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2 Functions
The following secondary side setting value of zone 2 results at address 3310 ZONE
Z2:
Figure 2-30
The Z1B overreach zone (address 3308 ZONE Z1B) is an externally controlled stage.
Z1B Overreach
Zone
It does not influence the Z1 zone normal stage. Consequently there is no changeover,
but the overreach zone is enabled or disabled depending on the position of the high-
voltage side circuit breaker.
The Z1B zone is usually enabled by an opened high-voltage circuit breaker. In this
case every impedance protection pickup can only be due to a fault in the protection
zone of the block, since the power system is disconnected from the block. Conse-
quently the fast tripping zone can be extended to between 100 % and 120 % of the
protection zone without any loss of selectivity.
The Z1B zone is activated via a binary input controlled by the circuit breaker auxiliary
contact (see Figure 2-30). The overreach zone is allocated an individual 3309 T-Z1B
time delay.
Final Stage
For short circuits outside the Z1 and Z2 zones, the device functions as a time-delayed
overcurrent protection. Its nondirectional final time T END is selected so that its time
value overreaches the second or third stage of the series-connected network distance
protection.
100
Time Grading for Machine Impedance Protection – Example
7UM61 Manual
C53000-G1176-C127-3
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