Airfield Lighting
Safegate Group
Manual
Date: October 2016
Ref: SL-RE-E_SL-RT-E_SL-RN-E_SL-RTN-E_SL-SB-E
Version: 1.4
Page 9 of 42
1.2.2.3
Secondary Cable Losses
The cable, including any extensions, between the isolation transformer and the light
fixture adds power losses (here expressed in Watts per meter).
Example of cable losses at different current and different cable areas
6.6 A Operation
2A Operation
2.5 mm
2
Cu-wire:
0.6 W/m
0.06 W/m
4.0 mm
2
Cu-wire:
0.4 W/m
0.04 W/m
Note: Secondary cable lengths should not exceed 100 m.
1.2.2.4
2A System
When dimensioning the isolation transformer size for a 2A-system (a series circuit
with SafeLED IQ 2A which is only supposed to run in 2A), it is important to know that
the regular method by adding up the total wattage on the isolation transformer
secondary side, cannot be used. This is because a standard isolation transformer
6.6/6.6A is marked with a maximum wattage running at 6.6A. According to Lenz Law
of Induction, the dimensioning property of a transformer is the total voltage, and not
the wattage, of the secondary side of the transformer in a 50/60Hz series circuit
system.
The consequence in a 2A-system is the wattage marked on a 6.6/6.6A isolation
transformer must generally be multiplied by the factor 0.3 to find the total wattage
which can be supplied from the transformer without saturating.
Note: The same dimensioning method must be used for a CCR, as the transformer
kVA-size marked on a CCR is normally calculated at 6.6A, not at 2A. There are also
more constrains to consider such as spare capacity. For more information, contact
Safegate for a complete CCR dimensioning procedure.
1.2.3
Transformer Selection Guidelines
Calculation Example for transformer selection:
1.2.3.1
6.6 A mode
Light fixture Runway Edge Elevated White-White for Precision Approach: 27 W
Secondary cable length 20 meters, 2.5 mm2, -> 0.6 W/m = 12 W cable power loss
Total load 27 W + 12 W =
39 W
Max total load for a 45 W transformer is 45 W at 6.6 A
Result:
Transformer rating should be at least
45 W
Note:
If the light fixture is used in ASP systems a 10 W margin should be added to the
transformer. This wattage is not being used but needs to be available for the power
line communication.
Total load for ASP systems 27 W + 12 W + 10 W =
49 W
Result:
Transformer rating should be at least
65 W
Note: It is not recommended to use transformers with lower rating than 65 W for ASP
installations.
1.2.3.2
2 A mode
Light fixture Runway Edge Elevated White-White for Precision Approach: 27 W
Secondary cable length 50 meters, 4.0 mm2 -> 0.04 W/m = 2 W cable power loss
