ABB RELION Series Technical Manual page 333

1MRS758755 A
REC615 and RER615
Technical Manual
Uo requires that all three phase-to-earth voltages are connected to the
protection relay. Uo cannot be calculated from the phase-to-phase
voltages.
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"
Io
fault
Yo
=
Uo
−
fault
GUID-B1E03EA1-E958-43F3-8A28-2D268138DE36 V1 EN
Admittance Clc mode = "Delta"
Section 4
Protection functions
(Equation 11)
327