The "PowerLux" Lighting Controller. 

Introduction: 

The PowerLux is a controller for low-pressure discharge lighting, specifically for fluorescent tubes.

Although reducing the supply voltage to a fluorescent tube reduces the light output, the greater the intensity, the less sensitive the eye becomes to changes in intensity. Slow changes are even less perceptible.

A number of lighting controllers use this principle, with a reduction in input power of 20% giving a 15% reduction in measured intensity but only an 8% reduction in perceived intensity.

These controllers are fitted between the switch and a single bank of lamps. When the switch is operated, the unit detects the application of the supply and waits until the lamps have struck before reducing the voltage applied to the lamps, either by phase control or by switching to a lower voltage secondary of a transformer These units require a separate unit for each bank of lamps because the voltage needs to be returned to the full supply voltage in order to ensure reliable starting.

The patented feature of the PowerLux controller is that it detects the switching of an additional bank of lamps and returns to the full supply voltage before the lamps strike. A single PowerLux unit can supply any number of individually switched lamps up to a maximum of l6Amps. It is capable of detecting the switching of an additional 38W tube onto an existing load of 16 Amps.

Energy savings:

At a suitable site, a 20% saving of power would be accompanied by an 8% reduction in perceived illumination.

At 16 Amps, 240V –

Saving = 16A x 20% x 0.8 PF x 240V 1,000 = 0.61 kW

For 7 days/week, 8 Hrs/day

Saving = 7 days x 8 hrs x 52 weeks x 0.61KW x £0.06/ kWh =£107/year

The UK government proposes to introduce a Climate Change Levy in April 2001. This will amount to a tax of 0.435p I kWhr of electrical energy consumed in industrial and commercial premises. From April 2001 the Powerlux will be able to save a further £7.76 / year making a total of £115 / year. To offset the effects of the levy, ETSU has been charged to compile a list of approved energy saving devices. Purchase of accredited devices will be eligible for 100% write-down against corporation tax liability in the first year of use leading to a saving of 35% of the purchase price. The payback period for the Powerlux is anticipated to be between 1 and 2 years depending on the particular installation.

As cost savings form the basis of any sale, it is very important that the controller is not sold into situations where no savings will be made. PowerLux will operate with, but will not produce any savings, where electronic starter / ballast or high frequency ballast units are fitted or central starting is installed.

The quality of the supply limits the potential savings. Fluorescent lamps need a minimum of 185 volts in order to strike The unit is designed to limit the tube voltage to a minimum of 210 volts, in order to avoid the lamps flickering during voltage dips and with a supply voltage of 225-230 volts, typical power savings can be as smalI as 5%. On the other hand where the supply voltage is 245 - 250 volts, power savings of 30% can be achieved. Another potential problem is the existence of harmonics generated in the neutral line. Unbalanced 3 phase loads cause current to flow in the neutral line and if the impedance is significant, equipment installed between one phase and the neutral will be subject to third harmonic distortion. The controller will operate under these circumstances but the impedance of the ballast chokes is increased significantly and the amount of supply voltage reduction that can be tolerated is greatly reduced. The situation is worsened when "power factor corrected" lamps are used.

In order to improve the power factor, the noise reduction capacitor fitted across the input terminals is increased from 47nF to 7uF In parallel with a choke of 0.4H, the resultant resonant frequency of 90Hz causes the harmonics to "ring" producing a highly distorted voltage waveform across the lamps.

Before installing a unit, it will be necessary to establish that the site is likely to allow savings of between 15 - 20% to be achieved. Ideally the supply voltage should be 230 volts or more, no electronic ballasts, high frequency ballasts or central starting should be fitted, the lamps should be fitted with small noise suppression capacitors and the power factor correction should be applied at the terminals of the incoming supply. The harmonic content of the supply should be checked to ensure that the neutral problem is avoided.

Description of the Unit

The unit is a microprocessor based designed to control 16 amps of current from a nominal supply voltage of 25OVAC, 50 Hz. The unit delays the firing of a triac for a period after the current zero crossing point in order to reduce the lamp voltage. The supply voltage and power factor are continuously monitored and the firing delay optimised to suit the particular conditions. Provided that the initial survey indicates that savings can be achieved, installation should be reduced to fitting and switching on. The unit is housed either in a custom designed injection moulded and die cast enclosure. or in a Fibox MNX enclosure.