Operation Principle - ABB RELION REX640 Technical Manual

1MRS759142 C
4.2.4.5
REX640
Technical Manual

Operation principle

The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "on" and "off".
The operation of EFPADM can be described using a module diagram. All the modules
in the diagram are explained in the next sections.
Io
IRES
Neutral
admittance
Uo
calculation
URES
RELEASE
BLOCK
GUID-80220F27-4046-4345-83AB-5CD6E091E01C V1 EN
Figure 246: Functional module diagram
Neutral admittance calculation
When the residual voltage exceeds the set threshold Voltage start value, an earth fault
is detected and the neutral admittance calculation is released.
To ensure a sufficient accuracy for the Io and Uo measurements, it is required that the
residual voltage exceeds the value set by Min operate voltage. If the admittance
calculation mode is "Delta", the minimum change in the residual voltage due to a fault
must be 0.01 × Un to enable the operation. Similarly, the residual current must exceed
the value set by Min operate current.
The polarity of the polarizing quantity Uo can be changed, that is,
rotated by 180 degrees, by setting the Pol reversal parameter to "True"
or by switching the polarity of the residual voltage measurement
wires.
As an alternative for the internal residual overvoltage-based start condition, the
neutral admittance protection can also be externally released by utilizing the
RELEASE input.
When Admittance Clc mode is set to "Delta", the external logic used must be able to
give RELEASE in less than 0.1 s from fault initiation. Otherwise the collected pre-
fault values are overwritten with fault time values. If it is slower, Admittance Clc mode
must be set to "Normal".
Neutral admittance is calculated as the quotient between the residual current and
residual voltage (polarity reversed) fundamental frequency phasors. The Admittance
Clc mode setting defines the calculation mode.
Admittance Clc mode = "Normal"
Timer
t
Operation
charasteristics
Blocking
logic
Section 4
Protection functions
OPERATE
START
FAULT_DIR
455