© 2012 Dranetz Technologies www.dranetz.com 800-372-6832 (U.S & Canada) +1-732-287-3680 (International)

HARMONICS & WAVEFORM MEASUREMENTS

LOW PASS FILTER & SINE WAVE FILTER FOR A 460V 100HP AC MOTOR WITH VFD

INTRODUCTION

Harmonics are an important PQ issue today. Variable

Frequency Drives (VFD), Uninterruptible Power Systems

(UPS), computers, LED lighting, electronic ballasts,

etc. are widely used in all kinds of facilities. It is well

known that such devices can cause many problems at

end user’s installations and utility networks, such as:

Voltage distortion, damaged capacitor banks, tripping

breakers, blown fuses, overheating of cables and

transformers, damage to PLC’s and sensitive electronic

loads, etc.

DESCRIPTION

Variable Frequency Dives are becoming very popular in

controlling AC motors for industrial and commercial

applications. They provide speed control for processes

such as ventilators, pumps, air compressors, elevators,

etc. at substantial energy savings. However, VFD’s

generate significant harmonic currents depending upon

the power electronics technology used (number of

pulses, SCR, thyristors, etc.). In many cases, they

exceed IEEE-519 recommendations and cause some of

the problems mentioned above. Also, Pulse Width

Modulated (PWM) drives can cause additional problems

in AC motors, such as premature bearing wear and

short-circuits in windings due to spikes from

modulation if the motor is not designed for this

condition.

In many applications, harmonic mitigation techniques

are required, along with proper power monitoring

instrumentation to measure the harmonics spectrum

and waveforms. This can be essential in assuring such

solutions meet customer requirements. Passive filters

have proven their effectiveness at reasonable prices.

This case study is a customer witness and performance

test carried out at the laboratory of a manufacturer of

two passive filters to be supplied. The test is

conducted with a 460V, 100HP AC motor with a 6-pulse

PWM VFD. One Low Pass Filter (LPF) is installed at the

input of the VFD (load side), and one Sine Wave Filter

(SWF) is installed at the output of the VFD (motor

side).

Figure 1: Low Pass Filter and Sine Wave Filter Locations

Four Dranetz PowerXplorer and PowerVisa Power

Quality analyzers were used to measure the

effectiveness of the filters, monitoring the points

shown in Figure 1 above: Low Pass Filter Input, Low

Pass Filter Output, Sine Wave Filter Input, and Sine

Wave Filter Output.

Figure 2: Test In Progress

Below are waveshapes captured during the test:

© 2012 Dranetz Technologieswww.dranetz.com 800-372-6832 (U.S & Canada) +1-732-287-3680 (International)

LPF OUTPUT (NO HARMONICS FILTERING)

LPF INPUT (HARMONICS FILTERING)

LPF Output voltage waveform (2)

(VFD input 460V 100HP AC motor)

15:43:35.87

23/06/2011

Thursday

15:43:35.88 15:43:35.89 15:43:35.90

-750

-500

-250

0

250

500

750

Volts

A-B [Salida fil tro LPF]V

%THDV Harmonics spectra (2)

(VFD input 460V 100HP AC motor)

H05

H10

H15

H20

H25

H30

H35

H40

H45

H50

0

1

2

3

4

5

6

%

A-B [Salida fil tro LPF]VHarm (max)

LPF Output current waveform (2)

(VFD input 460V 100HP AC motor)

15:43:35.85

23/06/2011

Thursday

15:43:35.86 15:43:35.87 15:43:35.88

-200

-100

0

100

200

Am

ps

A [Salida fil tro LPF]I

%THDI Harmonics spectra (2)

(VFD input 460V 100HP AC motor)

H05

H10

H15

H20

H25

H30

H35

H40

H45

H50

0

10

20

30

40

50

60

70

%

A [Salida fil tro LPF]IHarm (max)

LPF input voltage waveform (1)

15:20:09.850

23/06/2011

Thursday

15:20:09.860 15:20:09.870 15:20:09.880

-750

-500

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0

250

500

750

Volts

A-B V

%THDI Harmonics spectra (1)

H05

H10

H15

H20

H25

H30

H35

H40

H45

H50

0

10

20

30

40

50

60

70

%

A IHarm (max)

LPF input current waveform (1)

15:20:09.89

23/06/2011

Thursday

15:20:09.90 15:20:09.91 15:20:09.92 15:20:09.93

-100

-75

-50

-25

0

25

50

75

Am

ps

A I

%THDI Harmonics spectra (1)

H05

H10

H15

H20

H25

H30

H35

H40

H45

H50

0

10

20

30

40

50

60

70

%

A IHarm (max)

© 2012 Dranetz Technologieswww.dranetz.com 800-372-6832 (U.S & Canada) +1-732-287-3680 (International)

SWF INPUT (VFD OUTPUT TERMINALS) SWF OUTPUT (MOTOR TERMINALS)

CONCLUSIONS:

LPF (low pass filter) reduced VTHD from 6.3% to 1.5% and ITHD from 70% to 6%. Corresponding waveforms were also improved as well

SWF (Sine wave filter) effectively improved the voltage waveform at the 100HP AC motor terminals (as shown)

Dranetz Power Quality analyzers advanced capabilities were essential in measuring not only at VFD line side, but also measuring and capturing the PWM waveforms High frequency pulses at VFD output)!

The customer was very satisfied, not only with the filtering results, but with the Dranetz PQ analyzers. He said: “With other manufacturers like Fluke, one PQ instrument and one oscilloscope are required to be able to perform VFD & filtering tests, which implies more cost about instrumentation.”

The filter customer decided to buy one PowerGuide portable instrument from Arteche Inelap, an authorized Dranetz distributor in Mexico who is fully committed to Dranetz products

DRANETZ HAS PROVEN ONCE AGAIN TO BE THE LEADER IN TECHNOLOGY AND “STATE OF THE ART” IN THE PQ BUSINESS!

This case study was submitted by Ing. Leopoldo Martínez Basulto, Dranetz México

PWM without filter (3)

(VFD output terminals)

15:46:30.8223/06/2011Thursday

15:46:30.84 15:46:30.86

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Volt

s

A-B [Entrada fil tro SWF]V

PWM with SW filter (4)

(Filter output terminals)

15:46:30.8323/06/2011Thursday

15:46:30.84 15:46:30.85 15:46:30.86 15:46:30.87

-750

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0

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Volt

s

A-B V