OVERVIEW:

POLELINE is an interactive design tool to be used in designing overhead 
transmission lines on single 
wooden poles using AutoCAD 2000. It is intended to be used in a profile drawing 
of the transmission line, 
showing ground levels, with proposed locations and heights drawn in. POLELINE 
will calculate sag table 
data and pole-loading data for these pole locations and heights, and draw in the 
worst case cable curve 
between poles.It does not relieve the designer of design responsibility. If the 
results are not satisfactory, 
different pole locations or heights, or cable tensions can be tried.

DESIGN PROBLEM:

The problem for the designer is to select an overhead cable route for cables 
with the desired ampacity. Then 
he must determine the sagging tension, or tension that the line stringing team 
must apply to the cable as it is 
installed. The cable must not be pulled so tight that its maximum tension rating 
would be exceeded if the 
temperature dropped to the lowest expected ambient temperature with no current 
load in the cable after it is 
strung. (The cable will have shrunk to its shortest length under these 
conditions). It must not be so loose 
that under it highest current load and in the hottest expected ambient 
temperature it will have sagged below 
the required or desired clearance above road crossings, railroad crossings, etc. 
These road crossings, etc. 
should be shown on the profile drawing.

Another part of the design is to select poles that will support the calculated 
pole loading. Dead-end poles 
will require guying to offset the calculated horizontal loading.



COMMANDS:

The following commands will be available at the command line upon loading 
POLELINE.ARX :

SAG - draws cable (catenary curves) for worst case clearance, calculates and 
prints control span 
sag table.
POLELOAD- will calculate pole loading data and output it to profile drawing.	

SAG must be the first command used. Before using SAG (and POLELINE) you should 
have a surveyed 
profile drawing of your proposed overhead line route. You will need to know the 
horizontal and vertical 
scales of the drawing in feet per inch. These scales are usually not equal for a 
profile drawing. Poles should 
be placed on the profile drawing with preliminary heights and locations. You 
will also need to know what 
size and type of cable you are going to use, and have several mechanical 
parameters of the cable available. 
Select the cable on the basis of required ampacity, then get the following 
mechanical parameters:
$K
#WEIGHT PER FOOT (in pounds)- this should include any windage and ice loads.


#COEFFICIENT OF EXPANSION(as a fraction of the overall length per degree 
Fahrenheit)


#COEFFICIENT OF 10-YEAR CREEPAGE (as a fraction of overall length due to stretch 
from creepage 
over 10 years) - this is the amount the cable is expected to stretch from normal 
usage over a ten year period. 


#MAXIMUM TENSION- this will be the maximum tension that you want the cable to be 
subjected to after 
you have done any required and desired derating. The program will not derate 
further.


#MAXIMUM DESIGN TEMPERATURE- this will be the maximum temperature that the cable 
will 
operate under. It is a result of both ambient temperature and heating due to 
circuit load. 


#MINIMUM DESIGN TEMPERATURE- this will be the minimum ambient temperature 
expected-with no 
circuit load.


#NUMBER OF CIRCUIT CONDUCTORS- two or three usually. If you are running 
conductors at different 
heights, use SAG separately for each height.


##LOW and HIGH SAG TEMPERATURE- these are the upper and lower limits for the 
printed sag table 
results. They are the lowest and highest temperatures that the sagging crew 
might be working under.


#SAG TABLE INCREMENT- used in displaying sag table data. You can display the 
data at whatever 
integral temperature intervals you like.

DEFINITIONS:


SAG- to hang cable from overhead poles, and then pull it tight. How tight to 
pull it is the question. 
Another, more exact definition is the perpendicular distance from the middle of 
a straight line drawn 
between the two attachment points of  a sag span to the cable hanging between 
them.

#
 APPARENT SAG- The vertical distance from the middle of a straight line drawn 
between the two 
attachment points of a sag span to the cable hanging between them.

#
 SAG LENGTH- a continuous length of cable sagged between one or several poles at 
once. This length will 
usually be straight in the plan view, or nearly so.  It will be a catenary curve 
in the profile drawing. Since a 
poleline will usually consist of several spliced cables, there will be several 
sag lengths. Each sag length 
requires a control span and a corresponding sag table.


#
 SAG SPAN- the cable sagged between two poles. 

#
 CONTROL SPAN- a sag span in a sag length chosen to be used to measure the 
required apparent sag, as 
calculated and shown in the sag table for the ambient temperature at the time of 
the sagging activity. The 
control span should be chosen as one of the most level spans in the sag length.

#
 DEAD END- where a cable for a given sag length is tied off.

#
 SAG TABLE- a data table, usually shown on the profile drawing, that gives the 
sag and apparent sag of 
the control span of a sag length for a given ambient temperature. There should 
be a sag table and a control 
span for each sag span. 

#
#
 POLE LOAD- there is a vertical and horizontal force that will be exerted on a 
given pole due to the cables 
attached.  The pole should be sized to handle the vertical load. Unbalanced 
horizontal loads due to dead-
ended cables will have to be balance by other dead-ended cables and/or by guy 
wires.

#
 WORST CASE SAG- will be when the cable has been stretched to its greatest 
length, and is at its highest 
design temperature. The stretching will be due to both maximum loading and 
creepage. 


#
MAXIMUM TENSION- would occur before the cable has been stretched due to loading 
or creepage if the 
ambient temperature drops to the minimum while the circuit has no load.

#
WINDAGE LOAD- The additional load in pounds per foot of cable due to wind 
pressure. Look it up in 
available tables for wire size. One table source is a publication available from 
the US Government Printing 
Office, Wash DC 20402, entitled "TRANSMISSION LINE DESIGN MANUAL" by H. Farr,  
stock no. 
024-003-00135-0.


#
ICE LOAD- The additional load in pounds per foot of cable due to ice on lines. 
(Ice storm conditions, not 
relevant to all areas). Look up in available tables for wire size. See WINDAGE 
LOAD.


Use SAG once for each sagging length. When using SAG, after inputting parameters 
you will be asked to 
select the cable attachment points. Select them in order from left to right on 
the profile drawing. Then you 
will be asked to select the control span for the sag length. SAG will then 
calculate the sag table data, and 
then the worst case sag. The worst case sag curve will be drawn on the drawing. 
The control span worst 
case sag curve will be drawn in a different color. The worst case sag curve can 
be used to check vertical 
clearances on your profile drawing. This curve will be drawn using the give X 
and Y scales, so you cannot 
measure sag and apparent sag graphically from it (unless both scales are equal).

After you have used SAG you should move the sag data out of the way to a sag 
table on your drawing. 
Now you can use the POLELOAD command. POLELOAD will print the vertical loading 
for each pole, 
and the horizontal loading for dead-ends. POLELINE assumes that horizontal loads 
will be balanced at any 
pole that is not deadended. The designer will need to balance any unbalanced 
horizontal loads. These loads 
are typically due to a single dead-end cable, or a plan-view turn or bend.

The SAGTABLE command will print the sag data for any span in a given sag length, 
whether a control 
span or not.

The SPANDATA command can be used to verify the cable parameters that were used 
to calculate and draw 
a given sag length. These parameters are stored with the cable curve entities 
within the drawing.



FREQUENTLY ASKED QUESTIONS

How does POLELINE do its calculations?

	The program is based on the use of two formulas describing catenary 
curves. A catenary is the 
curve that any cable will describe when suspended from two points. These 
formulas give the rise from the 
lowest point to the end-point in terms of a given tension, and the length in 
terms of the low point and end-
point, and a given tension. They take into account the weight of the cable per 
unit length.
	The first thing calculated is the poleloading, which will be maximum if 
the cable is dropped to its 
lowest design temperature immediately after sagging, and before it has stretched 
from creepage. So the 
maximum allowable tension is applied at this lowest temperature to get the 
poleloading. First the low point 
is found by starting in the middle of the span, then taking  incremental steps 
along the x-axis in the 
direction of the low point, and testing to see when the difference between the 
two calculated end-point 
heights is the same as the difference between the original end-point heights. 
When it matches, the low point 
for that tension has been found. The length of this cable is calculated, and 
since it will be the shortest length 
possible, it will be used as a base for later calculations.
	The next thing is to find the worst-case curve for clearances, and draw it 
in. This will be when the 
cable has been stretched as far as it will ever be which will be at when it has 
undergone its 10-year 
creepage and its maximum mechanical loading and is being operated at the maximum 
design temperature. .
	The final job is to calculate the sag table. To start, the cable is 
brought back to its shortest length at 
minimum temperature and without creepage. It is then expanded for each 
temperature in the sag table to a 
new length. Now the job is to find a tension that will result in the cable 
having this length at sagging. To 
get this length the cable is let out (the tension decreased) incrementally 
from its maximum allowable 
tension.  At each test tension the low point is found, then the length. This 
process continues until the 
calculated length is longer than the desired length, or until the calculated 
length is within a desired range of 
the expanded length. If it is not in range, the cable is tightened up a couple 
of steps, then the step size is 
decreased. The cable is then let out again with the reduced step size.

How can I take into account windage and ice loading?

	These loading factors can be taken into account by adding in appropriate 
amounts to the weight 
per foot parameter. These amounts are available from several references, 
including the one listed under 
WINDAGE LOAD (above). It should be understood, though, that the worst-case curve 
drawn from the 
increased weight per foot parameter due to icing will not occur in the real 
world. The worst-case curve 
results mainly from expansion due to temperature. This highest temperature is 
usually not going to be 
compatible with ice, unless you are at the south pole. Also, though windage will 
increase the loading of the 
pole, it will not result in an increased length of the cable, and so will not 
change the worst-case curve.
	The upshot of all this is that the calculation will have to be run twice 
to factor in windage or 
windage/icing. Use the worst-case curve from the calculation without 
windage/icing. Use the poleloading 
data from the windage/icing calculation.

How long does the calculation take?

	This varies a great deal. The length of time required will increase with 
the steepness of the angle 
from one pole to the next, with the number of poles, with the tension applied, 
and with the number of sag 
table temperatures requested.
	The time required can vary from a few seconds to many minutes.

Can I abort a calculation?
	
	Yes, press the ESC key.

What does the information printed to the command line during the calculation 
mean?

	It tells what the current difference is between calculated endpoint height 
differential and actual 
pole-height differential at the current x-axis position. It also gives the total 
x-axis span and the current x-
axis step size.
	The information printed is not tremendously useful or meaningful. Its main 
purpose is to verify 
that the program is operating.

Will the program work if the sagged span  is so steep that the catenary low 
point is not on the span?

	Yes.

Sometimes the curve is not drawn, but the sag table is printed. What happened?

	I dont know, but I have always been able to correct it by either erasing 
the poles and redrawing 
them, or drawing a new pole over the top of the existing before running the 
calculation.

What if all of the cables are not attached to the pole at the same height?

	You will need to run a separate calculation for each height, and add up 
the pole loadings for each 
pole.

Does the calculation of pole loading take into account changes of direction in 
the poleline?

	No.  A sagging calculation is for a single cable run. You should string 
new cables anytime you 
have a major direction change, and make another calculation for the new cable.  
For minor direction 
changes you can roughly calculate the required guying tension and make sure your 
installed guying exceeds 
this requirement.

How is the sagging table data used?

            	The sagging crew foreman checks that table entry corresponding 
to the ambient temperature at the 
time of the cable sagging and gets the apparent sag. If the ambient temperature 
falls between two table 
entries he can interpolate between the two entries to get his apparent sag. A 
crewman climbs each of the 
two poles at the end of the control span after the cable is strung but not 
tightened. One crewman mounts a 
spotting scope on his pole at the apparent sag distance below the cable support 
height on his pole. The other 
crewman mounts a spotting target on his pole at the apparent sag distance below 
the cable support height 
on his pole. The cable is then pulled up until the bottom of it is inline 
between the spotting scope on one 
pole and the spotting target on the other pole. When this condition is met the 
cable will have been sagged to 
give the calculated clearances and tensions.

Will Poleload work if the poles are not set vertically?

No. You will need to do your own calculation for poles not set vertically.

Do the loading values from Poleload take into account one or all of the cables?

It takes into account the number of cables that were input in the data dialog 
box, and assumes they are all at 
the same height.

