GE LPS-D, Instruction Manual, Page: 87 / 436

GE Power Management LPS-D Line Protection System 2-
21
2 CALCULATION OF SETTINGS 2.3 PROTECTION SETTINGS
2
The Zone 4 functions should be set with a reach commensurate with the application, considering under-
reach 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.
403: Z4PCHARANG - Zone 4 Phase Characteristic Angle
• Blocking, Hybrid and POTT2 Schemes:
Set the Zone 4 characteristic angle to 10° less than the characteristic angle setting (Z2PCHARANG
R
) of
the Zone 2 functions at the remote terminal of the line; that is:
Z4PCHARANG = Z2PCHARANG
R
– 10°
• Step Distance and POTT1 Schemes:
This setting determines the characteristic shape and, consequently, the area of resistance coverage pro-
vided by the Zone 4 phase distance functions. Z4PCHARANG can be set to 80° to 120° in 5° steps. A 90°
setting is recommended; values lower than 90° should not be used except in blocking, hybrid and POTT2
types of schemes. If the desired reach, Z4PHREACH, with a 90° characteristic and with maximum load
flow does not allow the maximum allowable reach criteria to be met, then a "lens-shaped" characteristic
must be used. The settings of both Z4PHREACH and Z4PCHARANG may be evaluated by using the for-
mula associated with the method of Figure 2–4: MAXIMUM ALLOWABLE REACH on page 2–13.
405: Z4GRND - Zone 4 Ground Distance
Z4GRND can be set to YES or NO and determines whether or not Zone 4 ground-distance functions are used
in the application.
• Blocking, Hybrid, and POTT2 schemes
The Zone 4 ground distance functions are always required in these schemes; therefore, set
Z4GRND = YES
• Step Distance and POTT1 Schemes
If the Zone 4 ground distance functions are to be used to provide time-delayed backup protection, then set
Z4GRND = YES; otherwise, set Z4GRND = NO.
406: Z4GRDREACH - Z4 Ground Reach
• Blocking, Hybrid, and POTT2 Schemes
In a blocking scheme, the Zone 4 functions key the transmitter to send a blocking signal to the remote ter-
minal of the line to block tripping for an external fault (F1 for example) within reach of the Zone 2 functions
located at the remote terminal (see Figure 2–8: ZONE 4 FAULT EXAMPLE on page 2–19).
In a hybrid scheme, the Zone 4 functions prevent keying of the transmitter to block echoing of the trip sig-
nal that was received as a result of the operation of the remote Zone 2 functions for an external fault (at F1
for example) within their reach.
In a POTT2 scheme the Zone 4 functions establish transient blocking circuitry to prevent tripping during
fault clearing and fault current reversals.
In all of these schemes, it is imperative that the blocking functions be set with a reach that will allow them
to see all faults that the remote Zone 2 functions will see. The following guidelines are proposed: