Harmonics prediction on an installation with variable speed drives.

Question

I have been asked by a client to provide a harmonics prediction report on an installation with variable speed drives. I have never done one or been required to look into this before. Could someone assist me with the sort of information i would need. 
 We are installing around 15 Variable speed drives that will control numerous pumps and agitators around the process plant. It is a brand new facility, so at the moment I don't know the nature of the supply to the facility although i will be able to find this out soon. 
 The variable speed drives will range from 0.37kW and 5.5kW, 3 Phase so nothing big. 
 I basically need to know what sort of information I would need to obtain from the client and the VSD manufacturer, and then how I would compile that information into a report. 
 I assume i will need to provide a report on each drive rather than an overall report for the installation. 
 Any help will be greatly appreciated.

Jam · Accepted Answer

Are they looking at a compliance report with regards EREC G5/5? I would imagine that you're looking for a Stage 1 report which is reasonably straightforward with documents obtained from the manufacturer and supplier. 
 Distribution Code Annex 1 documents - EREC G5/5 
 That said there are specialists who make a living out of the more complex end of this type of work... if in doubt use them.

chrisbryant · Answer

Hi Gareth, 
 
 Given what you have said about the sizes of the VSD, I think an overall report for the installation would probably be the most use for the client and is probably what they need. 
 From the client you need to know the existing supply details and other load details. You may be able to gain the existing load details through some load monitoring if the site is operational. 
 From the VSD supplier you need to gather information relating to harmonic currents at the operating point of the drives. If you do not know the operating point or manufaccturer data isn't available for the particular operating point that you have then you can either work with the data that they do provide and adjust, or use the planning limit values from the EREC document, or take measurements from the drives

Joseph Chukwunweike · Answer

Harmonics Prediction Report for Variable Speed Drives (VSDs) Installation 
 Overview 
 This report provides a prediction of harmonic distortion levels for the installation of 15 Variable Speed Drives (VSDs) ranging from 0.37 kW to 5.5 kW, 3 Phase, which will control various pumps and agitators throughout the process plant. 
 Variable Speed Drives Specifications 
 
 Quantity: 15 VSDs 
 Power Ratings: 0.37 kW to 5.5 kW 
 Phases: 3 Phase 
 
 Harmonic Distortion Analysis

Harmonic Generation by VSDs: VSDs are known to generate harmonics due to their non-linear operation. The most significant harmonics typically generated by VSDs are the 5th, 7th, 11th, and 13th harmonics.

Total Harmonic Distortion (THD) Calculation: The Total Harmonic Distortion (THD) is an important parameter to assess the overall harmonic distortion in the system. It is the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency.

Harmonic Mitigation Techniques: To minimize the impact of harmonics, several techniques can be employed: 
 
 Passive Filters: Designed to block specific harmonic frequencies. 
 Active Harmonic Filters: More effective and can adapt to changes in the harmonic spectrum. 
 12-Pulse or 18-Pulse VSDs: These drives inherently produce fewer harmonics.

Calculation Assumptions 
 
 Load Distribution: Evenly distributed among all VSDs. 
 Power Factor: Assumed to be 0.95 for each VSD. 
 Impedance of the System: Assumed to be negligible for simplification. 
 
 Step-by-Step Harmonics Calculation

Determine Individual VSD Harmonic Currents: For each VSD rating, determine the harmonic currents generated at each harmonic frequency (5th, 7th, 11th, 13th).

Aggregate Harmonic Currents: Sum the harmonic currents from all VSDs to find the total harmonic current for each harmonic frequency.

Calculate THD: Use the formula: 
 THD=&sum;h=2&infin;(Ih2)/I1	ext{THD} = \sqrt{\sum_{h=2}^{\infty} (I_h^2)} / I_1 THD = h = 2 &sum; &infin; ​ ( I h 2 ​ ) ​ / I 1 ​ 
 where IhI_h I h ​ is the current at the hthh^{th} h t h harmonic and I1I_1 I 1 ​ is the current at the fundamental frequency.

Predicted Harmonic Distortion Levels

Harmonic Order 
 Current (A) per VSD 
 Total Current (A)

5th 
 20% of fundamental 
 Aggregated Value

7th 
 14% of fundamental 
 Aggregated Value

11th 
 9% of fundamental 
 Aggregated Value

13th 
 7% of fundamental 
 Aggregated Value

*Note: The exact current values will depend on the specific ratings and loads of each VSD. 
 Mitigation Recommendations

Install Passive Harmonic Filters: For each VSD or group of VSDs, passive harmonic filters can be used to attenuate specific harmonic frequencies.

Use Active Harmonic Filters: Consider the installation of active harmonic filters at the main distribution panel to dynamically compensate for harmonics generated by the VSDs.

Consider Multi-Pulse VSDs: Utilize 12-pulse or 18-pulse VSDs to inherently reduce the harmonic generation at the source.

Conclusion 
 The installation of 15 VSDs ranging from 0.37 kW to 5.5 kW is likely to introduce significant harmonic distortion into the electrical system. Proper analysis and mitigation strategies, such as the use of harmonic filters and multi-pulse drives, should be implemented to ensure compliance with harmonic standards and to maintain the reliability and efficiency of the plant's electrical system. 
 For precise harmonic analysis, a detailed study with real load conditions and system impedance should be conducted using harmonic analysis software or consulting with a power quality specialist.

Joseph Chukwunweike · Answer

You can run a MATLAB simulation to get the THD and thereafter have your analysis accordingly. 
 This is actually based on the real time parameters

Harmonics prediction on an installation with variable speed drives.

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