Four Step Directional Negative Phase Sequence Overcurrent Protection Ns4Ptoc; Identification; Application - ABB Relion REC670 Applications Manual

Section 7
Current protection
³
I 1
step3
EQUATION1204 V4 EN-US
where:
I
step2
Step 4
This step normally has non-directional function and a relatively long time delay. The task for
step 4 is to detect and initiate trip for earth faults with large fault resistance, for example tree
faults. Step 4 shall also detect series faults where one or two poles, of a breaker or other
switching device, are open while the other poles are closed.
Both high resistance earth faults and series faults give zero-sequence current flow in the
network. Such currents give disturbances on telecommunication systems and current to earth.
It is important to clear such faults both concerning personal security as well as risk of fire.
The current setting for step 4 is often set down to about 100 A (primary 3I
applications definite time delay in the range 1.2 - 2.0 s is used. In other applications a current
dependent inverse time characteristic is used. This enables a higher degree of selectivity also
for sensitive earth-fault current protection.
7.5 Four step directional negative phase sequence
overcurrent protection NS4PTOC
7.5.1

Identification

Function description
Four step negative sequence
overcurrent protection
7.5.2

Application

Four step negative sequence overcurrent protection NS4PTOC is used in several applications
in the power system. Some applications are:
• Earth-fault and phase-phase short circuit protection of feeders in effectively earthed
distribution and subtransmission systems. Normally these feeders have radial structure.
• Back-up earth-fault and phase-phase short circuit protection of transmission lines.
• Sensitive earth-fault protection of transmission lines. NS4PTOC can have better
sensitivity to detect resistive phase-to-earth-faults compared to distance protection.
• Back-up earth-fault and phase-phase short circuit protection of power transformers.
• Earth-fault and phase-phase short circuit protection of different kinds of equipment
connected to the power system such as shunt capacitor banks, shunt reactors and others.
128
3I
0
× ×
.2 I
step2
3I
02
is the chosen current setting for step 2 on the faulted line.
IEC 61850 IEC 60617
identification identification
NS4PTOC
I2
4
alt
4
IEC10000053 V1 EN-US
1MRK 511 358-UEN A
(Equation 44)
M15282-177 v4
). In many
0
GUID-E8CF8AA2-AF54-4FD1-A379-3E55DCA2FA3A v1
GUID-E1720ADA-7F80-4F2C-82A1-EF2C9EF6A4B4 v1
ANSI/IEEE C37.2
device number
46I2
GUID-343023F8-AFE3-41C2-8440-1779DD7F5621 v2
Application manual