Hitachi L300P - Manual (Page 193)

L300P Inverter
Motor C
ontrol
Acc
e
ssor
ies
5–3
Component Descriptions
AC Reactors,
Input Side This is useful in suppressing harmonics induced on the power supply lines, or when the main
power voltage imbalance exceeds 3% (and power source capacity is more than 500 kVA), or to
smooth out line fluctuations. It also improves the power factor.
In the following cases for a general-purpose inverter, a large peak current flows on the main
power supply side, and is able to destroy the inverter module:
• If the unbalanced factor of the power supply is 3% or higher
• If the power supply capacity is at least 10 times greater than the inverter capacity (the power
supply capacity is 500 kVA or more)
• If abrupt power supply changes are expected
Examples of these situations include:
1. Several inverters are connected in parallel, sharing the same power bus
2. A thyristor converter and an inverter are connected in parallel, sharing the same power bus
3. An installed phase-advance (power factor correction) capacitor opens and closes
Where these conditions exist or when the connected equipment must be highly reliable, install
an AC reactor between the power supply and the inverter. Also, where the effects of an indirect
lightning strike is possible, install a lightning conductor.
Example calculation:
VRS = 205V, VST = 203V, VTR = 197V,
where VRS is R-S line voltage, VST is S-T line voltage, VTR is T-R line voltage
Please refer to the documentation that comes with the AC reactor for installation instructions.
AC Reactor or
LCR Filter,
Output Side This reactor reduces the vibrations in the motor caused by the inverter’s switching waveforms,
by smoothing the waveforms to approximate commercial power quality. It is also useful to
reduce the reflected voltage wave phenomenon when wiring from the inverter to the motor is
more than 10m in length. Please refer to the documentation that comes with the AC reactor for
installation instructions.
Unbalance factor of voltage
Max. line voltage (min.) Mean line voltage –
Meanline voltage
----------------------------------------------------------------------------------------------------------- 100 ×
=
VRS VRS VST VTR + +
( ) 3 ⁄
–
VRS VST VTR + +
( ) 3 ⁄
-------------------------------------------------------------------------- 100 Ч
=
205 202 –
202
------------------------ 100 Ч 1.5% = =