PP quantities. When single-phase VT connections are used, the
27/59 elements operate as appropriate for the single-phase voltage applied.
Zero-Sequence (V
0
)Voltage
When four-wire VT connections are used, the BE1-CDS240 calculates the zero- sequence voltage. Zero-
sequence voltage measurement is not available when single-phase or three-wire VT connections are
used. The metering and protection elements utilize 3V
0
quantities.
Negative-Sequence (V
2
) Voltage
Negative-sequence voltage is calculated from the fundamental component of the three-phase voltage
inputs. It is only available on three-phase, three-wire or three-phase, four-wire systems. V
2
is calibrated to
the phase-to-neutral base. The effect is that the relay reports the same V
2
independent of whether the
relay is in 3-wire or 4-wire mode. The metering and protective functions utilize V
2
, not 3V
2
. Negative-
sequence measurements can accommodate either ABC or ACB phase-sequence.
Positive-Sequence (V
1
) Voltage
Positive-sequence voltage is calculated from the fundamental component of the three-phase voltage
inputs. It is only available on three-phase, three-wire or three-phase, four-wire systems. V
1
is calibrated to
the phase-to-neutral base. The effect is that the relay reports the same V
2
independent of whether the
relay is in 3-wire or 4-wire mode. The metering functions utilize V
2
, not 3V
2
. Positive-sequence
measurements can accommodate either ABC or ACB phase-sequence.
Frequency Measurement
Power system frequency is monitored on the A-N voltage input or the AB voltage input when in three-wire
mode and on A-phase current circuit one. When the applied signal is greater than 10 volts, or 0.5 amps
(0.1 amps for 1 A CTs) the BE1-CDS240 measures the frequency. The measured frequency on the
voltage input is used by the 81 function and applies to all measurements and calculations; the current
input is used in the sampling rate determination.
Frequency Compensation
Using the frequency measured on the voltage input, the BE1-CDS240 varies the sampling rate to
maintain 144 samples per cycle over a frequency of 40 to 63 hertz. If the voltage is too low for accurate
frequency measurement, or if the measured frequency is out of range, the frequency measured on the
current input is used to maintain the sample rate. If both voltage and current are too low or out of range
the ADC defaults to a sampling rate appropriate for the relay’s nominal frequency setting. Protection is
still provided for all functions except for negative-sequence current and voltage and volts/hz, but metering
and harmonic analysis accuracy is degraded. The sampling rate is adjusted every 50 milliseconds.
Nominal Frequency
F
nom
can be set for 50-hertz or 60-hertz power systems. When the voltage and current are too low for
reliable frequency measurement, the ADC sample rate defaults to operation at the nominal frequency
setting. Nominal frequency is also used in the volts/hertz (24) overexcitation calculation.