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3.2.4 Measurement of main circuit voltages, currents and powers
• Measurement of voltages and currents
When instruments for commercial frequency are used for measurement, measure the following circuits
using the following instruments.
• When installing instruments, etc. on the high power factor converter output side
When the wiring distance is long between the high power factor converter and inverter, the instruments
may generate heat due to line leakage currents in especially 400V class. Select the devices which have
large enough current rating.
• There is an output voltage across terminals P-N of the high power factor converter and this voltage can be
measured by a moving-coil instrument (tester). This voltage varies with the power supply voltage and
reduces when load is applied.
<Typical Measuring Points and Instruments>
<Typical Measuring Points and Instruments>
• Classification and Application of Indicating Electric Instruments by Operation Principle
Type Symbol Principle Indication
Applied
Instrument
Features
Moving-coil type
Uses force working between the
magnetic field of a permanent
magnet and a current flowing in
the moving coil.
DC
(Mean value)
Voltmeter,
ammeter,
resistance
meter,
thermometer,
flux meter,
speed meter
High in sensitivity and most often
used. Power consumption small,
rarely affected by external
magnetic field.
Moving-iron type
Uses force working between the
magnetic field of a current flowing
in the fixed coil and the moving
iron.
AC
(Effective value)
Voltmeter,
ammeter
Rigid in structure and low in price.
Greatly affected by external
magnetic field, frequency and
waveform.
Electrodynamic
type
Air
core
Uses force working between
currents flowing in two coils.
AC/DC
(Effective value)
Wattmeter,
voltmeter,
ammeter
Wattmeter is graduated equally.
Affected by external magnetic field
and consumes large power. May
be used as a standard AC/DC
instrument.
W
11
W
12
W
13
V
U
V
V
V
W
A
U
A
V
A
W
R4
S4
T4
P
N
V
+
-
To inverte
r
Power supply
Reactor 1
Reactor 2
External box
Converter
R4
S4
T4
P
N
V
+
Power supply
Reactor 1
Reactor 2
To inverter
External box Converter
Recommended: YOKOGAWA251
Digital power meter
(Can measure voltage, current,
power and power factor)
Power meter
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