| Magnetic HID Ballasts High Intensity Discharge (HID) lamps require some form of control
gear (ballasts) to: (1) Provide enough voltage to strike the arc in the lamp. This
function may be done with the ballast itself or with a separate electronic ignitor
circuit. (2) To control the arc wattage during warm-up and normal operation. In addition
ballasts may: (1) Provide a line voltage matching (transformer) function. (2) Provide
enhanced lamp wattage control (regulation) with respect to changes in line voltage and/or
lamp voltage. (3) Provide dimming or other control interface functions.
Two Coil Reactor
- Constant Wattage Auto-transformer (CWA)
- Peaked Lead Auto-transformer (PLA)
- Auto-Lag (AL)
- Constant Wattage Isolated (CWI)
Three Coil Reactor
- Magnetic Regulator (MR)
- Electro-Reg® (ER)
Magnetic Ballasts Can Be Grouped Into Three Basic
Categories:
1. Linear, non-regulating circuits including reactors and
Auto-Lag ballasts that provide for basic lamp operation. With the exception of the
self-ballasted lamp, the linear reactor is the most basic form of ballast. Power factor
will be in the 40-50% range. A capacitor can be added to get the circuit high power factor
(90% or above.) Power factor remains relatively constant throughout the life of the lamp.
The linear ballast pro-vides virtually no line voltage regulation, and outages due to the
line dips and brown-outs are typical. Ballast losses for reactor ballasts are lowest of
magnetic ballast types. The Auto-Lag Ballast is a reactor ballast combined with a step-up
or step-down auto-transformer which allows for input voltage.
The Auto-Lag ballast is a single magnetic frame two coil
device. (The use of a separate voltagetransformer and a reactor provides the same
operational circuit.)
2. The Constant Wattage Auto-transformer (CWA) bal last
represents a step up from the Auto-Lag. It is a ballast circuit which uses magnetic
saturation to maintain better lamp wattage regulation and improved dip tolerance. A
variation of the CWA, called the Peaked Lead Auto Regulator (PLA) is used for metal
halide. Another variation, the Constant Wattage Isolated (CWI) is an isolated winding
version of the PLA.
3. Three coil circuits that provide superior electrical and
lamp performance. The Mag-Reg (MR) and Electro-Reg (ER) ballasts are three coil, isolated
winding, high performance ballasts. The input and lamp windings are separated by a third
winding which offsets drastic changes in the demands of the lamp on the supply system and
maintains lamp stability during supply system variations. This circuit provides the
highest degree of lamp operating stability, waveform control, lowest harmonics, and
performance consis-tency thru the life of the lamp.
Electro-Reg is an isolated winding ballast system for
Metal Halide. It provides a significant increase in lamp life and color
consistency/stability thru lamp life.
HID Ballast Characteristics
Line Current - On some ballast types, the line current as
the lamp starts is less than steady state operating current, so that fuses and circuit
breaker ratings can be based strictly on the operating current values. For other ballasts,
the line starting current may be considerably higher than the steady state operating
value, so fuses, circuit breakers, and photoelectric control switches must be sized to
accommodate the higher starting current.
Power Factor - To be classes as "high power
factor" a ballast must have a power factor of at least 90%. Anything less is
considered "Normal Power Factor" or "Low Power Factor." A low power
factor ballast makes less efficient use of the distribution system. This requires larger
wire sizes, larger switches, circuit breakers, and distribution transformers for the
equivalent connected load. Occasionally, as lamps age, lamp operating parameters may
change and cause power factor of some high power factor ballasts to fall below 90%. It is
important to note that a NPF ballast is no less efficient than an equivalent HPF ballast.
Line Voltage Regulation - This is the change in lamp
watts due to line voltage variation. Consideration should be given to the variation in
line voltage and feeder voltage drop to be expected on a particular system where HID lamps
will be applied to ensure that the regulating capacity of the ballast is matched to the
regulation of the power system. A majority of modern power distribution systems are
required to operate between ±5% of nominal line voltage, although systems are
occasionally encountered which may vary as much as ±10% or more from nominal. Power
shortages may result in "brown-outs" in some areas, which can create lamp
starting problems especially with those ballasts designed for ±5% operation. In any case,
the expected fluctuation in the power system voltage is an important consideration in
ballast selection especially where long wiring runs are involved.
Extinction Voltage (Dip Tolerance) - All power
systems are subject to dips in the line voltage as loads are switched in and out, or as
other transient conditions occur. A good, stiff, well-regulated distribution circuit will
seldom see voltage dips of more than 10%, but on some circuits; dips of 20% or more may
occur. If the ballast is not capable of "riding through" the voltage dip and
sustaining the lamp, the lamp will extinguish and have to cool down before re-ignition.
Lamp drop out due to line voltage dips generally increase as lamps age. Ballasts with
improved dip tolerance may delay the onset of lamp drop out problems.
Fusing - Most luminaires are offered with a fusing
option. In the case of HID lighting, fusing is primarily used to isolate the individual
fixture. For example, if an industrial luminaire ballast shorts (draws very high line
current) then in all probability the breaker for the entire circuit will trip which will
turn off every luminaire on that circuit. If the luminaire is properly fused however, the
fuse would clear (open) prior to the tripping of the breaker and the circuit would still
be active. This is important where loss of all lighting on a particular circuit is a major
problem. The isolation fusing provided may also help in trouble shooting problems on the
circuit.
HID Ballast
Circuits |
