An electric ballast is a device placed in accordance with the load to limit the amount of current in the electrical circuit. It may be a fixed or variable resistor.
A familiar and widely used example is an inductive ballast used in fluorescent lamps to limit the current through a tube, which would otherwise rise to a destructive level due to the negative differential resistance of the tube-voltage characteristics.
Ballasts vary greatly in complexity. They may be simple like resistors, inductors or capacitors (or this combination) connected in series with the lamp; or as complex as electronic reply used in compact fluorescent lamps and high intensity discharge lamps.
Video Electrical ballast
Current restrictions
An electric ballast is a device that limits current through electrical loads. This is most commonly used when loads (such as arc discharge) have a decrease in terminal voltage when the current through the load increases. If such a device is connected to a constant voltage power supply, it will attract an increase amount of current until it will be destroyed or cause the power supply to fail. To prevent this, the ballast provides a positive resistance or a current-limiting reactance. Ballasts provide precise operation of negative resistance devices by limiting the flow.
Ballasts can also be used only to limit currents in ordinary positive resistance circuits. Prior to the advent of solid-state ignition, car ignition systems typically include ballast resistors to regulate the applied voltage to the ignition system.
Series resistors are used as a ballast to control current through LEDs.
Maps Electrical ballast
Resistor
Fixed resistor
For simple, low powered loads such as fluorescent or LED lights, fixed resistors are commonly used. Because the resistance of the large ballast resistor determines the current in the circuit, even in the face of the negative resistance introduced by the fluorescent lamp.
Ballasts are also components used in early model car engines that lower the supply voltage to the ignition system after the engine is turned on. Starting the engine requires a large amount of electric current from the battery, resulting in an equally important drop in voltage. To allow the engine to fire, the ignition system is designed to operate at this lower voltage. But once the vehicle starts and the starter is released, the normal operating voltage is too high for the ignition system. To avoid this problem, the reverse resistor is inserted in series with the ignition system, producing two different operating voltages for the starter and ignition system.
Sometimes, this ballast resistor will fail and the classic symptom of this failure is that the engine is running while it is being turned on (while the resistor is bypassed) but stops immediately when the crank stops (and the resistor is reconnected in the circuit via an ignition switch). Modern electronic ignition systems (used since the 1980s or late 70s) do not require a reversal resistors because they are flexible enough to operate at lower crank voltages or normal operating voltages.
Another common use of ballast resistors in the automotive industry adjusts the speed of the ventilation fan. The ballast is a fixed resistor with usually two middle taps, and the fan speed picker switch is used to cut off the ballast: all for full speed, and none for low-speed settings. A very common failure occurs when the fan keeps running at the next full speed setting (usually 3 of 4). This will cause a very short piece of coil resistor to be operated with a relatively high current (up to 10 A), eventually burning it. This will prevent the fan from running at a reduced speed setting.
In some consumer electronics appliances, especially in television in the era of valves (vacuum tubes), but also in some low-cost recording players, vacuum tube heaters are connected in series. Because the voltage drop across all heaters in the series is usually less than the primary mains voltage, it is necessary to provide the ballast to drop the excess voltage. A resistor is often used for this purpose, because it is cheap and works with AC and DC.
Variable-independent resistor
Some balast resistors have increased resistance properties as currents through them increase, and decreasing current resistance decreases. Physically, some such devices are often made like incandescent bulbs. Like a tungsten filament of a common incandescent bulb, when the current increases, the ballast resistor becomes hotter, its resistance rises, and the voltage drop increases. If the current decreases, the ballast resistor becomes cooler, the resistance decreases, and the voltage drop decreases. Therefore, the reverse resistor reduces the variation of the current, although variations in the applied voltage or changes in the rest of the electrical circuit. These devices are sometimes called "letters" and are used in circuit heating circuits of the 1930s to 1960s AC/DC radios and home TV receivers.
This property can cause more precise current control than just selecting the appropriate fixed resistor. The power lost in the resistive ballast is also reduced because a small portion of the overall power is dropped in response compared to what may be required with fixed resistors.
Previously, household clothes dryers occasionally inserted germs in series with ordinary incandescent lights; Incandescent lamps are operated as ballasts for disinfection lamps. A commonly used lamp at home in the 1960s in 220-240s of countries is a circular tube condensed by the main filament lamp that goes under normal. Self-ballasted mercury-vapor lamps incorporate the usual tungsten filaments inside the entire envelope of the lamp to act as ballasts, and that complement the red area less than the resulting light spectrum.
Reactive ballast
Because of the power to be lost, the resistor is not used as a ballast for lamps more than about two watts. Instead, reactance is used. Losses in the ballast due to its resistance and losses in its magnetic core may be significant, in the order of 5 to 25% of the electric lamp input power. A practical lighting design calculation should allow ballast losses in estimating the cost of running a lighting installation.
An inductor is very common in a line-frequency ballast to provide initial electrical conditions and proper operation to light a fluorescent lamp, fluorescent lamp, or high intensity discharge lamp (HID). (Because of the use of inductors, such ballasts are usually called magnetic ballasts .) The inductor has two benefits:
- Reactance limits the power available to the lamp with only minimal power loss in the inductor
- The surge in voltage generated when the current through the inductor is disconnected is quickly used in some circuits to first attack the arc in the lamp.
Inductor losses are currents that shift out of phase with voltage, producing a poor power factor. In a more expensive reply, the capacitor is often paired with the inductor to improve the power factor. In ballasts that control two or more lamps, the line-frequency ballasts generally use different phase relationships between multiple lamps. It not only reduces individual flickering lights, but also helps maintain high power factor. This ballast is often called the lead-lag ballast because the current in a single lamp leads the electrical phase and the current on the other lamp lags behind in the main phase.
In Europe, and most of the region is 220-240 V, the electric voltage is sufficient to power more than 20W lamps with series inductors. However, in North America and Japan, an electric voltage (either 120 V or 100 V) may not be enough to light more than 20 W with series inductor, so the autotransformer winding is included in the ballast to increase the voltage. The autotransformer is designed with sufficient leakage inductance (short circuit inductance) so that the current is properly constrained.
Because of the large inductors and capacitors to be used, the reactive ballasts operated at the channel frequencies tend to be large and heavy. They generally also produce an acoustic sound (hum of frequencies).
Prior to 1980 in the United States, PCB-based oils were used as an insulating oil in many ballasts to provide cooling and electrical insulation (see transformer oil).
Electronic and magnetic ballasts
Electronic ballasts use solid state electronic circuits to provide initial electrical conditions and proper operation for power discharge lamps. Electronic ballasts can be smaller and lighter than magnetic equivalents. Electronic ballasts are usually quieter than magnets, which produce buzzing frequencies with transformer lamination vibrations.
Electronic ballasts are often based on a SMPS topology, first fixing the input power and then cutting it at high frequencies. The advanced electronic ballast allows dimming through pulse-width modulation or through changing the frequency to a higher value. Ballasts incorporating microcontrollers (digital ballasts) can offer remote control and network monitoring such as LonWorks, DALI, DMX512, DSi or simple analog controls using a 0-10 V DC brightness control signal. Systems with remote-level light control over wireless mesh networks have been introduced.
Electronic ballasts typically supply power to light at frequencies 20,000 Hz or higher, than the main frequency 50 - 60 Hz ; this substantially removes the flicker stroboscopic effect, the product of the line frequency associated with fluorescent lighting (see photosensitive epilepsy). The high output frequency of the electronic ballast refreshes the phosphor in the fluorescent lamp so quickly that no flicker is visible. The flicker index, used to measure clear light modulation, has a range of 0.00 to 1.00, with 0 indicating the lowest possible flickering and 1 showing the highest. Lamps operated on magnetic ballasts have a flicker index between 0.04-0.07 while digital ballasts have a flicker index below 0.01.
As more gas remains ionized in the flow of the arc, the lamp operates at about 9% higher efficacy above about 10 kHz. The lamp efficiency increases sharply around 10 kHz and continues to increase to approximately 20 kHz. Electronic ballast retrofit for existing street lamps has been tested in several Canadian provinces around 2012; since then retrofit LEDs are becoming more common.
With higher efficiency of the ballast itself and higher lamp efficacy at higher frequencies, electronic ballasts offer higher system efficacy for low pressure lamps such as fluorescent lamps. For HID lamps, there is no increase in the efficacy of lamps in using higher frequencies, but for these lamps the ballast losses are lower at higher frequencies and also lower light shrinkage, which means the lamp produces more light during its entire life. Some types of HID lamps such as ceramic discharge metal halide lamps have reduced reliability when operated at high frequencies in the range of 20 - 200 kHz ; for these lamps the square wave of low frequency current drive is mostly used with frequencies in the range of 100 - 400 Hz , with the same advantage of lower light shrinkage.
Electronic ballast applications for HID lighting are increasingly popular. Most recent generation electronic ballasts can operate high pressure sodium (HPS) lamps as well as metal halide lamps, reducing the cost of building managers using both types of lights. The ballast initially serves as a starter for the arc, supplies high voltage impulses and, later, it acts as a limiter/regulator of electrical current within the circuit. Electronic ballasts also run much colder and lighter than their magnetic counterparts.
Ballast fluorescent lamp
Preheating
This technique uses a combination of cathode-filaments at each end of a lamp together with a mechanical or automatic (bi-metal or electronic) switch which initially connects the filament in series with the ballast to heat it up. When the filament is disconnected, the inductive pulse from the ballast starts the lamp. The system is described as "Heat" in North America and "Switch Start" in the UK, and has no special name in any other part of the world. The system is common in 200-240 V countries (and for 100-120 V lamps up to about 30 watts).
Although the inductive pulse makes it more likely that the light will start when the starter switch is open, it is not actually necessary. Ballasts in such systems can both be resistors. A number of fluorescent lampholders used filament lamps as ballasts in the late 1950s to 1960s. Specially manufactured lamps rated at 170 volts and 120 watts. The lamp has a thermal starter built into a 4 pin base. Power requirements are much greater than using inductive ballasts (although the currents are consumed equally), but the warmer glow of this type of ballast lamp is often favored by the user especially in the household environment.
Resistive bales are the only type that can be used when the only supply available to power a fluorescent lamp is DC. The fittings use a type of thermal starter (mostly because they have been out used long before the starter glow is found), but it is possible to insert a choke in the circuit whose sole purpose is to provide a pulse at the opening of the starter switch. to improve start. DC fittings are complicated by the need to reverse the polarity of the supply to the tube each time it starts. Failure to do so greatly shortens the life of the tube.
Instant Start
Instant ballast does not heat the electrode, instead of using a relatively high voltage (~ 600 V) to start the release arc. It is the most energy-efficient type, but produces the fewest lamp-start cycles, since the material is destroyed from the surface of the cold electrode whenever the lamp is turned on. Instant start ballasts are best suited for applications with long duty cycles, where lights are not often turned on and off. Although this is mostly used in countries with 100-120 volt power supply (for 40 W or more lamps), they are popular in other countries because lights start without a glance at the start switch system. Its popularity is short due to short lamp life.
Quick start
Fast ballast starts using tension and heats the cathode simultaneously. It provides superior lamp life and more lifespan, but uses a bit more energy because the electrodes at each end of the lamp continue to consume heating power when the lights are in operation. Again, although popular in the 100-120 volt states for 40 W lamps and above, the fast start is sometimes used in other countries especially where the flicker of the start switch system is undesirable.
Ballast dimmable
A dimmable ballast is very similar to a fast start ballast, but it usually has an incorporated capacitor to provide a power factor closer to the unity than a standard fast start ballast. Dimmers of quadrac lamp types can be used with dimming ballasts, which maintain heating currents while allowing controlled lamp currents. Resistor about 10k? required to be connected in parallel with the fluorescent tube to allow reliable firing of the quadrac at low light levels.
Start programmed
Used in high end electronic fluorescent ballasts. This ballast applies power to the first filament, it allows the cathode to heat up and then apply a voltage to the lamp to attack the arc. Lamp life usually operates up to 100,000 life/die cycles when using programmed ballast start. Once started, the filament voltage is reduced to improve the operating efficiency. This ballast provides the best life and mostly starts from the lamp, and is preferred for applications with very frequent power cycles such as visual inspection rooms and toilets with motion detector switches.
Hybrid
The hybrid ballast has a magnetic core-and-coil transformer and an electronic switch for the electrode heating circuit. Like a magnetic ballast, the hybrid unit operates at a power line frequency of 50 Hz in Europe, for example. This type of ballast, also referred to as the cathode-breaker ballast , releases the electrode-heating circuit after they turn on the light.
ANSI Ballast Factor
For lighting ballasts, ANSI ballast factors are used in North America to compare the light output (in lumens) of lights operated on ballasts compared to lights that operate on an ANSI reference ballast. The reference ballast operates the lamp in the rated nominal ANSI power rating. The practical ballast ballast factor should be considered in the lighting design; Low ballast factors can save energy, but will produce less light. With a fluorescent lamp, the ballast factor may vary from a reference value of 1.0.
Ballast triode
Early tube color TV sets use a triode of reply, such as the PD500, as a parallel shunt stabilizer for CRT acceleration voltages, to keep the CRT deflection factor constant.
See also
- Compact fluorescent lamp (CFL)
- Fluorescent lamp
- High-intensity discharge light (HID)
- Iron-hydrogen resistance
- Mercury vapor lamp
- Neon Lamp
- Sodium lamp
References
External links
- NEMA - National Electrical Manufacturers Association
Source of the article : Wikipedia
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