GE T60 Instruction Manual page 512
Transformer protection system
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Also See for T60:
- Instruction manual (796 pages) ,
- Communications manual (532 pages) ,
- Communications manual (526 pages)
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GROUPED ELEMENTS
Table 5-42: Negative-sequence directional overcurrent unit
Mode
Negative-sequence
Zero-sequence
Table 5-43: Negative-sequence directional unit
Direction
Compared phasors
Forward
–V_2 + Z_offset × I_2
Reverse
–V_2 + Z_offset × I_2
Z_offset is the offset impedance, for which magnitude is the OFFSET setting and angle is the FWD ECA.
The negative-sequence voltage must be greater than 0.02 pu to be validated for use as a polarizing signal. Additionally,
when offset impedance is applied and negative-sequence current is above 0.2 pu, compensated negative-sequence
voltage -V_2 + Z_offset x I_2 has to be above 0.02 pu in order to discriminate fault direction; otherwise when negative-
sequence current is less than 0.2 pu, -V_2 is then used as the polarizing signal. If the polarizing signal is not validated,
neither forward nor reverse indication is given. The following figure explains the usage of the voltage polarized directional
unit of the element. It shows the phase angle comparator characteristics for a phase A to ground fault, with settings of
ECA = 75° (element characteristic angle = centerline of operating characteristic)
FWD LA = 80° (forward limit angle = ± the angular limit with the ECA for operation)
REV LA = 80° (reverse limit angle = ± the angular limit with the ECA for operation)
The element incorporates a current reversal logic: if the reverse direction is indicated for at least 1.25 of a power system
cycle, the prospective forward indication is delayed by 1.5 of a power system cycle. The element emulates an
5
electromechanical directional device. Larger operating and polarizing signals result in faster directional discrimination,
bringing more security to the element operation.
5-294
Operating current
I
= |I_2| – K × I_1|
op
I
= 3 × (|I_0| – K × |I_1|) if |I_1| > 0.8 pu
op
I
= 3 × |I_0| if |I_1| ≤ 0.8 pu
op
I_2 × 1∠ECA
–(I_2 × 1∠ECA)
T60 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
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