Cross-Country Fault Example - GE L90 Instruction Manual

SINGLE-POLE TRIPPING

10.5.6 Cross-country fault example

Assume a single pole operation application where L90 relays are used to protect a two-terminal line, (terminals T1 and T2)
using phase and ground distance zone 1, 2, and 3 elements in a permissive over-reaching transfer trip scheme. The
performance of the system with one, two, and four-bit communications channels is outlined for a mid-line phase A-to-
ground fault and a co-incident phase B-to-ground fault just behind terminal T2. Assume also that the reclosers are enabled
and reset.
At T1 the following protection elements pick up:
• Ground Distance Zone 1, 2, and 3 for an AG fault
• Ground Distance Zone 2 and 3 for a BG fault
• Phase Distance Zone 2 and 3 for an AB fault
At T1, the phase selector determines the fault is type ABG. This response is independent from the distance elements; the
Phase Selector sees two forward faults.
At T2, the following protection elements pick up:
• Ground Distance Zone 1, 2, and 3 for an AG fault
At T2 the phase selector determines the fault is type AG. The reverse BG fault is likely to be ignored.
If a one-bit channel is used, terminal T1 trips three poles but terminal T2 trips phase A only, which is undesirable. See the
table.
Table 10-34: One-bit channel tripping
Terminal Remote data
Bit pattern received
RX1
T1 1
T2 1
If a two-bit channel is used, both terminals trip phase A only, which is desired. See the following table.
Table 10-35: Two-bit channel tripping
Terminal Remote data
Bit pattern received
RX1
T1 1
T2 1
If a four-bit channel is used, both terminals trip phase A only, which is desired. See the following table.
Table 10-36: Four-bit channel tripping
Terminal Remote data
Bit pattern received
RX1
T1 0
T2 1
10
10-50
Remote
determination of
fault type
Any
Any
Remote
determination of
RX2
fault type
0 AG
1 ABG
RX2 RX3 RX4
0 0 1
0 0 0
Local data
Local determination Trip output
of fault type
MULTI-P (ABG) Trip Three Phases
AG Trip Phase A
Local data
Local determination Trip output
of fault type
ABG Trip Phase A
AG Trip Phase A
Local data
Remote Local determination
determination Of of fault type
fault type
AG ABG
ABG AG
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
CHAPTER 10: THEORY OF OPERATION
Trip output
Trip Phase A
Trip Phase A