| A | $a_0$ | Coefficient a for partial transient temperature rise | 1/s |
| $a_{12}$ | Distance between phase 1 and 2 | mm |
| $a_{23}$ | Distance between phase 2 and 3 | mm |
| $a_{31}$ | Distance between phase 3 and 1 | mm |
| $A_{ab}$ | Cross-sectional area of armour bedding | mm$^2$ |
| $A_{ar}$ | Cross-sectional area of armour | mm$^2$ |
| $A_c$ | Cross-sectional area of conductor | mm$^2$ |
| $a_c$ | Skin and proximity effect coefficient a for PAC/GIL conductor | |
| $A_{comp}$ | Cross-sectional area of compartment | m$^2$ |
| $A_d$ | Cross-sectional area of duct wall | mm$^2$ |
| $A_{d,fill}$ | Free cross-sectional area inside duct | mm$^2$ |
| $A_{di}$ | Surface of duct inner wall | m$^2$ |
| $A_{do}$ | Surface of duct outer wall | m$^2$ |
| $A_e$ | Surface of object | m$^2$ |
| $A_{encl}$ | Cross-sectional area of enclosure | mm$^2$ |
| $a_{encl}$ | Skin and proximity effect coefficient a for PAC/GIL enclosure | |
| $A_{er}$ | Surface of object | m$^2$ |
| $A_f$ | Cross-sectional area of filler | mm$^2$ |
| $A_{hsf}$ | Cross-sectional area of fluid | mm$^2$ |
| $A_{hsi}$ | Cross-sectional area of insulation | mm$^2$ |
| $A_{hsj}$ | Cross-sectional area of outer jacket | mm$^2$ |
| $A_{hsp}$ | Cross-sectional area of fluid-filled pipe | mm$^2$ |
| $A_i$ | Cross-sectional area of insulation | mm$^2$ |
| $a_i$ | Parameter a for radial derivative of dielectric losses | |
| $A_{it}$ | Cross-sectional area of insulation (IEC 60853) | mm$^2$ |
| $A_j$ | Cross-sectional area of jacket | mm$^2$ |
| $A_k$ | Thermal property constant A | mm/s$^{1/2}$ |
| $a_m$ | Mean distance between the phases | mm |
| $A_{prot}$ | Cross-sectional area of protective cover | mm$^2$ |
| $a_{S1}$ | Length of 1st section (minor) | p.u. |
| $a_{S2}$ | Length of 2nd section (medium) | p.u. |
| $a_{S3}$ | Length of 3rd section (major) | p.u. |
| $A_{sc}$ | Cross-sectional area of screen | mm$^2$ |
| $A_{scb}$ | Cross-sectional area of screen bedding | mm$^2$ |
| $A_{scs}$ | Cross-sectional area of screen serving | mm$^2$ |
| $A_{sh}$ | Cross-sectional area of sheath | mm$^2$ |
| $A_{shj}$ | Cross-sectional area of sheath jacket | mm$^2$ |
| $a_{shj}$ | Factor $a_{shj}$ for jacket around each core | |
| $A_{skid}$ | Cross-sectional area of skid wires | mm$^2$ |
| $A_{sp}$ | Cross-sectional area of steel pipe | mm$^2$ |
| $A_t$ | Cross-sectional area of the tunnel | m$^2$ |
| $A_{tape}$ | Cross-sectional area of bedding/serving tapes | mm$^2$ |
| $a_{type}$ | Construction of armour | |
| $\alpha_0$ | Constant depending on the burial depth | |
| $\alpha_{ar}$ | Temperature coefficient of armour material | 1/K |
| $\alpha_{at}$ | Heat transfer coefficient to channel wall | W/(K.m$^2$) |
| $\alpha_c$ | Temperature coefficient of conductor material | 1/K |
| $\alpha_{encl}$ | Temperature coefficient of enclosure material | 1/K |
| $\alpha_f$ | Phase shift | ° |
| $\alpha_{gas}$ | Thermal diffusivity for gas | m$^2$/s |
| $\alpha_i$ | Temperature coefficient of conductivity of insulation material | 1/K |
| $\alpha_p$ | Factor $\alpha_p$ | |
| $\alpha_{sa}$ | Heat transfer coefficient for convection | W/(K.m$^2$) |
| $\alpha_{sc}$ | Temperature coefficient of screen material | 1/K |
| $\alpha_{sh}$ | Temperature coefficient of sheath material | 1/K |
| $\alpha_{skid}$ | Temperature coefficient of skid wire material | 1/K |
| $\alpha_{sp}$ | Temperature coefficient of steel pipe material | 1/K |
| $\alpha_{st}$ | Heat transfer coefficient for radiation | W/(K.m$^2$) |
| $\alpha_{sys}$ | Inclination angle in degrees | ° |
| $\alpha_t$ | Conductor to surface attainment factor | |
| B | $B$ | Susceptance | S/m |
| $b_0$ | Coefficient b for partial transient temperature rise | 1/s |
| $B_1$ | Loss coefficient $B_1$ of armour | $\Omega$/m |
| $B_2$ | Loss coefficient $B_2$ of armour | $\Omega$/m |
| $b_c$ | Skin and proximity effect coefficient b for PAC/GIL conductor | |
| $B_{EMF}$ | Magnetic field strength | $\mu$T |
| $b_{encl}$ | Skin and proximity effect coefficient b for PAC/GIL enclosure | |
| $B_k$ | Thermal property constant B | mm$^2$/s |
| $b_{Nu,r}$ | Factor b | |
| $b_{shj}$ | Factor $b_{shj}$ for jacket around each core | |
| $b_x$ | Shorter side of backfill | mm |
| $b_y$ | Longer side of backfill | mm |
| $\beta_0$ | Constant $\beta_0$ (Ovuworie) | |
| $\beta_1$ | Substitution coefficient $\beta_1$ for eddy-currents | |
| $\beta_6$ | Factor $|1-\beta(6)|$ | |
| $\beta_{ar}$ | Reciprocal of temperature coefficient of armour material | K |
| $\beta_b$ | Angle of exposed wetted surface of pipe | rad |
| $\beta_c$ | Reciprocal of temperature coefficient of conductor material | K |
| $\beta_{encl}$ | Reciprocal of temperature coefficient of enclosure material | K |
| $\beta_{gas}$ | Volumetric thermal expansion coefficient for gas | 1/K |
| $\beta_k$ | Reciprocal of temperature coefficient of resistance | K |
| $\beta_p$ | Factor $\beta_p$ | |
| $\beta_{sc}$ | Reciprocal of temperature coefficient of screen material | K |
| $\beta_{sh}$ | Reciprocal of temperature coefficient of sheath material | K |
| $\beta_{skid}$ | Reciprocal of temperature coefficient of skid wire material | K |
| $\beta_{sp}$ | Reciprocal of temperature coefficient of steel pipe material | K |
| $\beta_t$ | Attainment factor cable surface to ambient | |
| $\beta_X$ | Crossing angle [rad] | rad |
| $\beta_{xing}$ | Crossing angle [°] | ° |
| $\mathrm{Bi}_g$ | Biot number of the ground | |
| $\mathrm{Bi}_p$ | Biot number of the pipe | |
| C | $C_{av}$ | Heat capacity of the air flow | W/K |
| $C_b$ | Capacitance of insulation | F/m |
| $C_{bq}$ | Constants $C_1$ - $C_7$ of multi-layer backfill | |
| $c_c$ | Distance between the axis of a conductor and the cable center | mm |
| $C_{c1}$ | Thermal capacitance, 1st loop | J/(m.K) |
| $C_{c2}$ | Thermal capacitance, 2nd loop | J/(m.K) |
| $C_{c3}$ | Thermal capacitance, 3rd loop | J/(m.K) |
| $C_{c4}$ | Thermal capacitance, 4th loop | J/(m.K) |
| $c_{color}$ | Wiring color code | |
| $C_E$ | Capacitance to earth | F/m |
| $C_{g1}$ | Factor C1 for partially buried pipes | |
| $C_{g2}$ | Factor C2 for partially buried pipes | |
| $C_{g3}$ | Factor C3 for partially buried pipes | |
| $c_{gas}$ | Constant c for a gas under PAC/GIL conditions | |
| $c_{ij}$ | Coefficient c for view factor | |
| $C_{k1}$ | Non-adiabatic constant $C_1$ | mm/m |
| $C_{k2}$ | Non-adiabatic constant $C_2$ | K.m.mm$^2$/J |
| $C_{Mie}$ | Factor $C$ (Mie1905) | |
| $C_{Nu,L}$ | Factor C | |
| $c_{Nu,r}$ | Factor c | |
| $C_{Nu,w}$ | Factor C | |
| $c_{p,gas}$ | Specific heat capacity of gas at constant pressure | J/(kg.K) |
| $c_{p,soil}$ | Specific volumetric heat capacity of soil material | J/(kg.K) |
| $c_{p,w}$ | Specific heat capacity of water at constant pressure | J/(kg.K) |
| $c_{shj}$ | Factor $c_{shj}$ for jacket around each core | |
| $c_{type}$ | Construction of conductor | |
| $c_{v,gas}$ | Specific heat capacity of gas at constant volume | J/(kg.K) |
| $C_{v,soil}$ | Heat capacity of a unit volume of soil | J/(K.m$^3$) |
| $c_{v,w}$ | Specific heat capacity of water at constant volume | J/(kg.K) |
| $C_{vair}$ | Volumetric heat capacity of air | J/(K.m$^3$) |
| $CC_{pull}$ | Conduit clearance | mm |
| $CF_{pull}$ | Conduit fill | $\%$ |
| $CJ_{pull}$ | Conduit jamming ratio | |
| $\mathrm{cos}\varphi$ | Power factor | |
| $CR_{pull}$ | Conduit ratio | |
| $cuw_{sc}$ | Standard copper wire size | |
| 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 |
| $D_c$ | External diameter of conductor | m |
| $d_{ci}$ | Internal diameter of conductor | mm |
| $D_{ci}$ | Internal diameter of conductor | m |
| $D_{comp}$ | Diameter of compartment | m |
| $D_{core}$ | Diameter over core cable | mm |
| $D_{cs}$ | Diameter over conductor shield | mm |
| $d_{ct}$ | External diameter of conductor for transient calculations | mm |
| $d_{cw}$ | Average diameter of conductor wire strand | 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 | 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 |
| $D_{hsi}$ | Diameter over insulation | mm |
| $D_{hsj}$ | Diameter of outer jacket | mm |
| $D_i$ | Diameter over insulation including screen | mm |
| $d_{im}$ | Imaginary layer of soil | m |
| $D_{in}$ | Inner diameter of pipe | m |
| $D_{ins}$ | Diameter over insulation | mm |
| $D_{is}$ | Diameter over insulation screen | mm |
| $D_{it}$ | Diameter over insulation for transient calculations | mm |
| $D_j$ | Diameter over jacket | mm |
| $D_{lay,3c}$ | Diameter of mechanical neutral line | 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 | m |
| $d_{psc}$ | 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 |
| $\delta_i$ | Electrical thickness of insulation material | 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 |
| $\Delta \theta_{0x,h}$ | Temperature rise of the conductor by source h | 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 | K |
| $\Delta \theta_{c,t,corr}$ | Corrected transient temperature rise of conductor | K |
| $\Delta \theta_{c,t,\infty}$ | Steady-state temperature rise of conductor | K |
| $\Delta \theta_{c,t,o}$ | 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 |
| $\Delta \theta_{d,t}$ | Transient temperature rise by dielectric losses | K |
| $\Delta \theta_{duct}$ | Temperature rise by losses in ferromagnetic duct | K |
| $\Delta \theta_{e,t}$ | Transient temperature rise of outer surface | K |
| $\Delta \theta_{gas}$ | Temperature difference, conductor to enclosure | °C |
| $\Delta \theta_i$ | Temperature difference across insulation | K |
| $\Delta \theta_{i,max}$ | Temperature rise of insulation limitation | K |
| $\Delta \theta_{kp}$ | Temperature rise by buried object k | K |
| $\Delta \theta_{kp,t}$ | Transient temperature rise of outer surface by object k | K |
| $\Delta \theta_{max}$ | Maximum permissible conductor temperature rise | K |
| $\Delta \theta_p$ | Temperature rise by other buried objects | K |
| $\Delta \theta_{p,t}$ | Transient temperature rise of outer surface 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 |
| $\Delta \theta_{uh}$ | Temperature rise by crossing heat sources at z | K |
| $\Delta \theta_x$ | Critical soil temperature rise | K |
| $\Delta \theta_{x0}$ | VDE soil temperature rise | K |
| $\Delta W$ | Incremental heat generated | W |
| $\Delta w_d$ | Increment of volumetric density of dielectric losses in HVDC cables | W/m$^3$ |
| $\Delta z$ | Length of the interval | m |
| $Di_d$ | Inner diameter of duct | mm |
| $Di_{hsp}$ | Internal diameter of fluid-filled pipe | mm |
| $Di_p$ | Inner diameter of air-filled pipe with objects | mm |
| $Di_{sp}$ | Inner diameter of steel pipe | mm |
| $Di_t$ | Tunnel inner diameter | m |
| $Do_d$ | Outer diameter of duct | mm |
| $Do_{hsp}$ | External pipe diameter | mm |
| $Do_p$ | Outer diameter of air-filled pipe with objects | mm |
| $Do_{sp}$ | Outer diameter of steel pipe | mm |
| $Do_t$ | Tunnel/trough outer diameter | m |
| E | $E_{bs}$ | Installation constant E | |
| $e_{hor}$ | Horizontal clearance | mm |
| $E_i$ | Electrical field strength | kV/mm |
| $e_{limit}$ | Limit of thickness of soil layer | m |
| $e_{soil}$ | Thickness of soil layer | m |
| $e_{ver}$ | Vertical clearance | mm |
| $e_{wall}$ | Clearance to wall | mm |
| $EEC$ | Embodied energy and carbon | MJ/kg |
| $\epsilon_0$ | Vacuum permittivity | F/m |
| $\epsilon_c$ | Effective emissivity of conductor | |
| $\epsilon_{di}$ | Emissivity of duct inner surface | |
| $\epsilon_{do}$ | Emissivity of duct outer surface | |
| $\epsilon_e$ | Emissivity of cable surface | |
| $\epsilon_{encl}$ | Effective emissivity of enclosure | |
| $\epsilon_{gas}$ | Dielectric constant of gas in compartment | |
| $\epsilon_{hsj}$ | Effective emissivity of protective cover | |
| $\epsilon_i$ | Relative permittivity of insulation | |
| $\epsilon_k$ | Heat loss allowance factor | |
| $\epsilon_{prot}$ | Effective emissivity of protective cover | |
| $\epsilon_{rad}$ | Effective emissivity | |
| $\eta 0_{gas}$ | Reference dynamic viscosity of gas | Pa.s |
| $\eta_{di}$ | Reflectivity of (opaque) duct inner surface | |
| $\eta_{do}$ | Reflectivity of (opaque) duct outer surface | |
| $\eta_e$ | Reflectivity of (opaque) cable surface | |
| $\eta_{gas}$ | Dynamic viscosity of gas | Pa.s |
| $\eta_w$ | Dynamic viscosity of water | Pa.s |
| F | $f$ | System frequency | Hz |
| $F_{\alpha}$ | Inclination derating factor | p.u. |
| $F_{ar}$ | Factor $F_{ar}$ for armour losses | |
| $f_{ar}$ | Factor between a.c. and d.c. resistance of armour | $\Omega$/m |
| $f_{atm}$ | Relation atmospheric pressure to standard atmosphere | |
| $f_{cb}$ | Factor for cross-bonded earthing | |
| $F_e$ | Factor $F_e$ for eddy-current losses | |
| $F_{eq}$ | Factor for envelope circle for a group of equal circles | |
| $F_{form}$ | Form factor | |
| $F_g$ | Gravitational force | N/m |
| $F_{ij}$ | View factor object-object | |
| $F_k$ | Imperfect contact thermal factor | |
| $F_{lay,3c}$ | Effective length per unit lay length of twisted conductors | |
| $F_{lay,ar}$ | Effective length per unit lay length of armour | |
| $F_{lay,c}$ | Effective length per unit lay length of conductor strands | |
| $F_{lay,sc}$ | Effective length per unit lay length of screen wires | |
| $F_m$ | Radiation coefficient mutual | |
| $F_{mh}$ | Mutual heating coefficient | |
| $f_{ppc}$ | Factor of permissible pull | N/mm$^2$ |
| $F_{ppc}$ | Permissible pull force | N |
| $F_{pt}$ | Function of pressure and temperature | |
| $F_{pull}$ | Pulling force | N |
| $f_{rad}$ | Sidewall bearing pressure factor | N/m |
| $F_{rad}$ | Sidewall bearing pressure | N/m |
| $F_{red}$ | Reduction factor for the permissible current rating | |
| $F_{T10,1}$ | Factor Table 10, single cables | p.u. |
| $F_{T10,3}$ | Factor Table 10, trefoil groups | p.u. |
| $F_{T11,s}$ | Factor Table 11, first part | p.u. |
| $F_{T11,t}$ | Factor Table 11, second part | p.u. |
| $F_{T12}$ | Factor Table 12 | p.u. |
| $F_{T13}$ | Factor Table 13 | p.u. |
| $f_{wc}$ | Weight correction factor | |
| $F_x$ | Geometrical distance factor for multi-core cables | |
| G | $g$ | Standard acceleration of gravity | m/s$^2$ |
| $G$ | Conductance | S/m |
| $G_1$ | Geometric factor $G_1$ | |
| $G_2$ | Geometric factor $G_2$ for cables with separate sheaths | |
| $g_a$ | Substitution coefficient g | |
| $G_b$ | Geometric factor for backfill | |
| $g_{bs}$ | Installation constant g | |
| $G_{corr}$ | Geometric correction factor $G_{corr}$ for jacket around each core | |
| $g_{dry}$ | Geometric constant of circle with dried-out soil | p.u. |
| $G_{encl}$ | Factor G for the calculation of the Nusselt number | |
| $G_{FEA}$ | Geometric reference factor $G_{FEA}$ based on FEM fitting | |
| $G_{od}$ | Aspect ratio object/duct | |
| $g_s$ | Substitution coefficient $g_s$ for eddy-currents | |
| $G_{s00}$ | Factor $G_{s 0.0}$ | |
| $G_{s05}$ | Factor $G_{s 0.5}$ | |
| $G_{s10}$ | Factor $G_{s 1.0}$ | |
| $g_u$ | Geometric constant of circle in soil g | |
| $g_x$ | Geometric constant of circle with characteristic diameter | p.u. |
| $\gamma_{bessel}$ | Bessel constant | p.u. |
| $\gamma_c$ | Skin and proximity effect factor $\gamma$ for PAC/GIL conductor | |
| $\gamma_{encl}$ | Skin and proximity effect factor $\gamma$ for PAC/GIL enclosure | |
| $\gamma_{euler}$ | Euler's constant | m/s$^2$ |
| $\gamma_i$ | Electrical field coefficient of insulation material | mm/kV |
| $\gamma_{prop}$ | Cable propagation constant | km/s |
| $\gamma_t$ | Attainment factor for groups of cables | |
| $\gamma_X$ | Attenuation factor for crossing | 1/m |
| $GMD$ | Geometric mean distance between phases of the same system | mm |
| $GMR_{ar}$ | Geometric mean radius of armour | mm |
| $GMR_c$ | Geometric mean radius of conductor | mm |
| $GMR_{cc}$ | Geometric mean radius of conductor bundle | mm |
| $GMR_{sc}$ | Geometric mean radius of screen | mm |
| $\mathrm{Gr}_c$ | Grashof number, conductor to gas | |
| $\mathrm{Gr}_{da}$ | Grashof number, duct in air | |
| $\mathrm{Gr}_{encl}$ | Grashof number, gas to enclosure | |
| $\mathrm{Gr}_{gd}$ | Grashof number, gas to duct | |
| $\mathrm{Gr}_L$ | Grashof number, ground to air | |
| $\mathrm{Gr}_{od}$ | Grashof number, object to duct | |
| $\mathrm{Gr}_{og}$ | Grashof number, object to gas | |
| $\mathrm{Gr}_{prot}$ | Grashof number, surface to air | |
| H | $H$ | Distance center of pipe to ground | m |
| $H_1$ | Component of inductance $H_1$ of armour | H/m |
| $h_1$ | Factor $h_1$ for emergency load | |
| $H_2$ | Component of inductance $H_2$ of armour | H/m |
| $H_3$ | Component of inductance $H_3$ of armour | H/m |
| $h_{amb}$ | Pseudo film coefficient of ambient fluid at ground level | W/(K.m$^2$) |
| $h_{atm}$ | Height above sea level | m |
| $h_b$ | Height of the backfill | mm |
| $h_{bs}$ | Heat dissipation coefficient for black surfaces in free air | W/m$^2$/K$^{5/4}$ |
| $h_{buried}$ | Heat transfer coefficient wall to soil | W/(K.m$^2$) |
| $H_c$ | Heat energy content | MJ/m |
| $h_{conv,c}$ | Convection heat transfer coefficient, conductor to gas | W/(K.m$^2$) |
| $h_{conv,da}$ | Convection heat transfer coefficient, duct to air | W/(K.m$^2$) |
| $h_{conv,encl}$ | Convection heat transfer coefficient, gas to enclosure | W/m2.K |
| $h_{conv,gd}$ | Convection heat transfer coefficient, gas to duct | W/(K.m$^2$) |
| $h_{conv,od}$ | Convection heat transfer coefficient, object to duct | W/(K.m$^2$) |
| $h_{conv,og}$ | Convection heat transfer coefficient, object to gas | W/(K.m$^2$) |
| $h_{conv,sa}$ | Convection heat transfer coefficient, surface to air | W/(K.m$^2$) |
| $h_{era}$ | Convection heat transfer coefficient acc. ERA | W/(K.m$^2$) |
| $h_{ext}$ | External heat transfer coefficient | W/(K.m$^2$) |
| $h_{ground}$ | Heat transfer coefficient buried part of wall to soil | W/(K.m$^2$) |
| $h_{in}$ | Heat transfer coefficient inside | W/(K.m$^2$) |
| $h_{lg}$ | Ratio of heat dissipation coefficients | |
| $h_{rad,ce}$ | Radiation heat transfer coefficient, conductor to enclosure | W/(K.m$^2$) |
| $h_{rad,da}$ | Radiation heat transfer coefficient, duct to air | W/(K.m$^2$) |
| $h_{rad,od}$ | Radiation heat transfer coefficient, object to duct | W/(K.m$^2$) |
| $h_{rad,sa}$ | Radiation heat transfer coefficient, surface to air | W/(K.m$^2$) |
| $H_s$ | Sheath conductance | H/m |
| $h_{soil}$ | Heat transfer coefficient wall-soil | W/(K.m$^2$) |
| $H_{sun}$ | Intensity of solar radiation | W/m$^2$ |
| $h_t$ | Inner height | m |
| $h_{T4}$ | Ratio of thermal resistance to ambient | |
| $H_{tc}$ | Parameter H for trough | |
| $h_{tr}$ | Heat transfer coefficient | W/(K.m$^2$) |
| $H_{ts}$ | Parameter H depending on air velocity | |
| $H_x$ | Magnetic field x-component | mH |
| $H_y$ | Magnetic field y-component | mH |
| I | $I_1$ | Steady-state current before transient | A |
| $I_2$ | Emergency load current | A |
| $I_{ar}$ | Induced circulating current in armour | A/m |
| $I_c$ | Conductor current | A |
| $I_C$ | Capacitive load current | A/m |
| $I_{c,LF}$ | Conductor root mean square current | A |
| $I_{c,max}$ | Highest current load of line | A |
| $I_{c,peak}$ | Permissible peak cyclic load current | A |
| $I_{c,sum}$ | Total current for all parallel systems | A |
| $I_{Ce}$ | Capacitive earth short-circuit current | A/m |
| $I_{EMF}$ | Phase current for EMF calculation | A |
| $I_k$ | Permissible short-circuit current | kA |
| $I_{k0}$ | Phase-to-ground short-circuit current | kA |
| $I_{k1}$ | Phase-to-neutral short-circuit current | kA |
| $I_{k2}$ | Phase-to-phase short-circuit current | kA |
| $I_{k3}$ | Three-phase symmetric short-circuit current | kA |
| $I_{kAD}$ | Short-circuit current (adiabatic) | kA |
| $I_{kSC}$ | Effective short-circuit current | kA |
| $I_{method}$ | Current calculation method | |
| $I_R$ | Transient conductor current | A |
| $I_s$ | Induced circulating current in screen/sheath | A |
| $I_{sp}$ | Induced current in steel pipe | A/m |
| $inst_{air}$ | Installation in air | |
| $inst_{buried}$ | Installation buried underground | |
| $inst_{elec}$ | Installation of cables for electrical calculations | |
| $inst_{riser}$ | Installation of cables in riser | |
| $inst_{sea}$ | Installation of subsea cables | |
| $inst_t$ | Installation in air inside a room | |
| J | $j_{max}$ | Phase angle range | ° |
| K | $K_0$ | Coefficient K for a gas under PAC/GIL conditions | |
| $K_{02}$ | Factor $K_{0.2}$ | |
| $K_{06}$ | Factor $K_{0.6}$ | |
| $K_1$ | Screening factor | |
| $K_{10}$ | Factor $K_{1.0}$ | |
| $k_4$ | Thermal conductivity of soil | W/(m.K) |
| $K_A$ | Coefficient K to calculate in air | |
| $k_{air}$ | Thermal conductivity of air | W/(m.K) |
| $k_{ar}$ | Thermal conductivity of armour material | W/(m.K) |
| $K_{BICC}$ | Constant relating to conductor formation | |
| $k_{Boltzmann}$ | Boltzmann constant | J/K |
| $k_c$ | Thermal conductivity of conductor material | W/(m.K) |
| $K_{ce}$ | Radiation shape factor, conductor to enclosure | |
| $K_{cv}$ | Convection factor | |
| $K_{dyn}$ | Corrected dynamic friction coefficient | |
| $k_{encl}$ | Thermal conductivity of enclosure | W/(m.K) |
| $K_G$ | Factor $K_G$ | |
| $k_{gas}$ | Thermal conductivity for gas | W/(m.K) |
| $K_{GMR}$ | Geometric mean radius factor | |
| $k_H$ | Heinhold characteristic diameter coefficient | |
| $k_{hsf}$ | Thermal conductivity of fluid | W/(m.K) |
| $k_{hsi}$ | Thermal conductivity of insulation | W/(m.K) |
| $k_{hsj}$ | Thermal conductivity of outer jacket | W/(m.K) |
| $k_{hsp}$ | Thermal conductivity of fluid-filled pipe | W/(m.K) |
| $K_k$ | Specific short-circuit parameter | A.s$^{1/2}$/mm$^2$ |
| $k_l$ | Temperature rise factor in air | |
| $k_{LF}$ | Load loss constant coefficient | p.u. |
| $K_{od}$ | Diameter ratio object/duct | |
| $k_p$ | Proximity effect coefficient | |
| $K_{par}$ | Constant $K_{par}$ (Ovuworie) | |
| $k_{prot}$ | Thermal conductivity of protective cover | W/(m.K) |
| $K_r$ | Radiation shape factor | |
| $k_{r2}$ | Temperature rise ratio $\delta\theta_{SPK}/\delta\theta_c$ | p.u. |
| $k_s$ | Skin effect coefficient | |
| $k_{sa}$ | Convection factor (Heinhold) | |
| $k_{sa,1}$ | Factor 1 for convection heat transfer coefficient | |
| $k_{sa,2}$ | Factor 2 for convection heat transfer coefficient | |
| $k_{sc}$ | Thermal conductivity of screen material | W/(m.K) |
| $k_{sh}$ | Thermal conductivity of sheath material | W/(m.K) |
| $k_{skid}$ | Thermal conductivity of skid wires | |
| $k_{sp}$ | Thermal conductivity of steel pipe material | W/(m.K) |
| $k_t$ | Temperature rise ratio | p.u. |
| $K_t$ | Effective emissivity of surface | |
| $K_{vermeer}$ | Vermeer constant for convection heat transfer | |
| $k_w$ | Thermal conductivity of water | W/(m.K) |
| $K_x$ | Factor for fictitious diameter by Neher | |
| $k_X$ | Number of heat sources crossing | |
| $\kappa_i$ | Electrical conductivity of insulation material at 0°C | S/m |
| $\kappa_j$ | Electrical conductivity of jacket material at 0°C | S/m |
| L | $L_0$ | Reference length of the tunnel | m |
| $L_1$ | Inductance of phase 1 | H/m |
| $L_2$ | Inductance of phase 2 | H/m |
| $L_3$ | Inductance of phase 3 | H/m |
| $L_b$ | Vertical center of backfill | mm |
| $L_{b4}$ | Trench depth of multi-layer backfill | m |
| $L_c$ | Depth of laying of sources | mm |
| $L_{char}$ | Characteristic length earth surface | |
| $L_{cm}$ | Depth of laying | m |
| $L_{crit}$ | Critical system length | km |
| $L_d$ | Length of duct | m |
| $L_{deep}$ | Equivalent depth for deep burial | m |
| $L_{dry}$ | Depth of characteristic diameter of drying zone | m |
| $L_{dw}$ | Length of duct in water | m |
| $L_{earth}$ | Equivalent depth of earth return path | mm |
| $L_h$ | Depth of laying of crossing element | mm |
| $L_{lay,3c}$ | Length of lay of twisted conductors | mm |
| $L_{lay,ar}$ | Length of lay of armour | mm |
| $L_{lay,c}$ | Length of lay of conductor strands | mm |
| $L_{lay,sc}$ | Length of lay of screen wires | mm |
| $L_{leg}$ | Length of a section | m |
| $L_m$ | Inductance (mean) | H/m |
| $L_r$ | Depth of laying of the rated object | mm |
| $L_{sys}$ | System length | km |
| $L_T$ | Length of the tunnel | m |
| $\lambda_0$ | Substitution coefficient $\lambda_0$ for eddy-currents | |
| $\lambda_1$ | Loss factor of shield (screen and sheath) | |
| $\lambda_{11}$ | Loss factor of shield by circulating currents | |
| $\lambda_{12}$ | Loss factor of shield by eddy currents | |
| $\lambda_2$ | Loss factor of armour | |
| $\lambda_{21}$ | Loss factor of armour by circulating currents | |
| $\lambda_{22}$ | Loss factor of armour by eddy currents | |
| $\lambda_3$ | Loss factor of steel pipes for pipe-type cables | |
| $\lambda_4$ | Loss factor of magnetic steel ducts | |
| $\lambda_d$ | Factor for dielectric losses | |
| $\lambda_{gas}$ | Ratio $c_p/c_v$ | |
| $\lambda_i$ | Parameter $\lambda$ for linear density of dielectric losses | |
| $\lambda_t$ | Relaxation parameter | |
| $LF$ | Load factor | p.u. |
| $LF_w$ | Weekly load factor | p.u. |
| $LF_y$ | Yearly load factor | p.u. |
| $LME$ | London Metal Exchange | USD/mt |
| M | $M$ | Cyclic rating factor | p.u. |
| $m_0$ | Substitution coefficient $m_0$ for eddy-currents | Hz.m/$\Omega$ |
| $M_0$ | Coefficient M for partial transient temperature rise | s |
| $M_1$ | Corrected cyclic rating factor | K |
| $M_{ab}$ | Material of armour bedding | |
| $m_{ab}$ | Mass of armour bedding | kg/m |
| $M_{ar}$ | Material of armour | |
| $m_{ar}$ | Mass of armour | kg/m |
| $M_c$ | Material of conductor | |
| $m_c$ | Mass of conductor | kg/m |
| $M_{cable}$ | List of materials in a cable | |
| $M_{comp}$ | Material of insulating gas | |
| $M_d$ | Material of duct pipe | |
| $M_e$ | Substitution coefficient $M_e$ to calculate factor $F_e$ | |
| $m_{e1}$ | Parameter m of conductor | |
| $m_{e23}$ | Parameter m of screen | |
| $m_{e45}$ | Parameter m of sheath | |
| $m_{e67}$ | Parameter m of armour | |
| $m_{earth}$ | Parameter m of earth return | |
| $m_{EMF}$ | Number of time steps | |
| $M_{encl}$ | Material of enclosure | |
| $M_f$ | Material of filler | |
| $m_f$ | Mass of filler | kg/m |
| $M_{gas}$ | Gas and gas-mixtures | |
| $m_{hollow}$ | Mass of hollow cable | kg/m |
| $M_{hsf}$ | Fluid material | |
| $M_{hsi}$ | Material of insulation around pipe | |
| $M_{hsj}$ | Material of outer jacket | |
| $M_{hsp}$ | Material of fluid-filled pipe | |
| $M_i$ | Material of insulation | |
| $m_i$ | Mass of insulation | kg/m |
| $M_{IEEE}$ | Materials acc. IEEE 442 | |
| $M_j$ | Material of jacket | |
| $m_j$ | Mass of jacket | kg/m |
| $M_k$ | Thermal contact factor | s$^{1/2}$ |
| $m_{metal}$ | Mass of the metallic parts | kg/m |
| $M_{mol}$ | Molar mass | g/mol |
| $m_{mol}$ | Molecular mass | mol |
| $m_{Nu,L}$ | Factor m | |
| $m_{Nu,w}$ | Factor m | |
| $M_p$ | Material of pipes | |
| $M_{prot}$ | Material of protective cover | |
| $M_{riser}$ | Material of riser | |
| $M_{sc}$ | Material of screen | |
| $m_{sc}$ | Mass of metallic screen | kg/m |
| $M_{seabed}$ | Material of seabed | |
| $M_{sh}$ | Material of sheath | |
| $m_{sh}$ | Mass of metallic sheath | kg/m |
| $M_{shj}$ | Material of sheath jacket | |
| $m_{shj}$ | Mass of jacket over each core | kg/m |
| $M_{skid}$ | Material of skid wires | |
| $m_{skid}$ | Mass of skid wires | kg/m |
| $M_{soil}$ | Type of soils | |
| $M_{sp}$ | Material of containment for pipe-type cables | |
| $m_{sp}$ | Mass of steel pipe | kg/m |
| $M_{spf}$ | Steel pipe filling medium | |
| $m_{tape}$ | Mass of tapes | kg/m |
| $m_{tot}$ | Mass of cable | kg/m |
| $\mu$ | Loss factor | p.u. |
| $\mu_0$ | Vacuum permeability | H/m |
| $\mu_{dyn}$ | Dynamic friction coefficient | |
| $\mu_e$ | Longitudinal relative permeability | |
| $\mu_{earth}$ | Magnetic permeability of earth | H/m |
| $\mu_s$ | Relative permeability | |
| $\mu_t$ | Traverse relative permeability of steel wires | |
| $\mu_w$ | Loss factor for weekly load variation | p.u. |
| $\mu_y$ | Loss factor for yearly load variation | p.u. |
| N | $N_0$ | Coefficient N for partial transient temperature rise | s$^2$ |
| $n_{a,1}$ | Number of wires of 1st armour | |
| $n_{a,2}$ | Number of wires of 2nd armour | |
| $n_{ar}$ | Number of wires of armour | |
| $N_{Avogrado}$ | Avogadro constant | 1/mol |
| $N_b$ | Number of loaded objects in backfill | |
| $n_c$ | Number of conductors in object | |
| $N_c$ | Number of sources in system | |
| $n_{cc}$ | Number of conductors combined | |
| $n_{cg}$ | Number of conductors in PAC/GIL | |
| $n_{cw}$ | Number of wires in conductor | |
| $n_{cycle}$ | Number of load cycles | |
| $N_e$ | Substitution coefficient $N_e$ to calculate factor $F_e$ | |
| $N_{hor}$ | Number of cable groups beside each other | |
| $n_{Nu,r}$ | Factor n | |
| $N_{ph}$ | Number of phases in system | |
| $n_{ph}$ | Number of phases in a cable | |
| $N_{sea}$ | Number of subsea cables | |
| $n_{seg}$ | Number of segments in Milliken conductor | |
| $N_{sum}$ | Total number of objects in an air-filled space | |
| $n_{sw}$ | Number of screen wires | |
| $N_{sys}$ | Number of parallel systems in the same confinement | |
| $N_{ver}$ | Number of cable groups above each other | |
| $N_X$ | Number of intervals | |
| $\nu$ | Summation step 1 - $N_X$ | |
| $\nu_{air}$ | Kinematic viscosity for air | m$^2$/s |
| $\mathrm{Nu}_c$ | Nusselt number, conductor to gas | |
| $\mathrm{Nu}_{da}$ | Nusselt number, duct to air | |
| $\mathrm{Nu}_{encl}$ | Nusselt number, gas to enclosure | |
| $\nu_{gas}$ | Kinematic viscosity for gas | m$^2$/s |
| $\mathrm{Nu}_{gd}$ | Nusselt number, gas to duct | |
| $\mathrm{Nu}_L$ | Nusselt number, ground to air | |
| $\mathrm{Nu}_{od}$ | Nusselt number, object to duct | |
| $\mathrm{Nu}_{og}$ | Nusselt number, object to gas | |
| $\mathrm{Nu}_{prot}$ | Nusselt number, surface to air | |
| $\nu_{sc}$ | Elongation of screen | $\%$ |
| $\nu_{soil}$ | Soil moisture content | $\%$ |
| $\mathrm{Nu}_w$ | Nusselt number, surface to water | |
| $\nu_w$ | Kinematic viscosity for water | m$^2$/s |
| O | $\omega$ | Angular frequency | rad/s |
| P | $p_{a,1}$ | Length of lay of 1st armour | mm |
| $p_{a,2}$ | Length of lay of 2nd armour | mm |
| $p_{ab}$ | Factor apportioning the armour bedding | |
| $p_{atm}$ | Atmospheric air pressure | hPa |
| $P_C$ | Charging capacity | kvar/m |
| $p_{cb}$ | Minor ratio of section lengths | |
| $p_{comp}$ | Gas pressure in compartment | bar |
| $P_G$ | Active power generator-side | kW |
| $p_{gas}$ | Gas pressure | Pa |
| $p_i$ | Factor apportioning the insulation | |
| $p_j$ | Factor apportioning the jacket | |
| $P_L$ | Active power load-side | kW |
| $p_{Mie}$ | Factor $p$ (Mie1905) | |
| $p_{Nu,r}$ | Factor p | |
| $p_{shj}$ | Factor apportioning the sheath jacket | |
| $p_{soil}$ | Depth of image source | |
| $p_{tr}$ | Effective perimeter of trough | m |
| $p_w$ | Water pressure | bar |
| $P_X$ | Substitution coefficient P to calculate loss factor by circulating currents | |
| $\Phi_{air}$ | Relative humidity of air | $\%$ |
| $\phi_{ar}$ | Angle between armour and cable axis | rad |
| $\phi_{arc}$ | Angle of a bend | rad |
| $\phi_{el}$ | Angle to the plane of a section | rad |
| $\phi_{tr}$ | Parameter $\phi$ for trough | |
| $\pi$ | Archimedes' constant $\pi$ | |
| $\mathrm{Pr}_{air}$ | Prandtl number for air | |
| $\mathrm{Pr}_{gas}$ | Prandtl number for gas | |
| $\mathrm{Pr}_w$ | Prandtl number for liquids | |
| Q | $q_1$ | Ratio of losses affecting screen bedding/serving | |
| $q_2$ | Ratio of losses affecting armour bedding | |
| $q_3$ | Ratio of losses affecting jacket | |
| $q_4$ | Ratio of losses affecting environment | |
| $Q_A$ | Element A of two-part thermal circuit | J/(m.K) |
| $Q_{ab}$ | Thermal capacitance of armour bedding | J/(m.K) |
| $Q_{ar}$ | Thermal capacitance of armour | J/(m.K) |
| $q_{ar}$ | Ratio of losses armour | |
| $Q_B$ | Element B of two-part thermal circuit | J/(m.K) |
| $Q_{B,ab}$ | Element B of two-part thermal circuit of armour bedding | J/(m.K) |
| $Q_{B,d}$ | Element B of two-part thermal circuit, duct | J/(m.K) |
| $Q_{B,f}$ | Element B of two-part thermal circuit, filler | J/(m.K) |
| $Q_{B,i}$ | Element B of two-part thermal circuit, insulation | J/(m.K) |
| $Q_{B,j}$ | Element B of two-part thermal circuit, jacket | J/(m.K) |
| $Q_{B,s}$ | Element B of two-part thermal circuit, screen/sheath | J/(m.K) |
| $Q_c$ | Thermal capacitance of conductor | J/(m.K) |
| $q_{cb}$ | Major ratio of section lengths | |
| $Q_{ct}$ | Thermal capacitance of conductor (IEC 60853) | J/(m.K) |
| $Q_d$ | Thermal capacitance of duct wall | J/(m.K) |
| $Q_{d,fill}$ | Thermal capacitance of duct filling | J/(m.K) |
| $Q_f$ | Thermal capacitance of filler | J/(m.K) |
| $q_f$ | Ratio of losses affecting the filler | |
| $Q_G$ | Reactive power generator-side | kvar |
| $Q_i$ | Thermal capacitance of insulation | J/(m.K) |
| $Q_{it}$ | Thermal capacitance of insulation (IEC 60853) | J/(m.K) |
| $Q_{it1}$ | Thermal capacitance of insulation, 1st portion (IEC 60853) | J/(m.K) |
| $Q_{it2}$ | Thermal capacitance of insulation, 2nd portion (IEC 60853) | J/(m.K) |
| $Q_j$ | Thermal capacitance of jacket | J/(m.K) |
| $Q_L$ | Reactive power load-side | kvar |
| $q_{Mie}$ | Factor $q$ (Mie1905) | |
| $Q_s$ | Thermal capacitance of screen+sheath | J/(m.K) |
| $q_s$ | Ratio of losses screen/sheath | |
| $Q_{sc}$ | Thermal capacitance of screen | J/(m.K) |
| $Q_{scb}$ | Thermal capacitance of screen bedding | J/(m.K) |
| $Q_{scs}$ | Thermal capacitance of screen serving | J/(m.K) |
| $Q_{sh}$ | Thermal capacitance of sheath | J/(m.K) |
| $Q_{shj}$ | Thermal capacitance of sheath jacket | J/(m.K) |
| $Q_{sp}$ | Thermal capacitance of steel pipe | J/(m.K) |
| $Q_{sr}$ | Reactive power from shunt reactor | kvar |
| $Q_{tot}$ | Total thermal capacitance, transient | J/(m.K) |
| $Q_X$ | Substitution coefficient Q to calculate loss factor by circulating currents | |
| $q_x$ | Factor for characteristic diameter | |
| R | $R_0$ | Zero sequence resistance | $\Omega$/m |
| $r_1$ | Radius of the circle circumscribing the shaped conductors | mm |
| $R_1$ | Resistance of conductor before emergency rating | $\Omega$/m |
| $R_{ar}$ | Electrical resistance of armour | $\Omega$/m |
| $r_{arc}$ | Radius of a bend | m |
| $r_b$ | Equivalent radius of backfill | mm |
| $r_c$ | Radius of conductor | mm |
| $R_c$ | Electrical resistance of conductor | $\Omega$/m |
| $R_{c1}$ | Thermal resistance, 1st loop | K.m/W |
| $R_{c2}$ | Thermal resistance, 2nd loop | K.m/W |
| $R_{c20}$ | DC resistance of conductor at 20°C | $\Omega$/m |
| $R_{c3}$ | Thermal resistance, 3rd loop | K.m/W |
| $R_{c4}$ | Thermal resistance, 4th loop | K.m/W |
| $R_{cDC}$ | Electrical DC resistance of conductor | $\Omega$/m |
| $R_{CG}$ | Thermal resistance of multi-layer backfill | K.m/W |
| $R_{co}$ | Standard DC resistance of conductor | $\Omega$/km |
| $r_{core}$ | Radius over core cable | mm |
| $R_e$ | Electrical resistance of shield and armour | $\Omega$/m |
| $r_{e1}$ | Radius of conductor | m |
| $r_{e2}$ | Radius of screen (inner) | m |
| $r_{e3}$ | Radius of screen (outer) | m |
| $r_{e4}$ | Radius of sheath (inner) | m |
| $r_{e5}$ | Radius of sheath (outer) | m |
| $r_{e6}$ | Radius of armour (inner) | m |
| $r_{e7}$ | Radius of armour (outer) | m |
| $r_{e8}$ | Radius of jacket (outer) | m |
| $R_{earth}$ | Equivalent resistance of earth return path | p.u. |
| $R_{encl}$ | Electrical AC resistance of enclosure | $\Omega$/m |
| $R_{encl20}$ | Electrical DC resistance of enclosure at 20°C | $\Omega$/m |
| $R_{enclDC}$ | Electrical DC resistance of enclosure | $\Omega$/m |
| $R_{gas}$ | Specific gas constant | J/(kg.K) |
| $R_{gas0}$ | Universal molar gas constant | |
| $r_{ij}$ | Coefficient r for view factor | |
| $r_{isc}$ | Radius above the inner semi-conducting layer | mm |
| $R_{max}$ | Resistance of conductor at emergency rating | $\Omega$/m |
| $r_{mbi}$ | Minimal bending radius for installation | m |
| $r_{mbif}$ | Factor of minimal installation bending radius | |
| $r_{mbp}$ | Minimal bending radius during cable pulling | m |
| $r_{mbpf}$ | Factor of minimal pulling bending radius | |
| $r_o$ | Radius of object | m |
| $r_{osc}$ | Radius over capacitive insulation layers | mm |
| $R_{q11}$ | Thermal resistance 11 of multi-layer backfill | K.m/W |
| $R_{q12}$ | Thermal resistance 12 of multi-layer backfill | K.m/W |
| $R_{q13}$ | Thermal resistance 13 of multi-layer backfill | K.m/W |
| $R_{q21}$ | Thermal resistance 21 of multi-layer backfill | K.m/W |
| $R_{q22}$ | Thermal resistance 22 of multi-layer backfill | K.m/W |
| $R_{q31}$ | Thermal resistance 31 of multi-layer backfill | K.m/W |
| $R_{q32}$ | Thermal resistance 32 of multi-layer backfill | K.m/W |
| $r_s$ | Equivalent radius of screen and sheath | mm |
| $R_s$ | Electrical resistance of shield | $\Omega$/m |
| $R_{sc}$ | Electrical resistance of screen | $\Omega$/m |
| $R_{sh}$ | Electrical resistance of sheath | $\Omega$/m |
| $R_{skid}$ | Electrical resistance of skid wires | $\Omega$/m |
| $R_{so}$ | Resistance of screen and sheath at 20°C | $\Omega$/m |
| $R_{sp}$ | Electrical resistance of steel pipe | $\Omega$/m |
| $r_x$ | Radius to point x in insulation | mm |
| $\mathrm{Ra}_c$ | Rayleigh number, conductor to gas | |
| $\mathrm{Ra}_{encl}$ | Rayleigh number, gas to enclosure | |
| $\mathrm{Ra}_{gas}$ | Rayleigh number gas/duct | |
| $\mathrm{Ra}_L$ | Rayleigh number, ground to air | |
| $\mathrm{Ra}_{prot}$ | Rayleigh number, surface to air | |
| $\mathrm{Re}_{air}$ | Reynolds number for air | |
| $\mathrm{Re}_w$ | Reynolds number for water | |
| $RF$ | Reduction factor | |
| $\rho_4$ | Thermal resistivity of soil | K.m/W |
| $\rho_{4d}$ | Thermal resistivity of dry soil | K.m/W |
| $\rho_{ab}$ | Thermal resistivity of armour bedding | K.m/W |
| $\rho_{ab,1}$ | Thermal resistivity of 1st armour bedding | K.m/W |
| $\rho_{ab,2}$ | Thermal resistivity of 2nd armour bedding | K.m/W |
| $\rho_{ar}$ | Specific electrical resistivity of armour material | $\Omega$.m |
| $\rho_b$ | Thermal resistivity backfill | K.m/W |
| $\rho_{b1}$ | Thermal resistivity of surface layer | K.m/W |
| $\rho_{b2}$ | Thermal resistivity of middle layer | K.m/W |
| $\rho_c$ | Electrical resistivity of conductor material | $\Omega$.m |
| $\rho_{corr}$ | Thermal resistivity of corrugation filling | K.m/W |
| $\rho_{cr}$ | Thermal resistivity of conductor material | K.m/W |
| $\rho_{cs}$ | Thermal resistivity of conductor shield | K.m/W |
| $\rho_{ct}$ | Thermal resistivity of conductor tape | K.m/W |
| $\rho_d$ | Thermal resistivity of duct material | K.m/W |
| $\rho_{d,fill}$ | Thermal resistivity of bentonite filling | K.m/W |
| $\rho_{earth}$ | Specific electrical resistivity of soil | $\Omega$.m |
| $\rho_{encl}$ | Specific electrical resistivity of enclosure material | $\Omega$.m |
| $\rho_f$ | Thermal resistivity of filler | K.m/W |
| $\rho_{gas}$ | Gas density | kg/m$^3$ |
| $\rho_i$ | Thermal resistivity of insulation | K.m/W |
| $\rho_{is}$ | Thermal resistivity of insulation screen | K.m/W |
| $\rho_j$ | Thermal resistivity of jacket material | K.m/W |
| $\rho_{k2}$ | Thermal resistivity of the layer located above | K.m/W |
| $\rho_{k20}$ | Electrical resistivity of metallic component | $\Omega$.m |
| $\rho_{k3}$ | Thermal resistivity of the layer located below | K.m/W |
| $\rho_{ki}$ | Thermal resistivity of adjacent material | K.m/W |
| $\rho_p$ | Thermal resistivity of pipe material | K.m/W |
| $\rho_{sc}$ | Specific electrical resistivity of screen material | $\Omega$.m |
| $\rho_{scb}$ | Thermal resistivity of screen bedding | K.m/W |
| $\rho_{scs}$ | Thermal resistivity of screen serving | K.m/W |
| $\rho_{sh}$ | Specific electrical resistivity of sheath material | $\Omega$.m |
| $\rho_{shj}$ | Thermal resistivity of sheath jacket material | K.m/W |
| $\rho_{skid}$ | Specific electrical resistivity of skid wire material | $\Omega$.m |
| $\rho_{sp}$ | Specific electrical resistivity of steep pipe material | $\Omega$.m |
| $\rho_t$ | Thermal resistivity of wall | K.m/W |
| S | $s_{air}$ | Axial spacing between objects | m |
| $s_{b1}$ | Thickness of surface layer | m |
| $s_{b2}$ | Thickness of middle layer | m |
| $s_{b3}$ | Thickness from object to top of bedding layer | m |
| $s_{b4}$ | Thickness from object to bottom of bedding layer | m |
| $s_c$ | Separation of conductors in a system | mm |
| $s_{cm}$ | Separation of conductors in a system | m |
| $S_G$ | Apparent power generator-side | kVA |
| $S_{gas}$ | Sutherland's constant | K |
| $s_{ij}$ | Spacing between object i and j | |
| $S_k$ | Cross-sectional area of current carrying component | mm$^2$ |
| $s_{S1}$ | Spacing between phases in 1st section | p.u. |
| $s_{S2}$ | Spacing between phases in 2nd section | p.u. |
| $s_{S3}$ | Spacing between phases in 3rd section | p.u. |
| $\sigma$ | Stefan Boltzmann constant | W/m$^2$K$^4$ |
| $\sigma_{ab}$ | Volumetric heat capacity of armour bedding | J/(K.m$^3$) |
| $\sigma_{ab,1}$ | Volumetric heat capacity of 1st armour bedding | J/(K.m$^3$) |
| $\sigma_{ab,2}$ | Volumetric heat capacity of 2nd armour bedding | J/(K.m$^3$) |
| $\sigma_{ar}$ | Volumetric heat capacity of armour material | J/(K.m$^3$) |
| $\sigma_c$ | Volumetric heat capacity of conductor material | J/(K.m$^3$) |
| $\sigma_d$ | Volumetric heat capacity of duct material | J/(K.m$^3$) |
| $\sigma_{d,fill}$ | Volumetric heat capacity of duct filling | J/(K.m$^3$) |
| $\sigma_{encl}$ | Volumetric heat capacity of enclosure material | J/(K.m$^3$) |
| $\sigma_f$ | Volumetric heat capacity of filler | J/(K.m$^3$) |
| $\sigma_i$ | Volumetric heat capacity of insulation material | J/(K.m$^3$) |
| $\sigma_j$ | Volumetric heat capacity of jacket material | J/(K.m$^3$) |
| $\sigma_{k2}$ | Specific isobaric volumetric heat capacity of layer located below | J/(K.m$^3$) |
| $\sigma_{k3}$ | Volumetric heat capacity of layer located above | J/(K.m$^3$) |
| $\sigma_{kc}$ | Volumetric heat capacity of metallic component | J/(K.m$^3$) |
| $\sigma_{ki}$ | Volumetric heat capacity of adjacent material | J/(K.m$^3$) |
| $\sigma_{prot}$ | Specific isobaric volumetric heat capacity of protective cover | J/(K.m$^3$) |
| $\sigma_{sc}$ | Volumetric heat capacity of screen material | J/(K.m$^3$) |
| $\sigma_{scb}$ | Volumetric heat capacity of screen bedding | J/(K.m$^3$) |
| $\sigma_{scs}$ | Volumetric heat capacity of screen serving | J/(K.m$^3$) |
| $\sigma_{sh}$ | Volumetric heat capacity of sheath material | J/(K.m$^3$) |
| $\sigma_{shj}$ | Volumetric heat capacity of sheath jacket material | J/(K.m$^3$) |
| $\sigma_{skid}$ | Volumetric heat capacity of skid wires | J/(K.m$^3$) |
| $\sigma_{sp}$ | Volumetric heat capacity of steel pipe material | J/(K.m$^3$) |
| $\sigma_{sun}$ | Absorption coefficient of solar radiation | |
| T | $T0_{gas}$ | Gas reference temperature | K |
| $T_1$ | Thermal resistance between one conductor and sheath | K.m/W |
| $t_1$ | Thickness of insulation to sheath | mm |
| $t_{1t}$ | Thickness of insulation to sheath, transient | mm |
| $T_2$ | Thermal resistance of armour bedding | K.m/W |
| $t_2$ | Thickness of bedding under armour | mm |
| $t_{2i}$ | Thickness of insulation between conductors | mm |
| $T_3$ | Thermal resistance of jacket | K.m/W |
| $t_3$ | Thickness of serving over armour | mm |
| $T_{4d}$ | Thermal resistance for daily load cycle | K.m/W |
| $T_{4db}$ | Correction of thermal resistance for backfill | K.m/W |
| $T_{4fem}$ | Thermal resistance finite element method | K.m/W |
| $T_{4i}$ | Thermal resistance of medium in the duct | K.m/W |
| $T_{4ii}$ | Thermal resistance of the duct wall | K.m/W |
| $T_{4iii}$ | Thermal resistance to ambient | K.m/W |
| $T_{4\mu}$ | Thermal resistance to ambient | K.m/W |
| $T_{4pi}$ | Thermal resistance of medium in the air-filled pipe with objects | K.m/W |
| $T_{4pii}$ | Thermal resistance of the pipe wall | K.m/W |
| $T_{4piii}$ | Thermal resistance of the pipe to ambient | K.m/W |
| $T_{4ss}$ | Steady-state thermal resistance | K.m/W |
| $T_{4t}$ | Equivalent thermal resistance for tunnel | K.m/W |
| $T_{4w}$ | Thermal resistance for weekly load cycle | K.m/W |
| $T_{4y}$ | Thermal resistance for yearly load cycle | K.m/W |
| $T_A$ | Element A of equivalent thermal circuit | K.m/W |
| $T_a$ | Star thermal resistance of air | K.m/W |
| $T_{a0}$ | Apparent thermal resistance a | K.m/W |
| $t_{a,1}$ | Thickness of 1st armour | mm |
| $t_{a,2}$ | Thickness of 2nd armour | mm |
| $t_{ab}$ | Thickness of armour bedding | mm |
| $T_{ab}$ | Thermal resistance of armour bedding | K.m/W |
| $t_{ab,1}$ | Thickness of 1st armour bedding | mm |
| $t_{ab,2}$ | Thickness of 2nd armour bedding | mm |
| $T_{air}$ | Absolute air temperature | K |
| $t_{ar}$ | Thickness of armour | mm |
| $T_{at}$ | Thermal resistance by convection, air to tunnel | K.m/W |
| $T_{axial}$ | Axial thermal resistance due to the movement of air through the tunnel | K.m/W |
| $T_B$ | Element B of equivalent thermal circuit | K.m/W |
| $T_{b0}$ | Apparent thermal resistance b | K.m/W |
| $T_{bulk}$ | Bulk temperature | K |
| $t_c$ | Thickness of hollow conductor | mm |
| $T_C$ | Element C of equivalent thermal circuit | K.m/W |
| $t_{comp}$ | Thickness of compartment | m |
| $T_{conv,ce}$ | Thermal resistance by convection, conductor to enclosure | K.m/W |
| $T_{conv,od}$ | Thermal resistance by convection, object to duct | K.m/W |
| $T_{conv,sa}$ | Thermal resistance by convection, surface to air | K.m/W |
| $t_{corr}$ | Thickness of corrugation filling | mm |
| $t_{cs}$ | Thickness of conductor shield | mm |
| $T_{cs}$ | Thermal resistance of conductor shield | K.m/W |
| $t_{ct}$ | Thickness of conductor tape | mm |
| $T_{ct}$ | Thermal resistance of conductor tape | K.m/W |
| $T_d$ | Internal thermal resistance for dielectric losses | K.m/W |
| $t_d$ | Thickness of duct | mm |
| $T_{dsh}$ | Thermal resistance of corrugation filling | K.m/W |
| $T_e$ | External thermal resistance of tunnel | K.m/W |
| $t_{EMF}$ | Time step to calculate current source | s |
| $t_{encl}$ | Thickness of enclosure | m |
| $T_{eq}$ | Equivalent thermal resistance | K.m/W |
| $t_f$ | Thickness of filler/belt insulation | mm |
| $T_{gas}$ | Absolute gas temperature | K |
| $T_{hs}$ | Thermal resistance of heat source | K.m/W |
| $t_{hsi}$ | Thickness of insulation | mm |
| $T_{hsi}$ | Thermal resistance of insulation | K.m/W |
| $t_{hsj}$ | Thickness of outer jacket | mm |
| $T_{hsj}$ | Thermal resistance of outer jacket | K.m/W |
| $t_{hsp}$ | Thickness of pipe | mm |
| $T_{hsp}$ | Thermal resistance of fluid-filled pipe | K.m/W |
| $T_i$ | Thermal resistance of insulation | K.m/W |
| $t_i$ | Thickness of insulation | mm |
| $t_{icore}$ | Thickness of core insulation | mm |
| $t_{ins}$ | Thickness of insulation | mm |
| $T_{ins}$ | Thermal resistance of insulation | K.m/W |
| $T_{int}$ | Internal thermal resistance for current losses | K.m/W |
| $t_{is}$ | Thickness of insulation screen | mm |
| $T_{is}$ | Thermal resistance of insulation screen | K.m/W |
| $t_j$ | Thickness of jacket | mm |
| $T_j$ | Thermal resistance of jacket | K.m/W |
| $t_{jj}$ | Thickness of additional layer over jacket | mm |
| $t_k$ | Duration of short-circuit | s |
| $T_L$ | Thermal longitudinal resistance | K.m/W |
| $T_{mh}$ | Mutual thermal resistance between rated and crossing object(s) | K.m/W |
| $T_{mh,v}$ | Mutual thermal resistance between object(s) per slice | K.m/W |
| $T_o$ | Thermal resistance of the oil in the pipe | K.m/W |
| $t_p$ | Thickness of air-filled pipe with objects | mm |
| $t_{prot}$ | Thickness of protective cover | m |
| $T_{prot}$ | Thermal resistance of protective cover | K.m/W |
| $T_r$ | Total thermal resistance | K.m/W |
| $T_{rad,ce}$ | Radiation thermal resistance, conductor to enclosure | K.m/W |
| $T_{rad,od}$ | Radiation thermal resistance, object to duct | K.m/W |
| $T_{rad,sa}$ | Radiation thermal resistance, surface to air | K.m/W |
| $T_{rad,sun}$ | Solar radiation thermal resistance | K.m/W |
| $T_{riser}$ | Thermal resistance of riser/J-tubes in air/water | K.m/W |
| $T_s$ | Star thermal resistance of object | K.m/W |
| $T_{sa}$ | Thermal resistance by convection, surface to air | K.m/W |
| $t_{sc}$ | Thickness of the screen | mm |
| $t_{scb}$ | Thickness of screen bedding | mm |
| $T_{scb}$ | Thermal resistance of screen bedding | K.m/W |
| $t_{scs}$ | Thickness of screen serving | mm |
| $T_{scs}$ | Thermal resistance of screen serving | K.m/W |
| $t_{sh}$ | Thickness of the sheath | mm |
| $t_{sha}$ | Total thickness between separate sheath and armour | mm |
| $t_{shj}$ | Thickness of sheath jacket | mm |
| $T_{shj}$ | Thermal resistance of sheath jacket | K.m/W |
| $t_{skid}$ | Thickness of skid wires | mm |
| $t_{sp}$ | Thickness of steel pipe | mm |
| $T_{spf}$ | Thermal resistance of steel pipe filling | K.m/W |
| $T_{st}$ | Radiation thermal resistance, surface to tunnel | K.m/W |
| $T_{surf}$ | Absolute surface temperature | K |
| $t_t$ | Wall thickness | m |
| $T_t$ | Star thermal resistance of tunnel | K.m/W |
| $T_{tot}$ | Total thermal resistance, transient | K.m/W |
| $T_{tr}$ | Thermal resistance of trough | K.m/W |
| $T_{tw}$ | Thermal resistance of tunnel wall | K.m/W |
| $T_{wall}$ | Thermal resistance of pipe wall | K.m/W |
| $\mathrm{tan} \delta_i$ | Loss factor of insulation | |
| $\tau$ | Transient load period | s |
| $\tau_{ar}$ | Armour angle | rad |
| $\tau_L$ | Transient load period for deep burial | s |
| $\theta_{2K}$ | Temperature rise for 2K criterion | °C |
| $\theta_a$ | Ambient temperature | °C |
| $\theta_{abs}$ | Absolute temperature | K |
| $\theta_{air}$ | Ambient air temperature | °C |
| $\theta_{ar}$ | Temperature of armour | °C |
| $\theta_{at}$ | Air temperature under load | °C |
| $\theta_{at,0}$ | Air temperature with no load | °C |
| $\theta_{at,i}$ | Air temperature of previous iteration cycle | °C |
| $\theta_{at,L}$ | Air temperature in tunnel at outlet | °C |
| $\theta_{at,max}$ | Maximal permissibe air temperature | °C |
| $\theta_{at,z}$ | Air temperature in tunnel at z | °C |
| $\theta_c$ | Temperature of conductor | °C |
| $\theta_{c,t,0}$ | Temperature of conductor at transient step | °C |
| $\theta_{c,z}$ | Conductor temperature at z | °C |
| $\theta_{cmax}$ | Max. conductor temperature | °C |
| $\theta_{cmaxeo}$ | Max. emergency overload conductor temperature | °C |
| $\theta_{cmaxsc}$ | Max. short-circuit conductor temperature | °C |
| $\theta_{cs}$ | Temperature over conductor screen | °C |
| $\theta_{de}$ | Temperature of duct outer wall | °C |
| $\theta_{di}$ | Temperature of duct inner wall | °C |
| $\theta_{dm}$ | Mean temperature of the medium in the duct | °C |
| $\theta_e$ | External temperature of the object | °C |
| $\theta_{encl}$ | Temperature of enclosure | °C |
| $\theta_f$ | Temperature of filler for multi-core cables type SS with sheath | °C |
| $\theta_{film}$ | Film temperature | °C |
| $\theta_{gas}$ | Gas temperature | °C |
| $\theta_{hs}$ | Temperature of heat source | °C |
| $\theta_{hsi}$ | Temperature of pipe insulation | °C |
| $\theta_{hsj}$ | Temperature of outer jacket | °C |
| $\theta_{hsp}$ | Temperature of pipe | °C |
| $\theta_i$ | Temperature of insulation | °C |
| $\theta_{kf}$ | Final temperature | °C |
| $\theta_{ki}$ | Initial temperature | °C |
| $\theta_{kmax}$ | Maximal temperature of non-insulation material | °C |
| $\theta_{max}$ | Temperature of conductor at end of emergency loading | °C |
| $\theta_o$ | Outer surface temperature | °C |
| $\theta_{o,L}$ | Temperature of the surface of object at outlet | °C |
| $\theta_{o,z}$ | Temperature of the surface of object at z | °C |
| $\theta_{omax}$ | Max. outer surface temperature | °C |
| $\theta_R$ | Rated current transient to steady-state ratio | |
| $\theta_s$ | Temperature of screen/sheath | °C |
| $\theta_{sc}$ | Temperature of screen | °C |
| $\theta_{sh}$ | Temperature of sheath | °C |
| $\theta_{sp}$ | Temperature of steel pipe | °C |
| $\theta_{spf}$ | Mean temperature of the medium in the steel pipe | °C |
| $\theta_{surf}$ | Surface temperature | °C |
| $\theta_t$ | Temperature of inner tunnel wall | °C |
| $\theta_{t,L}$ | Temperature of tunnel wall at outlet | °C |
| $\theta_{t,z}$ | Temperature of tunnel wall at z | °C |
| $\theta_{tm}$ | Mean temperature between surface and air in tunnel or trough | °C |
| $\theta_{to}$ | Temperature of outer tunnel wall | °C |
| $\theta_{to,z}$ | Temperature of outer tunnel wall at z | °C |
| $\theta_w$ | Water temperature | °C |
| $\theta_x$ | Critical soil temperature | °C |
| $TQ$ | Cable thermal time constant | s |
| U | $u$ | Substitution coefficient u | |
| $U_0$ | Base voltage for tests | kV |
| $u_b$ | Substitution coefficient u | |
| $U_{buried}$ | OHTC of fully buried pipe | W/(K.m$^2$) |
| $U_d$ | Constant U for cables in ducts | K.m/W |
| $U_e$ | Line-to-ground voltage | kV |
| $U_{exposed}$ | OHTC of part of pipe in contact with water | W/(K.m$^2$) |
| $U_{ground}$ | OHTC of part of pipe in contact with ground | W/(K.m$^2$) |
| $U_{inwall}$ | OHTC of inside film and pipe wall | W/(K.m$^2$) |
| $U_m$ | Highest voltage for equipment | kV |
| $U_n$ | Rated line-to-line voltage | kV |
| $U_o$ | Operating voltage | kV |
| $U_{OHTC}$ | Overall heat transfer coefficient | W/(K.m$^2$) |
| $u_p$ | Substitution coefficient u | |
| $U_p$ | Constant U for air-filled pipe with objects | K.m/W |
| $U_{partially}$ | OHTC of partially buried pipe | W/(K.m$^2$) |
| $U_{spf}$ | Constant U for pipe-type cables | K.m/W |
| $U_{ti}$ | Circumference of inner rectangular tunnel wall | m |
| $U_{wall}$ | OHTC of pipe wall | W/(K.m$^2$) |
| V | $v_4$ | Ratio thermal resistivity dry/moist soil | |
| $V_{air}$ | Air velocity | m/s |
| $V_{air,min}$ | Air velocity required to remove all heat by ventilation | m/s |
| $V_{comp}$ | Gas volume | m$^3$ |
| $V_d$ | Constant V for cables in ducts | K.m/W |
| $V_{drop}$ | Voltage drop | V/(A.m) |
| $V_{fluid}$ | Velocity of fluid | cm/s |
| $V_{gas}$ | Volume percentage of second gas | $\%$ |
| $V_p$ | Constant V for air-filled pipe with objects | K.m/W |
| $V_{spf}$ | Constant V for pipe-type cables | K.m/W |
| $V_w$ | Velocity of water | cm/s |
| W | $w_{a,1}$ | Width of flat wires of 1st armour | mm |
| $w_{a,2}$ | Width of flat wires of 2nd armour | mm |
| $W_{a,L}$ | Heat removed by air at outlet | W/m |
| $W_{a,z}$ | Heat removed by air at z | W/m |
| $W_{ar}$ | Armour losses | W/m |
| $w_{ar}$ | Width of armour | mm |
| $w_b$ | Width of the backfill | mm |
| $w_{b4}$ | Distance to lateral edge of multi-layer backfill | m |
| $W_c$ | Conductor losses | W/m |
| $W_{conv,ce}$ | Convection heat transfer, conductor to enclosure | W/m |
| $W_{conv,da}$ | Convection heat transfer, duct to air | W/m |
| $W_{conv,gd}$ | Convection heat transfer, gas to duct | W/m |
| $W_{conv,od}$ | Convection heat transfer, object to duct | W/m |
| $W_{conv,og}$ | Convection heat transfer, object to gas | W/m |
| $W_{conv,sa}$ | Convection heat transfer, surface to air | W/m |
| $W_d$ | Dielectric losses | W/m |
| $w_d$ | Volumetric density of dielectric losses | W/m$^3$ |
| $W_{d,DC}$ | Dielectric losses in HVDC cables | W/m |
| $W_{de}$ | Losses outside of riser/J-tube | W/m |
| $W_{di}$ | Losses between cable and riser/J-tube | W/m |
| $W_{duct}$ | Losses in duct | W/m |
| $W_{encl}$ | Enclosure losses | W/m |
| $W_h$ | Heat generated by external object | W/m |
| $W_{hs}$ | Heat dissipation of heat source | W/m |
| $W_I$ | Ohmic losses per phase | W/m |
| $W_{rad,ce}$ | Radiation heat transfer, conductor to enclosure | W/m |
| $W_{rad,da}$ | Radiation heat transfer, duct to air | W/m |
| $W_{rad,od}$ | Radiation heat transfer, object to duct | W/m |
| $W_{rad,sa}$ | Radiation heat transfer, surface to air | W/m |
| $W_s$ | Screen and sheath losses | W/m |
| $W_{sar}$ | Total loss in shield and magnetic armour | W/m |
| $w_{sc}$ | Width of flat screen wire | mm |
| $W_{sp}$ | Losses in steel pipe | W/m |
| $W_{sum}$ | Sum of total losses of all systems | W/m |
| $W_{sun}$ | Solar radiation heat transfer to surface | W/m |
| $W_{sys}$ | Total losses of the system | W/m |
| $W_t$ | Total losses per phase | W/m |
| $w_t$ | Inner width | m |
| $W_{tot}$ | Total losses per object | W/m |
| X | $X_0$ | Zero sequence reactance | $\Omega$/m |
| $X_{ar}$ | Self reactance of armour | $\Omega$/m |
| $x_b$ | Horizontal center of backfill | mm |
| $X_c$ | Self reactance of conductor | $\Omega$/m |
| $X_G$ | Factor $X_G$ | |
| $X_{G2}$ | Factor $X_{G2}$ | |
| $X_K$ | Factor $X_K$ | |
| $X_m$ | Mutual reactance between conductors | $\Omega$/m |
| $x_p$ | Factor for proximity effect of conductors | |
| $x_{pos}$ | Horizontal x-position of multi-layer backfill | m |
| $x_s$ | Factor for skin effect on conductor | |
| $X_s$ | Self reactance of screen/sheath | $\Omega$/m |
| $X_{S1}$ | Reactance section 1 | $\Omega$/m |
| $X_{S2}$ | Reactance section 2 | $\Omega$/m |
| $X_{S3}$ | Reactance section 3 | $\Omega$/m |
| $\xi_X$ | Parameter $\xi$ for calculation of loss factor | |
| Y | $Y$ | Admittance | S/m |
| $y_{2K}$ | Depth for 2K criterion | mm |
| $y_c$ | Skin and proximity effect factor for PAC/GIL conductor | |
| $Y_d$ | Constant Y for cables in ducts | K.m/W |
| $y_{encl}$ | Skin and proximity effect factor for PAC/GIL enclosure | |
| $Y_G$ | Factor $Y_G$ | |
| $Y_i$ | Ordinates of the loss-load cycle | p.u. |
| $Y_K$ | Factor $Y_K$ | |
| $y_p$ | Proximity effect factor of conductors | |
| $Y_p$ | Constant Y for air-filled pipe with objects | K.m/W |
| $y_s$ | Skin effect factor of conductor | |
| $Y_{spf}$ | Constant Y for pipe-type cables | K.m/W |
| Z | $Z_0$ | Zero sequence impedance | $\Omega$/m |
| $z_{ar,i}$ | Impedance of armour inner surface | $\Omega$/m |
| $z_{ar,m}$ | Mutual impedance of armour | $\Omega$/m |
| $z_{ar,o}$ | Impedance of armour outer surface | $\Omega$/m |
| $Z_{bs}$ | Installation constant Z | |
| $Z_c$ | Self impedance of phase conductor | $\Omega$/m |
| $z_c$ | Factor z to calculate skin effect coefficients for conductor | |
| $z_{cc}$ | Impedance of conductor | $\Omega$/m |
| $Z_{char}$ | Surge Impedance | $\Omega$ |
| $z_{cs}$ | Impedance of conductor | $\Omega$/m |
| $z_{e1}$ | Impedance of conductor outer surface | $\Omega$/m |
| $z_{e2}$ | Impedance of insulation between conductor and screen | $\Omega$/m |
| $z_{e3}$ | Impedance of shield inner surface | $\Omega$/m |
| $z_{e4}$ | Mutual impedance of shield | $\Omega$/m |
| $z_{e5}$ | Impedance of shield outer surface | $\Omega$/m |
| $z_{earth}$ | Impedance of earth return in ground | $\Omega$/m |
| $z_{encl}$ | Factor z to calculate skin effect coefficients for enclosure | |
| $z_h$ | Location of the heat source | m |
| $z_{int}$ | Impedance of conductor | $\Omega$/m |
| $Z_K$ | Factor $Z_K$ | |
| $z_{kp}$ | Impedance between cable k and p in ground | $\Omega$/m |
| $Z_m$ | Mutual impedance between conductor and metal screen | $\Omega$/m |
| $z_{max}$ | Logitudinal thermal limit distance | m |
| $Z_{neg}$ | Negative sequence impedance | $\Omega$/m |
| $z_{os}$ | Impedance of outersheath jacket | $\Omega$/m |
| $Z_{pos}$ | Positive sequence impedance | $\Omega$/m |
| $z_r$ | Location of the hottest point | m |
| $Z_s$ | Self impedance of metal screen | $\Omega$/m |
| $z_{sc,i}$ | Impedance of screen inner surface | $\Omega$/m |
| $z_{sc,m}$ | Mutual impedance of screen | $\Omega$/m |
| $z_{sc,o}$ | Impedance of screen outer surface | $\Omega$/m |
| $z_{sc,sh}$ | Impedance of insulation between screen and sheath | $\Omega$/m |
| $z_{sh,i}$ | Impedance of sheath inner surface | $\Omega$/m |
| $z_{sh,m}$ | Mutual impedance of sheath | $\Omega$/m |
| $z_{sh,o}$ | Impedance of sheath outer surface | $\Omega$/m |
| $z_{ss}$ | Impedance of conductor | $\Omega$/m |
| $Z_x$ | Equivalent mutual impedance between cables | $\Omega$/m |
| $\zeta_{ab}$ | Density of armour bedding material | g/cm$^3$ |
| $\zeta_{ar}$ | Density of armour material | g/cm$^3$ |
| $\zeta_c$ | Density of conductor material | g/cm$^3$ |
| $\zeta_f$ | Density of filler material | g/cm$^3$ |
| $\zeta_i$ | Density of insulation material | g/cm$^3$ |
| $\zeta_j$ | Density of jacket material | g/cm$^3$ |
| $\zeta_M$ | Density of material | g/cm$^3$ |
| $\zeta_{od}$ | Radiation shape factor for touching cables | |
| $\zeta_{sc}$ | Density of metallic screen material | g/cm$^3$ |
| $\zeta_{sh}$ | Density of metallic sheath material | g/cm$^3$ |
| $\zeta_{shj}$ | Density of jacket material over each core | g/cm$^3$ |
| $\zeta_{skid}$ | Density of metallic skid wire material | g/cm$^3$ |
| $\zeta_{soil}$ | Density of soil material | kg/m$^3$ |
| $\zeta_{sp}$ | Density of steel pipe | g/cm$^3$ |
| $\zeta_{tape}$ | Density of tapes | g/cm$^3$ |
| $\zeta_w$ | Density of water | kg/m$^3$ |
