To ensure a sufficient accuracy for the IG and VG measurements, it is required that the
residual voltage exceeds the value set by Min trip voltage. If the admittance calculation
mode is "Delta", the minimum change in the residual voltage due to a fault must be 0.01
× Vn to enable the operation. Similarly, the residual current must exceed the value set by
Min trip current.
The polarity of the polarizing quantity VG 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 pickup 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"
GUID-A831002F-5145-4700-8D9A-C80FBF6757AF V1 EN (Equation 24)
Admittance Clc mode = "Delta"
Yo
IG IG
VG VG
IG
VG
fault prefault
fault prefault
=
−
− −
=
−( )
∆
∆
GUID-3AD86A5A-52E7-421E-96CC-C69838CB026C V1 EN (Equation 25)
Yo
Calculated neutral admittance [Siemens]
IG
fault
Residual current during the fault [Amperes]
VG
fault
Residual voltage during the fault [Volts]
IG
prefault
Prefault residual current [Amperes]
VG
prefault
Prefault residual voltage [Volts]
ΔIG Change in the residual current due to fault [Amperes]
ΔVG Change in the residual voltage due to fault [Volts]
1MAC059074-MB A Section 4
Protection functions
615 series ANSI 373
Technical Manual
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