VIII. CONDUCTOR AND LINE ANALYSIS

VIII-1 Conductor Thermal Rating

The integrity of conductors can be affected by temperature. It is commonly accepted that

aluminum begins to anneal at a conductor temperature of about 100°C. Annealing results

in loss of aluminum strength. For all aluminum conductors (AAC), this can be an

important consideration. Conductors that get much of their strength from steel

(aluminum conductor steel reinforced - ACSR) will tolerate more annealing. Annealing

is a cumulative affect and is a function of both aluminum temperature and time.

Conductors can withstand high fault currents for short times (tenth of seconds) that are

many times greater than the load current for which they are designed. A Figure in the

Aluminum Electrical Conductors Handbook indicates that an aluminum conductor may

lose 5% of its strength after 500 hours at 100°C or 2 hours at 150°C. Aluminum melts at

about 650°C. This temperature must be avoided.

Another consideration affected by conductor temperature is clearance. As conductor

temperature goes up, the conductor expands and the line sag increases. The exact

transmission line design and right-of-way maintenance dictate how much sag can be

tolerated. This must be evaluated on a line by line and span by span basis.

Historically, three current rating have been used for transmission line conductors.

SMECO’s definition of Emergency Rating is based on allowing the conductor to operate

at 75°C. This is conductor Rating 2 in the Transmission 2000 (T2000) database.

Conductor Rating 1 is the Normal Rating for this TLRP analysis. Normal Rating is a

current that is 75% of the Emergency Rating (Rating 2) current. SMECO’s system is

designed so that with the system in its normal configuration, conductor currents do not

exceed this Normal Rating. Conductor Rating 3 is defined as 115% of the Emergency

Rating 2 current for this TLRP analysis.

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 1

Electrical Heating

There are two main effects that add heat and two that remove heat from current carrying

conductors. The largest source of heating for conductors is I2R where I is the line current

and R is the resistance per unit length of the conductor. More current causes more

heating and higher temperatures cause increased resistance. Both effects must be

considered in current rating calculations.

The other effect that contributes to higher conductor temperatures is solar heating. Solar

heating is a function of transmission line orientation, time of year, time of day, latitude of

the service area, and clarity of the atmosphere. A conductor property that affects solar

heating is its absorptivity coefficient. This coefficient is a measure of the portion of

available solar energy that is absorbed by the conductor and is a function of conductor

age. Test data has indicated that a new aluminum conductor may have an absorption

coefficient of about 0.59 and that a conductor aged in service more than eight years in the

Washington D. C. area will have and absorption coefficient of about 0.92.

The two mechanisms that remove heat from line conductors are convection and radiation.

Convection has the most cooling power and is made up of the natural motion of air due to

temperature gradients and wind that is a function of meteorological effects. Wind speed

and its angle to the conductors is the most powerful line cooling affect.

Radiative cooling depends upon the temperature gradient between the conductor and the

surrounding atmosphere. It is a function of the conductor’s coefficient of emissivity.

Emissivity is a measure of the conductor’s ability to radiate energy. It is a function of the

conductor’s surface condition and gets higher as the conductor ages. Higher emissivity

coefficients indicate that more heat is radiated from the conductor. Test data has

indicated that a new aluminum conductor may have an emissivity coefficient of about 0.3

and that a conductor aged in service more than twenty years in the Washington D C. area

will have and absorption coefficient of about 0.82. Figure VIII-1 shows the results of

emissivity and absorptivity tests on conductor samples aged in the Washington D. C.

area.

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 2

Figure VIII-1: Absorptivity and Emissivity ACSR Conductors

The calculation of conductor current rating solves the energy balance relationship

equating heat energy going into the conductor to heat energy going out of the conductor

according to the principles indicated above. Computer programs are available from

manufacturers and as part of IEEE standards to compute conductor ratings.

POWER used the Southwire Company SWrate software program to calculate the thermal

ratings for the overhead transmission line conductors. The SWrate program is based on

IEEE Standard 738-1993, IEEE Standard for Calculating the Current-Temperature

Relationship of Bare Overhead Conductors.

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 3

The SWrate program input data includes the following:

- Air temperature (degrees C)

- Wind speed (feet/second)

- Wind angle relative to conductor (degrees)

- Elevation above sea level (feet)

- Latitude (degrees N)

- Solar time (hours)

- Conductor name

- Diameter (inches)

- Coefficient of emissivity

- Coefficient of solar absorptivity

- Conductor resistance (ohms/mile)

- Conductor temperature (degrees C)

- Date (month/day)

- Conductor orientation (north-south or east-west)

- Atmosphere (clear or industrial)

Input data that controls the conditions for the rating calculations is always a subject for

discussion. It must be decided upon by the operations, planning and system design

personnel. Considering SMECO’s 75°C conductor temperature Emergency Rating,

operating practice, summer conditions, geographical location and POWER’s experience,

the following data was used as input to the conductor rating program:

Emergency Conductor Temperature: 75°CAir temperature: 35°CWind Speed: 2.0 feet/secondWind Angle: 45°Elevation: 150 feetLatitude: 38.5°Emissivity coefficient: 0.7Absorptivity coefficient: 0.8Date: 07/01Solar Time: 12:00 PMNorth-South LinesClear Atmosphere

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 4

The above input data results in the following conductor currents and temperatures for

common aluminum conductors.

Table VIII-1: Current Ratings and Conductor Temperatures(Based on 75°C Conductor Temperature Criterion)

Cond.MCM

Cond.Type

Cond.Name

AmpacityRating 175% of

the 75°C Rating 2

Amps

ConductorTemp. with

Rating 1 Ampacity

°C

AmpacityRating 2

100% with 75°C Conductor

Temp.Amps

AmpacityRating 3115% of the 75°C Rating 2

Amps

Conductor Temp.With

Rating 3 Ampacity

°C2312 ACSR Thrasher 921 A 65.4 1228 A 1412 A 82.3

1750 AAC Jessamine 782 A 64.9 1043 A 1199 A 82.6

1590 ACSR Falcon 768 A 65.0 1024 A 1178 A 82.7

1590 AAC Coreopsis 744 A 64.8 992 A 1140 A 82.7

556.5 ACSR Dove 415 A 63.6 554 A 637 A 83.6

336.4 ACSR Linnet 306 A 62.9 408 A 469 A 84.1

2/0 ACSR Quail 163 A 61.6 218 A 251 A 86.2

The conductor ratings in Table VIII-1 are more conservative than necessary and they are

below the ampacity values that SMECO presently uses.

POWER suggests that SMECO can increase their Emergency Rating (Rating 2)

conductor temperature from 75°C to 85°C to take more advantage of the conductor’s

thermal capability. Also, the 115% of Emergency Rating 2 current may be increased to

allow the conductor temperatures to approach 100°C.

The following input data is recommended for the calculation of SMECO’s aluminum

conductor ampacity ratings:

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 5

Recommended Summer Conductor Rating DataEmergency Conductor Temperature: 85°CAir temperature: 35°CWind Speed: 2.0 feet/secondWind Angle: 45°Elevation: 150 feet.Latitude: 38.5°Emissivity coefficient: 0.7Absorptivity coefficient: 0.8Date: 07/01Solar Time: 12:00 PMNorth-South LinesClear Atmosphere

The above input data results in the following conductor current and temperature ratings for common aluminum conductors.

Table VIII-2: Summer (35°C Air) Current Ratings and Conductor Temperatures(Based on 85°C Conductor Temperature Criterion)

Cond.MCM

Cond.Type

Cond.Name

Ampacity Rating 175% of

the 85°C Rating 2

Amps

Conductor Temp. with

Rating 1 Ampacity

°C

Ampacity Rating 2

100%with 85°C Conductor

Temp.Amps

Ampacity Rating 3115% of the 85°CRating 2

Amps

Conductor Temp.With

Rating 3 Ampacity

°C2312 ACSR Thrasher 1105 A 70.8 1473 A 1694 A 95.8

1750 AAC Jessamine 932 A 70.3 1243 A 1429 A 96.2

1590 ACSR Falcon 915 A 70.3 1220 A 1403 A 96.2

1590 AAC Coreopsis 884 A 70.2 1179 A 1356 A 96.4

556.5 ACSR Dove 487 A 69.0 649 A 746 A 97.4

336.4 ACSR Linnet 355 A 68.3 474 A 545 A 97.9

2/0 ACSR Quail 185 A 66.2 247 A 284 A 100.3

The current values in Table VIII-2 are very close to the ratings that SMECO has

historically used for conductor ratings. It is believed that the results indicated in this

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 6

table are good for SMECO’s service area. They are based on reasonable assumptions

consistent with SMECO’s service area and consistent with SMECO’s past practice.

Winter conductor ratings may take advantage of lower air temperatures and should

employ a different month for solar heating considerations. POWER recommends that

SMECO use these effects and assume 20°C as a conservative winter air temperature and

February as a representative winter month for ampacity rating calculations. Combining

these recommendations with the previous recommendations yields the following set of

input data and winter ratings.

Recommended Winter Conductor Rating DataEmergency Conductor Temperature: 20°CAir temperature: 35°CWind Speed: 2.0 feet/secondWind Angle: 45°Elevation: 150 feetLatitude: 38.5°Emissivity coefficient: 0.7Absorptivity coefficient: 0.8Date: 02/01Solar Time: 12:00 PMNorth-South LinesClear Atmosphere

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 7

Table VIII-3: Winter (20°C Air) Current Ratings and Conductor Temperatures (Based on 85°C Conductor Temperature Criterion)

Cond.MCM

Cond.Type

Cond.Name

Ampacity Rating 175% of

the 85°C Rating 2

Amps

Conductor Temp. with

Rating 1 Ampacity

°C

Ampacity Rating 2

100% with 85°C Conductor

Temp.Amps

Ampacity Rating 3108% of the 85°C Rating 2

Amps

Conductor Temp. with

Rating 3 Ampacity

°C2312 ACSR Thrasher 1437 A 59.4 1916 2069 A 95.2

1750 AAC Jessamine 1201 A 59.1 1602 1730 A 95.4

1590 ACSR Falcon 1180 A 59.1 1573 1699 A 95.3

1590 AAC Coreopsis 1137 A 59.0 1516 1637 A 95.4

556.5 ACSR Dove 612 A 58.1 816 881 A 95.8

336.4 ACSR Linnet 443 A 57.7 591 638 A 96.2

2/0 ACSR Quail 227 A 54.9 303 327 A 98.4

Note that Conductor Rating 3 now must use 108% of the 85°C Emergency Rating to keep

the temperature below 100°C in the winter for all the conductors listed rather than 115%

as was the case in the summer. This is because heat into the conductor is proportional the

square of current. The 85°C conductor temperature allows more current with the 20°C

winter air temperature than with the 35°C summer air temperature. If the winter 85°C

Emergency Rating current were raised the same 15% as in the summer, the absolute

current increase would be more. The current squared effect would add more heat to the

conductor. The temperature would rise more resulting in the temperature of some

conductors going above 100°C.

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VIII-2 High Temperature Low Sag (HTLS) Conductors

There are a number of new High Temperature Low Sag (HTLS) conductors on the

market designed to operate at temperatures of 200°C to 300°C. This is well above the

normally accepted maximum operating temperature of 100°C allowed for more standard

AAC and ACSR conductors. These new conductors still employ aluminum as the main

current conducting medium. They have a core material inside the aluminum that

provides high mechanical strength with a low coefficient of thermal expansion. This

internal core material is the main difference between conductors supplied by the various

manufacturers. The new conductors are capable of carrying two to four times as much

current as the more standard AAC and ACSR conductors of similar diameters and

weights while minimizing sag.

Limited experience indicates that the new conductors perform as advertised. They tend

to cost two to six times more than standard conductors to purchase and install. Some

require special handling and equipment for installation and maintenance. When applying

these new conductors, only manufacturer recommended splices and dead ends must be

installed using extreme care. These tend to be the weak links in line construction and any

flaws at these points will most likely lead to conductor failures.

Since the conductors operate at very high temperatures, they must not be connected

directly to oil and/or paper insulated bushings. Leads from HTLS dead end towers to

equipment bushings may be constructed with a bundle of standard AAC or ACSR

conductors designed to carry the total current from the HTLS line without heating above

their normal limits.

The new HTLS conductors are generally used for specific applications or to solve

existing problems. For example, if reconductoring an existing line is required for load

purposes, and installing a larger conductor will require extensive structural work to

increase strength and/or height, an HTLS conductor may be considered. A trade-off can

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 9

be evaluated between cost of the HTLS conductor and the cost of the structural

modifications.

Currently, HTLS conductors are only used for specialized high current applications.

These applications tend to occur at voltages of 230 kV or less. Above that level, lines

tend to be designed with bundled conductors having sufficient current carrying capability

to avoid overload problems. Long high voltage lines sometimes have series capacitors

added to compensate for the line inductive reactance voltage drop and phase shift to

allow more current to flow in the normal line conductors than would be possible without

compensation.

The new HTLS conductors will probably have limited application for new line

construction. For new construction, the line will be designed with load current, sag and

conductor strength requirements taken into proper account. New lines will be installed at

a significantly lower cost using standard, accepted, and proven design techniques than

using HTLS conductors having higher costs and requiring special construction

techniques.

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 10

VIII-3 Transmission Line Parameters

Electrical characteristics of transmission lines are defined by their inductance, resistance,

and capacitance. These parameters are a function of the conductor characteristics and the

physical location of the conductors in space relative to each other and to earth. The

parameters are specified in two matrices. One matrix contains self and mutual

inductances and resistances. The other matrix contains phase to phase and phase to

ground capacitances. For the purpose of power flow and short circuit calculations, the

parameters are generally simplified into positive, negative, and zero sequence

components. Mutual coupling between sequence components are ignored. This

technique has proven to be acceptable for most steady state system performance

calculations. The present TLRP is concerned with power flow in the transmission system

and requires only the positive sequence impedances and capacitances of the transmission

lines. Thermal capabilities of the conductors are also of concern. This topic is

considered the Conductor Thermal Ratings section of this report.

Conductor properties are listed in many reference books and manufacturer’s catalogs.

Table IV-4, Conductor Data from References, lists data obtained from the various sources

indicated in the last column. Conductor ampacity ratings are a function of the

assumptions made for the calculations as indicated by the differences in the tabulated

values. Tabulated resistances are at 25°C and 75°C during steady state 60 hertz operation

except as noted. Skin effect at 60 hertz is included in the values listed. The inductances,

Xa, tabulated are at 60 hertz for a one foot triangular conductor configuration on a fully

transposed line. Conductor diameter, conductor resistance, and Xa are input to the line

parameter program for computing the impedance and capacitance matrices.

The reference data is in near complete agreement on the diameters and X a values. The

resistance values are reasonably close to the same values. Conductor temperature is

selected at 75°C for this TLRP analysis. This produces the most resistive voltage drop

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 11

and the most conservative system design. When there is disagreement among the data

sources, data from the Aluminum Conductor Handbook is used for this TLRP analysis.

Calculated Properties

The IEEE Standard 738-1993, IEEE Standard for Calculating the Current-Temperature

Relationship of Bare Overhead Conductors, method is used for conductor thermal

calculations in this report. Both the results in the following Table VIII-5 and the results

in the Conductor Thermal Rating section of this report were obtained by this method.

Table VIII-5 shows conductor ratings using the assumptions shown in the table foot

notes. These are the assumptions that have been historically used by SMECO for

conductor thermal rating calculations. The currents listed in the 75°C conductor

temperature column are in good agreement with SMECO’s corresponding data. The

second table below also lists electrical parameters computed for lines with the conductors

considered for use in the transmission system.

Electrical parameters are computed for line upgrades and new lines considered for the

transmission system. Line parameters are computed using the Line Constants subroutine

in the Alternate Transients Program, ATP. This program was initially developed by the

Bonneville Power Administration (BPA). It is not public domain software, but is

available free to licensed users. Transmission line configuration is based on 66 kV Steel

Pole, TP66EF7-S as shown on SMECO Drawing A 1340. This is the construction used

for the 2005 Hughesville bypass project.

Figure VIII-2 is a sample output from the ATP Line Constants subroutine for the 1590

MCM AAC Coreopsis conductor recommended for use in SMECO’s new construction.

Zero is entered in the Skin Effect field for the phase conductors because the 60 hertz skin

effect is already included in the resistance and inductance input data. Skin effect for the

57OPT fiber static wire is computed based on an assumed conductor thickness to outside

diameter ratio (T/D) of 0.25. The value of 1 for the phase conductor X-type tells the

program to use the Xa values entered at a one foot spacing for the inductance calculations

rather than calculating the conductor internal inductance based on tubular conductor

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 12

geometry. X-type of 4 is used for the static wire so that its internal inductance will be

computed based on tubular geometry. The 99999 in the reactance data column for the

static wire is a flag to the user that this value is not used in the calculations.

Conductor height at the pole is controlled by the pole geometry. A sag of ten feet (10’) is

assumed between poles and the subroutine computed the average conductor heights as

indicated.

Output from the subroutine shows the complete capacitance and impedance matrices of

symmetrical components. The positive and zero sequence values computed for the line

are listed near the bottom of Figure VIII-2. The positive and zero sequence propagation

velocities provide a sanity check on the calculation. For overhead lines, the positive

sequence wave propagation velocity is always a little less that the speed of light (186,000

miles per second) and the zero sequence propagation velocity is on the order of twenty

per cent less (150,000 miles per second). The Figure shows that the positive sequence

impedance of the line is 0.0749 + j0.626 ohms per mile and the positive sequence shunt

susceptance is j6.93 µmho/mile (Xc = -j144,000 ohm miles). These are the values upon

which new 1590 MCM AAC Coreopsis lines are based in this TLRP.

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 13

Table VIII-4: Conductor Data from References

Cond.Size

MCMCond. Type Code

NameDiameter

Inches

25oCR

Ohm/mile

75oCR

Ohm/ mile

Xa

Ohm/ mile

AmpacityAmperes

Reference

2312 ACSR Thrasher 0.0454 0.0528 0.343 Al Electrical Conductor Handbook2312 ACSR Thrasher 1.802 0.0446 0.0518 0.342 EPRI Trans Line Reference Book2312 ACSR Thrasher 1.802 0.0396* 0.0528* 1673** Sural (www.sural.com)2312 ACSR/AW Thrasher 1.802 0.0391* 0.0524* 1680** Sural (www.sural.com)

1750 AAC Jessamine 1.525 0.0587 0.0684 0.366 EPRI Trans Line Reference Book1750 AAC Jessamine 1.525 0.0522 0.0681 1408** Sural (www.sural.com)

1590 ACSR Falcon 0.0611 0.0721 0.358 Al Electrical Conductor Handbook1590 ACSR Falcon 1.545 0.0602 0.0712 0.358 EPRI Trans Line Reference Book1590 ACSR Falcon 1.545 0.0570* 0.0739* 1359** Sural (www.sural.com)1590 ACSR/AW Falcon 1.545 0.0555* 0.0704* 1391** Sural (www.sural.com)1590 ACSR Falcon 1.545 0.0611 0.0739 0.359 1200*** SMECO Conductor Characteristics

1590 AAC Coreopsis 0.0634 0.0743 0.372 Al Electrical Conductor Handbook1590 AAC Coreopsis 1.454 0.0636 0.0745 0.372 EPRI Trans Line Reference Book1590 AAC Coreopsis 1.454 0.0576* 0.0744* 1333** Sural (www.sural.com)1590 AAC Coreopsis 1.454 0.0635 0.0743 0.372 1174*** SMECO Conductor Characteristics

795 ACSR Drake 0.1170 0.1390 0.399 Al Electrical Conductor Handbook795 ACSR Drake 1.108 0.1190 0.1306 0.399 EPRI Trans Line Reference Book795 ACSR Drake 1.108 0.1129* 0.1388 907** Sural (www.sural.com)795 ACSR/AW Drake 1.108 0.1127* 0.1393 896** Sural (www.sural.com)795 ACSR Drake 1.108 0.1166 0.1390 0.399 788*** SMECO Conductor Characteristics

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 14

Table VIII-4: Conductor Data from References (continued)

Cond.Size

MCMCond. Type Code

NameDiameter

inches

25oCR

Ohm/mile

75oCR

Ohm/ mile

Xa

Ohm/ mile

AmpacityAmperes

Reference

556.5 ACSR Dove 0.1660 0.1980 0.420 Al Electrical Conductor Handbook556.5 ACSR Dove 0.927 0.1694 0.2026 0.420 EPRI Trans Line Reference Book556.5 ACSR Dove 0.927 0.1616* 0.1980* 726** Sural (www.sural.com)556.5 ACSR/AW Dove 0.927 0.1562* 0.1915* 737** Sural (www.sural.com)556.5 ACSR Dove 0.927 0.1655 0.1978 0.420 625*** SMECO Conductor Characteristics

336.4 ACSR Linnet 0.273 0.327 0.451 Al Electrical Conductor Handbook336.4 ACSR Linnet 0.720 0.2666* 0.3494* 529** Sural (www.sural.com)336.4 ACSR/AW Linnet 0.720 0.2586* 0.3162* 537** Sural (www.sural.com)336.4 ACSR Linnet 0.720 0.2728 0.3264 0.451 450*** SMECO Conductor Characteristics

4/0 Cu 7-strand 0.522 0.278 0.3030+ 0.503 420++ Westinghouse T&D Reference Book4/0 Cu 7-strand 0.5217 0.2808 0.3326 0.504 405*** SMECO Conductor Characteristics

2/0 ACSR Quail 0.6870 0.9290 0.590 295 Al Electrical Conductor Handbook2/0 ACSR Quail 0.4470 0.6653* 0.9293* 276** Sural (www.sural.com)2/0 ACSR/AW Quail 0.4470 0.6478* 0.7888* 301** Sural (www.sural.com)2/0 ACSR Quail 0.4470 0.6810 0.9320 0.590 231*** SMECO Conductor Characteristics

1/0 Cu 7-strand 0.3680 0.555 0.607+ 0.546 265++ Westinghouse T&D Reference Book1/0 Cu 7-strand 0.3684 0.5615 0.6658 0.546 259*** SMECO Conductor Characteristics

* Sural Resistance given at DC @ 200C, AC @ 750C.** Sural Ampacity for 250C ambient, 750C conductor, 2 feet/second wind, 0.5 coefficients of emissivity and absorption.*** SMECO Ampacity for 400C ambient, 750C conductor, 2 feet/second wind, 0.5 coefficients of emissivity and absorption.+ Westinghouse T & D reference Book, 500C for copper conductor resistance++ Westinghouse T & D Reference Book, 750C for copper conductor and 400C ambient for ampacity (Fig. 25)

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 15

Table VIII-5: Calculated Conductor and Line Properties

Cond.MCM

Cond.Type

Cond.Name

75oCCond.Amp

90oCCond.Amp

100oCCond.Amp

66 kV Steel Pole ConstructionTP66EF7-S SMECO Drawing A 1340

R1 X1 R0 X0 B1 B0Ohms / mile 10-6 Mho / mile

2312 ACSR Thrasher 1492 1764 1920 0.0534 0.597 0.615 2.120 7.256 3.227

1750 AAC Jessamine 1242 1468 1597

1590 ACSR Falcon 1215 1433 1558 0.0727 0.612 0.635 2.135 7.023 3.180

1590 AAC Coreopsis 1174 1386 1507 0.0749 0.626 0.637 2.149 6.935 3.162

795 ACSR Drake 788 927 1007

795 ACSRDrake2 cond. Bundle

1418* 1669*1813* 0.0701

0.461 0.630 1.963 9.227 3.632

556.5 ACSR Dove 624 732 792 0.1986 0.674 0.760 2.197 6.347 3.034

336.4 ACSR Linnet 450 528 573

4/0 Cu 7-strand 420

2/0 ACSR Quail 232 268 288

1/0 Cu 7-strand 265Ambient Temperature: 40oC Latitude: 38.5o

Wind Speed: 2 feet/second Clear AtmosphereNorth-South conductor Coefficient of Absorption: 0.5Wind Angle: 45o Coefficient of Emission: 0.5No Solar Effect * Bundle rating is 10% less than the conductor rating sumAltitude: 150 feet

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 16

Figure VIII-2: ATP Line Constants Example - 1590 MCM AAC Coreopsis

Line conductor table after sorting and initial processing. Table Phase Skin effect Resistance Reactance data specification Diameter Horizontal Avg height Row Number R-type R (Ohm/mi) X-type X(ohm/mi) or GMR (inches) X (feet) Y (feet) 1 1 .00000 .07430 1 .372000 1.45400 3.750 50.833 2 2 .00000 .07430 1 .372000 1.45400 3.750 43.833 3 3 .00000 .07430 1 .372000 1.45400 -3.750 43.833 4 0 .25000 1.18100 4 99999.000000 .46500 0.667 59.167Matrices are for earth resistivity = 1.00000000E+02 ohm-meters and frequency 6.00000000E+01 Hz. Correction factor = 1.00000000E-06Capacitance matrix, in units of [farads/mile ] for symmetrical components of the equivalent phase conductorRows proceed in sequence (0, 1, 2), (0, 1, 2), etc.; columns proceed in the sequence (0, 2, 1), (0, 2, 1), etc

0 8.387048E-09 0.000000E+00 1 2.120474E-10 -2.450550E-10 -1.931703E-10 -8.312831E-10 2 2.120474E-10 1.839555E-08 -2.450550E-10 1.931703E-10 2.452663E-25 8.312831E-10 Impedance matrix, in units of [ohms/mile ] for symmetrical components of the equivalent phase conductorRows proceed in sequence (0, 1, 2), (0, 1, 2), etc.; columns proceed in the sequence (0, 2, 1), (0, 2, 1), etc.

0 6.367723E-01 2.149059E+00

1 5.858032E-05 -2.618439E-02 -2.428065E-02 9.281198E-03

2 2.563464E-02 7.485916E-02 2.729865E-02 -2.506301E-02 6.257380E-01 9.213317E-03

Sequence Surge impedance Attenuation velocity Wavelength Resistance Reactance Susceptance magnitude(ohm) angle(degr.) db/mile miles/s miles ohm/mile ohm/mile mho/mile Zero : 8.41959E+02 -8.25235E+00 3.31893E-03 1.43094E+05 2.38489E+03 6.36772E-01 2.14906E+00 3.16184E-06Positive: 3.01451E+02 -3.41103E+00 1.08039E-03 1.80651E+05 3.01085E+03 7.48592E-02 6.25738E-01 6.93496E-06

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 17

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 18

VIII-4 Transmission Line Age Analysis

The table below lists SMECO’s 69 kV and 230 kV transmission lines according to age.

Locations of the lines from 1972 and older are shown on the Aging Transmission map

below. The oldest lines in SMECO’s transmission system were constructed in the 1950s

and have small conductors (2/0 ACSR and 336.4 MCM ACSR). Most of these lines on

the map below are either in service or available if needed. If they are performing

satisfactorily and not requiring excessive maintenance, it is recommended that they not

be changed until necessitated by system performance requirements or begin to require

excessive maintenance. SMECO has a program of pole inspection whereby each pole is

checked every five years. This identifies problems that occur over time and flags

maintenance needs before serious system problems develop due to aging.

The Bryantown Switching Station to Holland Switching Station Line 6730 was built in

1950 and is not being used in the present normal system configuration. The section of

the line from the Bryantown Switching Station to the new Bryantown Substation will be

needed by year 2025 in Load Block C when the Bryantown Substation is constructed.

This section of the line should be upgraded to 1590 MCM AAC conductor when the

substation is constructed so that it will be available for future system expansion.

Line 6712 from Hawkins Gate Switching Station to Bryantown Switching Stationwas

built in 1950. It is only 2/0 ACSR conductor, has some sections missing and is not

presently needed. The right-of-way for this line should be maintained. If the Hawkins

Gate Switching Station and/or Hughesville Substation transmission voltage is ever

increased, this line along with Line 6730 could provide a valuable transmission path from

Hawkins Gate to Calvert County (Holland Cliffs).

The Hughesville Substation to Cedarville Substation Line 6720 was built in 1951 and is

only 336.4 MCM ACSR conductor. This line will need to be upgraded to 1590 MCM

AAC conductor by year 2025 to handle the Cedarville Substation and West Brandywine

Substation loads. This portion of the line is 9.41 miles long. It could be upgraded in

sections over time as maintenance on the original old line is required.

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 19

Line 6715 from the Mattawoman Tap to the Mattawoman Substation was built in 1969

and is 336.4 MCM ACSR conductor. This conductor will need to be upgraded to serve

the substation load by year 2025. It is recommended that the conductor be upgraded to

1590 MCM AAC because it is a weak link between sections of 1590 MCM AAC

conductor. If Burches Hill becomes a viable supply point, Line 6715 will be valuable to

transfer power south from Burches Hill to Forest Park Substation and/or Waldorf

Substation. It could also be part of another path from Hughesville (Chalk Point supply)

to the Waldorf area if the rest of Line 6720 from Cedarville Substation to Burches Hill

were upgraded to 1590 MCM AAC conductor.

The portion of Line 6717 from LaPlata Substation to Marshall’s Tap was built in 1971

with 556.5 MCM ACSR conductor. This section of Line 6717 and the next section of the

same line between Marshall’s Tap and the Ripley Switching Station (also 556.5 MCM

ACSR built in 1992) are located in a main transmission path from the Hawkins Gate

supply point between 1590 MCM ACC sections. These two sections of Line 6717 should

both be upgraded to 1590 MCM AAC at the earliest convenient time.

Line 6756 from Valley Lee Substation to Piney Point Substation is 4.39 miles long and

was built in 1971 with 336.4 MCM ACSR conductor. This conductor is sufficient to

supply Piney Point Substation (38.6 MVA @ 66 kV) in the foreseeable future. The Piney

Point Substation maximum load is expected to be 12.6 MVA by 2025. If it were decided

to loop Redgate Substation with Piney Point and Valley Lee Substations, it would be

desirable to upgrade Line 6756 to 556.5 MCM ACSR to match the other sections of the

loop. When the line has to be rebuilt due to aging, it should be replaced with 556.4

MCM ACSR conductor.

With the exception of the Navy Line 6756 built in 1972 and Line 6775 built in 2004,

SMECO has not constructed any transmission lines with 336.4 MCM ACSR conductor

since 1971. Most of SMECO’s recent transmission construction has employed 1590

MCM AAC Coreopsis conductors. A few lines that serve only one or two substations

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 20

(radial) with total loads that were not expected to exceed about 50 MVA in locations

where loop feeds were not expected, have been built with 556.5 MCM ACSR conductors.

Table VIII-6: SMECO Transmission Lines Listed According to Age

SMECO

Line # Source Bus Load Bus

Length

Miles

Approximate

“As-Built"

Date

Conductor

Size

6775 PAX RIVER 2 PAX RIVER 1 1.3 1949 (Navy) 4/0 CU

6730 BRYANTOWN HOLLAND 9.3

1950 (Rvr

Xing 1986) 2/0 ACSR

6712 HAWK 69 BRYANTOWN 4.6 1950 2/0 ACSR

6720 CEDARVILLE W BRANDY TAP 5.48 1951 336.4 ACSR

6720 HUGHESVILLE CEDARVILLE 9.41 1951 336.4 ACSR

6720 W BRANDY TAP BURCHES 2.11 1951 336.4 ACSR

6715 MATTA TAP MATTAWOMAN 2.13 1969 336.4 ACSR

6750 HEWTSME SAINTANDREW 2.77 1970 1590 AAC

6750 HOLLYWOOD OAKVILLE 7.1 1970 1590 AAC

6750 HUGHESVILLE GOLDBEACH SW 3.41 1970 1590 AAC

6750 MECHANICS OAKVILLE 7 1970 1590 AAC

6750 SAINTANDREW HOLLYWOOD 2.87 1970 1590 AAC

6750 GOLDBEACH SW MECHANICS 2.44 1970 1590 AAC

6790 MORG 69 MORG EXIT 1 2.12 1971 336.4 ACSR

6717 LAPLATA MARSHALL TAP 2.81 1971 556.5 ACSR

6721 W BRANDY TAP WESTBRANDY 0.76 1971 336.4 ACSR

6790 MORG EXIT 1 TOMPKINSVILL 4.72 1971 556.5 ACSR

6703 CHALSM69 HUGHESVILLE 6.6 1972 1590 AAC

6713 MORG 69 NEWBURG 4.1 1972 556.5 ACSR

6713 FAULKNER LAPLATA 6.07 1972 556.5 ACSR

6740 HUGHESVILLE 6740 GOAB 4.879 1972 1590 AAC

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 21

Table VIII-6: SMECO Transmission Lines Listed According to Age (continued)

SMECO

Line # Source Bus Load Bus

Length

Miles

Approximate

“As-Built"

Date

Conductor

Size

6713 NEWBURG FAULKNER 3.48 1972 556.5 ACSR

6756 VALLEY LEE PINEY POINT 4.39 1972 336.4 ACSR

6747 NEW MARKET RYCEVILLE 2.77 1972 1590 AAC

6740 6740 GOAB LOVEVILLE 11.711 1972 1590 AAC

6781 ST LEON TAP CLVRT CLIFF2 5.93 1975 & 1994 1590 AAC

6787 BERTHA CLVRT CLIFF1 4.08 1975 & 1995 1590 AAC

6613 HAWK 69 LAPLATA 4.98 1975 1590 AAC

6733 HAWK 69 FOREST TAP1 4.5 1975 1590 AAC

6610 HUGHESVILLE BRYANTOWN 4.04 1975 1590 AAC

6610 BRYANTOWN FOREST PARK 4.16 1975 1590 AAC

6718 RIPLEY SW GRAYTON 9.23 1975 1590 AAC

6708 FARMING 1 PISCATAWAY2 0.28428 1975 750 AL

6710 FARMING 1 BOLTON TAP 1 1.4 1975 1590 AAC

6709 FARMING 2 PISCATAWAY1 0.24981 1975 750 AL

6719 MARSHALL TAP MARSHALL CRN 2.45 1975 556.5 ACSR

6710 MATTA TAP WALDORF TAP 1.1 1975 1590 AAC

6710 WALDORF TAP BOLTON TAP 2 3.6 1975 1590 AAC

6710 FOREST TAP2 MATTA TAP 3.9 1975 1590 AAC

6752 GOLDBEACH SW GOLDEN BEACH 2.8 1979 556.5 ACSR

6716 HAWK 69 BAN TAP B 3.03 1982 1590 AAC

6620 ACCOKEEK MASONSPRING2 5.03 1982 1590 AAC

6723 BANNISTER BAN TAP A 1.27 1982 1590 AAC

6716 BAN TAP B BANNISTER 1.27 1982 1590 AAC

6620 FARMING 2 ACCOKEEK 4.87 1982 1590 AAC

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 22

Table VIII-6: SMECO Transmission Lines Listed According to Age (continued)

SMECO

Line # Source Bus Load Bus

Length

Miles

Approximate

“As-Built"

Date

Conductor

Size

6742 LEONARD TAP1 LEONARDTOWN1 1.7 1982 1590 AAC

6743 LEONARD TAP2 LEONARDTOWN2 1.7 1982 1590 AAC

6705 CHALSM69 DUKES INN 2 4.092 1984 556.5 ACSR

6781 MUTUAL ST LEON TAP 2.34 1984 1590 AAC

6704 CHALSM69 HUGHESVILLE 6.6 1986 1590 AAC

2310 CHALSM69 HOLLAND 7.66 1986 1590 AAC

6701 CHALSM69 ROUTE 5 5.96 1986 556.5 ACSR

6702 CHALSM69 ROUTE 5 5.96 1986 556.5 ACSR

2320W SMRYCE72 HEW2320W 23.66 1986 1590 AAC

2320E SMRYCE74 HEW2320E 23.66 1986 1590 AAC

6765 LEXINGTON PK PAX RVR SW 0.21 1986 1590 AAC

6765 PAX 6765 TAP PAX SO GATE 0.26 1986 1590 AAC

6765 PAX RVR4 TAP PAX 6765 TAP 1.52 1986 1750 AL

6766 PAX SO GATE PAX RIVER 3 1.3 1986 1590 AAC

6701 ROUTE 5 NEW MARKET 5.24 1986 1590 AAC

6765 PAX RVR SW PAX RVR4 TAP 0.9 1986 1590 AAC

6740 BAREFOOT INDBRIDGE 1.97 1988 1590 AAC

6740 LOVEVILLE LEONARD TAP1 2.5 1988 1590 AAC

6740 INDBRIDGE LEONARD TAP2 6.36 1988 1590 AAC

6706 CHALSM69 PR FRED TAP 4.6 1989 556.5 ACSR

6611 WALDORF WESTLAKE 1.6 1989 1590 AAC

6612 WESTLAKE SAINTCHARLE 1.62 1989 1590 AAC

6607 BOLTON TAP 1 BOLTON 1.45 1989 1590 AAC

6608 BOLTON TAP 2 BOLTON 1.45 1989 1590 AAC

6786 DUKES INN 2 MUTUAL 5.098 1989 1590 AAC

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 23

Table VIII-6: SMECO Transmission Lines Listed According to Age (continued)

SMECO

Line # Source Bus Load Bus

Length

Miles

Approximate

“As-Built"

Date

Conductor

Size

6762 NAWCAD TAP NAWCAD 2.56 1989 556.5 ACSR

6706 PR FRED TAP PRINCE FRED1 0.87 1989 1590 AAC

6706 PR FRED TAP DUKES INN 2 0.962 1989 1590 AAC

6760 HEWTSME PATUXENTPK 1.8 1990 1590 AAC

6740 HEWTSME BAREFOOT 1.1 1992 1590 AAC

6725 HAWK 69 NEWTOWN 4.1 1992 1590 AAC

6788 SOLOMONS BERTHA 1.81 1992 1590 AAC

6622 BURCHES MATTAWOMAN 5.55 1992 1590 AAC

6782 HOLLAND SUNDERLAND 4.6 1992 1590 AAC

6727 RIPLEY SW McCONCHIE 3.84 1992 556.5 ACSR

6717 MARSHALL TAP RIPLEY SW 4.22 1992 556.5 ACSR

6767 PAX SO GATE SAINTJAMES 5.54 1992 1590 AAC

6711 WALDORF TAP WALDORF 0.88 1992 1590 AAC

6770 HEWTSME BRIDGE STMRY 3.61 1993 1590 AAC

6760 PATUXENTPK SAINTJAMES 6.7 1993 1590 AAC

6723 BAN TAP A SAINTCHARLE 1.97 1993 1590 AAC

6770 BRIDGE CALV SOLOMONS 1.15 1993 1590 AAC

6770 BRIDGE STMRY BRIDGE CALV 1.95985 1993 1000 CU

6779 HEWTSME LEXINGTON PK 1.12 1994 1590 AAC

6783 HOLLAND PRINCE FRED2 7.77 1996 1590 AAC

6764 PAX RVR4 TAP PAX RIVER 4 0.1 1996 336.4 ACSR

6755 BAREFOOT VALLEY LEE 7.36 1998 556.5 ACSR

6761 SAINTJAMES NAWCAD TAP 3.26 1999 556.5 ACSR

6717 RIPLEY SW MASONSPRING1 4.84 1999 1590 AAC

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 24

Table VIII-6: SMECO Transmission Lines Listed According to Age (continued)

SMECO

Line # Source Bus Load Bus

Length

Miles

Approximate

“As-Built"

Date

Conductor

Size

6761 NAWCAD TAP RIDGE 2.4 1999 556.5 ACSR

6741 LOVEVILLE MILESTOWN 6.67 2000 556.5 ACSR

6784 ST LEON TAP SAINTLEONARD 0.7 2001 556.5 ACSR

6733 FOREST TAP1 FOREST PARK 0.1 2002 1590 AAC

6710 FOREST TAP1 FOREST TAP2 0.1 2002 1590 AAC

6710 FOREST TAP2 FOREST PARK 0.1 2002 1590 AAC

6775 PAX RVR SW PAX RIVER 2 1.46 2004 336.4 ACSR

6785 SUNDERLAND MOUNTHARMONY 3.8 2005-2006 556.5 ACSR

6745 INDBRIDGE REDGATE 4 2005-2006 556.5 ACSR

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 25

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 26

VIII-5: Economic Transmission Conductor Analysis

Conductors considered for use in SMECO’s transmission system were 336.4 MCM

ACSR, 556.5 MCM ACSR, 1590 MCM AAC, and 2312 MCM ACSR. These conductors

covered the range of sizes that would reasonably be used for light through heavily loaded

transmission lines. The costs of using these conductors were evaluated over a twenty-

five (25) year period by computing the cost of line construction plus the present worth of

the cost of electrical power losses operated over a range of current levels.

The wholesale cost of electricity was based on SMECO’s present best cost estimate as

filed with the Maryland Public Service Commission. The cost was $0.05253 per kilowatt

hour (kWh). Annual cost escalation for future years of 2.9% was assumed as interpolated

from values in the 2004 Annual Energy Outlook published by the Energy Information

Administration. The annual interest rate of 7.91% that SMECO uses for

financial/economic analysis was used for the conductor cost analysis.

Construction costs per mile were based on SMECO’s most recent transmission

construction cost proposal for the 66 kV Hughesville bypass Line 6720 to the north and

Line 6750 to the south. Line 6720 uses 336.4 MCM ACSR conductors and Line 6750

uses 1590 MCM AAC conductors. Per mile construction costs for 336.4 MCM ACSR

single-circuit overhead transmission lines with no distribution underbuild were estimated

to be $281,415 per mile considering the most recent (12/29/2004) pole quotations. Costs

for other conductors sizes were interpolated and extrapolated form SMECO’s Line 6720

and Line 6750 cost data including the recent pole cost quotations. The cost of I2*R losses

in annual kilowatt hours considered a loss factor (LsF) of 0.327 as determined from

SMECO’s five year average load factor (LdF) of 53.61%. These factors are according to

the United States Department of Agriculture Rural Utilities Services Bulletin 1724D-104,

Engineering Economics Computer Workbook Procedure. Each year, after the first year,

has the 2.9 % escalation factor applied and the future year cost referred back to the

present worth at a 7.91% annual interest rate according to the number of years in the

future being considered. These calculations are according to sound economic principles

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 27

as described in the Engineering Economy text by C. Robert Emerson and William R.

Taylor published by Cardinal Publishers in 1979.

The twenty-five (25) year present worth cost of losses plus the initial construction cost

per mile are summed to yield the present worth cost of constructing and operating the

indicated conductors for twenty-five years. The calculation results and plots of 336.4

MCM ACSR, 556.5 MCM ACSR, 1590 MCM AAC, and 2312 MCM ACSR conductor

costs per mile at each current level over the allowable continuous operating current range,

up to the 1000C rated ampacity for each conductor, are shown on Figure VIII-3 and in

Tables VIII-7 through VIII-10. At each current level the lowest curve, on Figure VIII-3

indicates the lowest cost of owning and operating the conductors at that current level.

Theoretically the crossover points of the curves, on these figures, are the current levels

where a larger conductor should be selected. Since conductors are applied considering

future load growth, they should operate below their ampacity rating when they are

installed with the expectation that load current will increase over time.

The economic analysis establishes the basic criteria for selecting conductor sizes;

however, many times conductors are chosen for reasons other than economics. They

must provide capacity for emergency feeds, they must coordinate with existing upstream

and downstream facilities, and they must allow for future possible load growth to avoid

repetition of construction work. It also should be noted that the present worth of losses

will vary depending upon the escalation rate, interest rate, load factor, and number of

years included in the calculation. These values can and will vary with time and are

unlikely to exactly match the values used in this analysis. Therefore this analysis, while

very useful in establishing conductors that are reasonable choices for a given loading,

should not be construed as precise calculation.

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 28

The curves in Figure VIII-4 indicate the obvious conclusion that larger conductors are

more economical for higher currents. SMECO’s general practice is to use 556.5 MCM

ACSR and 1590 MCM AAC conductors for most transmission applications. There are

presently no conductors larger that 1590 MCM AAC used in SMECO’s transmission

system. The curves suggest that for currents above about 600 amperes the larger 2312

MCM ACSR conductor should be considered. The 1590 MCM AAC conductor used for

Line 6750 and for many other large conductor lines in SMECO’s transmission system has

a calculated ampacity of 1,174 amperes at 750C. It is recommended that this conductor

continue to be used in SMECO’s transmission system for applications where the current

will stay below this level. This will maintain consistency and minimize training, spare

parts, tools and equipment that would be required for larger conductors.

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 29

INSERT CHART – FIGURE VIII-3

INSERT TABLES

TABLE VIII-7

TABLE VIII-8

TABLE VIII-9

TABLE VIII-10

HLY 029-688 Rev 0 (12/07/05) 106869 VIII - 30