| A | $a_{\mathrm{0}}$ | Coefficient a for partial transient temperature rise | 1/s |
| $a_{\mathrm{12}}$ | Distance between phase 1 and 2 | mm |
| $a_{\mathrm{23}}$ | Distance between phase 2 and 3 | mm |
| $a_{\mathrm{31}}$ | Distance between phase 3 and 1 | mm |
| $A_{\mathrm{a}}$ | Cross-sectional area of armour | mm² |
| $A_{\mathrm{a_{\mathrm{1}}}}$ | Cross-sectional area of 1st armour | mm² |
| $A_{\mathrm{a_{\mathrm{2}}}}$ | Cross-sectional area of 2nd armour | mm² |
| $A_{\mathrm{ab_{\mathrm{1}}}}$ | Cross-sectional area of 1st armour bedding | mm² |
| $A_{\mathrm{ab_{\mathrm{2}}}}$ | Cross-sectional area of 2nd armour bedding | mm² |
| $A_{\mathrm{c}}$ | Cross-sectional area of conductor | mm² |
| $a_{\mathrm{c}}$ | Skin and proximity effect coefficient a for GIL conductor | |
| $A_{\mathrm{comp}}$ | Cross-sectional area of compartment | m² |
| $a_{\mathrm{constr}}$ | Construction of armour | |
| $A_{\mathrm{d}}$ | Cross-sectional area of duct wall | mm² |
| $A_{\mathrm{d_{\mathrm{fill}}}}$ | Free cross-sectional area inside duct | mm² |
| $A_{\mathrm{encl}}$ | Cross-sectional area of enclosure | mm² |
| $a_{\mathrm{encl}}$ | Skin and proximity effect coefficient a for GIL enclosure | |
| $A_{\mathrm{f}}$ | Cross-sectional area of filler | mm² |
| $A_{\mathrm{fluid}}$ | Cross-sectional area of fluid | mm² |
| $A_{\mathrm{i}}$ | Cross-sectional area of insulation | mm² |
| $A_{\mathrm{ins}}$ | Cross-sectional area of insulation | mm² |
| $A_{\mathrm{j}}$ | Cross-sectional area of jacket | mm² |
| $A_{\mathrm{k}}$ | Thermal property constant A | (mm²/s)½ |
| $a_{\mathrm{m}}$ | Mean distance between the phases | mm |
| $A_{\mathrm{prot}}$ | Cross-sectional area of protective cover | mm² |
| $a_{\mathrm{S1}}$ | Length of 1st section (minor) | p.u. |
| $a_{\mathrm{S2}}$ | Length of 2nd section (medium) | p.u. |
| $a_{\mathrm{S3}}$ | Length of 3rd section (major) | p.u. |
| $A_{\mathrm{sc}}$ | Cross-sectional area of screen | mm² |
| $A_{\mathrm{scb}}$ | Cross-sectional area of screen beddig | mm² |
| $A_{\mathrm{scs}}$ | Cross-sectional area of screen serving | mm² |
| $A_{\mathrm{sh}}$ | Cross-sectional area of sheath | mm² |
| $a_{\mathrm{T}}$ | Distance a of multi-layer backfill | m |
| $A_{\mathrm{t}}$ | Cross-sectional area of the tunnel | m² |
| $A_{\mathrm{tube}}$ | Cross-sectional area of fluid-filled tube | mm² |
| $a_{\mathrm{VdW}}$ | Van der Walls constant a | bar.L²/mol² |
| $\alpha_{\mathrm{ar}}$ | Temperature coefficient of armour material | 1/K |
| $\alpha_{\mathrm{at}}$ | Heat transfer coefficient to channel wall | W/K/m² |
| $\alpha_{\mathrm{c}}$ | Temperature coefficient of conductor material | 1/K |
| $\alpha_{\mathrm{encl}}$ | Temperature coefficient of enclosure material | 1/K |
| $\alpha_{\mathrm{f}}$ | Phase shift | ° |
| $\alpha_{\mathrm{gas}}$ | Thermal diffusivity for gas | m²/s |
| $\alpha_{\mathrm{M}}$ | Factor αM | |
| $\alpha_{\mathrm{sc}}$ | Temperature coefficient of screen material | 1/K |
| $\alpha_{\mathrm{sh}}$ | Temperature coefficient of sheath material | 1/K |
| $\alpha_{\mathrm{surf}}$ | Heat transfer coefficient earth surface | W/K/m² |
| $\alpha_{\mathrm{t}}$ | Conductor to surface attainment factor | |
| B | $B$ | Susceptance | S/m |
| $b_{\mathrm{0}}$ | Coefficient b for partial transient temperature rise | 1/s |
| $B_{\mathrm{1_{\mathrm{1}}}}$ | Loss coefficient B1 of 1st armour | Ω/m |
| $B_{\mathrm{1_{\mathrm{2}}}}$ | Loss coefficient B1 of 2nd armour | Ω/m |
| $B_{\mathrm{2_{\mathrm{1}}}}$ | Loss coefficient B2 of 1st armour | Ω/m |
| $B_{\mathrm{2_{\mathrm{2}}}}$ | Loss coefficient B2 of 2nd armour | Ω/m |
| $b_{\mathrm{c}}$ | Skin and proximity effect coefficient b for GIL conductor | |
| $B_{\mathrm{EMF}}$ | Magnetic field strength | µT |
| $b_{\mathrm{encl}}$ | Skin and proximity effect coefficient b for GIL enclosure | |
| $B_{\mathrm{k}}$ | Thermal property constant B | mm²/s |
| $b_{\mathrm{T}}$ | Distance b of multi-layer backfill | m |
| $b_{\mathrm{VdW}}$ | Van der Walls constant b | L/mol |
| $b_{\mathrm{x}}$ | Shorter side of backfill | mm |
| $b_{\mathrm{y}}$ | Longer side of backfill | mm |
| $\beta_{\mathrm{1}}$ | Substitution coefficient β1 for eddy-currents | |
| $\beta_{\mathrm{6}}$ | Factor |1 - β(6)| | |
| $\beta_{\mathrm{a_{\mathrm{1}}}}$ | Angle between armour and cable axis | rad |
| $\beta_{\mathrm{a_{\mathrm{2}}}}$ | Angle between 2nd armour and cable axis | rad |
| $\beta_{\mathrm{air}}$ | Volumetric thermal expansion coefficient of air | 1/K |
| $\beta_{\mathrm{ar}}$ | Reciprocal of temperature coefficient of armour material | K |
| $\beta_{\mathrm{c}}$ | Reciprocal of temperature coefficient of conductor material | K |
| $\beta_{\mathrm{encl}}$ | Reciprocal of temperature coefficient of enclosure material | K |
| $\beta_{\mathrm{gas}}$ | Volumetric thermal expansion coefficient for gas | 1/K |
| $\beta_{\mathrm{k}}$ | Reciprocal of temperature coefficient of resistance | K |
| $\beta_{\mathrm{M}}$ | Factor βM | |
| $\beta_{\mathrm{sc}}$ | Reciprocal of temperature coefficient of screen material | K |
| $\beta_{\mathrm{sh}}$ | Reciprocal of temperature coefficient of sheath material | K |
| $\beta_{\mathrm{t}}$ | Attainment factor cable surface to ambient | |
| $\beta_{\mathrm{T}}$ | Equivalent thermal resistance of the soil per unit surface | W/K.m² |
| $\beta_{\mathrm{X}}$ | Crossing angle in radians | rad |
| $\beta_{\mathrm{xing}}$ | Crossing angle in degrees | ° |
| C | $C_{\mathrm{av}}$ | Heat capacity of the air flow | W/K |
| $C_{\mathrm{b}}$ | Capacitance of insulation | F/m |
| $c_{\mathrm{constr}}$ | Construction of conductor | |
| $c_{\mathrm{gas}}$ | Constant c for a gas under GIL conditions | |
| $c_{\mathrm{ij}}$ | Coefficient c for view factor | |
| $C_{\mathrm{k1}}$ | Non-adiabatic constant C1 | mm/m |
| $C_{\mathrm{k2}}$ | Non-adiabatic constant C2 | K.m.mm²/J |
| $C_{\mathrm{Nu}}$ | Factor C | |
| $c_{\mathrm{p_{\mathrm{gas}}}}$ | Specific heat capacity at constant pressure | J/kg.K |
| $C_{\mathrm{q}}$ | Constants C1 to C7 of multi-layer backfill | |
| $c_{\mathrm{SI}}$ | Surge velocity of propagation | km/s |
| $c_{\mathrm{T}}$ | Distance c of multi-layer backfill | m |
| $c_{\mathrm{v_{\mathrm{gas}}}}$ | Specific heat capacity at constant volume | J/kg.K |
| $C_{\mathrm{vair}}$ | Volumetric heat capacity of air | J/K.m³ |
| $CC$ | Charging capacity | kvar/km |
| $CC_{\mathrm{p}}$ | Conduit clearance | % |
| $CF_{\mathrm{p}}$ | Conduit fill | % |
| $CR_{\mathrm{p}}$ | Conduit ratio in duct | % |
| $cuw$ | Standard copper wires | mm |
| D | $D_{\mathrm{1}}$ | Diameter below screen | mm |
| $D_{\mathrm{2_{\mathrm{1}}}}$ | Diameter below 1st armour | mm |
| $D_{\mathrm{2_{\mathrm{2}}}}$ | Diameter below 2nd armour | mm |
| $d_{\mathrm{a}}$ | Mean diameter of armour | mm |
| $D_{\mathrm{a_{\mathrm{1}}}}$ | External diameter of 1st armour | mm |
| $d_{\mathrm{a_{\mathrm{1}}}}$ | Mean diameter of 1st armour | mm |
| $d_{\mathrm{a_{\mathrm{2}}}}$ | Mean diameter of 2nd armour | mm |
| $D_{\mathrm{a_{\mathrm{2}}}}$ | External diameter of 2nd armour | mm |
| $d_{\mathrm{b}}$ | Diameter of the backfill | mm |
| $d_{\mathrm{c}}$ | External diameter of conductor | mm |
| $D_{\mathrm{c}}$ | Diameter of conductor | m |
| $d_{\mathrm{ci}}$ | Internal diameter of conductor | mm |
| $D_{\mathrm{comp}}$ | Diameter of compartment (metric) | m |
| $d_{\mathrm{comp}}$ | Diameter of compartment | mm |
| $d_{\mathrm{ct}}$ | External diameter of conductor for transient calculations | mm |
| $D_{\mathrm{e}}$ | External diameter of object | mm |
| $d_{\mathrm{e}}$ | Diameter of sheath and armour | mm |
| $d_{\mathrm{encl}}$ | Outer diameter of enclosure | mm |
| $D_{\mathrm{encl}}$ | Outer diameter of enclosure (metric) | m |
| $D_{\mathrm{eq}}$ | Equivalent diameter of a group of cables | mm |
| $D_{\mathrm{f}}$ | External diameter of the filler | mm |
| $d_{\mathrm{f}}$ | Spacing from hottest object in group | m |
| $d_{\mathrm{f_{\mathrm{1}}}}$ | Thickness of 1st armour | mm |
| $d_{\mathrm{f_{\mathrm{2}}}}$ | Thickness of 2nd armour | mm |
| $D_{\mathrm{hs}}$ | External diameter of heat source | mm |
| $D_{\mathrm{i}}$ | Diameter over insulation | mm |
| $d_{\mathrm{im}}$ | Imaginary layer of soil | m |
| $d_{\mathrm{ins}}$ | Diameter of insulation around tube | mm |
| $D_{\mathrm{it}}$ | Diameter below sheath | mm |
| $D_{\mathrm{o}}$ | Outer diameter | m |
| $D_{\mathrm{oc}}$ | External diameter of sheath | mm |
| $d_{\mathrm{pk1}}$ | Distance to mirrored buried object | mm |
| $d_{\mathrm{pk2}}$ | Distance between buried objects | mm |
| $d_{\mathrm{prot}}$ | Diameter of protective cover | mm |
| $d_{\mathrm{psc}}$ | Point source correction | m |
| $D_{\mathrm{s}}$ | Mean external diameter of the sheath | mm |
| $d_{\mathrm{s}}$ | Mean diameter of screen/sheath | mm |
| $d_{\mathrm{sc}}$ | Mean diameter of screen | mm |
| $d_{\mathrm{sh}}$ | Mean diameter of sheath | mm |
| $d_{\mathrm{soil}}$ | Soil dry density | kg/m³ |
| $d_{\mathrm{t}}$ | Earth covering | m |
| $d_{\mathrm{T}}$ | Distance d of multi-layer backfill | m |
| $d_{\mathrm{x}}$ | Equivalent diameter of a conductor | mm |
| $D_{\mathrm{x}}$ | Characteristic diameter | mm |
| $D_{\mathrm{x_{\mathrm{w}}}}$ | Characteristic diameter for weekly load | mm |
| $D_{\mathrm{x_{\mathrm{y}}}}$ | Characteristic diameter for yearly load | mm |
| $DC_{\mathrm{p}}$ | Diameter factor in duct | % |
| $\Delta _{\mathrm{1}}$ | Substitution coefficient Δ1 for eddy-currents | |
| $\delta _{\mathrm{1}}$ | Thickness of screening layer | mm |
| $\Delta _{\mathrm{2}}$ | Substitution coefficient Δ2 for eddy-currents | |
| $\delta _{\mathrm{ar}}$ | Equivalent thickness of armour | mm |
| $\delta _{\mathrm{k}}$ | Thickness of screen, sheath or armour | mm |
| $\delta _{\mathrm{soil}}$ | Soil thermal diffusivity | m²/s |
| $\Delta d_{\mathrm{sh}}$ | Depth of corrugation | mm |
| $\Delta H_{\mathrm{c}}$ | Heat of combustion coefficient | MJ/kg |
| $\Delta t$ | Length of time step | s |
| $\Delta \theta_{\mathrm{0t}}$ | Air temperature in tunnel increase | K |
| $\Delta \theta_{\mathrm{0x}}$ | Temperature rise of the conductor | K |
| $\Delta \theta_{\mathrm{0x_{\mathrm{1}}}}$ | Temperature rise of the conductor, first estimate | K |
| $\Delta \theta_{\mathrm{0x_{\mathrm{h}}}}$ | Temperature rise of the conductor by source h | K |
| $\Delta \theta_{\mathrm{a_{\mathrm{t}}}}$ | Corrected transient temperature rise of conductor | K |
| $\Delta \theta_{\mathrm{air}}$ | Temperature increase of air | K |
| $\delta \theta_{\mathrm{c}}$ | Ohmic steady-state temperature rise | K |
| $\Delta \theta_{\mathrm{c}}$ | Temperature rise of conductor | K |
| $\Delta \theta_{\mathrm{c_{\mathrm{t}}}}$ | Transient temperature rise of conductor by ohmic losses | K |
| $\Delta \theta_{\mathrm{d}}$ | Temperature rise by dielectric losses | K |
| $\Delta \theta_{\mathrm{e_{\mathrm{t}}}}$ | Transient temperature rise of outer surface | K |
| $\Delta \theta_{\mathrm{gas}}$ | Temperature difference conductor-enclosure | °C |
| $\Delta \theta_{\mathrm{kp}}$ | Temperature rise by buried object k | K |
| $\Delta \theta_{\mathrm{max}}$ | Maximum permissible conductor temperature rise | K |
| $\Delta \theta_{\mathrm{p}}$ | Temperature rise by other buried objects | K |
| $\Delta \theta_{\mathrm{R}}$ | Conductor temperature rise above ambient temperature | K |
| $\Delta \theta_{\mathrm{R_{\mathrm{\infty}}}}$ | Maximum permissible conductor temperature rise | °C |
| $\Delta \theta_{\mathrm{s}}$ | Temperature difference surface to ambient | K |
| $\delta \theta_{\mathrm{SPK}}$ | Peak cyclic temperature rise | K |
| $\Delta \theta_{\mathrm{sun}}$ | Temperature rise by solar radiation | K |
| $\Delta \theta_{\mathrm{t}}$ | Transient temperature rise of conductor | K |
| $\Delta \theta_{\mathrm{t_{\mathrm{\infty}}}}$ | Steady-state temperature rise of conductor | K |
| $\Delta \theta_{\mathrm{x}}$ | Critical soil temperature rise | K |
| $\Delta W$ | Incremental heat generated | W |
| $\Delta W_{\mathrm{0}}$ | Incremental heat 0 generated | W |
| $\Delta z$ | Length of the interval | m |
| $DF_{\mathrm{X}}$ | Derating factor for the permissible current | |
| $Di_{\mathrm{d}}$ | Inner diameter of duct | mm |
| $Di_{\mathrm{t}}$ | Diameter of the tunnel (inner) | m |
| $di_{\mathrm{tube}}$ | Internal diameter of fluid-filled tube | mm |
| $Do_{\mathrm{d}}$ | Outer diameter of duct | mm |
| $Do_{\mathrm{t}}$ | Diameter of the tunnel or trough (outer) | m |
| $do_{\mathrm{tube}}$ | External diameter of fluid-filled tube | mm |
| E | $E_{\mathrm{bs}}$ | Installation constant E | |
| $e_{\mathrm{hor}}$ | Horizontal clearance | mm |
| $E_{\mathrm{stress}}$ | Electrical field strength | kV/mm |
| $e_{\mathrm{ver}}$ | Vertical clearance | mm |
| $e_{\mathrm{wall}}$ | Clearance to wall | mm |
| $EEC$ | Embodied energy and carbon | MJ/kg |
| $\epsilon_{\mathrm{0}}$ | Vacuum permittivity | F/m |
| $\epsilon_{\mathrm{c}}$ | Effective emissivity of conductor | |
| $\epsilon_{\mathrm{encl}}$ | Effective emissivity of enclosure | |
| $\epsilon_{\mathrm{gas}}$ | Dielectric constant of gas in compartment | |
| $\epsilon_{\mathrm{i}}$ | Relative permittivity of insulation | |
| $\epsilon_{\mathrm{k}}$ | Heat loss allowance factor | |
| $\epsilon_{\mathrm{prot}}$ | Effective emissivity of protective cover | |
| $\epsilon_{\mathrm{rad}}$ | Effective emissivity | |
| $\eta0_{\mathrm{gas}}$ | Reference dynamic viscosity of gas | Pa.s |
| $\eta_{\mathrm{gas}}$ | Dynamic viscosity of gas | Pa.s |
| F | $f$ | System frequency | Hz |
| $F_{\mathrm{a_{\mathrm{1}}}}$ | Effective length per unit lay length of 1st armour | mm |
| $F_{\mathrm{a_{\mathrm{2}}}}$ | Effective length per unit lay length of 2nd armour | mm |
| $F_{\mathrm{cable}}$ | Maximum effective pulling force | N/m |
| $f_{\mathrm{cb}}$ | Factor for cross-bonded earthing | |
| $F_{\mathrm{e}}$ | Factor Fe for eddy-current losses | |
| $F_{\mathrm{eq}}$ | Mutual heating coefficient | |
| $F_{\mathrm{form}}$ | Form factor | |
| $F_{\mathrm{ij}}$ | View factor object-object | |
| $F_{\mathrm{in}}$ | Pulling force at beginning of a section | daN |
| $F_{\mathrm{k}}$ | Imperfect contact thermal factor | |
| $F_{\mathrm{m}}$ | Radiation coefficient mutual | |
| $F_{\mathrm{out}}$ | Pulling force at end of a section | daN |
| $F_{\mathrm{ppc}}$ | Permissible pull force on cable | daN |
| $f_{\mathrm{ppc}}$ | Factor of permissible pull | N/mm² |
| $F_{\mathrm{pt}}$ | Function of pressure and temperature | |
| $f_{\mathrm{SHF}}$ | Sheath factor | |
| $F_{\mathrm{x}}$ | Geometrical distance factor for multi-core cables | |
| G | $g$ | Standard acceleration of gravity | m/s² |
| $G$ | Conductance | S/m |
| $G_{\mathrm{1}}$ | Geometric factor G1 | |
| $G_{\mathrm{2}}$ | Geometric factor G2 for cables with separate sheaths | |
| $G_{\mathrm{b}}$ | Geometric factor for backfill | |
| $g_{\mathrm{bs}}$ | Installation constant g | |
| $G_{\mathrm{encl}}$ | Factor G to calculate Nusselt number | |
| $g_{\mathrm{s}}$ | Substitution coefficient gs for eddy-currents | |
| $G_{\mathrm{s00}}$ | Factor Gs 0.0 | |
| $G_{\mathrm{s05}}$ | Factor Gs 0.5 | |
| $G_{\mathrm{s10}}$ | Factor Gs 1.0 | |
| $\gamma_{\mathrm{a}}$ | Armour angle | rad |
| $\gamma_{\mathrm{bessel}}$ | Bessel constant | p.u. |
| $\gamma_{\mathrm{c}}$ | Skin and proximity effect factor γ for GIL conductor | |
| $\gamma_{\mathrm{encl}}$ | Skin and proximity effect factor γ for GIL enclosure | |
| $\gamma_{\mathrm{euler}}$ | Euler's constant | m/s² |
| $\gamma_{\mathrm{t}}$ | Attainment factor for groups of cables | |
| $\gamma_{\mathrm{X}}$ | Attenuation factor for crossing | 1/m |
| $GMD$ | Geometric mean distance | mm |
| $GMR$ | Geometric mean radius | mm |
| $\mathrm{Gr}_{\mathrm{c}}$ | Grashof number conductor-gas | |
| $\mathrm{Gr}_{\mathrm{encl}}$ | Grashof number gas-enclosure | |
| $\mathrm{Gr}_{\mathrm{L}}$ | Grashof number | |
| $\mathrm{Gr}_{\mathrm{prot}}$ | Grashof number surface-air | |
| H | $h_{\mathrm{1}}$ | Factor h1 for emergency load | |
| $H_{\mathrm{1_{\mathrm{1}}}}$ | Component of inductance H1 | H/m |
| $H_{\mathrm{1_{\mathrm{2}}}}$ | Component of inductance H1 of 2nd armour | H/m |
| $H_{\mathrm{2_{\mathrm{1}}}}$ | Component of inductance H2 | H/m |
| $H_{\mathrm{2_{\mathrm{2}}}}$ | Component of inductance H2 of 2nd armour | H/m |
| $H_{\mathrm{3_{\mathrm{1}}}}$ | Component of inductance H3 | H/m |
| $H_{\mathrm{3_{\mathrm{2}}}}$ | Component of inductance H3 of 2nd armour | H/m |
| $h_{\mathrm{atm}}$ | Height above sea level | m |
| $h_{\mathrm{b}}$ | Height of the backfill | mm |
| $h_{\mathrm{bs}}$ | Heat dissipation coefficient for black surfaces in free air | W/m²/K5/4 |
| $H_{\mathrm{c}}$ | Heat energy content | MJ/m |
| $h_{\mathrm{c}}$ | Convective heat transfer coefficient conductor-gas | W/K.m² |
| $h_{\mathrm{encl}}$ | Convective heat transfer coefficient gas to enclosure | W/m2.K |
| $h_{\mathrm{lg}}$ | Ratio of heat dissipation coefficients | |
| $h_{\mathrm{prot}}$ | Convective heat transfer coefficient surface-air | W/K.m² |
| $h_{\mathrm{rad_{\mathrm{ce}}}}$ | Radiation heat transfer coefficient conductor-enclosure | W/K.m² |
| $h_{\mathrm{rad_{\mathrm{sa}}}}$ | Radiation heat transfer coefficient surface-air | W/K.m² |
| $h_{\mathrm{roll}}$ | Height of roller above bottom | m |
| $H_{\mathrm{s}}$ | Sheath conductance | H/m |
| $H_{\mathrm{sun}}$ | Intensity of solar radiation | W/m² |
| $H_{\mathrm{T}}$ | Trench depth to bedding layer in multi-layer backfill | m |
| $h_{\mathrm{t}}$ | Inner height | m |
| $h_{\mathrm{T4}}$ | Ratio of thermal resistance to ambient | |
| $H_{\mathrm{tc}}$ | Parameter H for trough | |
| $h_{\mathrm{tr}}$ | Heat transfer coefficient | W/K.m² |
| $H_{\mathrm{ts}}$ | Parameter H depending on air velocity | |
| $H_{\mathrm{x}}$ | Magnetic field x-component | mH |
| $H_{\mathrm{y}}$ | Magnetic field y-component | mH |
| I | $I_{\mathrm{1}}$ | Steady-state current before transient | A |
| $I_{\mathrm{2}}$ | Emergency load current | A |
| $I_{\mathrm{C}}$ | Capacitive load current | A/km |
| $I_{\mathrm{c}}$ | Conductor current | A |
| $I_{\mathrm{c_{\mathrm{max}}}}$ | Highest current load of line | A |
| $I_{\mathrm{c_{\mathrm{peak}}}}$ | Permissible peak cyclic load current | A |
| $I_{\mathrm{Ce}}$ | Capacitive earth short-circuit current | A/km |
| $I_{\mathrm{EMF}}$ | Phase current for EMF calculation | A |
| $I_{\mathrm{k}}$ | Permissible short-circuit current | kA |
| $I_{\mathrm{kAD}}$ | Short-circuit current (adiabatic) | kA |
| $I_{\mathrm{kSC}}$ | Effective short-circuit current | kA |
| $I_{\mathrm{method}}$ | Current calculation method | |
| $I_{\mathrm{R}}$ | Transient conductor current | A |
| $inst_{\mathrm{air}}$ | Installation in air | |
| $inst_{\mathrm{sea}}$ | Installation of subsea cables | |
| $inst_{\mathrm{t}}$ | Installation in air inside a room | |
| J | $j_{\mathrm{max}}$ | Phase angle range | ° |
| $JR_{\mathrm{p}}$ | Jam ratio in duct | % |
| K | $K$ | Screening factor | |
| $K_{\mathrm{0}}$ | Coefficient K for a gas under GIL conditions | |
| $K_{\mathrm{02}}$ | Factor K0.2 | |
| $K_{\mathrm{06}}$ | Factor K0.6 | |
| $k_{\mathrm{1}}$ | Thermal conductivity of surface layer | W/K.m |
| $K_{\mathrm{10}}$ | Factor K1.0 | |
| $k_{\mathrm{2}}$ | Thermal conductivity of mid backfill layer | W/K.m |
| $k_{\mathrm{3}}$ | Thermal conductivity of bedding layer | W/K.m |
| $k_{\mathrm{4}}$ | Thermal conductivity of soil | W/K.m |
| $K_{\mathrm{A}}$ | Coefficient K to calculate in air | |
| $k_{\mathrm{air}}$ | Thermal conductivity of air | W/m.K |
| $K_{\mathrm{BICC}}$ | Constant relating to conductor formation | |
| $k_{\mathrm{Boltzmann}}$ | Boltzmann constant | J/K |
| $k_{\mathrm{c}}$ | Thermal conductivity of conductor material | K.m/W |
| $K_{\mathrm{ce}}$ | Radiation shape factor conductor-enclosure | |
| $K_{\mathrm{cv}}$ | Convection factor | |
| $K_{\mathrm{E}}$ | Surface heat conductance | W/m² |
| $k_{\mathrm{encl}}$ | Thermal conductivity of enclosure | W/m.K |
| $k_{\mathrm{fluid}}$ | Thermal conductivity of fluid | W/m.K |
| $k_{\mathrm{gas}}$ | Thermal conductivity for gas | W/m.K |
| $K_{\mathrm{GMR}}$ | Geometric mean radius factor | |
| $k_{\mathrm{H}}$ | Heinhold characteristic diameter coefficient | |
| $k_{\mathrm{ins}}$ | Thermal conductivity of insulation | W/m.K |
| $K_{\mathrm{k}}$ | Specific short-circuit parameter | A.s½/mm² |
| $k_{\mathrm{l}}$ | Temperature rise factor in air | |
| $k_{\mathrm{LF}}$ | Load loss constant coefficient | p.u. |
| $k_{\mathrm{p}}$ | Proximity effect coefficient | |
| $k_{\mathrm{prot}}$ | Thermal conductivity of protective cover | W/m.K |
| $K_{\mathrm{r}}$ | Radiation shape factor to ambient | |
| $k_{\mathrm{r2}}$ | Temperature rise ratio δθSPK/δθc | p.u. |
| $k_{\mathrm{s}}$ | Skin effect coefficient | |
| $k_{\mathrm{sa}}$ | Convection factor acc. Heinhold | |
| $k_{\mathrm{t}}$ | Temperature rise ratio | p.u. |
| $K_{\mathrm{t}}$ | Effective emissivity of surface | |
| $k_{\mathrm{tube}}$ | Thermal conductivity of fluid-filled tube | W/m.K |
| $K_{\mathrm{vermeer}}$ | Constant Kvermeer for convection heat transfer | |
| $K_{\mathrm{x}}$ | Factor for fictitious diameter by Neher | |
| $k_{\mathrm{X}}$ | Number of heat sources crossing | |
| L | $L_{\mathrm{0}}$ | Reference length of the tunnel | m |
| $L_{\mathrm{1}}$ | Inductance of phase 1 | H/m |
| $L_{\mathrm{2}}$ | Inductance of phase 2 | H/m |
| $L_{\mathrm{3}}$ | Inductance of phase 3 | H/m |
| $L_{\mathrm{b}}$ | Vertical center of backfill | mm |
| $L_{\mathrm{c}}$ | Depth of laying of sources | mm |
| $L_{\mathrm{char}}$ | Characteristic length | |
| $L_{\mathrm{cm}}$ | Depth of laying | m |
| $L_{\mathrm{cni}}$ | Imaginary laying depth with non-isothermal earth surface | m |
| $L_{\mathrm{crit}}$ | Critical system length | km |
| $L_{\mathrm{deep}}$ | Equivalent depth for deep burial | m |
| $L_{\mathrm{earth}}$ | Equivalent depth of earth return path | p.u. |
| $L_{\mathrm{h}}$ | Depth of laying of crossing element | mm |
| $L_{\mathrm{p}}$ | Length of a section | m |
| $L_{\mathrm{r}}$ | Depth of laying of the rated object | mm |
| $L_{\mathrm{sys}}$ | System length | km |
| $L_{\mathrm{T}}$ | Length of the tunnel | m |
| $\lambda_{\mathrm{0}}$ | Substitution coefficient λ0 for eddy-currents | |
| $\lambda_{\mathrm{1}}$ | Loss factor of screen and sheath | |
| $\lambda_{\mathrm{1c}}$ | Loss factor by circulating currents | |
| $\lambda_{\mathrm{1cb}}$ | Loss factor for solid bonding | |
| $\lambda_{\mathrm{1e}}$ | Loss factor by eddy currents | |
| $\lambda_{\mathrm{1es}}$ | Loss factor for single point bonding | |
| $\lambda_{\mathrm{2}}$ | Loss factor of armour | |
| $\lambda_{\mathrm{3}}$ | Loss factor of steel pipes | |
| $\lambda_{\mathrm{d}}$ | Factor for dielectric losses | |
| $\lambda_{\mathrm{gas}}$ | Ratio cp/cv | |
| $\lambda_{\mathrm{t}}$ | Relaxation parameter | |
| $LF$ | Load factor | p.u. |
| $LF_{\mathrm{w}}$ | Weekly load factor | p.u. |
| $LF_{\mathrm{y}}$ | Yearly load factor | p.u. |
| $LME$ | London Metal Exchange | USD/mt |
| M | $M$ | Cyclic rating factor | p.u. |
| $m$ | Mass of object | kg/m |
| $M_{\mathrm{0}}$ | Coefficient M for partial transient temperature rise | s |
| $m_{\mathrm{0}}$ | Substitution coefficient m0 for eddy-currents | Hz.m/Ω |
| $M_{\mathrm{1}}$ | Corrected cyclic rating factor | K |
| $M_{\mathrm{ab}}$ | Material of armour bedding | |
| $M_{\mathrm{c}}$ | Material of conductor | |
| $M_{\mathrm{cable}}$ | List of materials in a cable | |
| $M_{\mathrm{comp}}$ | Insulating gas material | |
| $M_{\mathrm{d}}$ | Material of duct pipe | |
| $M_{\mathrm{e}}$ | Substitution coefficient Me to calculate factor $F_e$ | |
| $m_{\mathrm{EMF}}$ | Number of time steps | |
| $M_{\mathrm{encl}}$ | Material of enclosure | |
| $M_{\mathrm{f}}$ | Material of filler | |
| $M_{\mathrm{fluid}}$ | Fluid material | |
| $M_{\mathrm{gas}}$ | Gas and gas-mixtures | |
| $M_{\mathrm{i}}$ | Material of insulation | |
| $M_{\mathrm{IEEE}}$ | Materials acc. IEEE 442 | |
| $M_{\mathrm{ins}}$ | Material of insulation around tube | |
| $M_{\mathrm{j}}$ | Material of jacket | |
| $M_{\mathrm{k}}$ | Thermal contact factor | s½ |
| $m_{\mathrm{mol}}$ | Molecular mass | mol |
| $M_{\mathrm{mol}}$ | Molar mass | g/mol |
| $m_{\mathrm{Nu}}$ | Factor m | |
| $M_{\mathrm{prot}}$ | Material of protective cover | |
| $M_{\mathrm{s}}$ | Factor Ms | |
| $M_{\mathrm{sc}}$ | Material of screen | |
| $M_{\mathrm{sh}}$ | Material of sheath | |
| $M_{\mathrm{soil}}$ | Type of soils | |
| $M_{\mathrm{tube}}$ | Material of fluid-filled tube | |
| $\mu$ | Loss factor | p.u. |
| $\mu_{\mathrm{0}}$ | Vacuum permeability | H/m |
| $\mu_{\mathrm{e}}$ | Longitudinal relative permeability | |
| $\mu_{\mathrm{p}}$ | Friction coefficient | |
| $\mu_{\mathrm{s}}$ | Relative permeability | |
| $\mu_{\mathrm{t}}$ | Traverse relative permeability of steel wires | |
| $\mu_{\mathrm{w}}$ | Loss factor for weekly load variation | p.u. |
| $\mu_{\mathrm{y}}$ | Loss factor for yearly load variation | p.u. |
| N | $N_{\mathrm{0}}$ | Coefficient N for partial transient temperature rise | s² |
| $n_{\mathrm{a_{\mathrm{1}}}}$ | Number of wires of 1st armour | |
| $n_{\mathrm{a_{\mathrm{2}}}}$ | Number of wires of 2nd armour | |
| $N_{\mathrm{Avogrado}}$ | Avogadro constant | 1/mol |
| $N_{\mathrm{b}}$ | Number of loaded objects in backfill | |
| $N_{\mathrm{c}}$ | Number of sources in system | |
| $n_{\mathrm{c}}$ | Number of conductors in object | |
| $n_{\mathrm{cc}}$ | Number of conductors combined | |
| $n_{\mathrm{cg}}$ | Number of conductors in GIL | |
| $n_{\mathrm{cw}}$ | Number of wires in conductor | |
| $N_{\mathrm{e}}$ | Substitution coefficient Ne to calculate factor $F_e$ | |
| $n_{\mathrm{ppc}}$ | Number of conductors/cables being pulled | |
| $N_{\mathrm{sea}}$ | Number of subsea cables | |
| $N_{\mathrm{sum}}$ | Total number of objects in an air-filled space | |
| $n_{\mathrm{sw}}$ | Number of screen wires | |
| $n_{\mathrm{tube}}$ | Number of tubes in heatsource | |
| $N_{\mathrm{X}}$ | Number of intervals | |
| $\nu$ | Summation step 1 to $N_X$ | |
| $\nu_{\mathrm{air}}$ | Kinematic viscosity for air | m²/s |
| $\mathrm{Nu}_{\mathrm{c}}$ | Nusselt number conductor-gas | |
| $\mathrm{Nu}_{\mathrm{encl}}$ | Nusselt number gas-enclosure | |
| $\nu_{\mathrm{gas}}$ | Kinematic viscosity for gas | m²/s |
| $\mathrm{Nu}_{\mathrm{L}}$ | Nusselt number | |
| $\mathrm{Nu}_{\mathrm{prot}}$ | Nusselt number surface-air | |
| $\nu_{\mathrm{soil}}$ | Soil moisture content | % |
| O | $\omega$ | Angular frequency | rad/s |
| P | $p_{\mathrm{a_{\mathrm{1}}}}$ | Length of lay of 1st armour | mm |
| $p_{\mathrm{a_{\mathrm{2}}}}$ | Length of lay of 2nd armour | mm |
| $p_{\mathrm{ab1}}$ | Factor apportioning the 1st armour bedding | |
| $p_{\mathrm{ab2}}$ | Factor apportioning the 2nd armour bedding | |
| $p_{\mathrm{atm}}$ | Atmospheric air pressure | Pa |
| $p_{\mathrm{cb}}$ | Minor ratio of section lengths | |
| $P_{\mathrm{cc}}$ | Substitution coefficient P to calculate loss factor by circulating currents | |
| $p_{\mathrm{comp}}$ | Gas pressure in compartment | bar |
| $p_{\mathrm{gas}}$ | Gas pressure | Pa |
| $p_{\mathrm{i}}$ | Factor apportioning the insulation | |
| $p_{\mathrm{j}}$ | Factor apportioning the jacket | |
| $P_{\mathrm{L}}$ | Active power at load receptor | kW |
| $p_{\mathrm{soil}}$ | Depth of image source | |
| $p_{\mathrm{tr}}$ | Effective perimeter of trough | m |
| $p_{\mathrm{VdW}}$ | Van der Walls equation | Pa |
| $\phi_{\mathrm{b}}$ | Parameter φ for trough | |
| $\phi_{\mathrm{p}}$ | Angle of a bend | rad |
| $\pi$ | Archimedes' constant π | |
| $\mathrm{Pr}_{\mathrm{air}}$ | Prandtl number for air | |
| $\mathrm{Pr}_{\mathrm{gas}}$ | Prandtl number for gas | |
| Q | $q_{\mathrm{1}}$ | Ratio of losses affecting screen bedding/serving | |
| $q_{\mathrm{2_{\mathrm{1}}}}$ | Ratio of losses affecting 1st armour bedding | |
| $q_{\mathrm{2_{\mathrm{2}}}}$ | Ratio of losses affecting 2nd armour bedding | |
| $q_{\mathrm{3}}$ | Ratio of losses affecting jacket | |
| $q_{\mathrm{4}}$ | Ratio of losses affecting environment | |
| $Q_{\mathrm{A}}$ | Element A of two-part thermal circuit | J/m.K |
| $Q_{\mathrm{a_{\mathrm{1}}}}$ | Thermal capacitance of 1st armour | J/m.K |
| $Q_{\mathrm{a_{\mathrm{2}}}}$ | Thermal capacitance of 2nd armour | J/m.K |
| $Q_{\mathrm{ab_{\mathrm{1}}}}$ | Thermal capacitance of 1st armour bedding | J/m.K |
| $Q_{\mathrm{ab_{\mathrm{2}}}}$ | Thermal capacitance of 2nd armour bedding | J/m.K |
| $Q_{\mathrm{B}}$ | Element B of two-part thermal circuit | J/m.K |
| $Q_{\mathrm{B_{\mathrm{ab1}}}}$ | Element B of two-part thermal circuit, 1st armour bedding | J/m.K |
| $Q_{\mathrm{B_{\mathrm{ab2}}}}$ | Element B of two-part thermal circuit, 2nd armour bedding | J/m.K |
| $Q_{\mathrm{B_{\mathrm{d}}}}$ | Element B of two-part thermal circuit, duct | J/m.K |
| $Q_{\mathrm{B_{\mathrm{f}}}}$ | Element B of two-part thermal circuit, filler | J/m.K |
| $Q_{\mathrm{B_{\mathrm{i}}}}$ | Element B of two-part thermal circuit, insulation | J/m.K |
| $Q_{\mathrm{B_{\mathrm{j}}}}$ | Element B of two-part thermal circuit, jacket | J/m.K |
| $Q_{\mathrm{B_{\mathrm{s}}}}$ | Element B of two-part thermal circuit, screen/sheath | J/m.K |
| $Q_{\mathrm{c}}$ | Thermal capacitance of conductor | J/m.K |
| $q_{\mathrm{cb}}$ | Major ratio of section lengths | |
| $Q_{\mathrm{cc}}$ | Substitution coefficient Q to calculate loss factor by circulating currents | |
| $Q_{\mathrm{d}}$ | Thermal capacitance of duct wall | J/m.K |
| $Q_{\mathrm{d_{\mathrm{fill}}}}$ | Thermal capacitance of duct filling | J/m.K |
| $Q_{\mathrm{f}}$ | Thermal capacitance of filler | J/m.K |
| $q_{\mathrm{f}}$ | Ratio of losses affecting the filler | |
| $Q_{\mathrm{i}}$ | Thermal capacitance of insulation | J/m.K |
| $Q_{\mathrm{i1}}$ | Thermal capacitance of insulation, 1st portion | J/m.K |
| $Q_{\mathrm{i2}}$ | Thermal capacitance of insulation, 2nd portion | J/m.K |
| $Q_{\mathrm{j}}$ | Thermal capacitance of jacket | J/m.K |
| $Q_{\mathrm{p}}$ | Quantity of lubricant | l/m |
| $Q_{\mathrm{sc}}$ | Thermal capacitance of screen | J/m.K |
| $Q_{\mathrm{scb}}$ | Thermal capacitance of screen bedding | J/m.K |
| $Q_{\mathrm{scs}}$ | Thermal capacitance of screen serving | J/m.K |
| $Q_{\mathrm{sh}}$ | Thermal capacitance of sheath | J/m.K |
| $Q_{\mathrm{t}}$ | Total thermal capacitance, transient | J/m.K |
| $q_{\mathrm{x}}$ | Factor for characteristic diameter | |
| R | $R_{\mathrm{0}}$ | Zero sequence resistance | Ω/m |
| $R_{\mathrm{1}}$ | Resistance of conductor before emergency rating | Ω/m |
| $R_{\mathrm{A}}$ | Electrical resistance of armour | Ω/m |
| $R_{\mathrm{A_{\mathrm{1}}}}$ | Electrical resistance of 1st armour layer | Ω/m |
| $R_{\mathrm{A_{\mathrm{2}}}}$ | Electrical resistance of 2nd armour layer | Ω/m |
| $r_{\mathrm{b}}$ | Equivalent radius of backfill | mm |
| $r_{\mathrm{c}}$ | Radius of conductor | mm |
| $R_{\mathrm{c}}$ | Resistance of conductor | Ω/m |
| $R_{\mathrm{CG}}$ | Thermal resistance of multi-layer backfill | K.m/W |
| $R_{\mathrm{co}}$ | DC resistance of conductor at 20°C | Ω/m |
| $R_{\mathrm{e}}$ | Electrical resistance of sheath and armour | Ω/m |
| $R_{\mathrm{e_{\mathrm{1}}}}$ | Electrical resistance of sheath and 1st armour | Ω/m |
| $R_{\mathrm{e_{\mathrm{2}}}}$ | Electrical resistance of sheath and 2nd armour | Ω/m |
| $R_{\mathrm{earth}}$ | Equivalent resistance of earth return path | p.u. |
| $R_{\mathrm{encl}}$ | Electrical resistance of enclosure | Ω/m |
| $R_{\mathrm{encl20}}$ | DC resistance of enclosure at 20°C | Ω/m |
| $r_{\mathrm{F}}$ | Radius below the insulation | mm |
| $R_{\mathrm{gas}}$ | Specific gas constant | |
| $R_{\mathrm{gas0}}$ | Universal molar gas constant | |
| $r_{\mathrm{I}}$ | Radius of the insulation | mm |
| $r_{\mathrm{ij}}$ | Coefficient r for view factor | |
| $R_{\mathrm{max}}$ | Resistance of conductor at emergency rating | Ω/m |
| $r_{\mathrm{mbi}}$ | Minimal bending radius for installation | m |
| $r_{\mathrm{mbif}}$ | Factor of minimal installation bending radius | |
| $r_{\mathrm{mbp}}$ | Minimal bending radius during cable pulling | m |
| $r_{\mathrm{mbpf}}$ | Factor of minimal pulling bending radius | |
| $R_{\mathrm{p}}$ | Radius of a bend | m |
| $R_{\mathrm{q1}}$ | Thermal resistance 1 of multi-layer backfill method | K.m/W |
| $R_{\mathrm{q11}}$ | Thermal resistance 11 of multi-layer backfill method | K.m/W |
| $R_{\mathrm{q12}}$ | Thermal resistance 12 of multi-layer backfill method | K.m/W |
| $R_{\mathrm{q13}}$ | Thermal resistance 13 of multi-layer backfill method | K.m/W |
| $R_{\mathrm{q2}}$ | Thermal resistance 2 of multi-layer backfill method | K.m/W |
| $R_{\mathrm{q21}}$ | Thermal resistance 21 of multi-layer backfill method | K.m/W |
| $R_{\mathrm{q22}}$ | Thermal resistance 22 of multi-layer backfill method | K.m/W |
| $R_{\mathrm{q23}}$ | Thermal resistance 23 of multi-layer backfill method | K.m/W |
| $R_{\mathrm{q24}}$ | Thermal resistance 24 of multi-layer backfill method | K.m/W |
| $R_{\mathrm{q3}}$ | Thermal resistance 3 of multi-layer backfill method | K.m/W |
| $R_{\mathrm{q31}}$ | Thermal resistance 31 of multi-layer backfill method | K.m/W |
| $R_{\mathrm{q32}}$ | Thermal resistance 32 of multi-layer backfill method | K.m/W |
| $R_{\mathrm{q33}}$ | Thermal resistance 33 of multi-layer backfill method | K.m/W |
| $R_{\mathrm{q34}}$ | Thermal resistance 34 of multi-layer backfill method | K.m/W |
| $R_{\mathrm{s}}$ | Electrical resistance of screen||sheath | Ω/m |
| $R_{\mathrm{sc}}$ | Electrical resistance of screen | Ω/m |
| $R_{\mathrm{sh}}$ | Electrical resistance of sheath | Ω/m |
| $R_{\mathrm{so}}$ | Resistance of screen and sheath at 20°C | Ω/m |
| $r_{\mathrm{x}}$ | Radius to point x in insulation | mm |
| $\mathrm{Ra}_{\mathrm{c}}$ | Rayleigh number conductor-gas | |
| $\mathrm{Ra}_{\mathrm{encl}}$ | Rayleigh number gas-enclosure | |
| $\mathrm{Ra}_{\mathrm{L}}$ | Rayleigh number | |
| $\mathrm{Ra}_{\mathrm{prot}}$ | Rayleigh number surface-air | |
| $\mathrm{Re}_{\mathrm{air}}$ | Reynolds number for air | |
| $RF$ | Reduction factor | |
| $\rho_{\mathrm{4}}$ | Thermal resistivity of soil | K.m/W |
| $\rho_{\mathrm{4d}}$ | Thermal resistivity of dry soil | K.m/W |
| $\rho_{\mathrm{ab}}$ | Thermal resistivity of armour bedding | K.m/W |
| $\rho_{\mathrm{ab_{\mathrm{2}}}}$ | Thermal resistivity of bedding between armour layers | K.m/W |
| $\rho_{\mathrm{ar}}$ | Specific electrical resistivity of armour material | Ω.m |
| $\rho_{\mathrm{b}}$ | Thermal resistivity backfill | K.m/W |
| $\rho_{\mathrm{b1}}$ | Thermal resistivity of surface layer | K.m/W |
| $\rho_{\mathrm{b2}}$ | Thermal resistivity of mid backfill layer | K.m/W |
| $\rho_{\mathrm{c}}$ | Electrical resistivity of conductor material | Ω.m |
| $\rho_{\mathrm{corr}}$ | Thermal resistivity of corrugation filling | K.m/W |
| $\rho_{\mathrm{cr}}$ | Thermal resistivity of conductor material | K.m/W |
| $\rho_{\mathrm{d}}$ | Thermal resistivity of duct material | K.m/W |
| $\rho_{\mathrm{d_{\mathrm{fill}}}}$ | Thermal resistivity of bentonite filling | K.m/W |
| $\rho_{\mathrm{earth}}$ | Specific electrical resistivity of soil | Ω.m |
| $\rho_{\mathrm{encl}}$ | Specific electrical resistivity of enclosure material | Ω.m |
| $\rho_{\mathrm{f}}$ | Thermal resistivity of filler | K.m/W |
| $\rho_{\mathrm{gas}}$ | Gas density | kg/m³ |
| $\rho_{\mathrm{i}}$ | Thermal resistivity of insulation | K.m/W |
| $\rho_{\mathrm{j}}$ | Thermal resistivity of jacket material | K.m/W |
| $\rho_{\mathrm{k2}}$ | Thermal resistivity of the layer located above | K.m/W |
| $\rho_{\mathrm{k20}}$ | Electrical resistivity of metallic component | Ω.m |
| $\rho_{\mathrm{k3}}$ | Thermal resistivity of the layer located below | K.m/W |
| $\rho_{\mathrm{ki}}$ | Thermal resistivity of adjacent material | K.m/W |
| $\rho_{\mathrm{m}}$ | Thermal resistivity of the screen | K.m/W |
| $\rho_{\mathrm{sc}}$ | Specific electrical resistivity of screen material | Ω.m |
| $\rho_{\mathrm{sh}}$ | Specific electrical resistivity of sheath material | Ω.m |
| $\rho_{\mathrm{t}}$ | Thermal resistivity of wall | K.m/W |
| S | $s_{\mathrm{1}}$ | Thickness of surface layer | m; |
| $s_{\mathrm{2}}$ | Thickness of mid backfill layer | m² |
| $s_{\mathrm{3}}$ | Thickness from object to upper boundary of bedding layer | m² |
| $s_{\mathrm{4}}$ | Thickness from object to lower boundary of bedding layer | m² |
| $s_{\mathrm{air}}$ | Axial spacing between objects | m |
| $s_{\mathrm{c}}$ | Separation of conductors in a system | mm |
| $S_{\mathrm{G}}$ | Apparent power at injecting point | kVA |
| $S_{\mathrm{gas}}$ | Sutherland's constant | K |
| $s_{\mathrm{ij}}$ | Spacing between object i and j | |
| $S_{\mathrm{k}}$ | Cross-sectional area of current carrying component | mm² |
| $s_{\mathrm{roll}}$ | Roller distance | m |
| $s_{\mathrm{S1}}$ | Spacing between phases in 1st section | p.u. |
| $s_{\mathrm{S2}}$ | Spacing between phases in 2nd section | p.u. |
| $s_{\mathrm{S3}}$ | Spacing between phases in 3rd section | p.u. |
| $s_{\mathrm{T}}$ | Distance to lateral edge of multi-layer backfill | m |
| $SI$ | Surge Impedance | Ω |
| $\sigma$ | Stefan Boltzmann constant | W/m²K4 |
| $\sigma_{\mathrm{ab}}$ | Specific heat capacity of armour bedding | J/K.m³ |
| $\sigma_{\mathrm{ar}}$ | Specific heat capacity of armour material | J/K.m³ |
| $\sigma_{\mathrm{c}}$ | Specific heat capacity of conductor material | J/K.m³ |
| $\sigma_{\mathrm{d}}$ | Specific heat capacity of duct material | J/K.m³ |
| $\sigma_{\mathrm{d_{\mathrm{fill}}}}$ | Specific heat capacity of duct filling | J/K.m³ |
| $\sigma_{\mathrm{encl}}$ | Specific heat capacity of enclosure material | J/K.m³ |
| $\sigma_{\mathrm{f}}$ | Specific heat capacity of filler | J/K.m³ |
| $\sigma_{\mathrm{fluid}}$ | Specific heat capacity of fluid | J/K.m³ |
| $\sigma_{\mathrm{i}}$ | Specific heat capacity of insulation material | J/K.m³ |
| $\sigma_{\mathrm{ins}}$ | Specific heat capacity of insulation | J/K.m³ |
| $\sigma_{\mathrm{j}}$ | Specific heat capacity of jacket material | J/K.m³ |
| $\sigma_{\mathrm{k2}}$ | Specific heat capacity of layer located below | J/K.m³ |
| $\sigma_{\mathrm{k3}}$ | Specific heat capacity of layer located above | J/K.m³ |
| $\sigma_{\mathrm{kc}}$ | Specific heat capacity of metallic component | J/K.m³ |
| $\sigma_{\mathrm{ki}}$ | Specific heat capacity of adjacent material | J/K.m³ |
| $\sigma_{\mathrm{prot}}$ | Specific heat capacity of protective cover | J/K.m³ |
| $\sigma_{\mathrm{sc}}$ | Specific heat capacity of screen material | J/K.m³ |
| $\sigma_{\mathrm{scb}}$ | Specific heat capacity of screen bedding | J/K.m³ |
| $\sigma_{\mathrm{scs}}$ | Specific heat capacity of screen serving | J/K.m³ |
| $\sigma_{\mathrm{sh}}$ | Specific heat capacity of sheath material | J/K.m³ |
| $\sigma_{\mathrm{sun}}$ | Absorption coefficient of solar radiation | |
| $\sigma_{\mathrm{tube}}$ | Specific heat capacity of fluid-filled tube | J/K.m³ |
| $\sigma_{\mathrm{y}}$ | Yield strength of metals for armour | MPa |
| $SP_{\mathrm{p}}$ | Sidewall pressure | N/m |
| T | $t$ | Thickness of insulation between conductors | mm |
| $T0_{\mathrm{gas}}$ | Gas reference temperature | K |
| $t_{\mathrm{1}}$ | Thickness of insulation to sheath | mm |
| $T_{\mathrm{1}}$ | Thermal resistance between one conductor and sheath | K.m/W |
| $t_{\mathrm{1t}}$ | Thickness of insulation to sheath, transient | mm |
| $T_{\mathrm{1t}}$ | Thermal resistance between one conductor and sheath, transient | K.m/W |
| $T_{\mathrm{2}}$ | Thermal resistance between sheath and armour | K.m/W |
| $t_{\mathrm{2}}$ | Thickness of bedding under armour | mm |
| $T_{\mathrm{2_{\mathrm{1}}}}$ | Thermal resistance between sheath and 1st armour layer | K.m/W |
| $T_{\mathrm{2_{\mathrm{2}}}}$ | Thermal resistance of material between armour layers | K.m/W |
| $T_{\mathrm{2_{\mathrm{f}}}}$ | Thermal resistance between sheath and armour bedding | K.m/W |
| $T_{\mathrm{3}}$ | Thermal resistance of jacket | K.m/W |
| $t_{\mathrm{3}}$ | Thickness of serving over armour | mm |
| $T_{\mathrm{4d}}$ | Transient thermal resistance for daily load | K.m/W |
| $T_{\mathrm{4db}}$ | Correction of thermal resistance for backfill | K.m/W |
| $T_{\mathrm{4i}}$ | Thermal resistance of medium in the duct | K.m/W |
| $T_{\mathrm{4ii}}$ | Thermal resistance of the duct wall | K.m/W |
| $T_{\mathrm{4iii}}$ | Thermal resistance to ambient | K.m/W |
| $T_{\mathrm{4\mu}}$ | Thermal resistance to ambient | K.m/W |
| $T_{\mathrm{4ss}}$ | Steady-state thermal resistance | K.m/W |
| $T_{\mathrm{4t}}$ | Equivalent thermal resistance for tunnel | K.m/W |
| $T_{\mathrm{4w}}$ | Transient thermal resistance for weekly load | K.m/W |
| $T_{\mathrm{4y}}$ | Transient thermal resistance for yearly load | K.m/W |
| $T_{\mathrm{a}}$ | Star thermal resistance of air | K.m/W |
| $T_{\mathrm{A}}$ | Element A of equivalent thermal circuit | K.m/W |
| $T_{\mathrm{a0}}$ | Apparent thermal resistance a | K.m/W |
| $t_{\mathrm{ab_{\mathrm{1}}}}$ | Thickness of 1st armour bedding | mm |
| $t_{\mathrm{ab_{\mathrm{2}}}}$ | Thickness of armour separation | mm |
| $T_{\mathrm{air}}$ | Absolute air temperature | K |
| $T_{\mathrm{at}}$ | Thermal resistance by convection air-tunnel | K.m/W |
| $T_{\mathrm{B}}$ | Element B of equivalent thermal circuit | K.m/W |
| $T_{\mathrm{b0}}$ | Apparent thermal resistance b | K.m/W |
| $t_{\mathrm{c}}$ | Thickness of hollow conductor | mm |
| $T_{\mathrm{C}}$ | Element C of equivalent thermal circuit | K.m/W |
| $t_{\mathrm{comp}}$ | Thickness of compartment | mm |
| $T_{\mathrm{conv_{\mathrm{ce}}}}$ | Thermal resistance by convection conductor-enclosure | K.m/W |
| $T_{\mathrm{conv_{\mathrm{sa}}}}$ | Thermal resistance by convection surface-air | K.m/W |
| $t_{\mathrm{corr}}$ | Thickness of corrugation filling | mm |
| $t_{\mathrm{cs}}$ | Thickness of conductor shield | mm |
| $t_{\mathrm{ct}}$ | Thickness of s.c. tape wrapped around conductor | mm |
| $T_{\mathrm{d}}$ | Internal thermal resistance for dielectric losses | K.m/W |
| $T_{\mathrm{e}}$ | External thermal resistance of tunnel | K.m/W |
| $t_{\mathrm{EMF}}$ | Time step to calculate current source | s |
| $t_{\mathrm{encl}}$ | Thickness of enclosure | mm |
| $T_{\mathrm{eq}}$ | Equivalent thermal resistance | K.m/W |
| $T_{\mathrm{f}}$ | Axial thermal resistance due to the movement of air through the tunnel | K.m/W |
| $t_{\mathrm{f}}$ | Thickness of filler/belt insulation | mm |
| $T_{\mathrm{gas}}$ | Absolute gas temperature | K |
| $T_{\mathrm{i}}$ | Internal thermal resistance for current losses | K.m/W |
| $t_{\mathrm{i}}$ | Thickness of core insulation | mm |
| $T_{\mathrm{\infty}}$ | Infinite bulk temperature (the ambient air temperature) | K |
| $t_{\mathrm{ins}}$ | Thickness of insulation | mm |
| $t_{\mathrm{is}}$ | Thickness of insulation screen | mm |
| $t_{\mathrm{j}}$ | Thickness of jacket | mm |
| $t_{\mathrm{jj}}$ | Thickness of additional layer over jacket | mm |
| $t_{\mathrm{k}}$ | Duration of short-circuit | s |
| $T_{\mathrm{L}}$ | Thermal longitudinal resistance | K.m/W |
| $T_{\mathrm{mh}}$ | Mutual thermal resistance between rated and crossing object | K.m/W |
| $T_{\mathrm{mh_{\mathrm{v}}}}$ | Mutual thermal resistance per slice | K.m/W |
| $T_{\mathrm{o}}$ | Thermal resistance of the oil in the pipe | K.m/W |
| $T_{\mathrm{prot}}$ | Thermal resistance of protective cover | K.m/W |
| $t_{\mathrm{prot}}$ | Thickness of protective cover | mm |
| $T_{\mathrm{r}}$ | Total thermal resistance | K.m/W |
| $T_{\mathrm{rad_{\mathrm{ce}}}}$ | Radiation thermal resistance conductor-enclosure | K.m/W |
| $T_{\mathrm{rad_{\mathrm{sa}}}}$ | Radiation thermal resistance surface-air | K.m/W |
| $T_{\mathrm{rad_{\mathrm{sun}}}}$ | Solar radiation thermal resistance | K.m/W |
| $T_{\mathrm{s}}$ | Star thermal resistance of object | K.m/W |
| $T_{\mathrm{sa}}$ | Thermal resistance by convection surface-air | K.m/W |
| $t_{\mathrm{sc}}$ | Thickness of the screen | mm |
| $t_{\mathrm{scb}}$ | Thickness of screen bedding | mm |
| $t_{\mathrm{scs}}$ | Thickness of screen serving | mm |
| $t_{\mathrm{sh}}$ | Thickness of the sheath | mm |
| $T_{\mathrm{st}}$ | Radiation thermal resistance surface-tunnel | K.m/W |
| $T_{\mathrm{surf}}$ | Absolute surface temperature | K |
| $t_{\mathrm{t}}$ | Tunnel wall thickness | m |
| $T_{\mathrm{t}}$ | Star thermal resistance of tunnel | K.m/W |
| $T_{\mathrm{tot}}$ | Total thermal resistance, transient | K.m/W |
| $T_{\mathrm{tr}}$ | Thermal resistance of trough | K |
| $T_{\mathrm{tw}}$ | Thermal resistance of tunnel wall | K.m/W |
| $\mathrm{tan}\delta _{\mathrm{i}}$ | Loss factor of insulation | |
| $\tau$ | Transient load period | s |
| $\theta_{\mathrm{2K}}$ | Temperature rise for 2K criterion | °C |
| $\theta_{\mathrm{a}}$ | Ambient temperature | °C |
| $\theta_{\mathrm{abs}}$ | Absolute temperature | K |
| $\theta_{\mathrm{air}}$ | Ambient air temperature | °C |
| $\theta_{\mathrm{ar}}$ | Temperature of armour | °C |
| $\theta_{\mathrm{ar_{\mathrm{1}}}}$ | Temperature of 1st armour layer | °C |
| $\theta_{\mathrm{ar_{\mathrm{2}}}}$ | Temperature of 2nd armour layer | °C |
| $\theta_{\mathrm{at}}$ | Air temperature | °C |
| $\theta_{\mathrm{at_{\mathrm{0}}}}$ | Air temperature in tunnel at inlet | °C |
| $\theta_{\mathrm{at_{\mathrm{i}}}}$ | Air temperature of previous iteration cycle | °C |
| $\theta_{\mathrm{at_{\mathrm{L}}}}$ | Air temperature in tunnel at outlet | °C |
| $\theta_{\mathrm{at_{\mathrm{z}}}}$ | Air temperature in tunnel at z | °C |
| $\theta_{\mathrm{c}}$ | Temperature of conductor | °C |
| $\theta_{\mathrm{c_{\mathrm{z}}}}$ | Conductor temperature at z | °C |
| $\theta_{\mathrm{cmax}}$ | Max. conductor temperature | °C |
| $\theta_{\mathrm{cmaxeo}}$ | Max. emergency overload conductor temperature | °C |
| $\theta_{\mathrm{cmaxsc}}$ | Max. short-circuit conductor temperature | °C |
| $\theta_{\mathrm{de}}$ | Temperature of duct outer wall | °C |
| $\theta_{\mathrm{di}}$ | Temperature of duct inner wall | °C |
| $\theta_{\mathrm{dm}}$ | Mean temperature of the medium in the duct | °C |
| $\theta_{\mathrm{e}}$ | External temperature of the object | °C |
| $\theta_{\mathrm{encl}}$ | Temperature of enclosure | °C |
| $\theta_{\mathrm{f}}$ | Temperature of filler for multi-core cables type SS with sheath | °C |
| $\theta_{\mathrm{gas}}$ | Gas temperature | °C |
| $\theta_{\mathrm{hs}}$ | Temperature of heat source | °C |
| $\theta_{\mathrm{kf}}$ | Final temperature | °C |
| $\theta_{\mathrm{ki}}$ | Initial temperature | °C |
| $\theta_{\mathrm{kmax}}$ | Maximal temperature of non-insulation material | °C |
| $\theta_{\mathrm{max}}$ | Temperature of conductor at end of emergency loading | °C |
| $\theta_{\mathrm{o}}$ | Outer temperature | °C |
| $\theta_{\mathrm{o_{\mathrm{L}}}}$ | Temperature of the surface of object at outlet | °C |
| $\theta_{\mathrm{o_{\mathrm{z}}}}$ | Temperature of the surface of object at z | °C |
| $\theta_{\mathrm{p}}$ | Angle to the plane of a section | rad |
| $\theta_{\mathrm{R}}$ | Rated current transient to steady-state ratio | |
| $\theta_{\mathrm{s}}$ | Temperature of screen/sheath | °C |
| $\theta_{\mathrm{sc}}$ | Temperature of screen | °C |
| $\theta_{\mathrm{sh}}$ | Temperature of sheath | °C |
| $\theta_{\mathrm{surf}}$ | Surface temperature | °C |
| $\theta_{\mathrm{t}}$ | Temperature of inner tunnel wall | °C |
| $\theta_{\mathrm{t_{\mathrm{L}}}}$ | Temperature of tunnel wall at outlet | °C |
| $\theta_{\mathrm{t_{\mathrm{z}}}}$ | Temperature of tunnel wall at z | °C |
| $\theta_{\mathrm{tm}}$ | Air temperature in channel | °C |
| $\theta_{\mathrm{to}}$ | Temperature of outer tunnel wall | °C |
| $\theta_{\mathrm{to_{\mathrm{z}}}}$ | Temperature of outer tunnel wall at z | °C |
| $\theta_{\mathrm{x}}$ | Critical soil temperature | °C |
| $TQ$ | Cable thermal time constant | s |
| U | $u$ | Substitution coefficient u | |
| $U_{\mathrm{0}}$ | Value of U0 for determination of test voltages | kV |
| $U_{\mathrm{d}}$ | Constant U for cables in ducts | K.m/W |
| $U_{\mathrm{e}}$ | Line-to-ground voltage | kV |
| $U_{\mathrm{m}}$ | Highest voltage for equipment | kV |
| $U_{\mathrm{n}}$ | Rated line-to-line voltage | kV |
| $U_{\mathrm{o}}$ | Operating voltage | kV |
| $U_{\mathrm{ti}}$ | Circumference of inner rectangular tunnel wall | m |
| V | $v_{\mathrm{4}}$ | Ratio of the thermal resistivities of dry and moist soils | |
| $V_{\mathrm{air}}$ | Air velocity | m/s |
| $V_{\mathrm{comp}}$ | Gas volume | m³ |
| $V_{\mathrm{d}}$ | Constant V for cables in ducts | K.m/W |
| $V_{\mathrm{drop}}$ | Voltage drop | V/A/km |
| $V_{\mathrm{gas}}$ | Volume percentage of second gas | % |
| $V_{\mathrm{m}}$ | Molar volume | m³/mol |
| W | $W_{\mathrm{A}}$ | Armour losses | W/m |
| $W_{\mathrm{a_{\mathrm{L}}}}$ | Heat removed by air at outlet | W/m |
| $W_{\mathrm{a_{\mathrm{z}}}}$ | Heat removed by air at z | W/m |
| $w_{\mathrm{b}}$ | Width of the backfill | mm |
| $W_{\mathrm{c}}$ | Conductor losses | W/m |
| $W_{\mathrm{conv_{\mathrm{ce}}}}$ | Convection heat transfer conductor-enclosure | W/m |
| $W_{\mathrm{conv_{\mathrm{sa}}}}$ | Convection heat transfer surface-air | W/m |
| $W_{\mathrm{d}}$ | Dielectric losses | W/m |
| $W_{\mathrm{encl}}$ | Enclosure losses | W/m |
| $w_{\mathrm{f_{\mathrm{1}}}}$ | Width of flat wires of 1st armour | mm |
| $w_{\mathrm{f_{\mathrm{2}}}}$ | Width of flat wires of 2nd armour | mm |
| $W_{\mathrm{h}}$ | Heat generated by external object | W/m |
| $W_{\mathrm{hs}}$ | Heat dissipation of heat source | W/m |
| $W_{\mathrm{I}}$ | Ohmic losses per phase | W/m |
| $w_{\mathrm{p}}$ | Weight correction factor | |
| $W_{\mathrm{p}}$ | Losses in ferromagnetic steel pipe | W/m |
| $W_{\mathrm{rad_{\mathrm{ce}}}}$ | Radiation heat transfer conductor-enclosure | W/m |
| $W_{\mathrm{rad_{\mathrm{sa}}}}$ | Radiation heat transfer surface-air | W/m |
| $W_{\mathrm{s}}$ | Screen and sheath losses | W/m |
| $W_{\mathrm{sA}}$ | Total loss in sheath and armour | W/m |
| $W_{\mathrm{sA_{\mathrm{1}}}}$ | Total loss in sheath and 1st armour | W/m |
| $W_{\mathrm{sA_{\mathrm{2}}}}$ | Total loss in sheath and 2nd armour | W/m |
| $w_{\mathrm{sc}}$ | Width of flat screen wire | mm |
| $W_{\mathrm{sum}}$ | Sum of total losses of all systems | W/m |
| $W_{\mathrm{sun}}$ | Solar radiation heat transfer to surface | W/m |
| $W_{\mathrm{sys}}$ | Total losses of the system | W/m |
| $W_{\mathrm{T}}$ | Trench width in multi-layer backfill | m |
| $W_{\mathrm{t}}$ | Total losses per phase | W/m |
| $w_{\mathrm{t}}$ | Inner width | m |
| $W_{\mathrm{tot}}$ | Total losses per object | W/m |
| X | $X_{\mathrm{0}}$ | Zero sequence reactance | Ω/m |
| $x_{\mathrm{b}}$ | Horizontal center of backfill | mm |
| $X_{\mathrm{c}}$ | Self reactance of conductor | Ω/m |
| $X_{\mathrm{G}}$ | Factor XG | |
| $X_{\mathrm{G2}}$ | Factor XG2 | |
| $X_{\mathrm{K}}$ | Factor XK | |
| $X_{\mathrm{m}}$ | Mutual reactance between cables | Ω/m |
| $x_{\mathrm{p}}$ | Factor for proximity effect of conductors | |
| $x_{\mathrm{pos}}$ | Horizontal x-position in multi-layer backfill | mm |
| $X_{\mathrm{s}}$ | Self reactance of screen/sheath | Ω/m |
| $x_{\mathrm{s}}$ | Factor for skin effect on conductor | |
| $X_{\mathrm{S1}}$ | Reactance section 1 | Ω/m |
| $X_{\mathrm{S2}}$ | Reactance section 2 | Ω/m |
| $X_{\mathrm{S3}}$ | Reactance section 3 | Ω/m |
| $\xi_{\mathrm{cb}}$ | Parameter ξ for calculation of loss factor | |
| Y | $Y$ | Admittance | S/m |
| $y_{\mathrm{2K}}$ | Depth for 2K criterion | mm |
| $y_{\mathrm{c}}$ | Skin and proximity effect factor for GIL conductor | |
| $Y_{\mathrm{d}}$ | Constant Y for cables in ducts | K.m/W |
| $y_{\mathrm{encl}}$ | Skin and proximity effect factor for GIL enclosure | |
| $Y_{\mathrm{G}}$ | Factor YG | |
| $Y_{\mathrm{i}}$ | Ordinates of the loss-load cycle | p.u. |
| $Y_{\mathrm{K}}$ | Factor YK | |
| $y_{\mathrm{p}}$ | Proximity effect factor of conductors | |
| $y_{\mathrm{s}}$ | Skin effect factor of conductor | |
| Z | $Z_{\mathrm{0}}$ | Zero sequence impedance | Ω/m |
| $Z_{\mathrm{bs}}$ | Installation constant Z | |
| $z_{\mathrm{c}}$ | Factor z to calculate skin effect coefficients for conductor | |
| $Z_{\mathrm{c}}$ | Self impedance of phase conductor | Ω/m |
| $z_{\mathrm{encl}}$ | Factor z to calculate skin effect coefficients for enclosure | |
| $z_{\mathrm{h}}$ | Location of the heat source | m |
| $Z_{\mathrm{K}}$ | Factor ZK | |
| $Z_{\mathrm{m}}$ | Mutual impedance between conductor and metal screen | Ω/m |
| $z_{\mathrm{max}}$ | Logitudinal thermal limit distance | m |
| $Z_{\mathrm{neg}}$ | Negative sequence impedance | Ω/m |
| $Z_{\mathrm{pos}}$ | Positive sequence impedance | Ω/m |
| $z_{\mathrm{r}}$ | Location of the hottest point | m |
| $Z_{\mathrm{s}}$ | Self impedance of metal screen | Ω/m |
| $Z_{\mathrm{x}}$ | Equivalent mutual impedance between cables | Ω/m |
| $\zeta_{\mathrm{M}}$ | Density of material | g/cm³ |
