GE MiCOM P40 Agile, Technical Manual, Page: 185 / 962

6.4.1 DYNAMIC TILTING
The dynamic tilting requirements are different for long lines and short lines:
Long lines
In the case of medium and long line applications where quadrilateral distance earth-fault characteristics are used,
Zn Dynamic Tilt should be enabled and the starting tilt angle should be -3° (as per the default settings). This tilt
compensates for possible current and voltage transformer and line data errors.
For high resistive faults during power exporting, the underreaching Zone 1 is only allowed to tilt down by the angle
difference between the faulted phase and negative sequence current
Ð
(Iph-I2) starting from the –3° set angle. This
ensures stability of Zone 1 for high resistance faults beyond the Zone 1 reach even during heavy load conditions
(high load angle between two voltage sources) and sufficient sensitivity for high resistance internal faults. The tilt
angle for all other zones (that are by nature overreaching zones) remain at -3°.
In the case of power importing, Zone 1 remains at –3° while all other zones are allowed to tilt up by the
Ð
(Iph-I2)
angle difference, starting from –3°. This increases the Zone 2 and Zone 4 resistive reaches and secures correct
operation in permissive overreach and blocking type schemes.
Short lines
For very short lines, typically below 10Miles (16km), the ratio of resistive to reactance reach setting (R/X) could
easily exceed 10. For such applications the geometrical shape of the quadrilateral characteristic could be such
that the top reactance line is close or even crosses the resistive axis as presented in the following figure:
V02748
R
Line angle
jX
-3 °
Z1
Iph -I 2
Iph -I 2
Total dynamic tilt starting from zero
Total dynamic tilt starting from -3°
High resistive internal fault
Figure 67: Over-tilting effect
In the case of high resistance external faults on a short line, particularly under heavy power exporting conditions,
Zone 1 remains stable due to dynamic downwards tilting of the impedance reach line. However, the detection of
high resistance internal faults especially towards the end of the line needs consideration. In such applications you
can choose to detect high resistance faults using highly sensitive Aided Directional Earth Fault scheme, or to clear
the fault with Distance ground protection. For the Distance to operate, it is necessary to eliminate over-tilting for
internal faults by reducing the initial -3° tilting angle to zero so that the overall impedance reach line tilt is equal to
Ð
(Iph-I2) angle only.
As shown in the previous figure, the internal resistive fault then falls in the Zone 1 operating characteristic.
However, for short lines the load angle is relatively low when compared to long transmission lines for the same
transfer capacity and therefore the impedance reach line dynamic tilting may be moderate. Therefore it may be
necessary to reduce the Zone 1 reach to guarantee Zone 1 stability. This is particularly recommended if the
distance protection is operating in an aided scheme. To summarise, for very short lines with large R/X setting
ratios, we recommend settiing the initial tilt angle to zero and the Zone 1 reach to 70-75% of the line impedance.
The above discussion assumes homogenous networks where the angle of the negative sequence current derived
at relaying point is very close to the total fault current angle. If the network is non-homogenous, there is a
difference in angle that causes inaccurate dynamic tilting. Therefore in such networks either quadrilateral with
fixed tilt angle or mho characteristic should be considered to avoid Zone 1 overreach.
P446SV Chapter 7 - Distance Protection
P446SV-TM-EN-1 153