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 Post subject: Voltage Optimisation
PostPosted: Wed Mar 07, 2012 3:27 pm 
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Has anybody got experience with voltage optimisation units. This is a fast expanding technology which basically involves reducing and clamping voltage in order to produce energy savings. This is undertaken in several ways by retrospectively inserting auto transormers or thyristor controlled reactors betweeen the low voltage secondaries of industrial transformers and main switchboards. I believe that the added impedance can have a marked and detrimental effect on incident energy levels. Your comments wil be much appreciated.


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PostPosted: Fri Mar 09, 2012 5:56 am 
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This is really more for the UK and europe markets that use 242 volts rather than 120 volts for US residential power. Its my understanding the units reduce the incoming 242 volts to 220. However, the reduced voltage causes appliances such as dryers and ovens and anything with heating elements to operate longer to get the same results as 242 volts. So from a energy saving stand point is it really saving money as claimed? As the saying goes... time is money. The longer appliances run the more it costs. I would like to see test data to backup the energy savings claims. This reminds me of the power factor correction gizmos - actually scams - that claim to save residential customers money by improving the power factor. Anytime a transformer is added to a circuit the xtmr Z% will change the short circuit fault cuurent.


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PostPosted: Mon Mar 12, 2012 2:55 am 
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Spot on Mike, voltage optimization unites reduce the incoming voltage to a property to more accordingly match the electrical start up of equipment, hence saving both money and carbon. As an employee at EMSc (UK) Ltd, we design and manufacture the market leading voltage optimization unit Powerstar, as well as a number of other energy saving products. It is not just the UK and Europe that can benefit from voltage optimization, as our new office in Australia will continue to prove. The voltage drop will depend on the electrical equipment used within a particular site but with reference to 242 volts, although this is the average, we have seen some sites have incoming voltage as high as 253. We have a number of case studies on our Powerstar website if you wish to see some test data Mike.


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PostPosted: Tue Mar 13, 2012 3:16 am 
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Thank you EMSc. As geh7752 said above anytime that impedance is inserted into a circuit this will change the short circuit current. I understand that there are various ways in which voltage optimisation units are built including autotransformers, retro fitted low loss transformeres with auto tap changers and variable chokes. I had a look at your site and noted some low figures for 1000kVA voltage optimisation units but just for clarity, would you like to demonstrate fault level attenuation using this particular unit. Working on the basis of a 1000kVA transformer feed there will be about 28kA at the TX terminals at a European harmonised voltage of 400 volts. If you insert your unit in circuit, what will be the actual fault level at the output terminals. Is the impedance fixed or dynamic? If the latter, how is this affected by load conditions?Some example calculations will very useful indeed. I am having some difficulty in modelling these units into software such as SKM so any information will be very much appreciated.


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PostPosted: Tue Mar 13, 2012 3:52 am 
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Hi Mike

I have just sent you a direct message regarding this.


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PostPosted: Tue Apr 17, 2012 2:19 am 
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Is there anymore information available on the subject of voltage optimisation reducing the potential fault current. I have maintenance customers who are asking me about this technology and it's one question i can't seem to find an answer on. Thanks


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PostPosted: Tue Apr 17, 2012 2:55 am 
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Hi Mike

If you contact the office one of our engineers would be more than happy to answer your question or indeed arrange an appointment to discuss this in person.

You can reach us on 01709 836200


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PostPosted: Tue Apr 17, 2012 2:57 am 
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Hi Alan

If you contact our office one of our engineers would be more than happy to answer your questions, or indeed book in an appointment to discuss this in person.

You can reach us on 01709 836200


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PostPosted: Wed Apr 18, 2012 3:30 am 
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Using small capacitor banks, autotransformers, and similar "helper" transformers has been widespread practice for some U.S. utilities for years with long lines where they need voltage "boosting" periodically. There is a chart floating around that shows the impact of increased/decreased voltage on motors. As you go below rated voltage, losses increase and torque decreases. As you go above, the opposite happens. HOWEVER, simultaneously with either direction, the rated life decreases significantly. Voltage "optimization" probably does nothing for energy savings (I'm not buying that one) but may significantly improve "carbon footprint" by reducing maintenance/replacements required. I've worked in plants that are severely (10-15%) out due to combating soft bus problems and excessive voltage makes a huge difference on electronic equipment.

AlanJB wrote:
Is there anymore information available on the subject of voltage optimisation reducing the potential fault current. I have maintenance customers who are asking me about this technology and it's one question i can't seem to find an answer on. Thanks


Read between the lines. You're adding an isolation transformer which magnetically isolates the input from output (at least with the non-autotransformer types). The answer is likely NO. On a very simplified scale, the key to reducing incident energy is to reduce arc energy X time. Arc energy is controlled by a variety of factors but increasing current is a recipe for increased arcing fault energy. If you insert an isolation transformer between the source and load, as a general rule, you may be able to make small taps up or down to adjust voltage but you are also reducing the impedance which increases fault current significantly, much more than the voltage tapping. I don't want to go too far with this since the effect of voltage and current on arc flash is still nonlinear but the overall concept is that trading very small voltage decreases for very large current increases is not a tradeoff that is desirable.


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PostPosted: Wed Apr 18, 2012 5:31 am 
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PaulEngr wrote:
If you insert an isolation transformer between the source and load, as a general rule, you may be able to make small taps up or down to adjust voltage but you are also reducing the impedance which increases fault current significantly, much more than the voltage tapping.


I'm sorry, but I don't understand this. When you add an isolation transformer, you ADD impedance, so you REDUCE the fault current. It's an (sometimes) easy way to lower the bolted fault current so overdutied equipment are not overdutied anymore, without replacing a whole MCC lineup or series-rating (which are not always available).


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PostPosted: Wed Apr 18, 2012 4:18 pm 
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Agreed. It adds impedance. I'm thinking of the case when you actually do a true voltage conversion and thus are trading lower volts for higher currents.


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PostPosted: Wed Apr 18, 2012 7:06 pm 
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Vincent B. wrote:
I'm sorry, but I don't understand this. When you add an isolation transformer, you ADD impedance, so you REDUCE the fault current. It's an (sometimes) easy way to lower the bolted fault current so overdutied equipment are not overdutied anymore, without replacing a whole MCC lineup or series-rating (which are not always available).


Adding impedance isn't a free lunch to fixing over duty equipment problems. Yes, it can reduce bolted fault current but transformers and line reactors expend energy in the form of heat and change power factors. Essential they become another maintenance headache and potential failure point. Decreasing bolted fault current can get AIC to a acceptable equipment level but ALSO decrease CB & fuse clearing times which increases arc fault incident energy. This is a big problem with T&M molded case breakers with fixed mag trip setting... all of a sudden a MCC line up went from Cat 2 to Cat 4 PPE by adding a upstream isolation transformer. Most customers don't understand how LOWERING bolted fault current INCREASES arc flash incident energy. That's were they get a short course on how to read a breaker TCC graph.


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