Aided Def Scheme Logic; Aided Def Introduction; Implementation; Aided Def Polarization - GE MiCOM P40 Technical Manual

Chapter 8 - Carrier Aided Schemes
5

AIDED DEF SCHEME LOGIC

5.1

AIDED DEF INTRODUCTION

High resistance faults may be difficult to detect using distance protection. A Directional Earth Fault DEF element is
sometimes used in conjunction with a communication scheme to provide protection against such faults. The use
of Aided-Trip logic in conjunction with the DEF element allows faster trip times, and can facilitate single-phase
tripping, if needed.
To use the Aided DEF protection you will need appropriate communication channels between terminals in the
scheme. The Programmable Scheme Logic (PSL) allows you to map signals for communication over the channels.
The signals you map may be signals to be sent to a remote terminal, or signals expected to be received from a
remote terminal. Two Aided DEF schemes are available.
With Aided DEF protection, the residual current (earth fault current) is compared with a threshold to determine the
presence of a fault, and a directionalising quantity to determine its direction. Directional measurements from
protecting terminals are then used in conjunction with teleprotection signals between the terminals, and aided
scheme logic to determine whether the fault is within the protected line (and hence trip), or outside the protected
line (and hence restrain).
5.2

IMPLEMENTATION

Aided DEF protection can be used with permissive over-reach schemes or blocking schemes.
The Aided DEF protection is enabled using the Directional E/F setting in the CONFIGURATION column. This makes
the settings in the AIDED DEF column visible.
The Aided DEF requires a polarizing quantity (selected in the DEF Polarizing setting) in conjunction with a
characteristic angle setting (DEF Char. Angle) to make the directional decision.
For all models a signal derived from the phase voltage inputs can be used for polarization. For certain models with
more VT inputs, a directly measured input can be used.
You have a choice between Zero Sequence Polarizing or Negative Sequence Polarizing for the Aided DEF element.
If you choose Zero Sequence Polarization, you have a choice to enable an innovative feature known as Virtual
Current Polarization to enhance the Aided DEF function.
Aided DEF protection is blocked if any of the following conditions are met:
An Any Trip signal is asserted by one of the integrated protection functions
●
The phase selector picks up on more than one phase
●
● Any of the signals Pole Dead A, Pole Dead B, or Pole Dead C are asserted
5.3

AIDED DEF POLARIZATION

There are essentially two ways of esablishing the direction of an earth fault:
Zero sequence polarization
●
Negative sequence polarization
●
Zero Sequence polarization normally uses the measurement of residual voltage (VN). This can only be achieved if a
5-limb VT or three single-phase VTs are used. A special form of zero sequence polarization called Virtual Current
Polarization is also possible with this device. Virtual Current Polarization allows directionalisation for low levels of
polarization voltage.
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P446SV
P446SV-TM-EN-1