Table of Contents
Advertisement
2.3 PROTECTION SETTINGS
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
2
•
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.
•
Blocking, Hybrid PUTT, POTT1, and POTT2 Schemes
The primary purpose of the Zone 2 functions in any of the pilot relaying schemes is to detect a fault any-
where on the transmission line and to work with the pilot channel to provide fast and secure tripping. To
this end, the functions must be set to reach beyond the remote terminal of the transmission line and this
requirement may be met by setting the functions with a reach of 125 to 200% of the transmission line.
Although the reach requirement would be met with such settings, the operating time might not be at the
optimum when taking into account the operating characteristics of the distance functions as shown below.
For example if the reach of the Zone 2 functions is set to 125% of line impedance, then the operating time
for remote faults would fall in the area of the upturn of the operating time characteristic, and tripping will be
affected accordingly. On the other hand, if the reach of the Zone 2 functions is set to 300% of the line or
greater, then the operating time for any line fault would fall along the flat part of the time characteristic, and
the fastest possible pilot tripping will be obtained for any fault. It is especially beneficial to use the settings
just described on short lines wherein the fastest possible tripping is required in terms of system stability.
With settings just described, the Zone 2 functions lose their usefulness to provide Zone 2 time-delayed
backup protection because coordination with Zone 2 functions in adjoining lines will not be achieved. In
that event, the Zone 2 timers can be turned off, or they can be set with a time delay corresponding to Zone
3 time if a third zone of protection is required. To obtain Zone 2 time-delayed protection, use the Zone 3
functions and set them with a Zone 2 reach (125% of line) and set the respective Zone 3 timers with a
Zone 2 time delay.
In any event, the Zone 2 functions should not be set with a reach any longer than the maximum allowable
reach ( MR ) described earlier.
2-
14
REACH (IN PERCENT)
Figure 2–5: OPERATING TIME CHARACTERISTIC
LPS-D Line Protection System
2 CALCULATION OF SETTINGS
2.3.3 Z2DISTANCE
100
GE Power Management
Advertisement
Table of Contents
