CHAPTER 15: THEORY OF OPERATION
THE D90
Plus
DISTANCE ELEMENTS
D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
637
Figure 549: Dynamic shift of the memory-polarized quadrilateral characteristic
Mutual zero-sequence compensation may raise concerns regarding directional integrity
on reverse faults in the situation when the relay gets
overcompensated
. This problem does
not affect the D90
Plus
because its ground distance elements use zero-sequence and
negative-sequence currents in extra directional comparators. Both the currents are from
the protected line and are not affected by any compensation as the latter applies only to
the reach defining comparators: the mho, reactance, and blinder characteristics.
Distance elements analysis
This subsection shows how to analyze the operation of the distance elements in steady
states using the results of short circuit studies. All quantities are secondary ohms, volts,
and amperes. Ground phase A and phase AB distance elements are analyzed. Assume the
following settings have been entered in the
Settings > Protection > Elements > Group 1 >
Ground Distance
menu.
$&'5
;
5
0HPRU\SRODUL]HG
UHYHUVHIDXOW
6HOISRODUL]HG
0HPRU\SRODUL]HG
IRUZDUGIDXOW