GE T60, Instruction Manual

Page: 341 / 796

GE Multilin T60 Transformer Protection System 5-195
5 SETTINGS 5.6 GROUPED ELEMENTS
5
zero-sequence impedance between the lines and the positive-sequence impedance of the protected line. It is impera-
tive to set this setting to zero if the compensation is not to be performed. Note that internally the mutual coupling com-
pensation is applied only if 3I_0>1.22*IG to ensure that no mutual coupling compensation is applied when the fault is
on the parallel line. Mutual coupling compensation is applied when distance source is assigned with 8F or 8L type DSP
module only and when the ratio of the protected line ground current to parallel line ground current is greater than 1.22.
• GND DIST Z1 ZOM/Z1 ANG: This setting specifies the angle difference between the mutual zero-sequence imped-
ance between the lines and the positive-sequence impedance of the protected line.
• GND DIST Z1 REACH: This setting defines the reach of the zone for the forward and reverse applications. In non-
directional applications, this setting defines the forward reach of the zone. The reverse reach impedance in non-direc-
tional applications is set independently. The angle of the reach impedance is entered as the
GND DIST Z1 RCA
setting.
The reach impedance is entered in secondary ohms.
To achieve specified operating speed of distance elements, the relay internally calculates source to line impedance
ratio (SIR) from fault phasors. In these calculations, line impedance is estimated based on the zone 1 reach setting.
Therefore, in order to calculate the SIR value properly and to maintain the optimal operating speed of the distance ele-
ments, you need to set zone 1 reach with a regular 80 to 85% of the line impedance reach setting, even when zone 1
is disabled.
• GND DIST Z1 RCA: This setting specifies the characteristic angle (similar to the maximum torque angle in previous
technologies) of the ground distance characteristic for the forward and reverse applications. In the non-directional
applications this setting defines the forward reach of the zone. The reverse reach impedance in the non-directional
applications is set independently. This setting is independent from the
GND DIST Z1 DIR RCA
setting (the characteristic
angle of an extra directional supervising function).
The relay internally performs zero-sequence compensation for the protected circuit based on the values
entered for
GND DIST Z1 Z0/Z1 MAG
and
GND DIST Z1 Z0/Z1 ANG
, and if configured to do so, zero-sequence com-
pensation for mutual coupling based on the values entered for
GND DIST Z1 Z0M/Z1 MAG
and
GND DIST Z1 Z0M/Z1
ANG
. The
GND DIST Z1 REACH
and
GND DIST Z1 RCA
should, therefore, be entered in terms of positive sequence
quantities. Refer to chapters 8 for additional information
• GND DIST Z1 REV REACH : This setting defines the reverse reach of the zone set to non-directional (
GND DIST Z1 DIR
setting). The value must be entered in secondary ohms. This setting does not apply when the zone direction is set to
“Forward” or “Reverse”.
• GND DIST Z1 REV REACH RCA : This setting defines the angle of the reverse reach impedance if the zone is set to
non-directional (
GND DIST Z1 DIR
setting). This setting does not apply when the zone direction is set to “Forward” or
“Reverse”.
• GND DIST Z1 POL CURRENT : This setting applies only if the
GND DIST Z1 SHAPE
is set to “Quad” and controls the
polarizing current used by the reactance comparator of the quadrilateral characteristic. Either the zero-sequence or
negative-sequence current could be used. In general, a variety of system conditions must be examined to select an
optimum polarizing current. This setting becomes less relevant when the resistive coverage and zone reach are set
conservatively. Also, this setting is more relevant in lower voltage applications such as on distribution lines or cables,
as compared with high-voltage transmission lines. This setting applies to both the zone 1 and reverse reactance lines
if the zone is set to non-directional. Refer to chapters 8 and 9 for additional information.
• GND DIST Z1 NON-HOMOGEN ANG : This setting applies only if the
GND DIST Z1 SHAPE
is set to “Quad” and provides
a method to correct the angle of the polarizing current of the reactance comparator for non-homogeneity of the zero-
sequence or negative-sequence networks. In general, a variety of system conditions must be examined to select this
setting. In many applications this angle is used to reduce the reach at high resistances in order to avoid overreaching
under far-out reach settings and/or when the sequence networks are greatly non-homogeneous. This setting applies to
both the forward and reverse reactance lines if the zone is set to non-directional. Refer to chapters 8 and 9 for addi-
tional information.
• GND DIST Z1 COMP LIMIT: This setting shapes the operating characteristic. In particular, it enables a lens-shaped
characteristic of the mho function and a tent-shaped characteristic of the quadrilateral function reactance boundary. If
the mho shape is selected, the same limit angle applies to mho and supervising reactance comparators. In conjunction
with the mho shape selection, this setting improves loadability of the protected line. In conjunction with the quadrilat-
eral characteristic, this setting improves security for faults close to the reach point by adjusting the reactance boundary
into a tent-shape.
• GND DIST Z1 DIR RCA: Selects the characteristic angle (or ‘maximum torque angle’) of the directional supervising
function. If the mho shape is applied, the directional function is an extra supervising function, as the dynamic mho
NOTE