2015 IEEE Rural Electric Power Conference Asheville, North Carolina

Factors Affecting Conductor Motion  Conductor Unit Weight (lbs. per ft.)  Fault Current in Conductor (amperes)  Duration of Fault Current (seconds)  Conductor Spacing  Conductor Tension & Sag  Mechanical Damping

 Larger substations that increase available fault currents.  Closer conductor spacing in order to minimize aesthetic impact of overhead lines.  Increased customer sensitivity to momentary interruptions and voltage dips.  Increased conductor sag due to the use of larger conductors while maintaining distribution tension limits. Why Interest now in Conductor Motion?

 D = the sag of a level span.  S = the span length.  H = the conductor tension.  w = the unit weight of the conductor. Figure 1: Catenary Parameters (Equation 1b) Catenary Parameters and Basic Equation

 F = the force in pounds per foot of conductor.  d = the spacing between the conductors in feet.  I = the symmetrical short-circuit current. (Equation 2) Magnetic Forces Between Conductors

(Equation 3)  d = the conductor diameter, in.  V W = the wind speed, mph.  F H = the horizontal wind force, lbs/ft. Wind Forces on Conductors

(Equation 4a)  W C = the conductor weight per unit length, lbs/ft. (Equation 4b)  X H = the horizontal deflection at midpoint of span, ft.  D = the midpoint sag of conductor at specified wind and conductor temperature, ft. Figure 2: Conductor Swing Conductor Displacement Due to Horizontal Forces

Calculation of Motion (Equation 4a)(Equation 4b)(Equation 2)  Apply Equations 4a & 4b to determine displacement using initial force based on conductor ‘at rest’ position with Equation 2.  Calculate displacement for 0.01 seconds.  Apply Equation 2 for new horizontal separation and reiterate with Equations 4a & 4b.  Continue iterations until limit is reached. Limit is when gravity vector equals vertical vector component of horizontal force acting on displaced conductor or horizontal position is reached. Also limit iterations to fault current duration.

NESC Requirements for Horizontal Spacing  NESC requirements are based principally on clearances to minimize contact during wind events.  NESC requirements are basically the same as in NBS Handbook 81 (1961).

Importance of Conductor Tension Typical 250' Span Conductor Final Sag - (IN.) ConductorDesign 60°F Initial # 60°F90°F167°F 75% - 60°F Initial # 60°F90°F167°F 1/0 ACSR /0 ACSR ACSR ACSR ACSR

Why Worry about 167°F (75 °C)? Conductor Ampacity Wind AngleBook*90°**45°**0°** 1/0 ACSR /0 ACSR ACSR ACSR  All values at 75°C (167°F) conductor temperature with 2 FPS wind. * 25°C Ambient ** 40°C Ambient  Values are combined effect of using 40°C (104°F) ambient and various wind angles.

Typical RUS Structures Figure 4 A : RUS C1Figure 4 B : RUS DC-C1  Phase-to-Phase faults more critical.

Conductor Size Required for 10,000 AMP Fault Soft Drawn CU - Start Temp 40ºC Example of Structure for Phase-to-Ground Fault Figure 5: Conductor Conflict for a C9 S TRUCTURE

Conductor Size Required for 14,500 AMP Fault Soft Drawn CU - Start Temp 40ºC Conductor Temperature Effect Conductor3 kA - 58~10 kA - 10~ 1/0 90°F27"37" (Horiz) 1/0 75% & 167°F45"47" (Horiz)

Time for Maximum Reverse Swing 3000 A for 58~ ConductorReturn Time (sec.)Displacement (inches) 1/0 ACSR /0 ACSR ACSR ACSR

Conclusions  Consider conductor temperature under load currents when determining maximum sags.  Consider maximum operating sags and available short circuit currents when evaluating allowable span lengths, design tensions and conductor spacing.  Include measurements of actual conductor sag/tension during inspections of conductor installations.  When investigating the occurrence of apparent miscoordination, consider the possibility of conductor clash on the source side of suspected fault locations.