Harmonic prediction at planning stage

[jpcqub]

Evening all. The new G5/4 regulation requires new (and possibly existing?) plant to comply within harmonic limits. At the design stage, you are required to forecast the harmonic levels the plant will generate. Now there seem to be a couple of companies offering to do this for you (at a tidy price) so I’m wondering does anyone on here know the main principles for doing it ‘in-house’?

Many thanks.

 

[davidbeach]

What is a G5/4 regulation?

 

[jghrist]

I'd start with IEEE std 519. This defines the limits and gives a good explanation of the principles involved. It also gives procedures for analysis of simple systems. For more complex systems, there are several software programs available.

 

[motorspert]

davidbeach
G5/4 is the UK specification governing the harmonics allowable on a utiloy network. Its often misused as it only refers to PCC (Point of common coupling) which will be the clients site incomer maybe at 11kV or 132kV. However, somewhere within the site on an LV board the harmonics could be shocking and causing problems with other equipment.

I am not familiar with IEEE519.

 

[CJCPE]

You could search IEEE.org for technical papers and publications in addition to IEEE519. Some items are free to those who are members of both IEEE and the sub-group sponsoring the publication.

Some companies selling harmonic mitigation equipment and services have white papers posted on their web sites.

Some print and online trade magazines have articles available online. See:

http://www.drivesurvey.com/index_library.cfm

http://www.drivesurvey.com/index_market.html

 

[ozmosis]

A very useful document is published by GAMBICA that explains what G5/4 is and how you can comply with it (actually, now it is in it's third edition and known officially as G5/4-1). GAMBICA is the Trade Association for Instrumentation, Control, Automation and Laboratory Technology in the UK.
Follow the link:

http://www.gambica.org.uk/

and click on "Publications". The document is "GAMBICA Guide to Energy Networks Association Recommendation G5/4-1, Third Edition"

To answer your question mark; yes, it can apply to existing equipment, if it is out of limits but somebody would have to complain to the Network Operator first for it to get that far.
There are a number of simulation tools that allow predictions of harmonics generated by certain products but if you have a substantial investment going on that involves the installation on non-linear loads, it is advisable to carry out measurments at your PCC (point of Common Coupling). This is not usually cheap but if you get the right company doing it, the recommendations they would make should pay for that particular investment.

 

[cflatters]

There are a number of useful guidance notes on the web if you search (try looking for some of the IEE publications).

You need to consider several things

1) The size and nature of the loads you are connecting to the network (preferably using manufacturers data)

2) The Power system configuration (zero sequence paths may be avoided)

3) System impedance plays a part, the higher your system fault level is the higher the impedance will be and the more the harmonic problems you will have.

Look at the power system from the bus (or buses concerned) and reduce the network to a Thevenin equivalent.

 

[ScottyUK]

The higher the system fault level the higher the impedance...? Surely they have an inverse relationship?


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I don't suffer from insanity. I enjoy it...

 

[ozmosis]

Scotty, that's my understanding too. Higher the fault level, the stronger the supply: lower impedance, and therefore lower risk of non-linear loads creating voltage distortion.

 

[CJCPE]

Higher available fault current means lower source impedance. With lower source impedance, there is less harmonic voltage due to harmonic currents flowing through the source impedance. However, higher source impedance reduces the harmonic current drawn by rectifier loads with capacitor filters such as PWM VFDs. If there are transformers or filter chokes between the drive and the point of common coupling with other equipment, the additional impedance reduces the harmonic current but the harmonic voltage across that impedance is not seen by the rest of the system.

 

[cflatters]

Yes sorry Scotty for picking up on the obvious error -

I had meant to say lower fault level