ABB 615 Series ANSI, Technical Manual

Page: 257 / 713

Section 4
1MAC050144-MB C
Protection functions
250 615 series ANSI
Technical Manual
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:
Equation 6
M the excitation level (V/f ratio or volts/hertz) in pu
E the internal induced voltage (emf)
fm the measured frequency
Vn the nominal phase-to-phase voltage
fn
the nominal frequency
Setting
Voltage selection
Setting
Phase supervision
Calculation of internal induced voltage (emf) E
phase-to-ground A or AB
phase-to-ground B or BC
phase-to-ground C or CA
phase-to-phase A or AB
phase-to-phase B or BC
phase-to-phase C or CA
Pos sequence N/A
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 IED, the positive-sequence alternative is recommended.
If the leakage reactance of the protected equipment is unknown or if the
measured voltage (Vm) 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.
 
) * ( * * 3
leak A A
X j I V E
 
 
) * ( * * 3
leak B B
X j I V E
 
 
) * ( * * 3
leak C C
X j I V E
 
) * ( * ) (
leak B A AB
X j I I V E
  
) * ( * ) (
leak C B BC
X j I I V E
  
) * ( * ) (
leak A C CA
X j I I V E
  
 
) * ( * * 3
1 1 leak
X j I V E
 
100
continuous Max Volt
f
V
f
E
M
n
n
m

