2 Functions
86
7SA522 Manual
C53000-G1176-C155-3
Figure 2-24 Release logic for one zone (example for Z1)
In total, the following zones are available:
Independent zones:
• 1st zone (fast tripping zone) Z1 with ;=; 5=, 5(=(; delayable
with 7SKDVH or 7PXOWLSKDVH,
• 2nd zone (backup zone) Z2 with ;=; 5=, 5(=(; may be
delayed by 7SKDVH or 7PXOWLSKDVH,
• 3rd zone (backup zone) Z3 with ;=; 5=, 5(=(; may be
delayed by 7'(/$<,
• 4th zone (backup zone) Z4 with ;=; 5=, 5(=(; may be
delayed by 7'(/$<,
• 5th zone (backup zone) Z5 with ;= (forward) and ;= (reverse); 5=
, 5(=(, delayable with 7'(/$<.
Dependent (controlled) Zone:
• Overreaching zone Z1B with ;=%; 5=%, 5(=%(; may be
delayed by 7%SKDVH or 7%PXOWLSKDVH.
2.2.2.2 Setting Notes
Grading Coordina-
tion Chart
It is recommended to initially create a grading coordination chart for the entire galvan-
ically interconnected system. This diagram should reflect the line lengths with their
primary reactances X in Ω/km. For the reach of the distance zones, the reactances X
are the deciding quantity.
The first zone Z1 is usually set to cover 85 % of the protected line without any trip time
delay (i.e. T1 = 0.00 s). The protection clears faults in this range without additional
time delay, i.e. the tripping time is the relay basic operating time.
The tripping time of the higher zones is sequentially increased by one time grading in-
terval. The grading margin must take into account the circuit breaker operating time
including the spread of this time, the resetting time of the protection equipment as well
as the spread of the protection delay timers. Typical values are 0.2 s to 0.4 s. The
reach is selected to cover up to approximately 80 % of the zone with the same set time
delay on the shortest neighbouring feeder.
When using a personal computer and DIGSI
®
to apply the settings, these can be op-
tionally entered as primary or secondary values.
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