Zone 3 Shaped Characteristics - Siemens 7SG164 Ohmega 400 Series Manual

1.1.4 Zone 3 Shaped Characteristics

In circumstances where the zone conditions come within the reach of the Zone 3 Characteristic
blinders can be applied to prevent load encroachment (See figure 7a, below).
1.1.4.1. Setting of Shape Factors.
The positions of the blinders are set using the shape factor 1 (SF1) and shape factor 2 (SF2) settings
which appear in the distance protection setting menu as part of the zone 3 settings. Each of these
settings has a range from 0.00 to 1.00 in 0.01 steps. Normally, both shape factors would be set to the
same value.
The shape factors control the ratio between the minor and major axes of the shaped characteristic, the
major axis being along the direction of the line angle, and the minor axis being at ninety degrees to the
line angle.
Selecting both SF1 and SF2 to a value S would result in a pair of blinders being placed parallel to the
line angle and equidistant from the protected line. The distance between the blinders in impedance
terms would be SZt, where Zt is the total impedance cover along the line, i.e. the forward impedance
setting Zf plus the reverse impedance setting Zr.
For example, if the relay was set to protect 24Ω in the forward direction and 8Ω in the reverse
direction, and the shape factors were both set to 0.5, then the blinders would be positioned so that the
characteristic had a width of 0.5*(24+8)Ω = 16Ω.
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7SG164 Ohmega 400 Series Impedance Functions
Obviously, this presents no problem for the
Quad characteristic, since the reach along
the resistive axis can be limited. But the
resistive reach of the Mho will depend
its impedance reach and the degree of offs
used.
The method of shaping the mho Zone 3 is to
use adjustable blinders. With a value of 1.0
the blinders are tangential to the circular
characteristic & have no shaping effect. Two
settings are available Shaping factor 1
adjusts the local end of the boundary
characteristic & shaping factor 2 adjusts the
remote end of the characteristic. A value of
1.0 is equivalent to the radius of the total
Zone 3 setting. If a lower value is used for
factor 1 than factor 2 the characteristic is
narrower near the origin allowing for a more
flexible load encroachment characteristic.
upon
et
Chapter 2 Page 8 of 21