ABB RELION REX640 Technical Manual page 492

Protection functions
Figure 279: Functional module diagram
Neutral admittance calculation
When the residual voltage exceeds the set threshold
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
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
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
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,
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
Clc mode setting defines the calculation mode.
Admittance Clc mode = "Normal"
Yo
=
Admittance Clc mode = "Delta"
Yo =
492
Io
IRES
admittance
Uo
calculation
URES
RELEASE
BLOCK
Min operate current .
The polarity of the polarizing quantity Uo can be changed, that is,
rotated by 180 degrees, by setting the
by switching the polarity of the residual voltage measurement wires.
Admittance Clc mode is set to "Delta", the external logic used must be able
Io
fault
Uo
−
fault
Io − Io
fault prefault
=
− ( Uo − Uo )
fault prefault
Neutral
Operation
charasteristics
Blocking
logic
Min operate voltage . If the admittance
∆ Io
− ∆ Uo
1MRS759142 F
Timer
OPERATE
t
FAULT_DIR
Voltage start value , an earth
Pol reversal parameter to "True" or
Admittance Clc
(Equation 58)
Technical Manual
START
Admittance
(Equation 57)
REX640