Figure 3.5-2 Phase Fault Angles; Figure 3.5-3 Application Of Directional Overcurrent Protection - Siemens 7PG2114 Application Manual

7PG2113/4/5/6 Solkor Applications Guide
Current lagging
MTA
V
Voltage
V
MTA
0
- 30
0
- 45
I
I
Plain Feeders
Transformer Feeders
(Overhead Lines)
(Cable Circuits)

Figure 3.5-2 Phase Fault Angles

Directional overcurrent elements allow greater fault selectivity than non-directional elements for interconnected
systems where fault current can flow in both directions through the relaying point. Consider the network shown in
fig. 2.6-3.
The Circuit breakers at A, B, E and G have directional overcurrent relays fitted since fault current can flow in both
directions at these points. The forward direction is defined as being away from the busbar and against the
direction of normal load current flow. These forward looking IDMTL elements can have sensitive settings applied
i.e. low current and time multiplier settings. Note that the relays may be programmed with forward, reverse and
non-directional elements simultaneously when required by the protection scheme.
A B
C D
E G
Load

Figure 3.5-3 Application of Directional Overcurrent Protection

©2010 Siemens Protection Devices Limited Chapter 7 Page 25 of 49