Transient Temperature Cooling of Transformers: I - Derivation and Evaluation of Equations

Whitman, L. C.

doi:10.1109/tpas.1967.291805

Cited by 1 publication

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References 4 publications

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“…. (21) Let us again consider the variation of the mean temperature of the conductor. Putting 6 av = 0, and 6 s = d ~ A0, When there is Joulean plus solar heat input during cooling, the solution to eqn.…”

Section: Conductor With Electrically Nonconducting Corementioning

confidence: 99%

Rating of bare overhead conductors for intermittent and cyclic currents

Morgan

1969

Proc. Inst. Electr. Eng. UK

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Equations are derived and solutions given for determining the variation with time of the temperature of bare overhead conductors carrying intermittent and cyclic currents. The temperature variation depends on the rate of heat input, the heat capacity of the conductor and the rate of total heat transfer. The latter is proportional to (temperature rise) 9 . If the heat transfer by radiation can be neglected, q = 1 for forced convection and approximately 1 • 25 for natural convection. If radiation is not negligible, q is greater than 1, the actual value being obtained from calculations or steady-state measurements. Thermal time constants can only be used when q = 1, and they are then only approximations. Measured heating-and cooling-time constants agree reasonably well with calculated values. The significance of the difference between heating-and cooling-time constants is discussed. f The importance of the heat source or sink formed by the core in steel-cored conductors is shown, and calculated values of the radial thermal conductivity are similar to those found from previous steady-state measurements. Calculated temperature/time characteristics for conductors in still air are in good agreement with measured characteristics. List of symbolsa = thermal diffusivity, m 2 /s c = specific heat capacity at constant pressure, J/kgdegC C = heat capacity per unit length, J/mdegC D = diameter of the circle circumscribing the conductor, m e = base of natural logarithm h = total heat-transfer coefficient, W/m 2 degC H = specific total heat-transfer coefficient, W/mdegC / = current, A J = current density, A/m 2 k = factor to allow for the increase of resistance due to skin effect, proximity, hysteresis and eddy currents / = length, m m = mass per unit length, kg/m n = integer p s = solar irradiance at conductor surface, W/m 2 P = power gain per unit length by Joule heating, W/m p s = power gain per unit length by solar irradiation, W/m P T = total power gain per unit length, W/m q = heat-transfer exponent r = radius, m R = d.c. resistance per unit length, Q/m / = time, s V = potential difference, V a = temperature coefficient of resistance, degC" 1 /3 = temperature coefficient of specific heat capacity, degC" 1 y = specific mass, kg/m 3 A = effective radial thermal conductivity, W/mdegC 6 = temperature rise, degC p = resistivity, Qm T = thermal time constant, s

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Section: Conductor With Electrically Nonconducting Corementioning

confidence: 99%

Rating of bare overhead conductors for intermittent and cyclic currents

Morgan

1969

Proc. Inst. Electr. Eng. UK

View full text Add to dashboard Cite

show abstract

Transient Temperature Cooling of Transformers: I - Derivation and Evaluation of Equations

Cited by 1 publication

References 4 publications

Rating of bare overhead conductors for intermittent and cyclic currents

Rating of bare overhead conductors for intermittent and cyclic currents

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