I.L. 40-201.9
Power Automation and Protection Division
3-6
REL 352 Version 1.00
quantity, respectively. They will produce output when the operating quantity leads the reference
quantity.
(V
AB
- I
AB
Z
P
)
eq. (5)
(V
CB
- I
CB
Z
P
)
eq. (6)
NOTE:
Phase-to-phase-to-ground faults will be detected by the operation of either
phase-to-ground or phase-to-phase units.
7.5.
Zone 2 and Zone 3 Distance Relaying
The optional back-up system in REL 352 consists of two zones of distance protection for both
phase and ground faults.
Each zone consists of four distance units that are able to detect all fault types. The impedance
units are three-phase-to- Ground units (ag, bg and cg) and a Phase-to-Phase unit.
The phase-to-ground units detect all Single Line-to- Ground Faults (SLGF), three-phase faults
and some phase-to-phase-to-ground faults within its operating characteristic. The ZGF and
ZGR (forward and reverse) settings apply to ground faults and 3 Phase faults.
The phase-to-phase unit detects all phase-to-phase faults and some phase-to-phase-to-ground
faults. Since this unit is inherently directional only the forward reach is used. ZP (forward phase
setting) applies to Phase-to-Phase faults.
NOTE:
All phase-to-phase-to-ground faults are covered by the operation of the de-
scribed units.
For the indication of a phase distance trip the following conditions have to occur:
1.
For a three-phase fault, the RT blinder (if the system has OST logic included) and no OSB
and the 3Ph output of the phase selector and any of the phase-to-ground units have to have
operated to indicate a three-phase fault.
2.
For a Phase-to-Phase fault only the Phase-to-Phase unit needs to operate to indicate a
Phase-to-Phase fault.
3.
For a phase-to-phase-to-ground fault either the phase-to-phase unit or the phase-to-
ground units have to operate to indicate a phase-to-phase-to-ground fault.
4.
For a single line to ground fault, any of the phase-to-ground fault units have to operate to
indicate a phase-to-ground fault.
The phase fault detection is supervised by I
L
, the low set overcurrent unit.
The phase-to-ground fault detection is supervised by I
0m
.
Each zone has its own timer to time coordinate with relays further away for step distance relay-
ing. Separate phase and ground timers are provided.
The impedance back-up logic is shown in
Figure 3-14.
7.6.
Directional Overcurrent Units
Phase and ground directional units (FDOP and FDOG) may be either in or out. When they are
in, the high-set overcurrent units (I
AH
, I
BH
, I
CH
and I
GH
) are directional. The ground directional
unit may either be zero sequence polarized or negative sequence polarized.
