ABB RELION REX640 - 11.7 Calculated measurements

of the measurement window. The frequency of the fault current affects the operate
time. The damping of the harmonics is quite low and practically determined by the
characteristics of the anti-aliasing filter of the protection relay current inputs.
When using measurement mode “Wide P-to-P”, the protection relay
accepts only Operate delay time setting value 800 ms or longer and
Operating curve type 5=”ANSI Def. Time” or 15=”IEC Def. Time”.
Operation accuracy in the frequency range 2...85 Hz is ±1.5% or ±0.003 × I
n
. Operate
time accuracy in definite time mode is ±1.0% of the set value or ±60 ms when I
Fault
=
2 × set Start value and the fault current frequency is 10...85 Hz.
11.7 Calculated measurements
Calculated residual current and voltage
The residual current is calculated from the phase currents according to equation:
Io I I I
A B C
= − + +( )
(Equation 404)
The residual voltage is calculated from the phase-to-earth voltages when the VT
connection is selected as “Wye” with the equation:
Uo U U U
A B C
= + +( ) / 3
(Equation 405)
Sequence components
The phase-sequence current components are calculated from the phase currents
according to:
I I I I
A B C0
3= + +( ) /
(Equation 406)
I I a I a I
A B C1
2
3= + ⋅ + ⋅( ) /
(Equation 407)
I I a I a I
A B C2
2
3= + ⋅ + ⋅( ) /
(Equation 408)
The phase-sequence voltage components are calculated from the phase-to-earth
voltages when VT connection is selected as “Wye” with the equations:
U U U U
A B C0
3= + +( ) /
(Equation 409)
General function block features
1MRS759142 F
1910 REX640
Technical Manual