Reduce your voltage – reduce your electricity costs
October 1st 2007

UK organisations are wasting electrical energy using too high a voltage explains Dr Alex Mardapittas of EMS (UK)

Although The Electricity Safety,Quality and Continuity Regulations 2002 amended the statutory electricity supply voltages down from 240 volts in the UK to 230V +10% or -6% (216V – 253V) with effect from the 1 January 2003, an average voltage of 242V is still supplied (approximately 12 volts - 5% - higher than the nominal 230V).This is because as electricity travels further away from the distribution areas, the voltage naturally drops and in order to ensure that the regulations are met, the power supplier will maintain grid voltage towards the top end of the limits. In addition, it is to the suppliers benefit to supply at high voltage as the transmission losses are less.

Does this higher voltage matter? Well yes it does.The higher the voltage the higher the energy consumption. As a rule of thumb, reducing the voltage by 5% will result in savings of 10%. In addition, higher voltage tends to increase the heat generation in motors, reducing their life, and generally reduces the life expectancy of electrical equipment, including lighting bulbs.

As the majority of electrical equipment is designed to run at the 220V nominal which is in place in Europe, there should be no problem operating at the UK's 230V nominal level. All electrical equipment is designed using parameters such as Voltage, Frequency, Capacity, etc.

Therefore, to ensure that these are operating at their optimum performance, they need to operate as close as possible to their design characteristics.

Transformers used in substations on sites have a series of "tappings" which allow the user to reduce the output voltage in a series of 2.5% steps to the level that is required.

Thus if the output voltage were 242V,we would normally recommend that the transformer be reduced one tapping at a time to 230V, however, this requires a detailed investigation.

As an engineering consultancy, EMS saw how many sites had excessive voltages and were thus spending excess on energy for no benefit.As a result EMS developed the PowerStar unit. PowerStar optimises the power at a company utilising multiple tapping transformers.

The unit obviously has a cost attached to it, but still gives very good payback periods and significant advantages over a simple tap change at the site transformer. In fact, sites which do not have a dedicated HV transformer are able to take advantage of voltage reduction savings, which they could not do previously.

The PowerStar unit is designed to reduce voltages to the UK nominal (230V) via variable impedance transformer technology. The advantages are many, including significant energy savings, reduced current and voltage harmonic distortions, improved power factor and also reduced maintenance costs with extended equipment life due to reduced operating temperatures and operating close to their design characteristics.

The graph (other page) demonstrates the energy savings achieved using PowerStar at a refrigerated storage depot. The results shown are over a 24hour period(one day without PowerStar and one day with PowerStar).

Such savings of around 12% in electrical energy are commonplace. Typical installations are at office blocks, local government buildings, manufacturing sites,warehousing, refrigerated storage facilities, hotels, hospitals and colleges or universities.

Savings will completely depend on the application, for example in manufacturing, where most of the electrical power is used in motors, savings will be less, average 12% while in administration type buildings savings can be significantly higher, average 16%.

The effect of reduced harmonic distortion is shown below at a printing machine electrical supply, where the two traces are measured concurrently either side of the EMS PowerStar unit. Total current harmonic distortions were significantly reduced by almost 50%. Also on the same trial,Voltage Harmonics were shown to have been reduced by 10%.

Identifying the opportunity for energy savings through voltage reduction cannot be simpler. EMS will issue a simple plug in logger which records site voltages for a continuous seven day period. If the results are promising, then a detailed site survey would be undertaken, with more in depth data logging. A fully costed quotation with an indication of likely savings and payback period are then issued.

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