Neutral Overvoltage (59N) - Siemens 7SR10 Argus Series Manual

2.14

Neutral Overvoltage (59N)

Neutral Voltage Displacement (NVD) protection is used to detect an earth fault where little or no earth current
flows.
This can occur where a feeder has been tripped at its HV side for an earth fault, but the circuit is still energised
from the LV side via an unearthed transformer winding. Insufficient earth current would be present to cause a trip,
but residual voltage would increase significantly; reaching up to 3-times the normal phase-earth voltage level.
If Neutral Overvoltage protection is used, it must be suitably time graded with other protections in order to prevent
unwanted tripping for external system earth faults.
EHV/HV
Typically NVD protection measures the residual voltage (3V
cones – see fig. 2.20 below.
© 2018 Siemens Protection Devices Limited
Transformer Feeder
HV CB
OC/EF
HV CB
Tripped
by local
protection
Figure 2-21 NVD Application
VT with
Open Delta
Secondary
3Vo
Relay
Figure 2-22 NVD Protection Connections
7SR10, 7SR11, 7SR12 Applications Guide
HV/MV
Earth
fault
NVD
MV CB tripped by:
1) Feeder unit protection or
2) Intertrip from HV feeder protection or
3) NVD protection
) directly from an open delta VT or from capacitor
0
Capacitor
Cone
Adaptor Unit
MV CB
Capacitor
Cone
Unit
3Vo
Relay
Chapter 7 Page 25 of 41