Fuji Electric FRENIC MEGA G2 Series - Measuring the Amount of Electricity in Main Circuit

7.5 Measuring the Amount of Electricity in Main Circuit
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7.5 Measuring the Amount of Electricity in Main Circuit
Because the voltage and current of the power supply (input, primary circuit) of the main circuit of the inverter and
those of the motor (output, secondary circuit) contain harmonic components, the readings may vary with the type of
the meter. Use meters indicated in Table 7.5-1 when measuring main circuit.
The power factor cannot be measured by a commercially available power-factor meter that measures the phase
difference between the voltage and current. To obtain the power factor, measure the power, voltage and current on
each of the input and output sides and use the following formula.
Three-phase input
Power factor =
Power (W)
√3 × voltage (V) × current (A)
× 100 (%)
Single-phase input
Power factor =
Power (W)
Voltage (V) × current (A)
× 100 (%)
Table 7.5-1 Meters for main circuit measurement
Item
Input (primary) side
Output (secondary) side
DC link bus
voltage
(P(+)-N(-))
Waveform
Voltage
Current
Voltage
Current
Name of
meter
Ammeter
AR, AS, AT
Voltmeter
VR, VS, VT
Wattmeter
WR, WT
Ammeter
AU, AV, AW
Voltmeter
VU, VV, VW
Wattmeter
WU, WW
DC voltmeter V
Type of
meter
Moving iron
type
Rectifier or
moving iron
type
Digital AC
power meter
Digital AC
power meter
Digital AC
power meter
Digital AC
power meter
Moving coil type
Symbol
of meter
⎯
⎯
⎯
⎯
If measuring the output current with a moving-iron type meter, and the output voltage with a rectifier type
meter, an error may occur. Furthermore, there is also a risk of meter burnout. To measure with greater
accuracy, the use of a digital AC power meter is recommended.
Fig. 7.5-1 Connection of meters