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Precautions for Maintenance and Inspection
3.2.8 Measurement of main circuit voltages, currents and power
z Measurement of voltages and currents
When instruments for commercial frequency are used for measurement, measure the following circuits using the
instruments given below.
When installing measuring instruments etc. on the output side of the power regeneration common converter,
choose the measuring instruments that have allowance in current rating since they may generate heat under the
influence of line-to-line leakage currents if the wiring distance between the power regeneration common converter
and inverter is long.
The DC voltage, which is developed across the terminals P/L+ and N/L- of the power regeneration common
converter, can be measured with a moving-coil instrument (tester). Though it varies with the power supply voltage,
the voltage will reduce under load.
< Typical Measuring Points and Instruments >
z Classification and application by the operation principles of electrical indicator
instruments
Measuring Points and Instruments
Type Symbol Principle Indication
Applicable
Instrument
Features
Moving-coil type
Utilizes the force that
works between the
magnetic field of the
permanent magnet and the
current flowing in the
moving coil.
DC
(Average
value)
Voltmeter,
ammeter,
resistance
meter,
thermometer,
flux meter,
rotating meter
High in sensitivity and most often
used. Affected little by consumed
power and external magnetic field.
Moving-iron type
Utilizes the force that is
produced between the
magnetic field of the
current flowing in the fixed
coil and the moving iron.
AC
(Effective
value)
Voltmeter,
ammeter
Rigidly structured and low priced.
Affected greatly by external
magnetic field, frequency and
waveform.
Electrodyn
amometer
type
Air
core
Utilizes the force that
works between the
currents flowing in two
coils.
AC/DC
(Effective
value)
Wattmeter,
Voltmeter,
ammeter
A wattmeter is graduated equally.
Affected greatly by external
magnetic field and large in power
consumption. Usable as an AC/DC
standard instrument.
Item Measuring Point Measuring Instrument
Remarks
(Reference Measured Value) *
Power supply voltage V1
Across R2/L1-S2/L2, S2/L2-
T2/L3, and T2/L3-R2/L1
Moving-iron type AC
voltmeter
Commercial power supply
Within permissible AC voltage
fluctuation (Refer to page 44)
Power supply side current
I
1
R2/L1, S2/L2 and T2/L3 line
currents
Moving-iron type AC
ammeter
Au
Av
Aw
W11
W12
W13
Vu
Vv
Vw
Power regeneration
common converter
R2/L1
S2/L2
T2/L3
P/L+
N/L-
V
+
-
Dedicated
stand-alone
reactor
Power
supply
To inverte
r