Low Pass Filter

Low Pass Filter

The type low pass harmonic filter can reduce harmonic to less than 5% THID and bring drive system in compliance with IEEE 519.


-          Adjustable Speed Drives

-          Elevator

-          X-Ray Machines

-          Welders

-          Grinders

-          Cranes & Hoists

-          UPS


LPF filters perform wide band filtering and attenuate the individual harmonic frequencies associated with three phase loads that use 6-pulse rectifiers. When properly selected and applied, the typical total harmonic current distortion at the filter input terminals can be less than 5% THD-I. Therefore the distortion at the utility metering point can meet IEEE 519. Actual distortion levels may vary for unbalanced line voltage and for pre- existing voltage distortion caused by other load.


Voltage regulation

Voltage regulation of Low Pass Harmonic Filters will vary depending on effective source impedance and on actual load. The table to the right illustrates the minimum and maximum voltages available at the output terminals of the Law Pass Harmonic Filter for various load conditions and for a range of effective source impedance values Vmin is the voltage available at full load operating conditions and Vmax is the output voltage under non load conditions.


Basic Version Filter KB ( When 8% or 12 % is acceptable)

The KB type filter includes two stages of filtering and take advantage of

pre-existing circuit inductance which may be in the form of either AC or DC reactors. It can be used without external AC or DC reactors for that case where the current distortion limit is above 5%. When the load (6 pulse diode rectifiers) includes AC or DC reactors, type KB filters will typically achieve distortion levels as low as 5% to 8% THID. Without additional AC or DC inductance, it achieves 8-12% THID


Standard version filter KS ( less than 5% at any loading condition)

The KS type filter includes all three stages and achieve £ 5% THID at any load condition when used in combination with six pulse diode rectifier. It can also be used with SCR rectifier with excellent result.

It can achieve 5% THID for VFD’ operating under any load condition and with any source impedance.


Technical specification

System Voltage:

200, 208, 220, 240, 380, 400, 415, 440, 480, 600, 660, 690

System Voltage tolerance:

+/- 5%

System Voltage unbalance:

up to 3% line voltage unbalance

( note: THID will increase above normal levels when line voltage is unbalanced)

Voltage regulation:

+/- 5% ( no load to full load)


50Hz +/- 1Hz or 60Hz +/- 1 Hz

Effective source impedance:


tility-0.1% to 6%

=> 3.5% to 5% voltage boost at output terminals

Generator -10% to 15%

=> 6% to 8% voltage boost at output terminals


6 pulse rectifier  loads only; not for use with any linear load

Service Factor: Voltage source inverters

1.0 x maximum ampere rating

Current source inverters

07 x maximum ampere rating

Power losses:

1% typical


1000 meters maximum

Relative Humidity:

95% maximum

Harmonic attenuated:

3rd - 50th

Residual harmonic current distortion:

Type KS

Typical contribution of harmonic current distortion at full load is 5% THID

Residual harmonic current distortion:

Type KB when VFD has internal AC or DC reactor

Typical contribution of harmonic current distortion at full load is 5% -8% THID;

varies depending on the inductance of the internal reactor in VFD

Residual harmonic current distortion: Type KB without any AC or DC reactor

Contribution of harmonic current distortion at full load is 8%-12% THID

IEEE - 519 compliance

Guarantee for all Isc/IL ratios when using "KS" version filter