Comparison Of Setting With Thr Relay - Siemens 7SG164 Ohmega 400 Series Manual

The above figure shows the position of blinders if different values are chosen for SF1 & SF2.

1.1.5 Comparison of Setting with THR Relay

In order to ease application of the characteristic, it is recommended that the same ratios of minor to
major axis are used as were provided with the THR relay. These are given in the table below.
The method of achieving the THR shaped characteristic resulted in the characteristic shape being
"waisted" with two distinct lobes. As a result, these lobes did have a reach slightly beyond the minor
axis width calculated from the shape factors. These values (ratios) are given below for reference.
Selecting different link positions on THR resulted in unequal lobe widths, giving an asymmetrical
characteristic. This could be advantageous for some applications, and this effect can be achieved by
selecting unequal values for SF1 and SF2. The value of SF1 controls the width of the "lobe" at the
local (relay) end of the characteristic, i.e. that part of the characteristic with reverse reach, and SF2
controls the width of the remote part of the characteristic. Selecting values from the above table will
result in similar profiles.
©2010 Siemens Protection Devices Limited
Ratio of minor to major
axis a/b
0.36
0.5
0.6
0.75
7SG164 Ohmega 400 Series Impedance Functions
THR maximum lobe
width (as ratio)
0.38
0.52
0.62
0.752
Chapter 2 Page 9 of 21