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 TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
Section IV-SERIES TYPE AIRFIELD LIGHTING
6-13. Series type lighting system compo-
socket before inserting the socket into the recep-
nents.
tacle. If the socket is replaced before putting the
lamp in it, the film cutout will puncture. Never
A series-type lighting system for airfield light-
re-use a punctured film disk. Paper, cardboard, or
ing includes luminaires, mounting structures for
other insulation should never be used as a substi-
the luminaires, the control system to switch lumi-
tute for the film cutout.
naires on and off and the power system which pro-
vides the constant-current to operate the lumi-
6-15. Series type lighting power supply
naires. Luminaires provide light distribution
equipment.
applicable to the type of airfield lighting involved.
In general, series type streetlighting systems
The main item of power supply equipment is the
should be phased out in accordance with depart-
constant-current transformer to supply the series
mental policy.
circuit power. The other item is the insulating
transformer, whose main purpose is to isolate each
6-14. Series type lighting controls and protec-
luminaire to prevent an open circuit when a lamp
tion.
burns out.
Low-voltage airfield lighting controls includes
a. Constant-current transformers. The trans-
power sources, control panels, relay equipment, ac-
former (usually called a regulator) has a movable
cessories, and circuits. Controls energize, de-
secondary winding that automatically changes posi-
energize, and select lamp brightness in accordance
tion to provide a constant-current output for any
with operational requirements. Control will nor-
varying load impedance, within its rating, when
mally be provided only at the control tower and the
supplied from an approximately constant-voltage
airfield lighting vault. Medium-voltage controls,
source. The balance point between coil weight and
utilize the following devices.
magnetic force may be adjusted to provide the de-
sired output current. Most existing constant-
primary feed of constant-current regulators in case
current transformers are oil-insulated; but dry type
of an open circuit in the series lighting circuit.
units, which are not much larger, are available and
__
b. Primary switches. A primary oil switch is usu-
should be considered for replacement of failed oil-
ally a single-pole, solenoid-operated oil switch.
insulated units whenever possible.
Air switches, provided as an integral part of dry-
(1) Loading. Constant-current regulators
type constant-current transformers, are also avail-
should be loaded as near to 100 percent as possible.
able.
It is generally accepted that overheating will not be
c. Series plug cutouts. Cutouts are plug-type
caused by any load between 50 percent and 100
units used to disconnect a series light circuit or its
percent of rated kW. Regulators, unlike transform-
constant current regulator. With the plug handle
ers, are rated in kW, not kVA.
assembly removed and secured, maintenance per-
(2) Operation. A constant-current regulator
sonnel are ensured of protection.
must never be operated with an open-circuit second-
d. Film cutouts. Film cutouts or film disks oper-
ary. However, a short circuit, even a bolted short, on
ate automatically and are inserted in older lamp
a secondary will have no immediate adverse effects
sockets to bypass failed lamps. Some circuits that
if a reasonable percentage of the load remains ener-
have more than one lamp on an insulating trans-
gized.
former will use film cutouts to bypass a burned-out
b. Insulating transformers. Insulating trans-
lamp and keep the other lamps supplied from that
transformer operating. Because of their size and
formers isolate the medium-voltage of a series
shape, they are sometimes referred to as "dimes."
circuit from the wiring and fixtures. In addition,
When current no longer flows because of lamp fail-
they are sometimes used to obtain higher or low-
ure or removal, full circuit voltage exists across the
er current for lamps having a different ampere rat-
cutout film, which then ruptures, allowing the se-
ing, or constant voltage for multiple lamps con-
ries circuit to be completed. A new film cutout of
nected to a series circuit. They are sometimes
proper rating must be used whenever a faulty lamp
referred to as isolating transformers. Unless the
is replaced. It is good practice to replace the cutouts
case and one secondary conductor are grounded, the
whenever lamps are replaced under a group re-
secondary must be treated as a medium-voltage cir-
placement program. Always screw the lamp into the
cuit:
6-6
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