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2.3 PROTECTION SETTINGS
1. If the reach of the Zone 2 ground distance functions (Z2GRDREACH) at the remote end of the line is
less than twice the positive-sequence impedance of the line, then the proposed setting is:
Z4GRDREACH = 0.85 x Z2GRDREACH
2. If the reach of the Zone 2 ground distance functions at the remote end is greater than twice the posi-
tive-sequence impedance of the line, then the proposed settings are:
Z4GRDREACH = 1.7 x Z2GRDREACH
2
where Z2GRDREACH
Z
= positive sequence impedance of protected line
1 L
With these proposed settings, proper coordination will be obtained between the tripping and blocking func-
tions at the remote terminal of the line. It may be possible to use a shorter setting or a longer setting than
proposed, but
1. If a longer settings is used, then the reach should be checked per the maximum allowable reach pro-
cedure given under Section 2.3.2: ZONE 2, 3, AND 4 DISTANCE FUNCTIONS on page 2–13.
2. If a shorter reach setting is used, then the reach should be checked to assure that the function will
operate for all faults that the remote Zone 2 function can operate for.
When series capacitors are used on the protected line or in lines adjacent to the protected line, set the
Zone 4 ground distance functions with a reach that is equal to or greater than the reach of the ground dis-
tance pilot tripping functions (normally Zone 2) at the remote end of the transmission line. For example:
Z4GRDREACH ≥ Z2GRDREACH
where Z2GRDREACH
at the remote end of the line.
•
Step Distance and POTT1 Schemes
In all other schemes, the Zone 4 ground distance functions can provide an additional zone of time-delayed
backup protection. They can be used to provide a fourth zone of protection in a straight Step Distance
scheme, or they can be reversed in direction to provide the so-called "reversed third" of protection.
The Zone 4 ground distance functions should be set with a reach commensurate with the application, con-
sidering underreach caused by intermediate fault current sources. Z4GRDREACH should never be set so
large as to:
1. Exceed the maximum allowable reach ( MR ), or
2. Cause loss of selectivity with any ground 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 Z4G_TIME with additional time delay.
407: Z4GCHARANG - Zone 4 Ground Characteristic Angle
•
Blocking and Hybrid Schemes
Set the Zone 4 characteristic angle to 10° less than the characteristic angle setting (Z2GCHARANG
the Zone 2 functions at the remote terminal of the line; that is:
Z4CHARANG = Z2CHARANG
•
Step Distance, POTT1, and POTT2 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 and lower than 90° should not be used except in blocking, hybrid and POTT2
types of schemes. If the desired reach, Z4GRDREACH, with a 90° characteristic and with maximum load
2-
22
R
= reach of phase Zone 2 functions at remote line terminal
R
R
is the reach of the ground distance pilot tripping functions (Zone 2 in this example)
R
– 10°
R
LPS-D Line Protection System
2 CALCULATION OF SETTINGS
R
– Z
1 L
) of
R
GE Power Management
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