GE ALPS Instruction Manual page 81

2 CALCULATION OF SETTINGS
302: Z3PHREACH - Zone 3 Phase Reach
In a Step Distance scheme Zone 3 provides backup protection for adjoining line sections out of the remote bus, and
Z3PHREACH should be set to see a multiphase fault at the end of the longest adjoining line section out of the remote bus,
considering such factors as arc resistance and underreach caused by intermediate fault current sources. Z3PHREACH
should never be set so large as to:
Exceed the maximum allowable reach ( MR ), or,
1.
2. Cause the Zone 3 functions to lose selectivity with the third 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 Z3P_TIME with additional time delay.
303: Z3PCHARANG - Zone 3 Phase Characteristic Angle
This setting determines the characteristic shape and, consequently, the area of resistance coverage provided by the Zone
3 phase distance functions. Z3PCHARANG can be set to 90° to 120° in 5° steps. A 90° setting is recommended. If the
desired reach, Z3PHREACH, 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 Z3PHREACH and
Z3PCHARANG may be evaluated by using the formula associated with the "Maximum Allowable Reach" method of Figure
2–5: MAXIMUM ALLOWABLE REACH on page 2–13.
304: Z3GROUND - Select Zone 3 Ground
Z3GROUND can be set to either YES or NO. When Zone 3 is used as part of a Step Distance scheme, and Zone 3 ground
distance functions are required then set Z3GROUND = YES. If Zone 3 is not used required, set Z3GROUND = NO.
305: Z3GRDREACH - Zone 3 Ground Reach
In a Step Distance scheme Zone 3 provides backup protection for adjoining line sections out of the remote bus, and
Z3GRDREACH should be set to see a multiphase fault at the end of the longest adjoining line section out of the remote
bus, considering such factors as arc resistance and underreach caused by intermediate fault current sources.
Z3GRDREACH should never be set so large as to:
1. Exceed the maximum allowable reach ( MR ), or,
2. To cause the Zone 3 functions to lose selectivity with the third zone ground 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 Z3G_TIME with additional time delay.
306: Z3GCHARANG - Zone 3 Ground Characteristic Angle
This setting determines the characteristic shape and, consequently, the area of resistance coverage provided by the Zone
3 phase distance functions. Z3GCHARANG can be set to 80 to 155° in 5° steps. A 90° setting is recommended. If the
desired reach, Z3GRDREACH, with a 90° characteristic and with maximum load flow does not allow the maximum allow-
able reach criteria to be met, then a "lens-shaped" characteristic must be used. The settings of both Z3GRDREACH and
Z3GCHARANG may be evaluated by using the formula associated with the "Maximum Allowable Reach" method of Figure
2–5: MAXIMUM ALLOWABLE REACH.
307: Z3P_TIME - Z3 Phase Timer
Z3P_TIME can be set from 0.10 to 10.00 seconds. If the Zone 3 phase distance functions are applied to provide traditional
third zone protection, then the Z3P_TIME time delay should be set long enough to coordinate with the second zone timers
in adjoining line sections. If the Zone 3 phase distance functions are used to provide traditional second zone protection
(described earlier), set Z3P_TIME with the appropriate time delay.
308: Z3G_TIME - Z3 Ground Timer
Z3G_TIME can be set from 0.10 to 10.00 seconds. If the Zone 3 ground distance functions are applied to provide traditional
third zone protection, then the Z3G_TIME time delay should be set long enough to coordinate with the second zone timers
in adjoining line sections. If the Zone 3 ground distance functions are used to provide traditional second zone protection
(described earlier), set Z3G_TIME with the appropriate time delay.
GE Power Management ALPS Advanced Line Protection System
2.3 PROTECTION SETTINGS
2-17
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