ERL L-PRO 4000, User Manual

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4 Protection Functions and Specifications
4-10 L-PRO 4000 User Manual D02706R02.30
Directional
Element
The relay includes a directional element that directly supervises the Zone 1 to
Zone 5 phase and ground distance elements, the 50/51/67, 50N/51N/67N, 46-
50/51/67 overcurrent elements, and the 50N/67F and 50N/67R elements in the
Communications Aided Tripping schemes. The directional element considers
negative-sequence impedance, zero-sequence impedance, or positive-se-
quence impedance, depending on relay settings and system conditions at the
time of the fault. The element declares a forward fault when the impedance de-
termined by the directional element is within 90° of the line impedance.
Figure 4.8: Fault Direction
The directional element in the relay is always enabled. The directional element
actually consists of 3 separate internal elements: a negative-sequence element,
a zero-sequence element, and a positive-sequence element. The negative-se-
quence and zero-sequence elements use directly measured currents and voltag-
es. The positive-sequence element uses directly measured current, and a
memory voltage from the ring filter. The sensitivity for the negative- and zero-
sequence elements may be set by the user, to correctly account for load condi-
tions and system configuration. Both of these elements may be disabled as
well. The positive-sequence element is always active.
Reverse
Forward
Line Impedance
R
jX
90.0
Line Z Angle