Lineman Forum: Transmission Poles - Lineman Forum

Could someone please assist me in my quest for knowledge?

Since all the recent events concerning the NE power outage, I have devoted a bit more time staring at Transmission Poles as I drive down the road. Typically, I tend to focus mostly on distribution poles and want to learn a little more in the arena of Transmission.

I have noticed that there's about 8-10 different types of transmission poles (not including steel cylinder poles).

Is there a reason or logic in the use of these poles that someone would care to explain? In distribution, we utilize classes of size and types of wood (ie. classes 1-5 using Douglas Fir and Ponderosa Pine woods) this is usually based on load and quantity of utilities on the pole.

Any knowledge is helpful

~L~

I looked for the transmission pole types but had no luck. Hope this helps in some way..................I found this transmission dictionary on the web, maybe it'll hekp in some way
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Access Charge
A charge for an energy service provider, or its customer, for access to a utility's transmission or distribution system. It is a charge for the right to send electricity over another entity’s transmission or distribution wires.

Aeolian Vibration
A high frequency, low amplitude, vertical resonant motion usually caused by steady, laminar cross winds at speeds between two and 15 mph. With this type of vibration, the tendency to vibrate increases as conductor tension increases, often resulting in an inability to take full advantage of a conductor’s tensile strength. Dampers installed on conductors can control this vibration.

Ahead Span
The span measured between a given structure and the structure beyond it, based on the beginning station as a reference.

Alternating Current
Electric current that flows in both directions.

Ampacity
The current carrying capacity of a conductor (expressed in amperes) under stated thermal conditions. Different materials have a different limit of ampacity depending upon the operating temperature. Those limits are set by the National Electrical Code (NEC).

Anchor
Piece of equipment that is installed into the ground to transfer the unbalanced force on a pole or structure to the earth without intermediate supports.

Anneal
Overheating of a conductor, causing it to expand, sag, weaken, and sometimes break. Usually caused by a combination of too much current passed through the conductor and high temperatures in the air surrounding the conductor.

Arrestor
Protective devices for limiting surge voltages on equipment by discharging or bypassing surge current. They serve as completely automatic surge diverters which function to discharge line overvoltages resulting from lightning strokes, switching surges, or other system disturbances.

Azimuth
Angular direction of the line as measured from north, normally in a clockwise direction.

Back Span
The span measured between a given structure and the structure behind it, or toward the station source.

Bayonet
An extension attached to the top of a pole, extending upward to connect another cable. Used in joint use applications for attaching fiber optic line and cable TV to the pole.

Bearing (Soil)
A measure of a particular type of soil’s strength capability measured in pounds per square foot.

Bearing (Survey)
Angular direction measured from north to south with respect to the east or west, normally not greater than 90 degrees.

Bisector
An imaginary line that bisects the line angle at a structure. On a tangent structure, the bisector is perpendicular to the line.

Brace
A piece of equipment used solely for additional support to another piece of equipment, such as a crossarm or transformer.

Buckling
: The inelastic bending of a pole caused by excessive vertical force, which may or may not cause pole failure. The taller an unguyed pole is the less vertical force may be applied to it without causing buckling.

Cable
Underground conductors used in cases when overhead construction becomes impracticable.

Cantilever Load
A load applied to an object that is supported only at one end. The wind load on a conductor places a cantilever load on a pin insulator.

Capacitor
A system of conductors and di-electrics so arranged that a large electrical charge is stored in a small volume. A capacitor is also used as a method of correction, when an inductive load is put into a system, such as a motor; the voltage and current are separated in phase causing a large energy loss. Once that happens a capacitor is added to the system to get the current and voltage back in phase. There are two types: electrostatic and electrolytic.

Catenary
The shape of a completely flexible cable, with constant weight per unit length, suspended between two supports. This is the approximated curve of line conductor, and can be simplified as the horizontal tension of the conductor divided by its weight per unit length. Although a catenary may be more accurate for longer spans, a parabola is more commonly used in most sag and tension calculations. (See Parabola)

Center Elevation
The relative ground elevation in feet at a particular point on the centerline of a line route.

Clearance
Clear space between the surface of the conductor and any other surface. Different conductors (depending on voltage) need different clearances as determined by NESC codes.

Clevis
A U-shaped attaching piece used to attach equipment to a pole, such as a neutral spool.

Compression Load
A force that increased the pressure on an object. The compression load on a pin insulator is the vertical load that results from a conductor strung between poles.

Conductor
A material, usually in the form of a wire, cable, or bus bar, suitable for carrying an electric current.
AAC: All Aluminum Conductor
AAAC: All Aluminum Alloy Conductor
ACSR: Aluminum Conductor Steel Reinforced
ACAR: Aluminum Conductor Aluminum Alloy Reinforced

Conduit
A type of insulation that protects a conductor during an underground installation. Usually PVC piping is used.

Creep
Non-elastic elongation of an aluminum conductor under tension, which has its length suspended between two points. Most creep will occur during the first two months after stringing, and all creep will have occurred within 10 years. Other materials have not been found to creep.

Crossarm
A support member attached to a pole horizontally for the purpose of supporting equipment or conductors. Crossarms have typical dimensions (5’ to 10’ in length) and standard sizes (3.75” x 4.75” to 5.75” x 5.75”). In many cases more than one crossarm is used on a pole. Crossarms used to support cutouts are referred to as cutout arms. One ended crossarms are referred to as alley arms. (See Framing)

Current
Electrons in the outermost shell of an atom are not closely bonded to the nucleus of that atom. Therefore they will detach and move in random directions, but when an electric pressure is applied to those electrons they give up that random motion and begin to flow in common direction. When the electrons are flowing in that common direction it is known as current.

Cutout
A cutout provides protection to the lines of the system and the various apparatus on those lines such as transformers and capacitor banks.

Deregulation
The elimination of regulation from a previously regulated industry or sector of an industry.

Direct Current
Current that only flows in one direction.

Distribution
The part of a power system that carries the lower, safer voltages, usually around 13-7 kV. This system runs from the substation to customers’ homes. When the voltage is needed to provide service to a residence another transformer is needed to convert the voltage into 120/240V so appliances in the home can function properly. (See Transmission)

Embedment
The depth a pole is buried. The general rule is that a pole is buried 10 percent of the pole length, plus two feet. Additional depth or special foundations are required for poles mounted on slopes, those with special strength requirements, those set in disturbed or poorly draining soils, or other similar circumstances.

Emissivity
The ability to absorb or emit heat, amount of heat transfer.

Fault
Happens when the system is open for a moment permitting the arc to become extinguished. The current ceases to flow and everything down the wire loses power.

Final Condition
This refers to the state of conductor in service for generally more than 10 years, or one that has experienced maximum zone loading at its maximum working tension. It is assumed that the conductor has been fully stressed and has crept to its full extent. This is typically where maximum sag of the conductor is found for a given loading combination.

Flicker
Percent of voltage change that occurs from a steady state voltage from an input of a high load. An equation is used to find the percent flicker.

Framing
Selection of the correct crossarm/support, brackets and insulator configuration. It is usually determined by the intended user, wire size, span length, and line angle on the insulator.

Galloping
A low frequency, high amplitude oscillation of the conductor which usually occurs when ice-covered conductors are exposed to cross winds between 10 and 45 mph. This type of movement is not as sensitive to conductor tension.

Grades of Construction
Different levels of construction that will help alleviate the probability that the conductor will fall to the ground.

Grounding
An effective grounding system is necessary (a) to avoid having dangerous potentials on non-current carrying equipment during electrical faults ( to ensure fast operation of electrical protective equipment under fault conditions and © to dissipate electrical charges caused by atmospheric conditions.

Guy
A brace or cable fastened to the pole to strengthen it and keep it in position. Guys are used wherever the wires tend to pull the pole out of its normal position.

Horizontal Span (Average Span)
Two adjacent spans are measured and then that distance is divided by two

HS Angle Group (Horizontal Span Angle Group)
A combination of a horizontal span and angle (bearing) in which the load trees are generated for the structure.

Hz
Hertz, a measure of frequency, one cycle per second.

Impedance
Can be referred to as resistance. It is the inability of the current to flow through a conductor.

Insulator
Device for attaching conductors to poles or structures while maintaining electrical isolation between the conductor and the pole, or between conductors. Higher voltage lines require longer insulators to prevent arcing between the conductor and the pole or other conductors. Insulators must be strong enough to withstand the loads presented by the conductors under extreme environmental conditions.

IP (Internet Protocol)
The Internet Protocol connects is the global system of interconnecting computers to each other. Most often this is simply called simply "the Internet."

kcmil (or KCM ) (1000 circular mils)
The area of aluminum equivalent to a circle 0.001 in diameter. KCM is also known as MCM, where the M represents the Roman numeral for 1,000.

Limiting Span
Also referred to as the “target span” or “controlling span,” the limiting span is the maximum allowable distance from pole to pole for a specific framing. This span is usually determined by the geometric properties of the framing such as galloping or conductor separation. This span may also be determined by the strength properties of the framing such as the strength of the insulators or crossarm.

Line Angle
The angle of deviation between the line back and the line ahead.

Load Case
Environmental conditions under which the forces are being measured. High wind, heavy ice, and cold are examples of different load cases. Also called “design loads.”

Load Point
The location at which a force is applied to a structure. This force can be in the form of a concentrated load that the user defines but is usually a load from a service or transformer that is attached to the pole.

Load Tree
A grid that displays all of the calculation results of the various environmental loads placed on the conductor, framing, and pole.

Load Type
The method of loading that is applied to a project. There are two typical methods of loading designated by the NESC, Type A and Type B. Different safety factors are used for Type A and Type B calculation; they are taken either from Table 253-1 or 253-2 of the 1997 NESC.

Loading
The different forces acting upon the structure, such as the pole and the conductors themselves.

Loading Zones or Districts
The NESC has divided the country up into light, medium, and heavy districts. The type of weather an area experiences determines its district. More snow, ice, and wind will give the district heavier loading requirements; in turn, less severe weather gives an area a lighter loading requirement.

Longitudinal
In line with the pole line.

Longitudinal Load
Loads applied in line with the pole line.

Maximum Working Tension (MWT)
The maximum tensions a conductor experiences during its service life. It is typically the highest working tension at a specific loading condition under the NESC or other standard.

Messenger
An additional support cable that conductors are wrapped around to give them more support.

MHz (Megahertz)
Megahertz, a measure of frequency, one million cycles per second.

Moment
A force acting on a structure and causing deflection at any particular point.

NESC (National Electrical Safety Code)
Sets standards for the entire country to insure life safety and fire safety.

Node
A point or region of a vibrating or oscillating system where the amplitude of the vibration or oscillation is minimal. Also, a place where a group of wires comes together and joins to make a junction.

OCF (Overload Capacity Factor)
A safety or fudge factor used in structural analysis. The actual load on a conductor is multiplied by its OCF as a safety measure.

Offset Clip
When stringing a line on a steep slope, the offset clip is a correction for the tendency of the conductor to slide downhill due to gravity. The goal is to get the insulators to hang plumb, and the offset clip is the correction made when the sliding conductor pulls the insulators out of plumb.

Parabola
A flexible conductor, with constant weight per unit of horizontal length — rather that the conductor length itself — suspended between two points is most commonly approximated as a parabola for sag and tension calculations. For longer spans, a catenary may be more accurate and give a greater sag value. (See Catenary)

Pedestal
A junction box where a secondary conductor can be transferred into a service conductor.

Per Unit
A uniform system of units that can be used in any method of calculations.

Phase
A hot lead coming out at an angle from a common generating point. Two main variations:
Three-phase: Three separate outputs from a common generating point making the angle between them 120 degrees.
Single-phase: One output coming from the generating point.

Pin
A cylindrical piece of metal or wood used for supporting or fastening equipment to something else, such as a clevis to a pole.

Pole
A structure used to hold up conductors and equipment in a power system.
Tangent pole: A pole that is a straight line with the one before and the one after it.
Angle pole: A pole at the junction where the line goes off at an angle.
Dead-end pole: The point where a power line comes to an end. The line only goes in one direction from that point.

Pole classes
ANSI classification categorizes poles by their ability to withstand a horizontal load located two feet from the pole top, without regard to species of pole (wood) or length of pole. This also takes into account the circumference of the pole at the top and compares it to the circumference six feet from the bottom of the pole.

Primary Conductor
The main conductor that carries the highest voltage. Can be in two forms.
Loop feed: The primary line continues on until it comes back to a source where it usually left at a normally open position.
Radial feed: The primary power line will run out to a load and end at a termination point.

Reclosers
Works as an automatic circuit breaker. Reclosers have the ability to distinguish between temporary and permanent faults by following curves set by the manufacturer. Once that fault is crossed a recloser will open and try to fix itself about three times so that manual labor isn’t needed.
Hydraulic: Used in single-phase. At lower ratings, they use a spring to close; at larger ratings they use a coil.
Electronic: Used on many three-phase units and preferred over hydraulic reclosers in areas with changing conditions because they can be adjusted with a short down period.

Resistance
The forces prohibiting the flow of current through a system. This is determined by the conductor’s length and the diameter of that same conductor. Resistance is measured in Ohms.

Restructuring
The reconfiguration of the traditional vertically integrated utility, separating the various functions of generation, transmission and distribution into individually operated and owned entities.

Riser
The conduit and conductor involved in the transition from overhead distribution to underground distribution. Usually runs down the pole and into an underground pedestal.

Rotation Angle
The orientation angle used for attaching a load point to a pole. This angle is referenced from the span back of the power line, is negative for counterclockwise angles, and is positive for clockwise angles.

RTS (Rated Tensile Strength)
The maximum stress which a material will sustain when slowly loaded to rupture. Each material is given this value to determine the maximum loads that can be applied to that material.

Ruling Span
A calculated equivalent span designated to represent the behavioral characteristics of a collective series of spans of random lengths, supported on suspension towers and terminated between two strain-type or deadend structures. Sag and tension calculations performed on the ruling span can be used on each span in the specified line.

Sag
The amount that a conductor will drop below the horizontal line that connects the poles where the conductors attach to the poles.

Scenario
Conductor condition under which the forces are being calculated. Examples are: intact, broken-ahead, broken-back, etc.

Tensile Load
The force that stretches an object when applied. A deadend suspension insulator has a tension load applied to it that is equal to the tension in the conductor.

Tension
A force used to measure how tight something is. Used in the utility industry to determine how tightlt to string the conductor between spans.

Transmission
A system of power lines carrying current at an extremely high voltage, such as 700kV, from substation to substation. These lines can be transported a great distance without a lot of voltage drop to a substation where they can be broken down into lower voltages. (See Distribution)

Transverse
In the direction of the bisector.

Transverse Loading
Forces applied to the structure perpendicular to the line, or along the bisector of an angle, typically due to wind loads on the poles and conductors. Also refers to tension in the conductors due to their change in direction for angled cases.

Ultimate Load
The maximum allowable factored load that may be applied to an object without failure occurring.

Uplift
An upward vertical force, usually occurring on a structure between two structures that are at higher elevation points in the line.

Voltage
The electric pressure of a circuit in an electric system measured in volts. It is generally a nominal rating based on the maximum normal effective difference of potential between any two conductors of the circuit.

Wholesale Power Market
The purchase and sale of electricity from generators to resellers (who sell to retail customers) along with the services needed to maintain reliability and power quality at the transmission level.

Wholesale Transaction
The sale of electricity from an electricity generator to a utility or other electric distribution system through the transmission lines.

Wire Group
A conductor designation to indicate conductor type (for example, DISTA is distribution circuit 1, DISTB is distribution circuit 2, TRANSA is transmission circuit 1, and NEUTA is neutral 1).

XYZ-Coordinate System for Map
The means of identifying the location of survey points with respect to some established reference point. X and Y are axes used to measure horizontal points. Z is the vertical axis used to measure elevation.