BALLAST:
Lamp Ballast:
Lamp ballasts provide the energy needed to start and sustain gas discharges in the UV lamp. The following photos show examples of a ballast and a ballast cabinet.
Ballast cabinets
Ballast
The design of the ballasts may have different forms based upon the specific site needs and UV manufacturer design. According to information supplied by different manufacturers, ballasts are expected to last for 10 to 15 years; however, the guaranteed life is from 1 to 3 years (USEPA, 2003).
Magnetic Ballast:
Magnetic ballasts may be capacitive or inductive. Capacitive ballasts use capacitors to regulate the current flow (USEPA, 2003). One advantage of the capacitive ballast is that it is not dependent on line voltage for delivering power to the UV lamp. Also small changes in the power quality are less likely to result in ballast failure. One disadvantage of the capacitive ballast is the potential for faster aging of the electrodes in the UV lamp due to more electrode sputtering.
Inductive ballasts use inductors in combination with the voltage and lamp properties to control the current flow. An advantage of the inductive ballast is that the UV lamp electrodes last longer because less electrode sputtering occurs. Other benefits of the inductive ballast include a more stable current output with greater resolution and control. Some disadvantages of the inductive ballast are: they are less efficient than capacitive ballasts, they cost more, they weigh more, and they take up more space.
Magnetic ballasts are typically used in reactors using medium pressure (MP) lamps.
Electronic Ballast:
Electronic ballasts are composed of several electronic components which act together as a switching power supply. The electronic ballast can send an electrical current up to 50,000 pulses per second to the lamp compared to 100 to 120 pulses per second by the magnetic ballast (USEPA, 2003). The amount of current supplied to the lamp changes as conditions change. For example, when the lamps are cold the ballast provides longer, more frequent pulses of current to the lamp. The pulses become shorter and less frequent as the lamps warm-up and reach normal operating conditions.
Electronic ballasts are a newer technology which means that there is not a large amount of historic operational data to review. The electronic ballasts used today are more reliable than the early models. Electronic ballasts are more efficient and more compact in size and weight. They also provide the ability for continuous power adjustment at different settings. A disadvantage is that power fluctuations may cause a failure but this can be offset by adding a buffer capacitor.
Operation of the ballasts generate heat. Too much heat can damage the components and disrupt current flow to the lamp. To keep ballast temperatures under the specified limit, low-pressure high-output (LPHO) and medium pressure (MP) reactors use cooling systems. Cooling systems are generally not necessary for low pressure (LP) reactors.
The selection of the ballast will be based upon site specific factors, and the specific UV manufacturer applications. Each type of ballast, the magnetic and electronic, have certain advantages and disadvantages. A summary of the comparative advantages and disadvantages is presented here.
Comparison of Magnetic and Electronic Ballasts (USEPA, 2003)
Magnetic Ballast
Electronic Ballast
Comparative Advantages
Less potential for power interference due to stored energy
More resistant to power surges
More resistant to high temperatures
Less prone to interference with electronic devices
Less prone to sputtering (inductive less than capacitive)
Proven technology (in use for nearly 70-years)
Less expensive More efficient
Lighter weight
Smaller size
Less potential for heat generation
Less potential for noise
Continuous power adjustment
Longer lamp operating life
Comparative Disadvantages
Less efficient (capacitive more efficient than inductive)
Heavier weight
Larger size
More potential for heat generation
More potential for noise.
Step-function power adjustment (number of steps proportional to number of inductors/capacitors)
Shorter lamp operating life
More potential for power interference due to stored energy (can be minimized by incorporating a capacitor)
Less resistant to power surges
Less resistant to high temperatures
More prone to interference with electronic devices
More potential for sputtering
Newer technology (limited operating experience, especially in larger
sizes)
More expensive
