What is the most effective way to bring down percentage ofT H D and

What is the most effective way to bring down percentage of<br>T H D and improve the Power Factor in a commercial installation.<br>I been trying with introducing capacitance with a unit from<br>a manufacturer. The company advocates to introduce the<br>capacitance from the end of the panel box. When panels are in serious it works. Panels connected in parallel do not<br>show any improvement.<br>Has any one any answers on this problem?<br><br>Thank you <br>Fritz

 

[bfuchs]

Fritz,<br><br>THD (Total Harmonic Distortion) is a measure of the harmonic disturbance on your network due to the loads connected. One can talk about THD in Volatge or Current.<br><br>Certain loads draw harmonic current.<br>In a normal installation, this current flows through the transformer.<br>When harmonic currents flow through the inductance of the transformer, they generate harmonic voltages which are present all over the network.<br><br>The question you must answer in your installation is : 'What do you want to reduce or get rid of ?'<br><br>If you want to reduce the voltage distortion, you have to(remember that U = Z.I) reduce the impedance of the transformer by installing a bigger transformer.<br><br>To reduce the current distortion, you must install filters (active or passive, check with specialists based on harmonic spectre and resonance risks). These have an low impedance between phases for high frequency signals (harmonics), that ensure that the harmonic current does not get released into the network, and stays trapped closed to the harmonic generating device.<br>

 

[bfuchs]

If you have mainly triplen harmonics (3rd, 9th, ...), and these are balanced on the phases, then using an isolating transfomer will prevent these harmonics from spreading up to the main transformer, and will remain confined to the isolated part of the network.<br><br>This works well with 3rd (Computers, fluo lamps, ...)<br>This does not work with 5th, 7th and 11th (from variable speed drives)<br><br>In your commercial building, I would say most of your loads are lights and PC based devices (including faxes, photocopiers, ...). This should work if you can put the transformer in the right place.<br><br>This will not reduce the THD on the isolated network : it will prevent the harmonics from spreading to the other parts of the upstream network though...

 

Thank you for your reply. [ Reduction of THD reply<br>By b. fuchs.<br>I am not a engineer, but a industrial electrician<br>all my live. 50 plus years and still active.<br>The power consumption can easily be reduced in most<br>plants with capacitance and a lot of common sense.<br>Improving performance by enlarging the trans<br>former on the supply side is new to me. <br>I will find out fast.<br>Thanks again. <br>Fritz<br>PS: any sugestion on this matter are very welcome<br><br>

 

[jbartos]

May I suggest to explore active power line conditioners which may include active harmonic filters. This is the latest state-of-the art in THD reduction and power factor improvement. The less expensive way is to use passive harmonic filters with automatic control of the capacitance (e.g. by Electrotek, etc.); however, this approach is not as effective as the first one.