User:Dh1949/Voltage Optimisation

Saving energy by voltage reduction
Reducing the voltage supplied to a premises can yield a significant reduction in energy consumption and bring benefits of increased equipment lifetime and reduced maintenance.

Referred to as "voltage optimisation", "voltage correction" or "voltage reduction", the technique has been understood for many years, and has recently received increasing interest as an effective means of reducing electricity bills, with savings of 10 – 20% being realised on many sites.

The voltage supplied to many premises is much higher than it needs to be, leading to excessive losses in many types of equipment. This is partly because of the need to allow for voltage drops across the supply network, but is also a consequence of the harmonisation of supply voltage throughout Europe.

Supply harmonisation

After thirteen years, the final step to harmonise European supply voltages to 230V ± 10% is scheduled for 1st January 2008, bringing the statutory supply limits to 207-253V, yet the average voltage in the UK is still around 242V. This means that in many cases electrical equipment is running at a voltage much higher than needed, resulting in excessive losses.

The UK for many years had a standardised supply (phase-to-neutral) voltage of 240V ±6%, whereas continental Europe had a nominal supply level of 220V.

Since 1st January 1995 the nominal voltage across Europe has been harmonised at 230V, with a supply tolerance in the UK of 230V -6% to +10% (216-253V), while in continental Europe the tolerance has been (230V -10% to +6% (207-244V). This meant that there was no incentive for suppliers to make any real change as the old supply limits lie almost entirely within the new limits!

From 1st January 2008, new supply tolerances of 230V ± 10% (207-253V) are scheduled to come into force.

The Institution of Electrical Engineers recommended in a 1996 report that for safety all electrical equipment needed to be tested across the range 230V -14% to +10%, so all equipment produced since then should be capable of working from 198V to 253V.

Voltage reduction equipment

The voltage supplied to a premises can be reduced by installing a voltage regulator on the main incoming supply (usually immediately after the main low-voltage circuit breaker). The regulator controls the voltage on each phase to a suitable level (typically 220V) and in the process also ensures that the phase voltages are properly balanced – helping to improve equipment efficiency and reliability in situations where the phases would otherwise have been unbalanced.

Voltage step-down transformers are also sometimes used for voltage reduction. While these devices are somewhat simpler in construction than voltage regulators, and should therefore be less expensive to install, they will not achieve the same levels of energy saving as a regulator. This is because the step-down ratio needs to be set to allow for variation in the supply voltage so as not to reduce the voltage on the site below the minimum acceptable level, and the voltage can therefore not be reduced to the optimum level. Also, a fixed ratio transformer will not correct any imbalance in the phase voltages.

Equipment effects

The energy savings are achieved by reducing the losses in the equipment being supplied, and vary according to the type of equipment. If the load is linear, a reduction in voltage from 240 to 230 will reduce the energy consumption by 8%, while a reduction to 220 Volts will yield a saving of 16%. However, the equipment will still operate correctly at the reduced voltage, as it is still well within the statutory limits, and there will usually also be benefits of increased lifetime.

However, voltage reduction does not work with all types of load. Variable-speed inverter drives, high-frequency lighting ballasts and switch-mode power supplies for example will generally not yield significant savings at reduced voltage – because the voltage fed to the load is generated electronically and is not affected by the supply voltage. Temperature-controlled heating is another type of load where no energy saving will be obtained, as the heater will still need to consume the same amount of energy to perform its required function.

Although it may not be applicable to all sites or all types of equipment, voltage reduction is nevertheless a highly effective energy-saving technique that is being used very successfully on many sites, and is well worth considering as part of your overall energy-reduction strategy.