AIRFIELD LIGHTING VAULT

The beginning of the airfield lighting system is the airfield lighting vault. The primary power feeder enters the vault and supplies power to all of the major components. These components, in turn, control and operate the airfield lights. The vault houses the high-voltage power cables, the current regulators, the relay cabinets, and the control panels.

The control cables are installed between the vault and the control tower or other control points. The high-voltage cables are connected to the regulators and run out to the lights. The lighting control panels are used to give local/ remote control of the system. The same type of remote control panel that is in the vault should also be installed in the control tower.

The airfield lighting vault should be about 3,000 feet from the runway. This distance ensures that no interference will occur with the airfield's operations, and still it is not so far away that voltage drops might cause a problem. The lengths of the control circuits between the control tower and the vault are limited by operational characteristics; for example, size of field, obstructions, and so forth. The minimum distance is 350 feet; this is to prevent the equipment in the vault from causing radio interference. If the control cable leads terminate into actuating coils of relays in the pilot relay cabinet, the maximum distance is 7,350 feet.

Safety

The airfield lighting vault should have certain items of safety equipment on hand and affixed to a board. This board should be in open display and easily accessible. It should be a minimum of 1/2 inch thick and 4 by 4 feet in width and length. The color should be dark green with white letters and borders.

On this board, some of the safety items you should have are as follows:

1. Operating instructions for the equipment in the vault

2. Resuscitation instructions

3. A phone and a list of emergency phone numbers

4. A first-aid kit

5. A switch stick with a minimum length of 5 feet, and a 300-pound pull ability

6. A hemp rope, 1/2 inch thick, with a minimum length of 15 feet

Figure 2-1.\Field arrangement direct installation.

7. Insulated fuse pullers (for secondary cartridge fuses)

8. A nonmetallic-encased flashlight marked with luminescent tape to aid in its location in the dark

9. A shorting stick

10. Rubber gloves

For the safety of personnel, the airfield lighting vault must be grounded. This may be accomplished by using two 1/2-inch-diameter, 8-foot-long, copper-plated electrodes, driven into the ground about 8 feet apart and connected in a loop with the vault or ground cable part of the ground grid. This typical connection is shown in figure 2-2.

Power Supply

In many cases, the power supply will not be all high or low voltage; in fact, in many expeditionary airfields, the system may be a combination of high and low voltage. However, if you are assigned to a naval air station, chances are that you may be required to maintain high-voltage airfield lighting systems. Basically,

Figure 2-2.\Vault grounding arrangement.

the systems are identical, but because of safety requirements, the high-voltage systems will have a few variables. As an example, take the isolation transformer (IT) in the high-voltage system; it serves to step the voltage down, but its primary purpose is to prevent an opening in the primary series loop when a lamp failure occurs. In a low-voltage system, the transformer is usually a 2:1 or 1:1 ratio unit that serves to maintain a closed loop, the same function as the one in the high-voltage system. Even though we will be talking primarily about high-voltage systems most of the time, the functions of the components will apply to either system.

In the 2,400/4,160-volt system, the four-wire wye primary source is usually from the base electrical system by means of either an overhead or an underground line. Inside the vault, the lines are connected to a suitable switch, then to a bus system consisting of heavy metal bars that are supported on insulators. This bus system may be mounted on either the wall or the ceiling.

The bus is divided into a high-voltage (2,400-volt) bus and a low-voltage (120/240-volt) bus for service as follows: The 2,400-volt bus supplies all of the 2,400-volt regulators and one or more distribution type of transformers. The distribution transformers supply 240 volts to the low-voltage bus that is connected to the regulators operating from this lower voltage as well as for light and power inside the lighting vault.

Where an emergency power supply is available for airfield lighting, a changeover switch makes the primary connection to the bus. This changeover switch in its normal position connects the bus to the base power source. Changing the switch to the emergency operation position connects the bus to the emergency power and, at the same time, disconnects the base power source.

Emergency power can be supplied by a completely automatic engine-driven generator. For example, failure of the base power causes the engine to start. In a matter of seconds, the changeover switch automatically shifts to the emergency position, connecting the generator to the airfield lighting bus.

At many advance bases, this automatic feature may not exist. Then, you become its replacement. The generator should have a kilowatt (kW) rating capable of handling the airfield lighting systems, runway edge lights, threshold lights, approach lights, distance markers, optical launching system (OLS), and other circuits that may be used. The generator is three phase; its voltage output varies from 120/240 volts delta or 120/208 volts wye to 2,400/4,160 volts, and it has to be capable of being operated at frequencies of 50 or 60 hertz (Hz).