Setting Guidelines (Time Delay); Setting Guidelines (Directional Element) - GE MiCOM P40 Agile Technical Manual

P14x
approximately 20% below the lowest calculated negative phase sequence fault current contribution to a specific
remote fault condition.
9.5.2

SETTING GUIDELINES (TIME DELAY)

Correct setting of the time delay for this function is vital. You should also be very aware that this element is applied
primarily to provide back-up protection to other protection devices or to provide an alarm. It would therefore
normally have a long time delay.
The time delay set must be greater than the operating time of any other protection device (at minimum fault level)
that may respond to unbalanced faults such as phase overcurrent elements and earth fault elements.
9.5.3

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, directional 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.
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Chapter 6 - Current Protection Functions
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