Zone 1 Reach Setting (Z1%)
The Zone 1 reach is typically set short of the forward remote terminal. Thus, the Zone 1
elements provide instantaneous protection for phase-phase, three-phase, and phase-ground
faults in the first 75-80% of the transmission line. The remainder of the line is protected by
the overreaching Zone 2 elements. While the percent error of the impedance element reach is
less than 5%, errors in the CT and PT ratios, modeled transmission line data, and fault study
data do not permit Zone 1 element settings of 100%.
In this example, the Zone 1 distance elements at Breaker 3 must not reach past Bus C. To
prevent overreaching due to the sources of error listed above, the required reach for the
Zone 1 three-phase and phase-phase elements is 80% of the positive-sequence impedance of
Line 2.
The reach settings for the phase distance elements are a percentage of the positive-sequence
line impedance settings along the line angle. When the MTA setting differs from the positive-
sequence line angle, the relay calculates the mho circle diameter with the following equation:
For this example, the diameter of the Zone 1 mho circle along the MTA is:
For the relay at Breaker 3:
- Setting Limit Check
The primary limit check allows Zone 1 percent reach settings of 0 - 2000%. The secondary
setting check allows secondary reach settings of 0.125 - 64 ohms secondary along the MTA.
Calculations:
PTR=2000:1
PTR/CTR=10
CTR = 200: l
The Z1 % setting of 80 for this example lies within primary and secondary setting limits of the
relay.
Date Code 920508
Applications
5-13
SEL-221F, -1 Instruction Manual
Summary of Contents for SEL-221F
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Page 110: ...Example Event Report 2 4 12 Event Reporting SEL 221F 1 Instruction Manual Date Code 930830 ...
Page 158: ...SETTINGS SHEET FOR SEL 221F RELAY PAGE 2 OF 6 DATE Date Code 921110 ...
Page 160: ...SETTINGS SHEET PAGE 4 OF 6 FOR SEL 221F RELAY DATE Date Code 930601 ...
Page 161: ...SETTINGS SHEET PAGE 5 OF 6 FOR SEL 221F RELAY DATE Date Code 961208 ...
Page 229: ...SEL 200 Series Relay Main Board Troubleshooting Test Points and Jumper Locations ...