Toshiba GRZ100 B Series, Instruction Manual, Page: 135 / 447

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2.7 Fault Locator
2.7.1 Application
The fault locator incorporated in the GRZ100 measures the distance to fault on the protected line
using local voltages and currents. The measurement result is expressed as a percentage (%) of the
line length and the distance (km) and is displayed on the LCD on the relay front panel. It is also
output to a local PC or RSM (relay setting and monitoring) system.
To measure the distance to fault, the fault locator requires minimum 3 cycles as a fault duration
time.
In distance to fault calculations, the change in the current before and after the fault has occurred is
used as a reference current, alleviating influences of the load current and arc voltage. As a result,
the location error is a maximum of
±
2.5 km for faults at a distance of up to 100 km, and a
maximum of
±
2.5% for faults at a distance between 100 km and 250 km.
Note: If abnormal settings far from actual transmission line impedance, e.g. resistance value
so larger than reactance value, etc., are done, the location error will be larger.
The fault locator cannot correctly measure the distance to fault during a power swing.
Fault location is enabled or disabled by setting "Fault locator" to "ON" or "OFF" on the "Fault
record" screen in the "Record" sub-menu.
2.7.2 Distance to Fault Calculation
The distance to fault x
1
is calculated from equation (1) and (2) using the local voltage and current
of the fault phase and a current change before and after the fault occurrence. The current change
before and after the fault occurrence represented by I
β
" and I
α
" is used as the reference current.
The impedance imbalance compensation factor is used to maintain high measuring accuracy even
when the impedance of each phase has great variations.
Distance calculation for phase fault (in the case of BC-phase fault)
x
1
=
Im(Vbc ⋅ I β ") × L
{Im(R1 ⋅ Ibc × I β ") + Re(X1 ⋅ Ibc ⋅ I β ")} × Kbc
(1)
where,
Vbc = fault voltage between faulted phases = Vb
−
Vc
Ibc = fault current between faulted phases = Ib
−
Ic
I
β
" = change of fault current before and after fault occurrence = (Ib-Ic)
−
(ILb-ILc)
ILb, ILc = load current
R1 = resistance component of line positive sequence impedance
X1 = reactance component of line positive sequence impedance
Kbc = impedance imbalance compensation factor
Im( ) = imaginary part in parentheses
Re( ) = real part in parentheses
L = line length (km)