17 NEUTRAL ADMITTANCE PROTECTION
Neutral admittance protection works by calculating the neutral admittance from the neutral input current and
voltage (I
N
/V
N
). The neutral curr
ent input is measured with an earth fault or sensitive earth fault current
transformer and the neutral voltage is based on the internally derived quantity VN.
Three single stage elements are provided:
● Overadmittance YN>: This is non-directional, providing both start and time delayed trip outputs. The trip
may be blocked by a logic input
● Overconductance GN>: This is non-directional or directional, providing both start and time delayed trip
outputs. The trip may be blocked by a logic input
● Oversusceptance BN>: This is is non-directional or directional, providing both start and time delayed trip
outputs. The trip may be blocked by a logic input
The overadmittance elements YN>, GN> and BN> will operate providing the neutral voltage remains above the set
level for the set operating time of the element. They are blocked by operation of the fast VTS block signal from the
VT supervision function.
The overadmittance elements provide measurements of admittance, conductance and susceptance that also
appear in the fault record.
The overadmittance elements are capable of initiating auto-reclose by means of YN>, GN> and BN> settings in the
AUTO-RECLOSE menu column.
17.1 NEUTRAL ADMITTANCE OPERATION
The admittance protection is non-directional. Hence, provided the magnitude of admittance exceeds the set value
YN> Set and the magnitude of neutral voltage exceeds the set v
alue VN Threshold, the device will operate.
E00709
Note:
Y = G +jB
Operate
Admittance:
Non-Directional
B
Y > Ys
Ys
G
Y
Figure 81: Admittance protection
17.2 CONDUCTANCE OPERATION
The conductance protection may be set non-directional, directional forward or directional reverse. Hence, provided
the magnitude and the directional criteria ar
e met for conductance and the magnitude of neutral voltage exceeds
the set value VN Threshold, the device will operate. The correction angle causes rotation of the directional
boundary for conductance through the set correction angle.
Chapter 6 - Current Protection Functions P14x
156 P14xEd1-TM-EN-1
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