ABB eVM1 Installation And Service Instructions Manual page 45

14.5.1.1 Nominal Primary Current
Channels 1...3 are used for phase current measurement based on the Rogowski sensor input.
The Nominal Primary Current is the load rated current; the protection function setting range is
adjusted automatically according to the Nominal Primary Current value entered.
The threshold setting range of each protection is expressed in primary current Ampere [A], typically
from is 0.5 In to 20 In where In is the Nominal Primary Current value entered.
14.5.1.2 CCT Earth Nominal Primary Current and CCT Presence
Earth fault protection functions can operate on measured or calculated earth current.
When an earth fault protection is activated the earth current is calculated from the vectorial sum
of the three phase currents if the CCT is not present (blank box). This can be done in networks with
low-resistance neutral earthing in which large zero-sequence currents occur. When the CCT Presence
box is ticked the earth current is directly measured on the channel 4. To provide the earth current
signal a residual current transformer must be connected in the primary circuit.
This option should be used in networks with high-resistance, compensated or isolated neutral
point, where low amplitude earth fault currents occur, to provide higher sensitivity.
The CCT Earth Nominal Primary Current is the residual current transformer rated current, Ine/1 [A/
A]. The earth fault protection function setting range is adjusted automatically according to the CCT
Earth Nominal Primary Current value entered.
14.5.1.3 Analog value measurement and processing
The four available high precision Analog Input channels allow acquisition and processing of three
phase currents through the Rogowski current sensors fitted on the Circuit-breaker contact arms
and an earth current (if an optional earth current sensor is present).
The four signals are sampled at a frequency of 600 Hz with 16 bits of resolution.
The Discrete Fourier Transform (DFT) is calculated for each signal in order to extract the RMS
value of the fundamental component (i.e. 50 or 60 Hz).
All protection functions are based on the fundamental component RMS value at the rated network
frequency.
14.5.1.4 General constraints
· Channels 1...3 are used for phase current measurement based on the Rogowski sensor input;
Board Input Rated Value (IRV) is 0.150 V for 180 A primary current at 50 Hz.
· Channel 4 can be used for earth current measurement based on external residual current
transformer input; Board Input Rated Value (IRV) is 1 A.
Residual current transformers with rated secondary current different from 1A must not be
used; their use may damage the earth current input and/or provide erroneous measurements.
Note
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