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Technical - Control Gear

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Control Gear Options:

Standard Switch Start
Electronic Starters (ES)
High Frequency (HF)

High Frequency Dimming (HFD)
Separate Switching Facility (DS)

Emergency Units


Control Gear Options

As discussed within the 'fluorescent basics' section, ionisation within a fluorescent lamp results in the release of electrons and the creation of positive ions. This action causes an increase in lamp current and may cause more collisions, more ionisation etc. If this process is not controlled, the lamp current will rise to a level that would result in the destruction of the lamp. For this reason, a standard fluorescent lamp must be connected to some form of current limiting device. A starting device is also necessary to provide the characteristics required to strike the lamp.

Standard Switch Start

This is the term given to the form of control gear which for many years has been the industry standard. The lamp current is limited by a wire wound magnetic choke or ballast. The choke, which is basically a coil of wire, makes the circuit inductive, stepping the out of phase with the voltage. To reduce this phase difference and improve the efficiency of the circuit it is necessary to include a power factor correction capacitor. Starting is achieved by the use of a glow starter which consists of a sealed glass vessel containing either two bi-metallic contacts or one fixed and one bi-metallic contact. When power is applied to the lamp circuit, an arc produced between the two starter contacts heats them until they close. While the contacts are closed, the lamp cathodes are heated and so emit electrons. When the starter contacts have cooled sufficiently they open, causing the magnetic field in the choke to collapse. This creates a high voltage between the cathodes (in the order of 800V) which strikes the lamp. The standard switch start circuit cannot be dimmed.

Electronic Starters (ES)

Electronic starters can be used as a direct replacement for the glow starter. Through the use of solid state electronics, these starters perform the same function as the glow starter but are less damaging to the lamp cathodes and therefore extend the useful life of the lamp. If there is insufficient cathode emitter material to sustain the discharge, a glow starter will continue making attempts to strike the lamp until either the lamp is changed, or the starter or some other component in the circuit fails. Most electronic starters employ a safety shut down system for failed lamps preventing the constant strike/re-strike cycle associated with older standard switch start installations. Most glow starters cannot be used in temperatures below 0ºC. Standard Electronic starters will reliably strike a lamp at much lower temperatures (down to -20ºC) with special variants available for even colder installations (down to -40ºC). It should be noted however, that at these temperatures the lumen output from a fluorescent lamp is very poor. Although more expensive to purchase than the more common glow starter, electronic starters need not be replaced when lamps are changed and will usually continue to function for more than 10 years.

High Frequency (HF)

High frequency electronic control gear consists of a single ballast unit that performs the functions of all of the major components in a standard switch start circuit. Through the use of solid state electronics the HF ballast creates a discharge frequency of 25-40kHz. This is far higher than standard switch start circuits (100Hz) and results in a vast improvement in the quality of the light produced. Lamp flicker is eliminated and as HF operation is more efficient than normal operation, significant savings can be made in energy costs. Most HF control gear also incorporates a warm start facility to extend the useful life of the lamp.

High Frequency Dimming (HFD)

Dimming is not possible when using standard switch start or constant output high frequency control gear. If the dimming of fluorescent lamps is required, special control gear must be used. Several types of high frequency dimming system exist but the most common types employ a 1-10V low voltage analogue control line which is totally independent of the mains supply and links each luminaire and the dimmer unit. The dimmer unit is basically a variable resistance which is placed across the analogue control line. As this system is analogue, it is both limited in the scope of operation and susceptible to interference. Other systems exist that use a digital code to communicate between the ballast units. This system is less affected by interference and offers the user greater functionality. The latest HFD units use the relatively new DALI industry standard for digital control. This new system will allow building management and lighting control systems to communicate with luminaires from different manufacturers using the same language. It is even possible for the luminaires to report operating conditions such as lamp failures etc. When dimmed using HFD control gear, fluorescent luminaires require less energy than equivalent non-dimmable circuits further increasing the potential for energy savings.

Separate Switching Facility (DS)

If a luminaire is wired so that it contains two or more separate fluorescent circuits within the same body then each circuit can be switched independently. This allows the output of a fluorescent luminaire to be controlled without the need for a dimming system. Part of each luminaire can be switched off when not required therefore reducing wasted energy. The separate switching principle can be applied to most types of control gear at a fraction of the cost of upgrading to high frequency dimming.

Emergency Units

In the event of a complete power failure, some form of emergency lighting must be installed to provide adequate illumination for the evacuation of a building. This emergency lighting can either take the form of dedicated emergency luminaires which illuminate only when required, or standard luminaires which are supplied with factory fitted emergency units. Emergency units fitted to standard luminaires can be supplied equipped with a dedicated emergency lamp (Non-maintained) or a system that illuminates one of the existing lamps within the luminaire in the event of a power failure (Maintained). The type of system employed is dependant upon the type of luminaire but generally, standard fluorescent luminaires are fitted with maintained emergency systems. The power for emergency operation is normally supplied by a rechargeable battery system. This may be a single central battery system supplying the whole building or self contained battery packs within each luminaire.

 
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