5-244 L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
GROUPED ELEMENTS CHAPTER 5: SETTINGS
5
Figure 5-130: Ground distance zones 2 and higher pickup logic
Ground directional supervision
A dual (zero-sequence and negative-sequence) memory-polarized directional supervision applied to the ground distance
protection elements has been shown to give good directional integrity. However, a reverse double-line-to-ground fault can
lead to bad operation of the ground element in a sound phase if the zone reach setting is increased to cover high
resistance faults.
Ground distance zones 2 and higher use an additional ground directional supervision to enhance directional integrity. The
element’s directional characteristic angle is used as a maximum torque angle together with a 90° limit angle.
The supervision is biased toward operation in order to avoid compromising the sensitivity of ground distance elements at
low signal levels. Otherwise, the reverse fault condition that generates concern has high polarizing levels so that a correct
reverse fault decision can be reliably made.
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