Basler BE1-CDS220, Instruction Manual

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BE1-CDS220 Input And Output Functions 3-1
SECTION 3 • INPUT AND OUTPUT FUNCTIONS
GENERAL
BE1-CDS220 relays have two sets of three-phase current measurement inputs, an optional ground
current measurement input, eight contact sensing (programmable) inputs, six general purpose output
contacts, and one dedicated, fail-safe alarm output contact. Each input and output is isolated and brought
out to separate terminal blocks. This section describes the functioning and setup of these inputs and
outputs.
INPUT CURRENT
Currents from the secondary of a CT in power system equipment are applied to internal current
transformer primaries. The internal current transformers provide isolation from the monitored line currents
and step the currents down to internal circuit levels. Secondary current from each internal CT is converted
to a voltage signal, and filtered by an analog, low-pass, anti-aliasing filter.
Current 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. From the digitally filtered samples, the relay extracts the magnitude and angle of
the fundamental, second harmonic, and fifth harmonic components of each three-phase input and the
fundamental of the optional independent ground current input.
Frequency Compensation
The frequency of the power system is monitored on the C phase input for CT circuit one. When the
current applied to phase C of CT circuit one, is greater than 10% nominal, the BE1-CDS220 relay
measures the frequency and varies the sampling rate to maintain 144 samples per cycle over a frequency
range of 40 to 63 hertz. If the C phase current on input circuit one is too low for the frequency to be
accurately read, or the measured frequency is outside this range, the relay ADC defaults to 144 samples
per cycle of the nominal frequency. Protection is still provided for all functions except for negative
sequence, but accuracy is degraded.
Compensated Restraint And Operate Currents For Differential Protection
As described in Section 1, General Information, it is necessary to provide phase angle, zero sequence,
and tap compensation to the measured currents prior to their use by the differential protection. The
current measurement function calculates compensated currents for restraint and operate currents, and for
second and fifth harmonic operate currents. Tap compensation setup is covered in Section 4, Protection
and Control, Phase Differential Protection.
Neutral and Negative Sequence Current Measurement
The BE1-CDS220 relay also calculates the neutral and negative sequence components from the
fundamental component of each of the three-phase current inputs. The relay can be set to accommodate
either ABC or ACB phase sequence in calculating the negative sequence component.
Fast-Dropout Current Detector
The relay includes a separate, fast-dropout current measurement algorithm for use by the breaker failure
function and the breaker trip speed monitoring function. This measurement algorithm has a sensitivity of
10% nominal rating and detects the interruption of current in the circuit breaker in less than a cycle.
Setting Up the Current Measurement Functions
Settings for the current measurement functions are provided in Table 3-1.