Areva MiCOM P225, Техническое руководство

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User Guide P225/EN FT/B11
MiCOM P225 Page 15/52
4.6 The MEASUREMENTS1 and MEASUREMENT2 menus
•
The measurements of the phase currents and the earth current are expressed as true
root-mean-square values. For a 50 Hz motor, the harmonics are taken into account up
to the 10th order; for a 60 Hz motor the harmonics are taken into account up to the 8th
order.
•
The measurements of the phase-phase voltage VAC is expressed as true root-mean-
square values.
•
The measurement of the symmetrical components is taken from the fundamental
component of the current. The positive and negative sequence components of the
current are calculated on the basis of the three phase currents, and the zero phase
sequence component is calculated from the earth current input. The following
formulae are used to calculate the symmetrical components:
) I ² a I a I( 3 / 1 I
C B A
positive
⋅ + ⋅ + ⋅ =
) I a I ² a I( 3 / 1 I
C B A
negative
⋅ + ⋅ + ⋅ =
earth
0
I 3 / 1 I
⋅ =
•
The frequency is measured if:
−
the amplitude of voltage VAC is above 5V
−
or if the amplitude of at least one of the three phase currents is greater than 10%
of In (In is the rating of the phase current inputs, 1A or 5A defined in the CT
RATIO submenu, on the line "LINE CT SEC =").
Where the frequency cannot be calculated, the relays displays "****".
•
The phase current maximeter retains the greatest current value of one of the three
phases outside the motor starting phase. This variable is expressed as a true RMS
value.
•
The
I
2/
I
1 value is the ratio of the symmetrical components "negative-sequence
current" over "positive-sequence current'.
•
The active, reactive and apparent powers are derived assuming that the voltage
system is balanced.
•
The active and reactive energy counters represent the energies absorbed by the
motor. When these counters reach respectively 20GWh and 20GVARh, they are
automatically reset.
These counters can be reset by pressing the " key (without password).
The energy calculation is updated every second.
•
The power factor is the ratio of the active power over the apparent power.