Jump height of overhead-line conductors after the sudden release of ice loads

Abstract

SynopsisA series of tests was performed on a five-span section of 132kV line to determine the jump height of the conductors after the release of simulated ice loads from the centre span. The use of semitension assemblies at the suspension towers reduced the maximum jump height compared with that obtained with standard suspension-insulator strings, but did not prevent the phase conductors from passing dangerously close to each other. The importance of the sag in determining the jump height is stressed, and experimental and theoretical values for sag and jump height are compared.It was shown experimentally that the large sag differences resulting from some arrangements of ice loading brought phase conductors close together, and that the clearance to ground of the bottom conductor of the loaded span was reduced below the safety level for ice loads in excess of 1 lb/ft. It is concluded that, with heavy ice loads, phase-to-phase flashover can only be prevented by ensuring sufficient horizontal separation between phases. List of symbolsA •-cross-sectional area of conductor = 0-00245 ft 2 b -half spacing between suspension clamps of semitension assemblies = 5-6ft for unbraced, and 5 Oft for braced assemblies E = mean value of Young's modulus for conductor = 1-915 x 10 9 lbf/ft 2 E c -additional energy stored in unit length of conductor at midspan due to the added load w h ftlbf/ft W x -total work done by the added load in moving the suspensions, ftlbf / 0 = stress in the unloaded conductor, lbf/ft 2 / = stress in the loaded conductor, lbf/ft 2 f H = stress in the conductor at the maximum jump height, lbf/ft 2 g = acceleration due to gravity, ft/s 2 h = jump height of conductor above unloaded position after release of load, ft H = jump height of conductor above loaded position after release of load, ft / -distance between suspension points, ft L u -length of the unstrained conductor in a span, ft L o = length of the unloaded conductor in a span, ft L = length of the loaded conductor in a span, ft T s = tension in insulator string, lbf i Ac * q = loading factor = w l R -length of the suspension = 7 ft for the standard string, 9ft for the unbraced, and 8 ft for the braced semitension assemblies T o -tension acting parallel to the chord in the unloaded conductor, lbf T -tension acting parallel to the chord in the loaded conductor, lbf T k -kinetic energy of rising conductor, ftlbf U = strain energy in conductor, ftlbf V <=•-potential energy of conductor, ftlbf = gain in potential energy by conductor at maximum jump height, ftlbf/ft Paper 4552 P, first received 15th April and in revised form 3rd July 1964 Mr. Morgan and Mr. Swift are with the Central Electricity Research Laboratories 1736 v = velocity of travelling wave of displacement, ft/s vt > 0 = weight per unit length of the conductor alone = 0-57 lb/ft iv = weight per unit length of the conductor plus ropes, clips and hooks = 0-65 lb/ft w/ = weight per unit length of ice load, lb/ft x = horizontal deflection of a suspension point, ft X = total horizontal deflection of ...

An Improved Algebraic Method for Finding the Jump Height of Iced Transmission Lines

“…The authors of [9] have simulated for unzipping effect considering three tests after ice shedding. The authors of [10] have considered five span system to analyze its dynamic behavior and to investigate on finding the jump height. They were the first to propose a theoretical method to find the jump height; however the calculations neglect the tension variations and vertical displacement [7].…”

Dynamic Analysis of Overhead Power Lines after Ice–Shedding Using Finite Element Method

“…Very approximate practical models were suggested as early as the 1940s [4]. With the improvement of computational mechanics, numerical simulation methods (over all the FEM) were used to study ice-shedding from the power lines eg in [5][6][7] dynamic responses of transmission lines with different parameters, bundle conductors and five-span line section after ice-shedding is numerically simulated. In [8], a new theoretical method to calculate the jump height of the overhead power line after ice-shedding is presented.…”

Experimental Investigation of Dynamic Force on The Performance of Wet Snow Shedding

“…A more frequent problem arises when the load is suddenly released. The conductor springs upwards and if the horizontal spacing between phase conductors is small, flashover between conductors may happen (Morgan and Swift, 1964). As an example, when there is a conductor of 2 phases, and a heavy load remains on the top-phase conductor, while the bottomphase conductor snow has fallen.…”

“…As an example, when there is a conductor of 2 phases, and a heavy load remains on the top-phase conductor, while the bottomphase conductor snow has fallen. The second hazard is conductor jump arising from the sudden release of snow from conductors; this can cause them to rise to heights which exceed the normal spacing between both conductors (Morgan and Swift, 1964).…”

“…In addition snow shedding generates strong conductor motion, which applies transient dynamic forces to the towers, and causes conductor swing toward each other, these dynamic forces can cause cascading of the towers, resulting in heavy damage to the line (Morgan and Swift, 1964). Impulse loads due to sudden snow shedding are another source of trouble in power networks.…”