Home Lighting Control Nuclear Power Contacts Links


XYLENE POWER LTD.

POWER LINE CARRIER LIGHTING CONTROL

CABLE LOSS

14 AWG 2 wire BX Cable (3/8" armour)

Data supplied by Systel indicates that at 100 kHz, the impedance of one Systel 2 lamp 70 watt ballast is 380 0hms inductive. Thus three such ballasts connected in parallel have an impedance of 380 / 3 = 127 ohms inductive. The corresponding inductance value is given by:
127 / (6.28 X 10^5) = 202 uH.
Hence three parallel connected ballasts have about the same impedance as two series connected 100 uH inductors.

At low frequencies the same three ballasts at full load draw 3 X 70 = 210 watts. The equivalent resistance of these three parallel connected ballasts is given by: R = V^2/P = (120)^2/210 = 68.6 ohms. This resistance can be approximately simulated by two series connected 36 ohm resistors.

We can conduct cable attenuation tests using a measured 100 m length of #14 2 wire (plus ground) 3/8 inch diameter armour cable.


Thus, by using various terminations consisting of series/parallel combinations of 4 100 uH inductors and 4 36 ohm resistors, at 127 kHz we can prepare a table of the following form:
Termination------Equiv.No. of Ballasts------Transfer Ratio = Vb / Va
200 uH3
100 uH6
66.67 uH9
50 uH12
40 uH15
33.3 uH18.439
25 uH24.382
72 R3
36 R6
24 R9
18 R12
14.4 R15
12 R18
9 R24.234

Consider the case of the 9 ohm resistive termination. If we assume that for a 200 m cable the loss is (Vb / Va)^2 = (.234)^2 = .0547, and if we operate under the guideline that the cable loss fraction should be greater than 1/20 = .05, then we find that the maximum allowable cable length may be as short as 200 m for a fully loaded lighting circuit that contains a substantial fraction of incandescent lamps. However, if all the fixtures are fluorescent only,then the data for the 25 uH termination indictes that (Vb / Va)^3 = (.382)^3 = .0557, pointing to a maximum branch lighting circuit length of 300 m. Note that the maximum branch lighting circuit length decreases as the connected load increases.

Back Next

This web page last updated September 20, 2005

Home Lighting Control Nuclear Power Contacts Links