Siemens SIPROTEC 7SA6 Manual page 249

Distance protection relay for all voltage levels

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Assignment to the

C53000-G1176-C156-2

Directional characteristic with quadrature or memorized voltages

Using the fault detection modes I , U/ I or U/ I / ϕ according to Subsection 6.2.2 the im-

pedances, that were calculated from the valid loops, are assigned, after the pick-up,

to the zone characteristics set for the distance protection. To avoid unstable signals at

the boundaries of a polygon, the characteristics have a hysteresis of approximately

5 % i.e. as soon as it has been determined that the fault impedance lies within a pol-

ygon, the boundaries are increased by 5 % in all directions. The loop information is

also converted to faulted phase indication

Using the impedance pick-up the loop impedances calculated according to Subsection

6.2.3 are also assigned to the zone characteristics set for the distance protection, but

without a query of an explicite fault detection scheme. The pick-up range of the Dis-

tance Protection is determined from the thresholds of the largest-set polygon taking

into consideration the respective direction. Here the loop information is also converted

into faulted phase indication.

"Pick-up" signals are also generated for each zone and converted into phase informa-

tion, e.g. Dis.Pickup L1 Z1 for zone Z1 and phase L1. This means that each phase

and each zone is provided with separate pick-up information. The information is then

processed in the zone logic (see Subsection 6.2.5) and by additional functions (e.g.

signal transmission logic, Subsection 6.6.1).

The loop information is also converted to phase indications. Further conditions for the

"pick-up" of a zone are that the direction must be in accordance with the configured

direction for the zone and that the zone is not blocked by the power swing blocking

(see Subsection 6.3.1). Furthermore the Distance Protection system must not be

switched off totally or blocked. Figure 6-33 shows the conditions mentioned.