Transformer cans with no primary

6.6- and 20-amp strings on airport runways... listed in US FAA regs.

--s falke

non-incandescent

Why? The only thing I see is to save wire and this saving is overcome by the need for constant current regulation.

technology >

Well..it's saving a lot of wire - runways are very long.

I was told one reason that series lighting is still used for airport lighting is that it ensures that all the lamps are the same brightness. Apparently if some lamps are dimmer at one end of the runway, it can cause problems for pilots.

Bill

( who's got a little lights'n'plugs job going at an airport right now, as a matter of fact.)

Reliability, maybe? If a lamp shorts, others still run. If a lamp opens, there is a gizmo that shorts that part of the loop. Individual transformers are used for lamps on runways, but in traditional incandescent street lighting, mogul lamp bases had a replaceable "mica shot" that would spark though and short the open filament.

See "Dime" at

--s falke

transformers

Agreed that all run if a lamp either shorts or is open- that is a good point How likely is a short in a lamp? In the case of the runway lights there is still the need for a constant current regulation. . Mind you, constant current control is far easier now than in the days of the old series streetlights where the controller was a magnetic device with the secondary coil floating above the primary on the core- magnetic forces balanced against a counterweight were used to control the distance between coils and the mutual coupling to achieve approximately constant current operation. Big and clumsy. Bill Shymanski has injdicated two reasons- a) a saving of wire which I believe, in the absence of hard information to the contrary, might cost less than the current control. b) same light intensity from all lights-this may be a better reason

Thanks- I knew about these as a kid and wished then that they put them into Xmas tree lights (which they did eventually ).

A constant current system allows for easy monitoring of blown bulbs. When a bulb is blown it has a device that shrts it out to maintain the current path. This is seen as a decrease in voltage a croos the string of lights that can signal a warning to check bulbs or that the runway may not be usable. Constant current also makes for an easy way to control brightness. Runway lights have 5 brightness steps.Didnt know seies lights were used for street lights but possibly for the same reasons..

Thanks for the perspective - . As for series street lighting- this was a thing of the past and possibly the main intent was to save wire Running a

2000V 20 light string at 5A had advantages . The constant current regulators were large and cumbersome so the balance of costs is questionable. Changes in distribution practices etc shifted the balance towards parallel operation and the proliferation of non-incandescent bulbs finished off the series street lighting systems. Modern current control and the specific requirements of runway lights as you and others have indicated make series circuits sensible in this case.

Actually, I think that the reason for series street light lamps was that the ORIGINAL street light lamps were Cooper-Hewitt arc lamps. As such, they needed a current source, and the series string permitted the use of one regulator per string, rather than one per lamp. When incandescents were sufficiently developed they simply designed a bulb to work on the existing constant-current circuits.

Remember too that street lighting existed before general electrification was widespread. The series string also made DC feasible, as it permitted the use of high voltage DC with low voltage lamps. Running streetlights on low-voltage DC would have required an exorbitant amount of copper or many generators/converters to overcome the voltage drop issues.

Very good points and I think you hit it on the head. Thank you. "AC" series street lights still existed at least to the late 40's in some places (hey the system is obsolete but still doing its job-why fix it?). The cost of a single regulator /transformer (say 2KV secondary) might have been less than the cost of copper even then. However, with general electrification (as you indicate) the economic balance would shift toward service voltage lamps supplied from the local distribution transformers. That doesn't mean that existing infrastructure would be ripped out.

Don Kelly snipped-for-privacy@peeshaw.ca remove the urine to answer