The Active Reactor

The Device

The device consists of an electronic control unit which controls an HID lamp in a pre programmed manner. The mode of operation of the device is variable power, constant light, as opposed to a conventional ballast which operates predominantly at constant power, variable light. These two different modes of operation greatly affect lamp energy consumption and lamp performance.

The device also controls a pre programmed lamp start up sequence for optimum lamp starting.

Because the device uses feedback in its operation and control strategy, the lamp is immune, to a very large extent, to lamp disturbances such as variations in supply voltage and lamp temperature variations.

Figure 1.

Variable Lamp Power Operation

The Active Reactor varies the power to the lamp, starting with a low power for a new lamp and gradually increasing the power with lamp age to full power for an old lamp.The power is designed to maintain the design light level throughout life.



	Energy Saving


	Metal Halide Lamps	typically 18% in energy saving without dimming

	High Pressure Sodium Lamps	typically 25% in energy saving without dimming

Lamp life extension

Because lamps controlled by the Active Reactor run all their life below their rated power, the mechanisms which reduce lamp life and lumen maintenance are inhibited to a significant extent. These mechanisms are (in simplified form):

Running a lamp at lower power means the lamp runs at a lower thermal loading and consequently diffusion of the amalgam through the arc tube is reduced; moreover, chemical reactions within the arc tube (between the amalgam and the arc tube and the electrodes) are also reduced. Amalgam diffusion and reactions within the arc tube are the chief causes of lamp ageing.

Running the lamp at lower power also means the lamp (and electrode) current is lower and therefore the electrodes are not “burnt” to the same extent. Burnt electrodes (particularly from overheated lamps) are a major cause of lamp failure.

The Active Reactor also has a preset starting current during lamp ignition. This current is such that the glow to arc phase time is minimised which reduces electrode sputtering during lamp starting.

The above detrimental effects on lamp life and lumen maintenance are negated to a significant extent by the Active Reactor. Field and laboratory trials have indicated that increase in lamp useful life is typically


Metal Halide Lamps	typically 50% increase

High Pressure Sodium Lamps	typically 100% increase

Circuit and Operation

Circuit Diagram

The PCB is shown in figure 1 (above) and a schematic wiring diagram of the Active Reactor is shown in figure 2 (below). The following describes the operation of the circuit:

The Active Reactor is connected into the circuit be removing the standard reactor ballast and replacing it with the Active Reactor components. The power factor capacitor and ignitor remain in the circuit.

The Active Reactor components are:

a	the Active Reactor printed circuit board which contains the electronics to control the lamp power and lamp starting.
b	a Main Ballast which supplies approx 75% of the lamp power. For example, for a 400 watt HPS lamp this power is 300 watt.
c	a Current Injector (Control Ballast) which supplies approx 25% of the lamp power. For example, for a 400 watt HPS lamp this power is 100 watt.


	Active Reactor Legend


	MB		Main Ballast
	CB		Control Ballast (Current Injector)
	SW		Electronically Program Controlled Triac Switch
	PCB		Active Reactor Printed Circuit Board


	*Figure 2.*

Operation

The Active Reactor utilises the main ballast as the primary source of power for the lamp and injects additional current (and power) into the circuit via the control ballast to achieve the required lamp operating conditions.

The minimum power the lamp can run at is typically 75% rated power when the control ballast is turned off completely. The maximum power the lamp can run at is typically 100% rated power when the control ballast is turned on fully. Hence the lamp can run at any instant, at any point in its life, between 75% and 100% power by appropriate current injection into the lamp.

This operation is summarised below:



Main ballast	Control ballast	Lamp power


ON	fully OFF	75%


ON	fully ON	100%


ON	partially ON/OFF	75 -100%

The 25% variable power which can be delivered to the lamp is just enough to offset the 30% flux depreciation during the life of a lamp.

Operating Characteristics

If the Active Reactor electronics fails then the lamp runs only on the main ballast at 75% rated power for the remainder of its life.

On a new lamp the control ballast is substantially turned off while on an old lamp the control ballast is substantially turned on.

The Active Reactor can operate to specification for input voltage variations of +/- 10%. Above these voltage variations it will still operate but will not regulate the power to the specified value.

The Active Reactor monitors the supply voltage, ballast voltage, lamp voltage and lamp current to control the lamp power.

The Active Reactor uses the lamp voltage as the basis for determining lamp life. Typically the following values are used:



Lamp	MH lamp	HPS lamp


New Lamp	130V	100V


Old lamp	160V	170V

Thus if a lamp fails and is replaced by a new lamp it will automatically be adjusted in power to run at the same light output as it did before it failed, that is, at the same light output as all the other lamps in the installation.

The Active Reactor can be dimmed by applying a 10V DC voltage to the DIM inputs on the PCB. Dimming is step dimming only. The light output for the HPS and MH lamps is shown below.



Lamp Operation	MH lamp	HPS lamp


Initial Lumens	100%	100%


Constant Lumens	80%	70%

Dim Lumens	60%	50%

That is, MH lamps can be dimmed 25% below their constant lumen operation and HPS lamps can be dimmed 30% below their constant lumen operation.

The energy savings achievable for both MH and HPS lamps powered by Active Reactors in constant lumens and dimmed modes are tabled below:



Lamp Operation	MH lamp	HPS lamp

Constant Lumens	18%	25%

Dim Lumens	30%	42%

The actual energy savings achieved will depend on the time weighted average of time spent in constant lumens and dim modes.

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