| 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 |
| $A_{a}$ | Cross-sectional area of armour | mm$^2$ |
| $A_{a_{1}}$ | Cross-sectional area of 1st armour | mm$^2$ |
| $A_{a_{2}}$ | Cross-sectional area of 2nd armour | mm$^2$ |
| $A_{ab_{1}}$ | Cross-sectional area of 1st armour bedding | mm$^2$ |
| $A_{ab_{2}}$ | Cross-sectional area of 2nd armour bedding | mm$^2$ |
| $a_{c}$ | Skin and proximity effect coefficient a for GIL conductor | |
| $A_{c}$ | Cross-sectional area of conductor | mm$^2$ |
| $A_{comp}$ | Cross-sectional area of compartment | m$^2$ |
| $a_{constr}$ | Construction of armour | |
| $A_{d}$ | Cross-sectional area of duct wall | mm$^2$ |
| $A_{d_{fill}}$ | Free cross-sectional area inside duct | mm$^2$ |
| $A_{encl}$ | Cross-sectional area of enclosure | mm$^2$ |
| $a_{encl}$ | Skin and proximity effect coefficient a for GIL enclosure | |
| $A_{f}$ | Cross-sectional area of filler | mm$^2$ |
| $A_{fluid}$ | Cross-sectional area of fluid | mm$^2$ |
| $A_{i}$ | Cross-sectional area of insulation | mm$^2$ |
| $A_{ins}$ | Cross-sectional area of insulation | mm$^2$ |
| $A_{j}$ | Cross-sectional area of jacket | mm$^2$ |
| $A_{k}$ | Thermal property constant A | (mm$^2$/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 beddig | mm$^2$ |
| $A_{scs}$ | Cross-sectional area of screen serving | mm$^2$ |
| $A_{sh}$ | Cross-sectional area of sheath | mm$^2$ |
| $A_{t}$ | Cross-sectional area of the tunnel | m$^2$ |
| $a_{T}$ | Distance a of multi-layer backfill | m |
| $A_{tube}$ | Cross-sectional area of fluid-filled tube | mm$^2$ |
| $a_{VdW}$ | Van der Walls constant a | bar.L$^2$/mol$^2$ |
| $\alpha_{ar}$ | 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 | $^{\circ}$ |
| $\alpha_{gas}$ | Thermal diffusivity for gas | m$^2$/s |
| $\alpha_{M}$ | Factor $\alpha_M$ | |
| $\alpha_{sa}$ | 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 |
| $\alpha_{st}$ | Heat transfer coefficient for radiation | W/K/m$^2$ |
| $\alpha_{surf}$ | Heat transfer coefficient earth surface | W/K/m$^2$ |
| $\alpha_{t}$ | Conductor to surface attainment factor | |
| B | $B$ | Susceptance | S/m |
| $b_{0}$ | Coefficient b for partial transient temperature rise | 1/s |
| $B_{1_{1}}$ | Loss coefficient $B_1$ of 1st armour | $\Omega$/m |
| $B_{1_{2}}$ | Loss coefficient $B_1$ of 2nd armour | $\Omega$/m |
| $B_{2_{1}}$ | Loss coefficient $B_2$ of 1st armour | $\Omega$/m |
| $B_{2_{2}}$ | Loss coefficient $B_2$ of 2nd armour | $\Omega$/m |
| $b_{c}$ | Skin and proximity effect coefficient b for GIL conductor | |
| $B_{EMF}$ | Magnetic field strength | $\mu$T |
| $b_{encl}$ | Skin and proximity effect coefficient b for GIL enclosure | |
| $B_{k}$ | Thermal property constant B | mm$^2$/s |
| $b_{T}$ | Distance b of multi-layer backfill | m |
| $b_{VdW}$ | Van der Walls constant b | L/mol |
| $b_{x}$ | Shorter side of backfill | mm |
| $b_{y}$ | Longer side of backfill | mm |
| $\beta_{1}$ | Substitution coefficient $\beta_1$ for eddy-currents | |
| $\beta_{6}$ | Factor $|1 - \beta(6)|$ | |
| $\beta_{a_{1}}$ | Angle between armour and cable axis | rad |
| $\beta_{a_{2}}$ | Angle between 2nd armour and cable axis | rad |
| $\beta_{air}$ | Volumetric thermal expansion coefficient of air | 1/K |
| $\beta_{ar}$ | Reciprocal of temperature coefficient of armour material | K |
| $\beta_{c}$ | 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 |
| $\beta_{M}$ | Factor $\beta_M$ | |
| $\beta_{sc}$ | Reciprocal of temperature coefficient of screen material | K |
| $\beta_{sh}$ | Reciprocal of temperature coefficient of sheath material | K |
| $\beta_{T}$ | Equivalent thermal resistance of the soil per unit surface | W/K.m$^2$ |
| $\beta_{t}$ | Attainment factor cable surface to ambient | |
| $\beta_{X}$ | Crossing angle in radians | rad |
| $\beta_{xing}$ | Crossing angle in degrees | $^{\circ}$ |
| C | $C_{av}$ | Heat capacity of the air flow | W/K |
| $C_{b}$ | Capacitance of insulation | F/m |
| $c_{constr}$ | Construction of conductor | |
| $c_{gas}$ | Constant c for a gas under 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 |
| $C_{Nu}$ | Factor C | |
| $c_{p_{gas}}$ | Specific heat capacity at constant pressure | J/kg.K |
| $C_{q}$ | Constants $C_1$ to $C_7$ of multi-layer backfill | |
| $c_{SI}$ | Surge velocity of propagation | km/s |
| $c_{T}$ | Distance c of multi-layer backfill | m |
| $c_{v_{gas}}$ | Specific heat capacity at constant volume | J/kg.K |
| $C_{vair}$ | Volumetric heat capacity of air | J/K.m$^3$ |
| $CC$ | Charging capacity | kvar/km |
| $CC_{p}$ | Conduit clearance | % |
| $CF_{p}$ | Conduit fill | % |
| $CR_{p}$ | Conduit ratio in duct | % |
| $cuw$ | Standard copper wires | mm |
| D | $D_{1}$ | Diameter below screen | mm |
| $D_{2_{1}}$ | Diameter below 1st armour | mm |
| $D_{2_{2}}$ | Diameter below 2nd armour | mm |
| $d_{a}$ | Mean diameter of armour | mm |
| $D_{a_{1}}$ | External diameter of 1st armour | mm |
| $d_{a_{1}}$ | Mean diameter of 1st armour | mm |
| $d_{a_{2}}$ | Mean diameter of 2nd armour | mm |
| $D_{a_{2}}$ | External diameter of 2nd armour | mm |
| $d_{b}$ | Diameter of the backfill | mm |
| $d_{c}$ | External diameter of conductor | mm |
| $D_{c}$ | Diameter of conductor | m |
| $d_{ci}$ | Internal diameter of conductor | mm |
| $D_{comp}$ | Diameter of compartment (metric) | m |
| $d_{comp}$ | Diameter of compartment | mm |
| $d_{ct}$ | External diameter of conductor for transient calculations | mm |
| $D_{e}$ | External diameter of object | mm |
| $d_{e}$ | Diameter of sheath and armour | mm |
| $d_{encl}$ | Outer diameter of enclosure | mm |
| $D_{encl}$ | Outer diameter of enclosure (metric) | m |
| $D_{eq}$ | Equivalent diameter of a group of cables | mm |
| $D_{f}$ | External diameter of the filler | mm |
| $d_{f}$ | Spacing from hottest object in group | m |
| $d_{f_{1}}$ | Thickness of 1st armour | mm |
| $d_{f_{2}}$ | Thickness of 2nd armour | mm |
| $D_{i}$ | Diameter over insulation | mm |
| $d_{im}$ | Imaginary layer of soil | m |
| $d_{ins}$ | Diameter of insulation around tube | mm |
| $D_{it}$ | Diameter below sheath | mm |
| $D_{o}$ | Outer diameter | m |
| $D_{oc}$ | External diameter of sheath | mm |
| $d_{pk1}$ | Distance to mirrored buried object | mm |
| $d_{pk2}$ | Distance between buried objects | mm |
| $d_{prot}$ | Diameter of protective cover | mm |
| $d_{psc}$ | Point source correction | m |
| $D_{s}$ | Mean external diameter of the sheath | mm |
| $d_{s}$ | Mean diameter of screen/sheath | mm |
| $d_{sc}$ | Mean diameter of screen | mm |
| $d_{sh}$ | Mean diameter of sheath | mm |
| $d_{soil}$ | Soil dry density | kg/m$^3$ |
| $d_{t}$ | Channel covering | m |
| $d_{T}$ | Distance d of multi-layer backfill | 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 |
| $DC_{p}$ | Diameter factor in duct | % |
| $\delta _{1}$ | Thickness of screening layer | mm |
| $\Delta _{1}$ | Substitution coefficient $\Delta_1$ for eddy-currents | |
| $\Delta _{2}$ | Substitution coefficient $\Delta_2$ for eddy-currents | |
| $\delta _{ar}$ | Equivalent thickness of armour | mm |
| $\delta _{k}$ | Thickness of screen, sheath or armour | mm |
| $\delta _{soil}$ | Soil thermal diffusivity | m$^2$/s |
| $\delta _{t}$ | Channel covering correction | m |
| $\Delta d_{sh}$ | 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 of the conductor | K |
| $\Delta \theta_{0x_{1}}$ | Temperature rise of the conductor, first estimate | K |
| $\Delta \theta_{0x_{h}}$ | Temperature rise of the conductor by source h | K |
| $\Delta \theta_{a_{t}}$ | Corrected transient temperature rise of conductor | K |
| $\Delta \theta_{air}$ | Temperature increase of air | K |
| $\delta \theta_{c}$ | Ohmic steady-state temperature rise | K |
| $\Delta \theta_{c}$ | Temperature rise of conductor | K |
| $\Delta \theta_{c_{t}}$ | Transient temperature rise of conductor by ohmic losses | K |
| $\Delta \theta_{ce}$ | Temperature difference conductor to surface | K |
| $\Delta \theta_{d}$ | Temperature rise by dielectric losses | K |
| $\Delta \theta_{e_{t}}$ | Transient temperature rise of outer surface | K |
| $\Delta \theta_{gas}$ | Temperature difference conductor-enclosure | $^{\circ}$C |
| $\Delta \theta_{kp}$ | Temperature rise by buried object k | K |
| $\Delta \theta_{max}$ | Maximum permissible conductor temperature rise | K |
| $\Delta \theta_{p}$ | Temperature rise by other buried objects | K |
| $\Delta \theta_{R}$ | Conductor temperature rise above ambient temperature | K |
| $\Delta \theta_{R_{\infty}}$ | Maximum permissible conductor temperature rise | $^{\circ}$C |
| $\Delta \theta_{s}$ | Temperature difference surface to ambient | K |
| $\delta \theta_{SPK}$ | Peak cyclic temperature rise | K |
| $\Delta \theta_{sun}$ | Temperature rise by solar radiation | K |
| $\Delta \theta_{t}$ | Transient temperature rise of conductor | K |
| $\Delta \theta_{t_{\infty}}$ | Steady-state temperature rise of conductor | K |
| $\Delta \theta_{tube}$ | Temperature difference surface to tube | K |
| $\Delta \theta_{x}$ | Critical soil temperature rise | K |
| $\Delta W$ | Incremental heat generated | W |
| $\Delta W_{0}$ | Incremental heat 0 generated | W |
| $\Delta z$ | Length of the interval | m |
| $DF_{X}$ | Derating factor for the permissible current | |
| $Di_{d}$ | Inner diameter of duct | mm |
| $Di_{t}$ | Diameter of the tunnel (inner) | m |
| $di_{tube}$ | Internal diameter of fluid-filled tube | mm |
| $Do_{d}$ | Outer diameter of duct | mm |
| $Do_{t}$ | Diameter of the tunnel or trough (outer) | m |
| $do_{tube}$ | External diameter of fluid-filled tube | mm |
| E | $E_{bs}$ | Installation constant E | |
| $e_{hor}$ | Horizontal clearance | mm |
| $E_{stress}$ | Electrical field strength | kV/mm |
| $e_{ver}$ | 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 | |
| $\epsilon_{cable}$ | Emissivity of cable surface | |
| $\epsilon_{di}$ | Emissivity of duct/tube inner surface | |
| $\epsilon_{do}$ | Emissivity of duct/tube outer surface | |
| $\epsilon_{encl}$ | Effective emissivity of enclosure | |
| $\epsilon_{gas}$ | Dielectric constant of gas in compartment | |
| $\epsilon_{i}$ | Relative permittivity of insulation | |
| $\epsilon_{k}$ | Heat loss allowance factor | |
| $\epsilon_{prot}$ | Effective emissivity of protective cover | |
| $\epsilon_{rad}$ | Effective emissivity | |
| $\eta0_{gas}$ | Reference dynamic viscosity of gas | Pa.s |
| $\eta_{gas}$ | Dynamic viscosity of gas | Pa.s |
| F | $f$ | System frequency | Hz |
| $F_{a_{1}}$ | Effective length per unit lay length of 1st armour | mm |
| $F_{a_{2}}$ | Effective length per unit lay length of 2nd armour | mm |
| $f_{atm}$ | Relation atmospheric pressure to standard atmosphere | |
| $F_{cable}$ | Maximum effective pulling force | N/m |
| $f_{cb}$ | Factor for cross-bonded earthing | |
| $F_{e}$ | Factor $F_e$ for eddy-current losses | |
| $F_{eq}$ | Mutual heating coefficient | |
| $F_{form}$ | Form factor | |
| $F_{ij}$ | View factor object-object | |
| $F_{in}$ | Pulling force at beginning of a section | daN |
| $F_{k}$ | Imperfect contact thermal factor | |
| $F_{m}$ | Radiation coefficient mutual | |
| $F_{out}$ | Pulling force at end of a section | daN |
| $f_{ppc}$ | Factor of permissible pull | N/mm$^2$ |
| $F_{ppc}$ | Permissible pull force on cable | daN |
| $F_{pt}$ | Function of pressure and temperature | |
| $f_{SHF}$ | Sheath 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 | |
| $G_{b}$ | Geometric factor for backfill | |
| $g_{bs}$ | Installation constant g | |
| $G_{encl}$ | Factor G to calculate Nusselt number | |
| $g_{s}$ | Substitution coefficient $g_s$ for eddy-currents | |
| $G_{s00}$ | Factor $G_{s 0.0}$ | |
| $G_{s05}$ | Factor $G_{s 0.5}$ | |
| $G_{s10}$ | Factor $G_{s 1.0}$ | |
| $\gamma_{a}$ | Armour angle | rad |
| $\gamma_{bessel}$ | Bessel constant | p.u. |
| $\gamma_{c}$ | Skin and proximity effect factor $\gamma$ for GIL conductor | |
| $\gamma_{encl}$ | Skin and proximity effect factor $\gamma$ for GIL enclosure | |
| $\gamma_{euler}$ | Euler's constant | m/s$^2$ |
| $\gamma_{t}$ | Attainment factor for groups of cables | |
| $\gamma_{X}$ | Attenuation factor for crossing | 1/m |
| $GMD$ | Geometric mean distance | mm |
| $GMR$ | Geometric mean radius | mm |
| $Gr_{c}$ | Grashof number conductor-gas | |
| $Gr_{encl}$ | Grashof number gas-enclosure | |
| $Gr_{L}$ | Grashof number | |
| $Gr_{prot}$ | Grashof number surface-air | |
| H | $h_{1}$ | Factor $h_1$ for emergency load | |
| $H_{1_{1}}$ | Component of inductance $H_1$ | H/m |
| $H_{1_{2}}$ | Component of inductance $H_1$ of 2nd armour | H/m |
| $H_{2_{1}}$ | Component of inductance $H_2$ | H/m |
| $H_{2_{2}}$ | Component of inductance $H_2$ of 2nd armour | H/m |
| $H_{3_{1}}$ | Component of inductance $H_3$ | H/m |
| $H_{3_{2}}$ | Component of inductance $H_3$ of 2nd armour | H/m |
| $h_{atm}$ | 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$^{5/4}$ |
| $H_{c}$ | Heat energy content | MJ/m |
| $h_{c}$ | Convective heat transfer coefficient conductor-gas | W/K.m$^2$ |
| $h_{encl}$ | Convective heat transfer coefficient gas to enclosure | W/m2.K |
| $h_{lg}$ | Ratio of heat dissipation coefficients | |
| $h_{prot}$ | Convective heat transfer coefficient surface-air | W/K.m$^2$ |
| $h_{rad_{ce}}$ | Radiation heat transfer coefficient conductor-enclosure | W/K.m$^2$ |
| $h_{rad_{sa}}$ | Radiation heat transfer coefficient surface-air | W/K.m$^2$ |
| $h_{roll}$ | Height of roller above bottom | m |
| $H_{s}$ | Sheath conductance | H/m |
| $H_{sun}$ | Intensity of solar radiation | W/m$^2$ |
| $H_{T}$ | Trench depth to bedding layer in multi-layer backfill | m |
| $h_{t}$ | 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 |
| $I_{c}$ | Conductor current | A |
| $I_{C}$ | Capacitive load current | A/km |
| $I_{c_{max}}$ | Highest current load of line | A |
| $I_{c_{peak}}$ | Permissible peak cyclic load current | A |
| $I_{Ce}$ | Capacitive earth short-circuit current | A/km |
| $I_{EMF}$ | Phase current for EMF calculation | A |
| $I_{k}$ | Permissible 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 |
| $inst_{air}$ | Installation in air | |
| $inst_{sea}$ | Installation of subsea cables | |
| $inst_{t}$ | Installation in air inside a room | |
| J | $j_{max}$ | Phase angle range | $^{\circ}$ |
| $JR_{p}$ | Jam ratio in duct | % |
| K | $K$ | Screening factor | |
| $K_{0}$ | Coefficient K for a gas under GIL conditions | |
| $K_{02}$ | Factor $K_{0.2}$ | |
| $K_{06}$ | Factor $K_{0.6}$ | |
| $k_{1}$ | Thermal conductivity of surface layer | W/K.m |
| $K_{10}$ | Factor $K_{1.0}$ | |
| $k_{2}$ | Thermal conductivity of mid backfill layer | W/K.m |
| $k_{3}$ | Thermal conductivity of bedding layer | W/K.m |
| $k_{4}$ | Thermal conductivity of soil | W/K.m |
| $K_{A}$ | Coefficient K to calculate in air | |
| $k_{air}$ | Thermal conductivity of air | W/m.K |
| $K_{BICC}$ | Constant relating to conductor formation | |
| $k_{Boltzmann}$ | Boltzmann constant | J/K |
| $k_{c}$ | Thermal conductivity of conductor material | K.m/W |
| $K_{ce}$ | Radiation shape factor conductor-enclosure | |
| $K_{cv}$ | Convection factor | |
| $K_{E}$ | Surface heat conductance | W/m$^2$ |
| $k_{encl}$ | Thermal conductivity of enclosure | W/m.K |
| $k_{fluid}$ | Thermal conductivity of fluid | W/m.K |
| $k_{gas}$ | Thermal conductivity for gas | W/m.K |
| $K_{GMR}$ | Geometric mean radius factor | |
| $k_{H}$ | Heinhold characteristic diameter coefficient | |
| $k_{ins}$ | Thermal conductivity of insulation | W/m.K |
| $K_{int}$ | Radiation shape factor cable-duct/tube | |
| $K_{k}$ | 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. |
| $k_{p}$ | Proximity effect coefficient | |
| $k_{prot}$ | Thermal conductivity of protective cover | W/m.K |
| $K_{r}$ | Radiation shape factor to ambient | |
| $k_{r2}$ | Temperature rise ratio $\delta\theta_{SPK}/\delta\theta_c$ | p.u. |
| $k_{s}$ | Skin effect coefficient | |
| $k_{sa}$ | Convection factor acc. Heinhold | |
| $k_{sa_{1}}$ | Factor 1 for convectional heat transfer coefficient | |
| $k_{sa_{2}}$ | Factor 2 for convectional heat transfer coefficient | |
| $K_{t}$ | Effective emissivity of surface | |
| $k_{t}$ | Temperature rise ratio | p.u. |
| $k_{tube}$ | Thermal conductivity of fluid-filled tube | W/m.K |
| $K_{vermeer}$ | Vermeer constant for convection heat transfer | |
| $K_{x}$ | Factor for fictitious diameter by Neher | |
| $k_{X}$ | Number of heat sources crossing | |
| 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 |
| $L_{c}$ | Depth of laying of sources | mm |
| $L_{char}$ | Characteristic length | |
| $L_{cm}$ | Depth of laying | m |
| $L_{cni}$ | Imaginary laying depth with non-isothermal earth surface | m |
| $L_{crit}$ | Critical system length | km |
| $L_{deep}$ | Equivalent depth for deep burial | m |
| $L_{earth}$ | Equivalent depth of earth return path | p.u. |
| $L_{h}$ | Depth of laying of crossing element | mm |
| $L_{p}$ | Length of a section | 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 screen and sheath | |
| $\lambda_{1c}$ | Loss factor by circulating currents | |
| $\lambda_{1cb}$ | Loss factor for solid bonding | |
| $\lambda_{1e}$ | Loss factor by eddy currents | |
| $\lambda_{1es}$ | Loss factor for single point bonding | |
| $\lambda_{2}$ | Loss factor of armour | |
| $\lambda_{3}$ | Loss factor of steel pipes | |
| $\lambda_{d}$ | Factor for dielectric losses | |
| $\lambda_{gas}$ | Ratio $c_p$/$c_v$ | |
| $\lambda_{t}$ | 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 | $m$ | Mass of object | kg/m |
| $M$ | Cyclic rating factor | p.u. |
| $M_{0}$ | Coefficient M for partial transient temperature rise | s |
| $m_{0}$ | Substitution coefficient $m_0$ for eddy-currents | Hz.m/$\Omega$ |
| $M_{1}$ | Corrected cyclic rating factor | K |
| $M_{ab}$ | Material of armour bedding | |
| $M_{c}$ | Material of conductor | |
| $M_{cable}$ | List of materials in a cable | |
| $M_{comp}$ | Insulating gas material | |
| $M_{d}$ | Material of duct pipe | |
| $M_{e}$ | Substitution coefficient $M_e$ to calculate factor $F_e$ | |
| $m_{EMF}$ | Number of time steps | |
| $M_{encl}$ | Material of enclosure | |
| $M_{f}$ | Material of filler | |
| $M_{fluid}$ | Fluid material | |
| $M_{gas}$ | Gas and gas-mixtures | |
| $M_{i}$ | Material of insulation | |
| $M_{IEEE}$ | Materials acc. IEEE 442 | |
| $M_{ins}$ | Material of insulation around tube | |
| $M_{j}$ | Material of jacket | |
| $M_{k}$ | Thermal contact factor | s$^{1/2}$ |
| $M_{mol}$ | Molar mass | g/mol |
| $m_{mol}$ | Molecular mass | mol |
| $m_{Nu}$ | Factor m | |
| $M_{prot}$ | Material of protective cover | |
| $M_{s}$ | Factor $M_s$ | |
| $M_{sc}$ | Material of screen | |
| $M_{sh}$ | Material of sheath | |
| $M_{soil}$ | Type of soils | |
| $M_{tube}$ | Material of fluid-filled tube | |
| $\mu$ | Loss factor | p.u. |
| $\mu_{0}$ | Vacuum permeability | H/m |
| $\mu_{e}$ | Longitudinal relative permeability | |
| $\mu_{p}$ | Friction coefficient | |
| $\mu_{s}$ | 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 | |
| $N_{Avogrado}$ | Avogadro constant | 1/mol |
| $N_{b}$ | Number of loaded objects in backfill | |
| $N_{c}$ | Number of sources in system | |
| $n_{c}$ | Number of conductors in object | |
| $n_{cc}$ | Number of conductors combined | |
| $n_{cg}$ | Number of conductors in GIL | |
| $n_{cw}$ | Number of wires in conductor | |
| $N_{e}$ | Substitution coefficient $N_e$ to calculate factor $F_e$ | |
| $n_{ppc}$ | Number of conductors/cables being pulled | |
| $N_{sea}$ | Number of subsea cables | |
| $N_{sum}$ | Total number of objects in an air-filled space | |
| $n_{sw}$ | Number of screen wires | |
| $n_{tube}$ | Number of tubes in heatsource | |
| $N_{X}$ | Number of intervals | |
| $\nu$ | Summation step 1 to $N_X$ | |
| $\nu_{air}$ | Kinematic viscosity for air | m$^2$/s |
| $Nu_{c}$ | Nusselt number conductor-gas | |
| $Nu_{encl}$ | Nusselt number gas-enclosure | |
| $\nu_{gas}$ | Kinematic viscosity for gas | m$^2$/s |
| $Nu_{L}$ | Nusselt number | |
| $Nu_{prot}$ | Nusselt number surface-air | |
| $\nu_{soil}$ | Soil moisture content | % |
| 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 |
| $p_{ab1}$ | Factor apportioning the 1st armour bedding | |
| $p_{ab2}$ | Factor apportioning the 2nd armour bedding | |
| $p_{atm}$ | Atmospheric air pressure | hPa |
| $p_{cb}$ | Minor ratio of section lengths | |
| $P_{cc}$ | Substitution coefficient P to calculate loss factor by circulating currents | |
| $p_{comp}$ | Gas pressure in compartment | bar |
| $p_{gas}$ | Gas pressure | Pa |
| $p_{i}$ | Factor apportioning the insulation | |
| $p_{j}$ | Factor apportioning the jacket | |
| $P_{L}$ | Active power at load receptor | kW |
| $p_{soil}$ | Depth of image source | |
| $p_{tr}$ | Effective perimeter of trough | m |
| $p_{VdW}$ | Van der Walls equation | Pa |
| $\phi_{b}$ | Parameter $\phi$ for trough | |
| $\phi_{p}$ | Angle of a bend | rad |
| $\pi$ | Archimedes' constant $\pi$ | |
| $Pr_{air}$ | Prandtl number for air | |
| $Pr_{gas}$ | Prandtl number for gas | |
| Q | $q_{1}$ | Ratio of losses affecting screen bedding/serving | |
| $q_{2_{1}}$ | Ratio of losses affecting 1st armour bedding | |
| $q_{2_{2}}$ | Ratio of losses affecting 2nd 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 |
| $Q_{a_{1}}$ | Thermal capacitance of 1st armour | J/m.K |
| $Q_{a_{2}}$ | Thermal capacitance of 2nd armour | J/m.K |
| $Q_{ab_{1}}$ | Thermal capacitance of 1st armour bedding | J/m.K |
| $Q_{ab_{2}}$ | Thermal capacitance of 2nd armour bedding | J/m.K |
| $Q_{B}$ | Element B of two-part thermal circuit | J/m.K |
| $Q_{B_{ab1}}$ | Element B of two-part thermal circuit, 1st armour bedding | J/m.K |
| $Q_{B_{ab2}}$ | Element B of two-part thermal circuit, 2nd 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 | |
| $Q_{cc}$ | Substitution coefficient Q to calculate loss factor by circulating currents | |
| $Q_{d}$ | 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 | |
| $Q_{i}$ | Thermal capacitance of insulation | J/m.K |
| $Q_{i1}$ | Thermal capacitance of insulation, 1st portion | J/m.K |
| $Q_{i2}$ | Thermal capacitance of insulation, 2nd portion | J/m.K |
| $Q_{j}$ | Thermal capacitance of jacket | J/m.K |
| $Q_{p}$ | Quantity of lubricant | l/m |
| $Q_{sc}$ | 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 |
| $Q_{t}$ | Total thermal capacitance, transient | J/m.K |
| $q_{x}$ | Factor for characteristic diameter | |
| R | $R_{0}$ | Zero sequence resistance | $\Omega$/m |
| $R_{1}$ | Resistance of conductor before emergency rating | $\Omega$/m |
| $R_{A}$ | Electrical resistance of armour | $\Omega$/m |
| $R_{A_{1}}$ | Electrical resistance of 1st armour layer | $\Omega$/m |
| $R_{A_{2}}$ | Electrical resistance of 2nd armour layer | $\Omega$/m |
| $r_{b}$ | Equivalent radius of backfill | mm |
| $r_{c}$ | Radius of conductor | mm |
| $R_{c}$ | Resistance of conductor | $\Omega$/m |
| $R_{CG}$ | Thermal resistance of multi-layer backfill | K.m/W |
| $R_{co}$ | DC resistance of conductor at 20$^{\circ}$C | $\Omega$/m |
| $R_{e}$ | Electrical resistance of sheath and armour | $\Omega$/m |
| $R_{e_{1}}$ | Electrical resistance of sheath and 1st armour | $\Omega$/m |
| $R_{e_{2}}$ | Electrical resistance of sheath and 2nd armour | $\Omega$/m |
| $R_{earth}$ | Equivalent resistance of earth return path | p.u. |
| $R_{encl}$ | Electrical resistance of enclosure | $\Omega$/m |
| $R_{encl20}$ | DC resistance of enclosure at 20$^{\circ}$C | $\Omega$/m |
| $r_{F}$ | Radius below the insulation | mm |
| $R_{gas}$ | Specific gas constant | |
| $R_{gas0}$ | Universal molar gas constant | |
| $r_{I}$ | Radius of the insulation | mm |
| $r_{ij}$ | Coefficient r for view factor | |
| $R_{max}$ | 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 | |
| $R_{p}$ | Radius of a bend | m |
| $R_{q1}$ | Thermal resistance 1 of multi-layer backfill method | K.m/W |
| $R_{q11}$ | Thermal resistance 11 of multi-layer backfill method | K.m/W |
| $R_{q12}$ | Thermal resistance 12 of multi-layer backfill method | K.m/W |
| $R_{q13}$ | Thermal resistance 13 of multi-layer backfill method | K.m/W |
| $R_{q2}$ | Thermal resistance 2 of multi-layer backfill method | K.m/W |
| $R_{q21}$ | Thermal resistance 21 of multi-layer backfill method | K.m/W |
| $R_{q22}$ | Thermal resistance 22 of multi-layer backfill method | K.m/W |
| $R_{q23}$ | Thermal resistance 23 of multi-layer backfill method | K.m/W |
| $R_{q24}$ | Thermal resistance 24 of multi-layer backfill method | K.m/W |
| $R_{q3}$ | Thermal resistance 3 of multi-layer backfill method | K.m/W |
| $R_{q31}$ | Thermal resistance 31 of multi-layer backfill method | K.m/W |
| $R_{q32}$ | Thermal resistance 32 of multi-layer backfill method | K.m/W |
| $R_{q33}$ | Thermal resistance 33 of multi-layer backfill method | K.m/W |
| $R_{q34}$ | Thermal resistance 34 of multi-layer backfill method | K.m/W |
| $R_{s}$ | Electrical resistance of screen$||$sheath | $\Omega$/m |
| $R_{sc}$ | Electrical resistance of screen | $\Omega$/m |
| $R_{sh}$ | Electrical resistance of sheath | $\Omega$/m |
| $R_{so}$ | Resistance of screen and sheath at 20$^{\circ}$C | $\Omega$/m |
| $r_{x}$ | Radius to point x in insulation | mm |
| $Ra_{c}$ | Rayleigh number conductor-gas | |
| $Ra_{encl}$ | Rayleigh number gas-enclosure | |
| $Ra_{L}$ | Rayleigh number | |
| $Ra_{prot}$ | Rayleigh number surface-air | |
| $Re_{air}$ | Reynolds number for air | |
| $RF$ | 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 |
| $\rho_{ab_{2}}$ | Thermal resistivity of bedding between armour layers | 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 mid backfill layer | K.m/W |
| $\rho_{c}$ | Electrical resistivity of conductor material | $\Omega$.m |
| $\rho_{cable}$ | Reflectivity of cable surface | |
| $\rho_{corr}$ | Thermal resistivity of corrugation filling | K.m/W |
| $\rho_{cr}$ | Thermal resistivity of conductor material | K.m/W |
| $\rho_{d}$ | Thermal resistivity of duct material | K.m/W |
| $\rho_{d_{fill}}$ | Thermal resistivity of bentonite filling | K.m/W |
| $\rho_{di}$ | Reflectivity of duct/tube inner surface | |
| $\rho_{do}$ | Reflectivity of duct/tube outer surface | |
| $\rho_{earth}$ | 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 |
| $\rho_{j}$ | 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 |
| $\rho_{m}$ | Thermal resistivity of the screen | K.m/W |
| $\rho_{sc}$ | Specific electrical resistivity of screen material | $\Omega$.m |
| $\rho_{sh}$ | Specific electrical resistivity of sheath material | $\Omega$.m |
| $\rho_{t}$ | Thermal resistivity of wall | K.m/W |
| S | $s_{1}$ | Thickness of surface layer | m; |
| $s_{2}$ | Thickness of mid backfill layer | m$^2$ |
| $s_{3}$ | Thickness from object to upper boundary of bedding layer | m$^2$ |
| $s_{4}$ | Thickness from object to lower boundary of bedding layer | m$^2$ |
| $s_{air}$ | Axial spacing between objects | m |
| $s_{c}$ | Separation of conductors in a system | mm |
| $S_{G}$ | Apparent power at injecting point | 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$^2$ |
| $s_{roll}$ | Roller distance | m |
| $s_{S1}$ | 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. |
| $s_{T}$ | Distance to lateral edge of multi-layer backfill | m |
| $SI$ | Surge Impedance | $\Omega$ |
| $\sigma$ | Stefan Boltzmann constant | W/m$^2$K$^4$ |
| $\sigma_{ab}$ | Specific heat capacity of armour bedding | J/K.m$^3$ |
| $\sigma_{ar}$ | Specific heat capacity of armour material | J/K.m$^3$ |
| $\sigma_{c}$ | Specific heat capacity of conductor material | J/K.m$^3$ |
| $\sigma_{d}$ | Specific heat capacity of duct material | J/K.m$^3$ |
| $\sigma_{d_{fill}}$ | Specific heat capacity of duct filling | J/K.m$^3$ |
| $\sigma_{encl}$ | Specific heat capacity of enclosure material | J/K.m$^3$ |
| $\sigma_{f}$ | Specific heat capacity of filler | J/K.m$^3$ |
| $\sigma_{fluid}$ | Specific heat capacity of fluid | J/K.m$^3$ |
| $\sigma_{i}$ | Specific heat capacity of insulation material | J/K.m$^3$ |
| $\sigma_{ins}$ | Specific heat capacity of insulation | J/K.m$^3$ |
| $\sigma_{j}$ | Specific heat capacity of jacket material | J/K.m$^3$ |
| $\sigma_{k2}$ | Specific heat capacity of layer located below | J/K.m$^3$ |
| $\sigma_{k3}$ | Specific heat capacity of layer located above | J/K.m$^3$ |
| $\sigma_{kc}$ | Specific heat capacity of metallic component | J/K.m$^3$ |
| $\sigma_{ki}$ | Specific heat capacity of adjacent material | J/K.m$^3$ |
| $\sigma_{prot}$ | Specific heat capacity of protective cover | J/K.m$^3$ |
| $\sigma_{sc}$ | Specific heat capacity of screen material | J/K.m$^3$ |
| $\sigma_{scb}$ | Specific heat capacity of screen bedding | J/K.m$^3$ |
| $\sigma_{scs}$ | Specific heat capacity of screen serving | J/K.m$^3$ |
| $\sigma_{sh}$ | Specific heat capacity of sheath material | J/K.m$^3$ |
| $\sigma_{sun}$ | Absorption coefficient of solar radiation | |
| $\sigma_{tube}$ | Specific heat capacity of fluid-filled tube | J/K.m$^3$ |
| $\sigma_{y}$ | Yield strength of metals for armour | MPa |
| $SP_{p}$ | Sidewall pressure | N/m |
| T | $t$ | Thickness of insulation between conductors | mm |
| $T0_{gas}$ | Gas reference temperature | K |
| $t_{1}$ | Thickness of insulation to sheath | mm |
| $T_{1}$ | Thermal resistance between one conductor and sheath | K.m/W |
| $T_{1t}$ | Thermal resistance between one conductor and sheath, transient | K.m/W |
| $t_{1t}$ | Thickness of insulation to sheath, transient | mm |
| $t_{2}$ | Thickness of bedding under armour | mm |
| $T_{2}$ | Thermal resistance between sheath and armour | K.m/W |
| $T_{2_{1}}$ | Thermal resistance between sheath and 1st armour layer | K.m/W |
| $T_{2_{2}}$ | Thermal resistance of material between armour layers | K.m/W |
| $T_{2_{f}}$ | Thermal resistance between sheath and armour bedding | K.m/W |
| $t_{3}$ | Thickness of serving over armour | mm |
| $T_{3}$ | Thermal resistance of jacket | K.m/W |
| $T_{4d}$ | Transient thermal resistance for daily load | K.m/W |
| $T_{4db}$ | Correction of thermal resistance for backfill | 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 |
| $T_{4ss}$ | Steady-state thermal resistance | K.m/W |
| $T_{4t}$ | Equivalent thermal resistance for tunnel | K.m/W |
| $T_{4w}$ | Transient thermal resistance for weekly load | K.m/W |
| $T_{4y}$ | Transient thermal resistance for yearly load | 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 |
| $t_{ab_{1}}$ | Thickness of 1st armour bedding | mm |
| $t_{ab_{2}}$ | Thickness of armour separation | mm |
| $T_{air}$ | Absolute air temperature | K |
| $T_{at}$ | Thermal resistance by convection air-tunnel | K.m/W |
| $T_{B}$ | Element B of equivalent thermal circuit | K.m/W |
| $T_{b0}$ | Apparent thermal resistance b | K.m/W |
| $t_{c}$ | Thickness of hollow conductor | mm |
| $T_{C}$ | Element C of equivalent thermal circuit | K.m/W |
| $t_{comp}$ | Thickness of compartment | mm |
| $T_{conv_{ce}}$ | Thermal resistance by convection conductor-enclosure | K.m/W |
| $T_{conv_{sa}}$ | Thermal resistance by convection surface-air | K.m/W |
| $t_{corr}$ | Thickness of corrugation filling | mm |
| $t_{cs}$ | Thickness of conductor shield | mm |
| $t_{ct}$ | Thickness of s.c. tape wrapped around conductor | mm |
| $T_{d}$ | Internal thermal resistance for dielectric losses | 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 | mm |
| $T_{eq}$ | Equivalent thermal resistance | K.m/W |
| $t_{f}$ | Thickness of filler/belt insulation | mm |
| $T_{f}$ | Axial thermal resistance due to the movement of air through the tunnel | K.m/W |
| $T_{gas}$ | Absolute gas temperature | K |
| $t_{i}$ | Thickness of core insulation | mm |
| $T_{i}$ | Internal thermal resistance for current losses | K.m/W |
| $T_{\infty}$ | Infinite bulk temperature (the ambient air temperature) | K |
| $t_{ins}$ | Thickness of insulation | mm |
| $t_{is}$ | Thickness of insulation screen | mm |
| $t_{j}$ | Thickness of jacket | mm |
| $t_{jj}$ | 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 | K.m/W |
| $T_{mh_{v}}$ | Mutual thermal resistance per slice | K.m/W |
| $T_{o}$ | Thermal resistance of the oil in the pipe | K.m/W |
| $t_{prot}$ | Thickness of protective cover | mm |
| $T_{prot}$ | Thermal resistance of protective cover | K.m/W |
| $T_{r}$ | Total thermal resistance | K.m/W |
| $T_{rad_{ce}}$ | Radiation thermal resistance conductor-enclosure | K.m/W |
| $T_{rad_{ext}}$ | Radiation thermal resistance duct/tube-air | K.m/W |
| $T_{rad_{int}}$ | Radiation thermal resistance surface-duct/tube | K.m/W |
| $T_{rad_{sa}}$ | Radiation thermal resistance surface-air | K.m/W |
| $T_{rad_{sun}}$ | Solar radiation thermal resistance | K.m/W |
| $T_{s}$ | Star thermal resistance of object | K.m/W |
| $T_{sa}$ | Thermal resistance by convection surface-air | K.m/W |
| $t_{sc}$ | Thickness of the screen | mm |
| $t_{scb}$ | Thickness of screen bedding | mm |
| $t_{scs}$ | Thickness of screen serving | mm |
| $t_{sh}$ | Thickness of the sheath | mm |
| $T_{st}$ | Radiation thermal resistance surface-tunnel | K.m/W |
| $T_{surf}$ | Absolute surface temperature | K |
| $T_{t}$ | Star thermal resistance of tunnel | K.m/W |
| $t_{t}$ | Tunnel wall thickness | m |
| $T_{tot}$ | Total thermal resistance, transient | K.m/W |
| $T_{tr}$ | Thermal resistance of trough | K |
| $T_{tw}$ | Thermal resistance of tunnel wall | K.m/W |
| $\mathrm{tan}\delta _{i}$ | Loss factor of insulation | |
| $\tau$ | Transient load period | s |
| $\theta_{2K}$ | Temperature rise for 2K criterion | $^{\circ}$C |
| $\theta_{a}$ | Ambient temperature | $^{\circ}$C |
| $\theta_{abs}$ | Absolute temperature | K |
| $\theta_{air}$ | Ambient air temperature | $^{\circ}$C |
| $\theta_{ar}$ | Temperature of armour | $^{\circ}$C |
| $\theta_{ar_{1}}$ | Temperature of 1st armour layer | $^{\circ}$C |
| $\theta_{ar_{2}}$ | Temperature of 2nd armour layer | $^{\circ}$C |
| $\theta_{at}$ | Air temperature with load | $^{\circ}$C |
| $\theta_{at_{0}}$ | Air temperature with no load | $^{\circ}$C |
| $\theta_{at_{i}}$ | Air temperature of previous iteration cycle | $^{\circ}$C |
| $\theta_{at_{L}}$ | Air temperature in tunnel at outlet | $^{\circ}$C |
| $\theta_{at_{z}}$ | Air temperature in tunnel at z | $^{\circ}$C |
| $\theta_{c}$ | Temperature of conductor | $^{\circ}$C |
| $\theta_{c_{z}}$ | Conductor temperature at z | $^{\circ}$C |
| $\theta_{cmax}$ | Max. conductor temperature | $^{\circ}$C |
| $\theta_{cmaxeo}$ | Max. emergency overload conductor temperature | $^{\circ}$C |
| $\theta_{cmaxsc}$ | Max. short-circuit conductor temperature | $^{\circ}$C |
| $\theta_{de}$ | Temperature of duct outer wall | $^{\circ}$C |
| $\theta_{di}$ | Temperature of duct inner wall | $^{\circ}$C |
| $\theta_{dm}$ | Mean temperature of the medium in the duct | $^{\circ}$C |
| $\theta_{e}$ | External temperature of the object | $^{\circ}$C |
| $\theta_{encl}$ | Temperature of enclosure | $^{\circ}$C |
| $\theta_{f}$ | Temperature of filler for multi-core cables type SS with sheath | $^{\circ}$C |
| $\theta_{gas}$ | Gas temperature | $^{\circ}$C |
| $\theta_{hs}$ | Temperature of heat source | $^{\circ}$C |
| $\theta_{kf}$ | Final temperature | $^{\circ}$C |
| $\theta_{ki}$ | Initial temperature | $^{\circ}$C |
| $\theta_{kmax}$ | Maximal temperature of non-insulation material | $^{\circ}$C |
| $\theta_{max}$ | Temperature of conductor at end of emergency loading | $^{\circ}$C |
| $\theta_{o}$ | Outer temperature | $^{\circ}$C |
| $\theta_{o_{L}}$ | Temperature of the surface of object at outlet | $^{\circ}$C |
| $\theta_{o_{z}}$ | Temperature of the surface of object at z | $^{\circ}$C |
| $\theta_{p}$ | Angle to the plane of a section | rad |
| $\theta_{R}$ | Rated current transient to steady-state ratio | |
| $\theta_{s}$ | Temperature of screen/sheath | $^{\circ}$C |
| $\theta_{sc}$ | Temperature of screen | $^{\circ}$C |
| $\theta_{sh}$ | Temperature of sheath | $^{\circ}$C |
| $\theta_{surf}$ | Surface temperature | $^{\circ}$C |
| $\theta_{t}$ | Temperature of inner tunnel wall | $^{\circ}$C |
| $\theta_{t_{L}}$ | Temperature of tunnel wall at outlet | $^{\circ}$C |
| $\theta_{t_{z}}$ | Temperature of tunnel wall at z | $^{\circ}$C |
| $\theta_{tm}$ | Mean temperature between surface and air in tunnel or trough | $^{\circ}$C |
| $\theta_{to}$ | Temperature of outer tunnel wall | $^{\circ}$C |
| $\theta_{to_{z}}$ | Temperature of outer tunnel wall at z | $^{\circ}$C |
| $\theta_{tube}$ | Temperature of tube | $^{\circ}$C |
| $\theta_{x}$ | Critical soil temperature | $^{\circ}$C |
| $TQ$ | Cable thermal time constant | s |
| U | $u$ | Substitution coefficient u | |
| $U_{0}$ | Base voltage for tests | kV |
| $U_{d}$ | Constant U for cables in ducts | K.m/W |
| $U_{e}$ | Line-to-ground voltage | kV |
| $U_{m}$ | Highest voltage for equipment | kV |
| $U_{n}$ | Rated line-to-line voltage | kV |
| $U_{o}$ | Operating voltage | kV |
| $U_{ti}$ | Circumference of inner rectangular tunnel wall | m |
| V | $v_{4}$ | Ratio thermal resistivity dry/moist soil | |
| $V_{air}$ | Air velocity | 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/km |
| $V_{gas}$ | Volume percentage of second gas | % |
| $V_{m}$ | Molar volume | m$^3$/mol |
| W | $W_{A}$ | Armour losses | W/m |
| $W_{a_{L}}$ | Heat removed by air at outlet | W/m |
| $W_{a_{z}}$ | Heat removed by air at z | W/m |
| $W_{air}$ | Losses between cable and j-tube | W/m |
| $w_{b}$ | Width of the backfill | mm |
| $W_{c}$ | Conductor losses | W/m |
| $W_{conv_{ce}}$ | Convection heat transfer conductor-enclosure | W/m |
| $W_{conv_{sa}}$ | Convection heat transfer surface-air | W/m |
| $W_{d}$ | Dielectric losses | W/m |
| $W_{encl}$ | Enclosure losses | W/m |
| $w_{f_{1}}$ | Width of flat wires of 1st armour | mm |
| $w_{f_{2}}$ | Width of flat wires of 2nd armour | mm |
| $W_{h}$ | Heat generated by external object | W/m |
| $W_{hs}$ | Heat dissipation of heat source | W/m |
| $W_{I}$ | Ohmic losses per phase | W/m |
| $w_{p}$ | Weight correction factor | |
| $W_{p}$ | Losses in pipe | W/m |
| $W_{rad_{ce}}$ | Radiation heat transfer conductor-enclosure | W/m |
| $W_{rad_{ext}}$ | Radiation heat transfer duct/tube-air | W/m |
| $W_{rad_{int}}$ | Radiation heat transfer surface-duct/tube | W/m |
| $W_{rad_{sa}}$ | Radiation heat transfer surface-air | W/m |
| $W_{s}$ | Screen and sheath losses | W/m |
| $W_{sA}$ | Total loss in sheath and armour | W/m |
| $W_{sA_{1}}$ | Total loss in sheath and 1st armour | W/m |
| $W_{sA_{2}}$ | Total loss in sheath and 2nd armour | W/m |
| $w_{sc}$ | Width of flat screen wire | mm |
| $W_{sum}$ | 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 |
| $W_{T}$ | Trench width in multi-layer backfill | m |
| $W_{t}$ | Total losses per phase | W/m |
| $w_{t}$ | Inner width | m |
| $W_{tot}$ | Total losses per object | W/m |
| $W_{tube}$ | Losses outside of j-tube | W/m |
| X | $X_{0}$ | Zero sequence reactance | $\Omega$/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 cables | $\Omega$/m |
| $x_{p}$ | Factor for proximity effect of conductors | |
| $x_{pos}$ | Horizontal x-position in multi-layer backfill | mm |
| $x_{s}$ | 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 |
| $\xi_{cb}$ | 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 GIL conductor | |
| $Y_{d}$ | Constant Y for cables in ducts | K.m/W |
| $y_{encl}$ | Skin and proximity effect factor for 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 | |
| $y_{s}$ | Skin effect factor of conductor | |
| Z | $Z_{0}$ | Zero sequence impedance | $\Omega$/m |
| $Z_{bs}$ | Installation constant Z | |
| $z_{c}$ | Factor z to calculate skin effect coefficients for conductor | |
| $Z_{c}$ | Self impedance of phase conductor | $\Omega$/m |
| $z_{encl}$ | Factor z to calculate skin effect coefficients for enclosure | |
| $z_{h}$ | Location of the heat source | m |
| $Z_{K}$ | Factor $Z_K$ | |
| $Z_{m}$ | Mutual impedance between conductor and metal screen | $\Omega$/m |
| $z_{max}$ | Logitudinal thermal limit distance | m |
| $Z_{neg}$ | Negative sequence impedance | $\Omega$/m |
| $Z_{pos}$ | Positive sequence impedance | $\Omega$/m |
| $z_{r}$ | Location of the hottest point | m |
| $Z_{s}$ | Self impedance of metal screen | $\Omega$/m |
| $Z_{x}$ | Equivalent mutual impedance between cables | $\Omega$/m |
| $\zeta_{M}$ | Density of material | g/cm$^3$ |
