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 xUn 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. 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"
GUID-B1E03EA1-E958-43F3-8A28-2D268138DE36 V1 EN (Equation 16)
Admittance Clc mode = "Delta"
Yo
Io Io
Uo Uo
Io
Uo
fault prefault
fault prefault
=
−
− −
=
−( )
∆
∆
GUID-B0611FF1-46FD-4E81-A11D-4721F0AF7BF8 V1 EN (Equation 17)
Yo Calculated neutral admittance [Siemens]
Io
fault
Residual current during the fault [Amperes]
Uo
fault
Residual voltage during the fault [Volts]
Io
prefault
Prefault residual current [Amperes]
Uo
prefault
Prefault residual voltage [Volts]
ΔIo Change in the residual current due to fault [Amperes]
ΔUo Change in the residual voltage due to fault [Volts]
1YHT530004D05 D Section 4
Protection functions
615 series 313
Technical Manual
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