Table 842: Voltages and currents used for induced voltage (emf) E calculation
Voltage selection
setting
Phase
supervision
setting
Calculation of internal induced voltage (emf) E
1
phase-to-earth A or AB
E U I j X
A A leak
= ⋅ + ⋅ ⋅
( )
3 ( )
(Equation 240)
phase-to-earth B or BC
E U I j X
B B leak
= ⋅ + ⋅ ⋅
( )
3 ( )
(Equation 241)
phase-to-earth C or CA
E U I j X
C C leak
= ⋅ + ⋅ ⋅
( )
3 ( )
(Equation 242)
phase-to-phase A or AB
E U I I j X
AB A B leak
= + − ⋅ ⋅
( )
( ) ( )
(Equation 243)
phase-to-phase B or BC
E U I I j X
BC B C leak
= + − ⋅ ⋅
( )
( ) ( )
(Equation 244)
phase-to-phase C or CA
E U I I j X
CA C A leak
= + − ⋅ ⋅
( )
( ) ( )
(Equation 245)
Pos sequence N/A
E U I j X
leak
= ⋅ + ⋅ ⋅
( )
3
1 1
( )
(Equation 246)
If all three phase or phase-to-phase voltages and phase currents
are fed to the protection relay, the positive-sequence alternative is
recommended.
If the leakage reactance of the protected equipment is unknown or if the
measured voltage (U
m
) is to be used in the excitation level calculation,
then by setting the leakage reactance value to zero the calculated
induced voltage (E) is equal to the measured voltage.
The calculated U/f ratio is scaled to a value based on the nominal U
n
/f
n
ratio.
However, the highest allowed continuous voltage (in % U
n
) can be defined by
setting the parameter
Voltage Max Cont
to change the basis of the voltage. The
measured voltage is compared to the new base value to obtain the excitation level.
1
Voltages, currents and the leakage reactance X
leak
in the calculations are given in volts, amps and
ohms.
1MRS759142 F Protection functions
REX640
Technical Manual
887
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