Voltage selection setting Phase supervision
setting
Calculation of internal induced voltage (emf) E
1)
phase-to-phase B or BC
E V I I j X
BC B C leak
= + − × ×
( )
( ) ( )
GUID-AF78379A-78B9-466A-85E1-593333656FB8 V2 EN
phase-to-phase
C or CA
E V I I j X
CA C A leak
= + − × ×
( )
( ) ( )
GUID-90521B6F-C9B3-411F-82AD-E5AAF3D3ACEA V2 EN
Pos sequence
N/A
E V I j X
leak
= × + × ×
( )
3
1 1
( )
GUID-E79E33FD-02FF-4E92-80A4-C7FEBB99C839 V2 EN
1) Voltages, currents and the leakage reactance X
leak
in the calculations are given in volts, amps and ohms.
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 (V
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 V/f ratio is scaled to a value based on the nominal V
n
/f
n
ratio. However, the
highest allowed continuous voltage (in % V
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.
The excitation level (M) can be calculated:
M
E
f
V
f
Volt Max continuous
m
n
n
=
⋅
100
GUID-2712EB3B-0126-44B6-AABC-AA4BD2569FFB V1 EN (Equation 120)
M
excitation level (V/f ratio or volts/hertz) in pu
E internal induced voltage (emf)
f
m
measured frequency
V
n
nominal phase-to-phase voltage
f
n
nominal frequency
Section 4 1MAC059074-MB A
Protection functions
644 615 series ANSI
Technical Manual
To Next Page
Loading...
