Description

Voltage optimisation involves installing a specialist device in series with the mains electricity supply to provide an optimum supply voltage to suit the site’s installed electrical equipment. Optimisation is not voltage reduction, it should improve power quality by balancing phase voltages and filtering harmonics and transients. The optimising device must be efficient in its operation so that energy is not wasted in the optimisation process.

Background

The UK electrical supply standard is 230 volts with a tolerance of ± 10%, ie. the voltage range can be 207 to 253 volts. Line losses are generally reduced by distribution at higher voltages soparts of the system could be at 250 volts other parts at 210 volts. Generally equipment manufactured for the UK and European markets is designed to run at 220 volts. Therefore, in some cases equipment is being run at a higher voltage than necessary and this can lead to wasted energy.

Effects of over-voltage on electrical loads

Resistive loads: The resistance of an electrical load is fixed by its physical construction. From first principles resistance (R) = Volts (V) / Current (I); R=V/IIf a 2.4 ohm (Ω) resistive load is subject to a voltage of 240V then the current flow will be 100 amps. The power drawn will be V x I = 24,000 watts. If the same load is subjected to 220V the current flow will be 91.67 amps and the power drawn will be 20,166 watts. A reduction in power of 16%. This reduced power will mean reduced heat output from the load and is only an energy saving if the heat is not required. If the load is used as part of a heating process then temperature and throughput will also be reduced. If the heat is not required (for example in a tungsten filament lamp) then there will be an energy saving.

Three phase motors: Motors are designed for a fixed voltage and frequency. The magnetism in the motor is dependent on the relationship between voltage and frequency. Over voltage will result in an over-magnetised motor which will be overloaded during operation resulting in overheating and wasted energy. Conversely under voltage results in under-magnetism and the torque of the motor is reduced. The speed of the motor is not affected as that is dependent on the frequency of the supply and the number of poles in the motor.

Dependent on site electrical supply conditions and the voltage rating of the motors installed there will be small savings if over-voltage is occurring. Reducing the voltage below the motor rating will result in a loss of performance.

Lighting: Incandescent lighting subjected to over-voltage will run hotter, waste energy and have a reduced life. If the lamp is run at a lower voltage than design then there will be a loss of light output. Some types of fluorescent lighting already have a form of optimisation built into the control system and will therefore perform no different under voltage optimisation. Other type of lighting with resistive or reactive ballasts will benefit to a greater or lesser degree, dependent on type and configuration, from optimisation if over-voltage is occurring. In the majority of cases if the voltage is controlled at less than the design voltage of the lighting installation then there will be a reduction in light output.

Energy Savings

Carbon Trust Loans in Action Case Study: Buxton Press Ltd. used a Carbon Trust loan to finance the installation of a device to adjust the supply voltage of the site to 230 volts which is the design voltage of the printing machinery purchased from Germany. The capital cost of the equipment from ‘PowerPerfector’ was just under £40,000. The Carbon Trust estimated savings at £13,000 per annum giving a payback period of just over 3 years. The savings would also reduce the company’s carbon emissions by 104 tonnes. However, the savings are predictions only and have yet to be measured. (Source: Carbon Trust web site)