HID Ballast Circuit and Principle

What is HID Ballast?

HID ballast is a device that is used to control the voltage and arc current of High Intensity Discharge lamps during their operation.

Classification of HID Ballast

HID ballasts are classified into several categories. They are

1. Reactor ballast
2. Lag ballast
3. Regulator ballast
4. Auto regulator ballast

Short description about these types is given below.

Reactor Ballast

• This reactor ballast is essentially a wire coil on an iron core placed in series with lamp.
• A capacitor is introduced to correct the power factor and this capacitor must be inserted across the line.
• The voltage change in the lamp due to the reactor is 18%, for wattage it is 5 % change and 5 % line voltage change.
• It regulates the lamp voltage very well but regulates the line voltage very poor.
• The reactor ballast provides low current crest factor of about 1.5.
• Amount of the starting voltage it can provide to the lamp has limitation up to the line voltage.

The reactor ballast is shown below.
 

Lag Ballast

• A combination of auto transformer and a reactor forms lag ballast.
• This lag ballast has same regulation characteristics as the reactor ballast.
• But lag ballast overcomes the starting voltage limitation, i.e. more than line voltage.
• It is bulk in size with greater loss.
• A lag ballast cost higher.

Lag ballast is shown below.

Regulator Ballast

• Regulator ballast has isolated primary and secondary windings.
• It achieves current limiting through a series capacitor.
• This capacitor leads the current to lead the secondary voltage.
• With regulator ballast an excellent regulation is obtained.
• By using this regulator ballast, the change in line voltage is ± 13 % and about ± 3 % is the lamp wattage change.
• Its power factor is about 0.95.
• It minimizes the grounding and the fusing problems.
• Higher current crest factor is only its disadvantage as this crest factor lies between 1.65 to 2.0.

A regulator ballast is shown below.
 

Auto Regulator Ballast

• The auto regulator ballast has the features of both the lag ballasts and the regulator ballasts.
• This auto regulator ballast is most popular and it is intended as tradeoff.
• Its cost is less and it does not provide isolation between primary and secondary.
• It has bad regulation property.
• It causes in variation of line voltage with ± 10 % and wattage variation is ± 5 %.

The auto regulator ballast is shown below.

What is Current Crest Factor for HID Ballast?

The current crest factor is the ratio of the peak to rms current of the HID ballast, i.e.

Which Ballast is Used in Sodium Lamp?

A different kind of ballast is used in sodium lamp. Crest factor should not exceed 1.8 for proper lamp operation. As in the sodium lamp, ionization of xenon gas needs very high voltage, so starting voltage with higher value must be obtained from this kind of special ballast. The lamp wattage is controlled closely to control the amalgam vaporization. The feature of this ballast is given below.

• It is bulky electromagnetic ballasts.
• It is combined with igniters.
• It has much better lumen maintenance capability.
• Recently electronic ballasts has been introduced to perform the same tasks more efficiently.

What are the Ballast Losses in Different Ballasts?

The HID ballast losses are given below.