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L30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
GROUPED ELEMENTS
CHAPTER 5: SETTINGS
5
The phase directional elements (one for each of phases A, B, and C) determine the phase current flow direction for steady
state and fault conditions and can be used to control the operation of the phase overcurrent elements via the
BLOCK
inputs
of these elements.
Figure 5-112: Phase A directional polarization
This element is intended to apply a block signal to an overcurrent element to prevent an operation when current is flowing
in a particular direction. The direction of current flow is determined by measuring the phase angle between the current
from the phase CTs and the line-line voltage from the VTs, based on the 90° or quadrature connection. If there is a
requirement to supervise overcurrent elements for flows in opposite directions, such as can happen through a bus-tie
breaker, two phase directional elements should be programmed with opposite element characteristic angle (ECA) settings.
To increase security for three phase faults very close to the VTs used to measure the polarizing voltage, a voltage memory
feature is incorporated. This feature stores the polarizing voltage the moment before the voltage collapses, and uses it to
determine direction. The voltage memory remains valid for one second after the voltage has collapsed.
The main component of the phase directional element is the phase angle comparator with two inputs: the operating signal
(phase current) and the polarizing signal (the line voltage, shifted in the leading direction by the characteristic angle, ECA).
The table shows the operating and polarizing signals used for phase directional control.
PHASE DIR 1
EVENTS: Disabled
Range: Disabled, Enabled
The TARGET setting is not user-selectable and forced to "Disabled". If Targets are required from directional
elements, it can be achieved by assigning directional element output to a digital element, where targets selection
can be used as required.
