GE LPS-O Instruction Manual page 53

2 CALCULATION OF SETTINGS
Figure 2–5: R-X DIAGRAM FOR ZONE 4 DISTANCE FUNCTIONS
The Zone 4 phase distance functions in the LPS-O system are not provided with offset because they use an
adaptive memory feature to provide the operation needed for bolted three-phase faults at the relay location.
The adaptive memory works as follows:
1. If the fault voltage is less than 10 percent of rated voltage, then the voltage prior to the fault will be used to
polarize the Zone 4 functions. This voltage will be held, and the functions will remain picked up, until the
fault is cleared, at which time they will reset.
2. If the voltage is greater than 10 percent of rated voltage, then the voltage prior to the fault will be held for 5
cycles and will then revert to the actual fault voltage. The functions will stay picked up for the duration of
the fault and will reset when the fault clears.
In either case, the functions will provide a continuous output for the duration of the fault and will thus meet the
requirements of the particular application.
401: Z4PHASE - Z4 Phase Distance
Z4PHASE can be set to YES or NO and determines whether or not the functions are to be used in the applica-
tion.
If the Zone 4 phase distance functions are to be used to provide time-delayed backup protection, then set
Z4PHASE = YES; otherwise, set Z4PHASE = NO.
402: Z4PHREACH - Z4 Phase Distance Reach
The Zone 4 phase distance functions can be used to provide an additional zone of time-delayed backup pro-
tection. They can be used to provide a fourth zone of protection in a straight step distance scheme, or they can
be used to provide the so-called "reversed third zone" of protection.
The Zone 4 functions should be set with a reach commensurate with the application, considering underreach
caused by intermediate fault current sources. Z4PHREACH should never be set so large as to:
1. Exceed the maximum allowable reach ( MR ), or,
2. To cause loss of selectivity with phase distance functions providing time-delayed backup on any 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 Z4P_TIME with additional time delay.
GE Power Management
X
OFFSET
Zr
LPS-O Line Protection System
2.3 PROTECTION SETTINGS
R
2
2-
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