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Switching onto a fault
To determine the reaction of the distance protection when closing onto a short circuit, use the parameter in
address 1532 SOTF zone. If set to Inactive, there is no special reaction, i.e. all distance stages operate
according to their preset zone parameters. The setting Zone Z1B causes all faults inside the overreaching
zone Z1B (in the direction specified for these zones) to be cleared without delay after the closure of the circuit
breaker. If Z1B undirect. is set, zone Z1B is also relevant but it acts in both directions, regardless of the
operating direction set in address 1651 or 1751 Op. mode Z1B. The setting to Zone Z1 causes all faults
inside the zone Z1 (in the direction specified for this zone) to be cleared without delay after the closure of the
circuit breaker. This setting is only useful if a delay time has been set for zone Z1. If Z1 undirect. is set, the
zone Z1 is relevant, however, it acts in both directions, regardless of the operating direction set in address 1701
Op. mode Z1. The setting PICKUP implies that the non-delayed tripping following line energization is activated
for all recognized faults in any zone (i.e. with general fault detection of the distance protection).
Blocking of Zone Z1
When the differential protection is active, zone Z1 can be blocked by setting 1533 Z1 blkd by diff to YES;
this means that there will be no measurement and no pickup in Z1 as long as the differential protection is ef-
fective (No. 3120 „Diff active"). Zone Z1 will be reactivated immediately when the differential protection
is ineffective, e.g. due to a communication failure. With address 1533 Z1 blkd by diff set to NO, zone Z1
operates independently of the differential protection.
Zone Z1 can also be blocked by the binary input 3610 „>BLOCK Z1-Trip". This binary input allows, for in-
stance, to specify further blocking conditions relating to the interaction with the differential protection using
CFC. The effect of the binary input does not depend on the status of the differential protection.
Load range (only for impedance pickup)
When using the impedance pickup function on long heavily loaded lines, the risk of encroachment of the load
impedance into the tripping characteristic of the distance protection may exist. To exclude the risk of unwanted
fault detection by the distance protection during heavy load flow, a load trapezoid characteristic may be set for
tripping characteristics with large R-reaches, which excludes such unwanted fault detection by overload. This
load trapezoid characteristic does not apply to the other pickup modes since the trip polygons are only released
after pickup and the pickup function fulfills the task of distinguishing clearly between load operation and short-
circuit. This load area is considered in the description of the tripping characteristics (see also Sections 2.5.2
and 2.5.3).
The R value R load (Ø-E) (address 1541) refers to the phase-to-earth loops, R load (Ø-Ø) (address
1543) to the phase-to-phase loops. The values are set somewhat (approx. 10 %) below the minimum expected
load impedance. The minimum load impedance appears when the maximum load current and minimum oper-
ating voltage exist.
For a 1-pole tripping, the setting of the load trapezoid characteristic for earth loops must consider the load
current in the earth path. This is very critical for double circuit lines (on a tower with significant coupling between
both lines). Due to the zero sequence mutual coupling, a significant amount of load current will flow in the „zero
sequence" path when the parallel line has a single pole open condition. The R setting for the ground loops (or
load encroachment setting) must take into account the ground current that flows when the parallel line has a
single pole open condition.
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
Functions
2.5 Distance Protection
135
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