GE LPS-O - Z2 DISTANCE; 201: Z2 PHASE; 202: Z2 PHREACH

2-
10
LPS-O Line Protection System GE Power Management
2.3 PROTECTION SETTINGS 2 CALCULATION OF SETTINGS
2
The maximum allowable reach ( MR ) is based on the criteria shown above in Figure 2–2: MAXIMUM ALLOW-
ABLE REACH and can be calculated as follows:
where = minimum load impedance (ohms)
B = Characteristic angle (degrees)
= 90
°
for a circle
> 90
°
for a lens
C = angle of minimum load impedance (degrees)
D = angle of maximum reach (degrees)
Note that this is the maximum reach that can be safely made based on the given parameters. It is based on
maintaining a 40
°
margin between the angle B and the angle A shown in Figure 2–2: MAXIMUM ALLOWABLE
REACH. A circular Mho characteristic (
B = 90
°
) should be used when possible. However, for larger load flows
(smaller load impedances) and for longer reaches, it may be necessary to resort to a lenticular characteristic (
B
> 90
°
) to remain within the allowable limit. Lenticular settings greater than 120
°
should never be used. Simi-
larly, the characteristic angle should never be set less than 90
°
.
For each application, a desired reach should be determined and then checked against the
MR using a circular
Mho characteristic. If the desired reach is less than the
MR , then the setting is acceptable. If the desired reach
is greater than the
MR , then the angle B should be increased until MR equals, or just exceeds, the desired
reach.
2.3.3 Z2DISTANCE
201: Z2PHASE - Zone 2 Phase Distance Function
The choice of settings is YES or NO. Set
Z2PHASE
= YES if the Zone 2 phase functions are to be used, other-
wise set
Z2PHASE
= NO.
202: Z2PHREACH - Zone 2 Phase Distance Reach
• Step Distance Scheme
In this scheme, the Zone 2 functions must be set to see a multi-phase fault at the remote bus, considering
such factors as arc resistance and underreach that may be caused by intermediate fault current sources.
Typically, on a two-terminal line,
Z2PHREACH
would be set for 125 to 150% of the positive sequence
impedance of the protected line.
Z2PHREACH
should never be set so large as to:
1. Exceed the maximum allowable reach (
MR ), or,
2. Cause the Zone 2 functions to lose selectivity with the second zone phase distance functions on the
shortest adjoining line section. If this requirement cannot be met by limiting the reach, then it may be
necessary to get this selectivity by setting timer
PUTL2P
with additional time delay.
MR
B 40
°
–
()
Z
L
×
sin
220
°
B
–
E
–
()
sin
----------------------------------------------=
Z
L
EDC
–=