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145
Measurement of main circuit voltages, currents and powers
5
MAINTENANCE AND INSPECTION
5.2 Measurement of main circuit voltages, currents and powers
Measurement method of voltage and current at each section
When instruments for commercial frequency are used for measurement, measure the following circuits with the instruments
given below.
When installing meters etc. on the output side of the converter
When the converter-to-motor wiring length is long, especially in the 400V class, the meters may generate heat due to line-
to-line leakage current. Therefore, choose the equipment which has enough allowance for the current rating.
Voltage is output between the terminal P and N of the converter, and it can be measured using a moving-coil type meter
(tester). The voltage changes by the power supply voltage, but it decreases when a load is applied.
[Examples of Measuring Points and Instruments]
[Examples of Measuring Points and Instruments]
Operation principle and application of electric meters
Type Symbol Operation Principle Command Applicable meter Characteristic
Moving-coil type
Uses kinetic power generated
between the magnetic field of
a permanent magnet and the
current that flows through the
moving-coil.
DC
(average value)
Voltmeter/ammeter/
resistance meter/
thermometer/flux
meter/speed meter
High sensitivity and
commonly used.
Energy saving, small
influence of magnetic
field
Moving-iron meter
Uses kinetic power generated
between the the moving-iron
and the magnetic field of the
current that flows though the
fixed coil.
AC
(effective value)
Voltmeter/ammeter
Strong structure and
inexpensive,
Large influence from
external magnetic
field, frequency, and
waveform
Ammeter type Air-core coil
Uses kinetic power generated
between the currents that
flow through two different
coils.
AC/DC
(effective value)
Wattmeter/
voltmeter/ammeter
Scale is divided
equally when using a
wattmeter.
Large influence from
external magnetic
field, high energy
consumption
This can be used as a
standard meter for AC
and DC.
Filter capacitor
Limit resistor
Inrush current limit MC
ConverterOutside box
Reactor 1
R4
/L14
S4
/L24
T4
/L34
P/+
N/-
+
-
V
Reactor 2
Power
supply
W11
W12
W13
Vu
Vv
Vw
Au
Av
Aw
To the Inverte
r
Recommended product :
(Voltage, current, power, and power factor can be measured.)
Wattmeter
YOKOGAWA251
DIGITAL POWER METER
R4
/L14
S4
/L24
T4
/L34
P/+
N/-
+
-
V
Power
supply
ConverterOutside box
To the Inverte
r
Filter capacitor
Limit resistor
Inrush current limit MC
Reactor 1
Reactor 2
HC2.book 145 ページ ２０１２年１１月１９日 月曜日 午前１０時５２分