# Documentation

 Symbol Name Unit D $D_{ab}$ Diameter over armour bedding mm $D_{ar}$ External diameter of armour mm $d_{ar}$ Mean diameter of armour mm $d_b$ Diameter of the backfill mm $d_{b3}$ Distance c of multi-layer backfill m $d_{b4}$ Distance d of multi-layer backfill m $d_c$ External diameter of conductor mm $D_c$ Diameter of conductor m $d_{ci}$ Internal diameter of conductor mm $D_{comp}$ Diameter of compartment (metric) m $d_{comp}$ Diameter of compartment mm $d_{ct}$ External diameter of conductor for transient calculations mm $D_{di}$ Inner diameter of duct m $D_{do}$ Outer diameter of duct m $D_{dry}$ Diameter of drying zone m $D_e$ External diameter of object mm $d_e$ Equivalent diameter of screen/sheath and armour mm $d_{encl}$ Outer diameter of enclosure mm $D_{encl}$ Outer diameter of enclosure (metric) m $D_{eq}$ Equivalent diameter of a group of round objects mm $D_{ext}$ Overall outer diameter of pipe m $D_f$ External diameter of the filler mm $d_f$ Spacing from hottest object in group m $D_i$ Diameter over insulation mm $d_{im}$ Imaginary layer of soil m $D_{in}$ Inner diameter of pipe m $D_{ins}$ Diameter over insulation without insulation screen mm $d_{ins}$ Diameter of insulation around pipe mm $D_{it}$ Diameter over insulation for transient calculations mm $d_j$ Diameter below jacket mm $D_j$ Diameter over jacket mm $D_o$ Outer diameter m $d_{pk1}$ Distance to mirrored buried object mm $d_{pk2}$ Distance between buried objects mm $d_{prot}$ Diameter of protective cover mm $d_{psc}$ Point source correction m $D_{ref}$ Reference diameter for determination of OHTC m $d_s$ Equivalent diameter of screen and sheath mm $D_{sc}$ Diameter over screen mm $d_{sc}$ Mean diameter of screen mm $D_{scb}$ Diameter over screen bedding mm $D_{scs}$ Diameter over screen serving mm $D_{sh}$ Diameter over sheath mm $d_{sh}$ Mean diameter of sheath mm $D_{shb}$ Diameter below sheath mm $D_{shj}$ Diameter of sheath jacket mm $D_{soil}$ Outer diameter of soil layer m $d_t$ Channel covering m $d_w$ Depth under water m $D_{wall}$ Outer diameter of steel pipe m $d_x$ Equivalent diameter of a conductor mm $D_x$ Characteristic diameter mm $D_{x,w}$ Characteristic diameter for weekly load mm $D_{x,y}$ Characteristic diameter for yearly load mm $\Delta_1$ Substitution coefficient $\Delta_1$ for eddy-currents $\delta_1$ Thickness of screening layer mm $\Delta_2$ Substitution coefficient $\Delta_2$ for eddy-currents $\delta_{ar}$ Equivalent thickness of armour mm $\delta_d$ Distance between cable and duct m $\delta_k$ Thickness of screen, sheath or armour mm $\delta_{soil}$ Soil thermal diffusivity m$^2$/s $\Delta d_{sh}$ Depth of corrugation mm $\Delta H_c$ Heat of combustion coefficient MJ/kg $\Delta t$ Length of time step s $\Delta \theta_{0t}$ Air temperature in tunnel increase K $\Delta \theta_{0x}$ Temperature rise by crossing heat sources K $\Delta \theta_{0x,1}$ Temperature rise of the conductor, first estimate K $\Delta \theta_{0x,h}$ Temperature rise of the conductor by source h K $\Delta \theta_{a,t}$ Corrected transient temperature rise of conductor K $\Delta \theta_{air}$ Temperature increase of air K $\Delta \theta_c$ Temperature rise of conductor K $\delta \theta_c$ Ohmic steady-state temperature rise K $\Delta \theta_{c,t}$ Transient temperature rise of conductor by ohmic losses K $\Delta \theta_{ce}$ Temperature difference, conductor to surface K $\Delta \theta_d$ Temperature rise by dielectric losses K $\Delta \theta_{e,t}$ Transient temperature rise of outer surface K $\Delta \theta_{gas}$ Temperature difference, conductor to enclosure °C $\Delta \theta_{kp}$ Temperature rise by buried object k K $\Delta \theta_{max}$ Maximum permissible conductor temperature rise K $\Delta \theta_p$ Temperature rise by other buried objects K $\Delta \theta_R$ Conductor temperature rise above ambient temperature K $\Delta \theta_{R,\infty}$ Maximum permissible conductor temperature rise °C $\Delta \theta_s$ Temperature difference surface to ambient K $\delta \theta_{SPK}$ Peak cyclic temperature rise K $\Delta \theta_{sun}$ Temperature rise by solar radiation K $\Delta \theta_t$ Transient temperature rise of conductor K $\Delta \theta_{t,\infty}$ Steady-state temperature rise of conductor K $\Delta \theta_x$ Critical soil temperature rise K $\Delta \theta_{x0}$ VDE soil temperature rise K $\Delta W$ Incremental heat generated W $\Delta z$ Length of the interval m $Di_d$ Inner diameter of duct mm $di_{pipe}$ Internal diameter of fluid-filled pipe mm $Di_{sp}$ Inner diameter of steel pipe mm $Di_t$ Tunnel inner diameter m $Do_d$ Outer diameter of duct mm $do_{pipe}$ External pipe diameter mm $Do_{sp}$ Outer diameter of steel pipe mm $Do_t$ Tunnel/trough outer diameter m