the other end. Everything that is placed between these two CT groups (including
CBs) are included in the protected zone.
To apply the exact (voltage-based) method of charging current compensation, the
power line's positive and zero-sequence capacitances must be known. If not known,
the approximate method can be applied instead.
Table
4 shows the power system parameters in this example.
Table 4: Power system parameters
Power line data Value Remark
Number of three-phase CT groups
(each group represents an
independent source of information
about the current)
2
A two-end power line with one three-phase CT group installed at each
end.
Setting NoOfUsedCTs is used to indicate to L4CPDIF how many
current input channels (2, 3 or 4) with current samples are to be read
and processed.
Source impedance at both ends
4.84 Ω -
Power line length 200 km -
Rated voltage 220 kV -
Line impedance ZL ≈ XL 58.64 Ω -
Total zero sequence line
capacitance, C0
7.751e-9 x 200 7.751e-9 F per 1 km of line
Total positive sequence line
capacitance, C1
12.74e-9 x 200 12.74e-9 F per 1 km of line
Charging current
(measured without charging current
compensation)
92 A
Measured at rated voltage as the differential current under normal load.
Rated current 1000 A
Table 5 shows the relevant settings in this example.
Table 5: Relevant settings
Setting
Value Remark
IdMin 0.20 20 % of IBase = 1000 A
Must be set above the maximum possible charging current (in this
example set to approximately 2 x of that value).
EndSection1
1.00 100 % of IBase = 1000 A
EndSection2 3.00 300 % of IBase = 1000 A
SlopeSection2 0.50 Slope = 50 %
SlopeSection3 1.00 Slope = 100 %
IdMinHigh 1.00 100 % of IBase = 1000 A
tIdMinHigh 1000 Interval of initial decreased sensitivity in ms.
Table continues on next page
1MRK 505 382-UEN B Section 4
Analog and binary signal transfer for line differential protection
Communication set-up 670/650 series 2.2 49
Application Guide
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