Fault Locator; Fault Type Determination - GE D30 Instruction Manual

CHAPTER 9: THEORY OF OPERATION

9.5 Fault locator

9.5.1 Fault type determination

Fault type determination is required for calculation of fault location. The algorithm uses the angle between the negative
and positive sequence components of the relay currents. To improve accuracy and speed of operation, the fault
components of the currents are used; that is, the pre-fault phasors are subtracted from the measured current phasors. In
addition to the angle relationships, certain extra checks are performed on magnitudes of the negative and zero-sequence
currents.
The single-ended fault location method assumes that the fault components of the currents supplied from the local (A) and
remote (B) systems are in phase. The figure shows an equivalent system for fault location.
E
A
The following equations hold true for this equivalent system.
where
m = sought pu distance to fault
Z = positive sequence impedance of the line
The currents from the local and remote systems can be parted between their fault (F) and pre-fault load (pre) components:
and neglecting shunt parameters of the line:
Inserting the I and I equations into the V
A B
Assuming the fault components of the currents, I
impedance, does not have any imaginary part gives:
D30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
Figure 9-9: Equivalent system for fault location
distance to fault
Local bus
Z mZ
I
A
A
V
F
V
A
V = m Z I ⋅ ⋅ + R
A A
I = I +
A AF
I = I
–
B BF
equation and solving for the fault resistance yields:
A
V m Z I
–
A
R = ------------------------------ -
F

I ⋅ 1

AF
and I are in phase, and observing that the fault resistance, as
AF BF
V m Z I ⋅ ⋅
–

A
------------------------------ -
Im

I
AF
Remote
bus
(1-m)Z Z
I
B
R
F
V
B
⋅ ( I + I )
F A B
I
Apre
I
Apre
⋅ ⋅
A
I

BF
+ ----- -

I
AF

A
= 0

FAULT LOCATOR
B
E
B
842780A1.CDR
Eq. 9-7
Eq. 9-8
Eq. 9-9
Eq. 9-10
Eq. 9-11
9-21
9