3.4.3 SETTING GUIDELINES (DIRECTIONAL ELEMENT)
Where negative phase sequence current may flow in either direction through an IED location, such as parallel lines
or ring main systems, dir
ectional control of the element should be employed (VT models only).
Directionality is achieved by comparing the angle between the negative phase sequence voltage and the negative
phase sequence current and the element may be selected to operate in either the forward or reverse direction. A
suitable relay characteristic angle setting (I2> Char Angle) is chosen to provide optimum performance. This setting
should be set equal to the phase angle of the negative sequence current with respect to the inverted negative
sequence voltage (–V2), in order to be at the centre of the directional characteristic.
The angle that occurs between V2 and I2 under fault conditions is directly dependent on the negative sequence
source impedance of the system. However, typical settings for the element are as follows:
● For a transmission system the relay characteristic angle (RCA) should be set equal to –60°
● For a distribution system the relay characteristic angle (RCA) should be set equal to –45°
For the negative phase sequence directional elements to operate, the device must detect a polarising voltage
above a minimum threshold, I2> V2pol Set. This must be set in excess of any steady state negative phase
sequence voltage. This may be determined during the commissioning stage by viewing the negative phase
sequence measurements in the device.
P54A/B/C/E Chapter 9 - Current Protection Functions
P54xMED-TM-EN-1 201
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