Operation Manual 37107F
MFR 3 - Multi Function Relay
© Woodward
Page 11/165
Measuring
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Voltage
The control unit performs three-phase true RMS measurement of two star or delta voltage systems (generator
and mains). This unit can be delivered with the following measuring voltage ranges (rated values). The vol-
tage measuring is specific to the part number ordered (please note chapter "Technical Data", page 138):
- [1] 66/115 Vac
- [4] 230/400 Vac
Frequency
The measured voltages are digitally filtered for frequency measurement. The control unit performs three-
phase true RMS measurement of the frequency if the measured voltages exceed the rated value (100/400 Vac)
by 15 %. This ensures rapid and precise measurement of the frequency. Frequency is still measured correctly
if voltage is only measured in one phase.
Current
The control unit performs three-phase true RMS current measurement.
Real power
The control unit performs three-phase true RMS power measurement. This is accomplished by real-time mul-
tiplication of the wye voltage and instantaneous conductor current values (three-phase measurement) or the
phase voltage V
L12
and the current I
L1
(single-phase measurement).
Re-active power
The control unit performs single-phase true RMS re-active power measurement, which is calculated from ap-
parent power and active power.
Power factor
Power factor is determined as a time measurement between the filtered measured values of the voltage V
L12
and the conductor current I
L1
.
Real energy
The positive real energy is integrated with a time measurement. The counter is controlled in the non-volatile
memory and has reverse counting protection. The data is saved in three-minute time frames with a resolution
of 1 Watt-hour. The display automatically updates the measured units when required to go to a larger refer-
ence. This permits the control unit to count up to 4,290 GWh. The counter is not PTB-calibrated.
