| 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$^2$ |
| $A_{c}$ | Cross-sectional area of conductor | mm$^2$ |
| $a_{c}$ | Skin and proximity effect coefficient a for GIL conductor | |
| $A_{comp}$ | Cross-sectional area of compartment | m$^2$ |
| $A_{d}$ | Cross-sectional area of duct wall | mm$^2$ |
| $A_{d_{fill}}$ | Free cross-sectional area inside duct | mm$^2$ |
| $A_{encl}$ | 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$^2$ |
| $A_{ins}$ | Cross-sectional area of insulation | mm$^2$ |
| $A_{j}$ | Cross-sectional area of jacket | mm$^2$ |
| $A_{k}$ | Thermal property constant A | mm/s$^{1/2}$ |
| $a_{m}$ | Mean distance between the phases | mm |
| $A_{pipe}$ | Cross-sectional area of fluid-filled pipe | mm$^2$ |
| $A_{prot}$ | 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$^2$ |
| $a_{T}$ | Distance a of multi-layer backfill | m |
| $A_{t}$ | Cross-sectional area of the tunnel | m$^2$ |
| $a_{type}$ | Construction of armour | |
| $a_{VdW}$ | Van der Walls constant a | bar.L$^2$/mol$^2$ |
| $\alpha_{0}$ | Constant depending on the burial depth | |
| $\alpha_{ar}$ | Temperature coefficient of armour material | 1/K |
| $\alpha_{at}$ | Heat transfer coefficient to channel wall | W/K/m$^2$ |
| $\alpha_{c}$ | Temperature coefficient of conductor material | 1/K |
| $\alpha_{encl}$ | Temperature coefficient of enclosure material | 1/K |
| $\alpha_{f}$ | Phase shift | $^{\circ}$ |
| $\alpha_{gas}$ | 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 |
| $\beta_{0}$ | Constant $\beta_0$ acc. Ovuworie | |
| $\beta_{1}$ | 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 |
| $\beta_{b}$ | Angle of exposed wetted surface of pipe | rad |
| $\beta_{c}$ | Reciprocal of temperature coefficient of conductor material | K |
| $\beta_{encl}$ | Reciprocal of temperature coefficient of enclosure material | K |
| $\beta_{gas}$ | Volumetric thermal expansion coefficient for gas | 1/K |
| $\beta_{k}$ | Reciprocal of temperature coefficient of resistance | K |
| $\beta_{M}$ | Factor $\beta_M$ | |
| $\beta_{sc}$ | Reciprocal of temperature coefficient of screen material | K |
| $\beta_{sh}$ | Reciprocal of temperature coefficient of sheath material | K |
| $\beta_{t}$ | Attainment factor cable surface to ambient | |
| $\beta_{T}$ | Equivalent thermal resistance of the soil per unit surface | W/(K.m$^2$) |
| $\beta_{X}$ | Crossing angle in radians | rad |
| $\beta_{xing}$ | Crossing angle in degrees | $^{\circ}$ |
| $\mathrm{Bi}_{g}$ | Biot number of the ground | |
| $\mathrm{Bi}_{p}$ | Biot number of the pipe | |
| C | $C_{av}$ | Heat capacity of the air flow | W/K |
| $C_{b}$ | Capacitance of insulation | F/m |
| $C_{b3}$ | Factor C3 for partially buried pipes | |
| $C_{g1}$ | Factor C1 for partially buried pipes | |
| $C_{g2}$ | Factor C2 for partially buried pipes | |
| $c_{gas}$ | 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 |
| $C_{\mathrm{Nu}_{L}}$ | Factor C | |
| $C_{\mathrm{Nu}_{w}}$ | Factor C | |
| $c_{p_{gas}}$ | Specific heat capacity at constant pressure | J/kg.K |
| $c_{p_{soil}}$ | Specific heat capacity of soil | J/kg.K |
| $c_{p_{w}}$ | 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 |
| $c_{type}$ | Construction of conductor | |
| $c_{v_{gas}}$ | Specific heat capacity at constant volume | J/kg.K |
| $c_{v_{w}}$ | 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 |
| $d_{a_{1}}$ | Mean diameter of 1st armour | mm |
| $D_{a_{1}}$ | External 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 |
| $D_{ext}$ | Overall outer diameter of pipe | m |
| $D_{f}$ | External diameter of the filler | mm |
| $d_{f}$ | Spacing from hottest object in group | m |
| $d_{f_{1}}$ | Thickness of 1st armour | mm |
| $d_{f_{2}}$ | Thickness of 2nd armour | mm |
| $d_{im}$ | Imaginary layer of soil | m |
| $D_{in}$ | Inner diameter of pipe | m |
| $D_{ins}$ | Diameter over insulation | mm |
| $d_{ins}$ | Diameter of insulation around pipe | mm |
| $D_{it}$ | Diameter below sheath | mm |
| $d_{j}$ | Diameter below jacket | m |
| $D_{o}$ | 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 |
| $D_{ref}$ | Reference diameter for determination of OHTC | 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$^3$ |
| $D_{soil}$ | Outer diameter of soil layer | m |
| $d_{T}$ | Distance d of multi-layer backfill | m |
| $d_{t}$ | Channel covering | m |
| $d_{w}$ | Depth under water | m |
| $D_{wall}$ | Outer diameter of steel pipe | m |
| $d_{x}$ | Equivalent diameter of a conductor | mm |
| $D_{x}$ | Characteristic diameter | mm |
| $D_{x_{w}}$ | Characteristic diameter for weekly load | mm |
| $D_{x_{y}}$ | Characteristic diameter for yearly load | mm |
| $DC_{p}$ | Diameter factor in duct | % |
| $\Delta _{1}$ | Substitution coefficient $\Delta_1$ for eddy-currents | |
| $\delta _{1}$ | Thickness of screening layer | mm |
| $\Delta _{2}$ | Substitution coefficient $\Delta_2$ for eddy-currents | |
| $\delta _{ar}$ | Equivalent thickness of armour | mm |
| $\delta _{k}$ | 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 |
| $\Delta \theta_{c}$ | Temperature rise of conductor | K |
| $\delta \theta_{c}$ | Ohmic steady-state temperature rise | K |
| $\Delta \theta_{c_{t}}$ | Transient temperature rise of conductor by ohmic losses | K |
| $\Delta \theta_{ce}$ | Temperature difference conductor to surface | K |
| $\Delta \theta_{d}$ | Temperature rise by dielectric losses | K |
| $\Delta \theta_{e_{t}}$ | Transient temperature rise of outer surface | K |
| $\Delta \theta_{gas}$ | Temperature difference conductor-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 |
| $DF$ | Derating factor for the permissible current | |
| $Di_{d}$ | Inner diameter of duct | mm |
| $di_{pipe}$ | Internal diameter of fluid-filled pipe | mm |
| $Di_{t}$ | Tunnel inner diameter | m |
| $Do_{d}$ | Outer diameter of duct | mm |
| $do_{pipe}$ | External pipe diameter | mm |
| $Do_{t}$ | Tunnel/trough outer diameter | m |
| E | $E_{bs}$ | Installation constant E | |
| $e_{hor}$ | Horizontal clearance | mm |
| $e_{limit}$ | Limit of thickness of soil layer | m |
| $e_{soil}$ | Thickness of soil layer | m |
| $E_{stress}$ | 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 tube inner surface | |
| $\epsilon_{do}$ | Emissivity of 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 |
| $\eta_{w}$ | Dynamic viscosity of water | 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 |
| $\mathrm{Gr}_{c}$ | Grashof number conductor-gas | |
| $\mathrm{Gr}_{encl}$ | Grashof number gas-enclosure | |
| $\mathrm{Gr}_{L}$ | Grashof number ground-air | |
| $\mathrm{Gr}_{prot}$ | Grashof number surface-air | |
| H | $H$ | Distance center of pipe to ground | m |
| $h_{1}$ | 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 |
| $h_{amb}$ | Pseudo film coefficient of ambient fluid at ground level | W/(K.m$^2$) |
| $h_{atm}$ | Height above sea level | m |
| $h_{b}$ | Height of the backfill | mm |
| $h_{bs}$ | Heat dissipation coefficient for black surfaces in free air | W/m$^2$/K$^{5/4}$ |
| $h_{buried}$ | Heat transfer coefficient wall to soil | W/(K.m$^2$) |
| $H_{c}$ | Heat energy content | MJ/m |
| $h_{c}$ | Convective heat transfer coefficient conductor-gas | W/(K.m$^2$) |
| $h_{conv_{sa}}$ | Convective heat transfer coefficient surface-air | W/(K.m$^2$) |
| $h_{encl}$ | Convective heat transfer coefficient gas to enclosure | W/m2.K |
| $h_{ext}$ | External heat transfer coefficient | W/(K.m$^2$) |
| $h_{ground}$ | Heat transfer coefficient buried part of wall to soil | W/(K.m$^2$) |
| $h_{in}$ | The internal heat transfer coefficient (or inside film coefficient) is also a convection coefficient, calculated from the Nusselt number of the internal fluid. It is the heat transfer by convection at the inner surface of the pipe wall in contact with the pipeline product (gas, oil, water, and possibly solids. In cables, there is no fluid flow at the inner surface of the insulation. In GIL, the convection of the gas inside the chamber is considered separately. In both cases, the value of $h_{in}$ is set to quasi-infinity in order to eliminate the its influence. | W/(K.m$^2$) |
| $h_{lg}$ | Ratio of heat dissipation coefficients | |
| $h_{rad_{ce}}$ | 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 |
| $h_{soil}$ | Heat transfer coefficient wall-soil | W/(K.m$^2$) |
| $H_{sun}$ | 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/(m.K) |
| $K_{10}$ | Factor $K_{1.0}$ | |
| $k_{2}$ | Thermal conductivity of mid backfill layer | W/(m.K) |
| $k_{3}$ | Thermal conductivity of bedding layer | W/(m.K) |
| $k_{4}$ | Thermal conductivity of soil | W/(m.K) |
| $K_{A}$ | Coefficient K to calculate in air | |
| $k_{air}$ | Thermal conductivity of air | W/(m.K) |
| $K_{BICC}$ | 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-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 | |
| $K_{par}$ | Constant acc. Ovuworie | |
| $k_{pipe}$ | Thermal conductivity of fluid-filled pipe | W/(m.K) |
| $k_{prot}$ | 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 | |
| $k_{t}$ | Temperature rise ratio | p.u. |
| $K_{t}$ | Effective emissivity of surface | |
| $K_{vermeer}$ | Vermeer constant for convection heat transfer | |
| $k_{w}$ | Thermal conductivity of water | W/(m.K) |
| $K_{x}$ | Factor for fictitious diameter by Neher | |
| $k_{X}$ | Number of heat sources crossing | |
| 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 earth surface | |
| $L_{cm}$ | Depth of laying | 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. |
| $m_{0}$ | Substitution coefficient $m_0$ for eddy-currents | Hz.m/$\Omega$ |
| $M_{0}$ | Coefficient M for partial transient temperature rise | s |
| $M_{1}$ | Corrected cyclic rating factor | K |
| $M_{ab}$ | Material of armour bedding | |
| $M_{c}$ | 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 pipe | |
| $M_{j}$ | Material of jacket | |
| $M_{k}$ | Thermal contact factor | s$^{1/2}$ |
| $M_{mol}$ | Molar mass | g/mol |
| $m_{mol}$ | Molecular mass | mol |
| $m_{\mathrm{Nu}_{L}}$ | Factor m | |
| $m_{\mathrm{Nu}_{w}}$ | Factor m | |
| $M_{pipe}$ | Material of fluid-filled pipe | |
| $M_{prot}$ | Material of protective cover | |
| $M_{s}$ | Factor $M_s$ | |
| $M_{sc}$ | Material of screen | |
| $M_{seabed}$ | Material of seabed | |
| $M_{sh}$ | Material of sheath | |
| $M_{soil}$ | Type of soils | |
| $\mu$ | 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 conductors in object | |
| $N_{c}$ | Number of sources in system | |
| $n_{cc}$ | Number of conductors combined | |
| $n_{cg}$ | Number of conductors in GIL | |
| $n_{cw}$ | Number of wires in conductor | |
| $n_{cycle}$ | Number of load cycles | |
| $N_{e}$ | Substitution coefficient $N_e$ to calculate factor $F_e$ | |
| $n_{ppc}$ | 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 | |
| $N_{X}$ | Number of intervals | |
| $\nu$ | Summation step 1 to $N_X$ | |
| $\nu_{air}$ | Kinematic viscosity for air | m$^2$/s |
| $\mathrm{Nu}_{c}$ | Nusselt number conductor-gas | |
| $\mathrm{Nu}_{encl}$ | Nusselt number gas-enclosure | |
| $\nu_{gas}$ | Kinematic viscosity for gas | m$^2$/s |
| $\mathrm{Nu}_{L}$ | Nusselt number ground-air | |
| $\mathrm{Nu}_{prot}$ | Nusselt number surface-air | |
| $\nu_{soil}$ | Soil moisture content | % |
| $\mathrm{Nu}_{w}$ | Nusselt number surface-water | |
| $\nu_{w}$ | Kinematic viscosity for water | m$^2$/s |
| O | $\omega$ | Angular frequency | rad/s |
| P | $p_{a_{1}}$ | Length of lay of 1st armour | mm |
| $p_{a_{2}}$ | Length of lay of 2nd armour | mm |
| $p_{ab1}$ | 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 |
| $p_{w}$ | Water pressure | bar |
| $\phi_{b}$ | Parameter $\phi$ for trough | |
| $\phi_{p}$ | Angle of a bend | rad |
| $\pi$ | Archimedes' constant $\pi$ | |
| $\mathrm{Pr}_{air}$ | Prandtl number for air | |
| $\mathrm{Pr}_{gas}$ | Prandtl number for gas | |
| $\mathrm{Pr}_{w}$ | Prandtl number for liquids | |
| Q | $q_{1}$ | Ratio of losses affecting screen bedding/serving | |
| $q_{2_{1}}$ | 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 method | 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 | |
| $r_{o}$ | Radius of object | m |
| $R_{p}$ | 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 |
| $\mathrm{Ra}_{c}$ | Rayleigh number conductor-gas | |
| $\mathrm{Ra}_{encl}$ | Rayleigh number gas-enclosure | |
| $\mathrm{Ra}_{L}$ | Rayleigh number ground-air | |
| $\mathrm{Ra}_{prot}$ | Rayleigh number surface-air | |
| $\mathrm{Re}_{air}$ | Reynolds number for air | |
| $\mathrm{Re}_{w}$ | Reynolds number for water | |
| $RF$ | Reduction factor | |
| $\rho_{4}$ | Thermal resistivity of soil | K.m/W |
| $\rho_{4d}$ | Thermal resistivity of dry soil | K.m/W |
| $\rho_{ab}$ | Thermal resistivity of armour bedding | K.m/W |
| $\rho_{ab_{2}}$ | 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 tube inner surface | |
| $\rho_{do}$ | Reflectivity of 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 |
| $\rho_{w}$ | Density of water | kg/m$^3$ |
| 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$^3$ |
| $\sigma_{pipe}$ | Specific heat capacity of fluid-filled pipe | 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 | |
| $\sigma_{y}$ | 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 |
| $T_{1}$ | Thermal resistance between one conductor and sheath | K.m/W |
| $t_{1}$ | Thickness of insulation to sheath | mm |
| $T_{1t}$ | Thermal resistance between one conductor and sheath, transient | K.m/W |
| $t_{1t}$ | Thickness of insulation to sheath, transient | mm |
| $T_{2}$ | Thermal resistance between sheath and armour | K.m/W |
| $t_{2}$ | Thickness of bedding under armour | mm |
| $T_{2_{1}}$ | 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 |
| $T_{3}$ | Thermal resistance of jacket | K.m/W |
| $t_{3}$ | Thickness of serving over armour | mm |
| $T_{4d}$ | 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 |
| $T_{i}$ | Internal thermal resistance for current losses | K.m/W |
| $t_{icore}$ | Thickness of core insulation | mm |
| $T_{\infty}$ | Infinite bulk temperature (the ambient air temperature) | K |
| $T_{ins}$ | Thermal resistance of insulation | K.m/W |
| $t_{ins}$ | 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 tube-air | K.m/W |
| $T_{rad_{int}}$ | Radiation thermal resistance surface-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 |
| $t_{t}$ | Tunnel wall thickness | m |
| $T_{t}$ | Star thermal resistance of tunnel | K.m/W |
| $T_{tot}$ | Total thermal resistance, transient | K.m/W |
| $T_{tr}$ | Thermal resistance of trough | K |
| $T_{tw}$ | Thermal resistance of tunnel wall | K.m/W |
| $T_{wall}$ | Thermal resistance of pipe wall | K.m/W |
| $\mathrm{tan}\delta _{i}$ | Loss factor of insulation | |
| $\tau$ | Transient load period | s |
| $\tau_{L}$ | Transient load period deep burial | 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 |
| $\theta_{w}$ | Water temperature | $^{\circ}$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 |
| $u_{b}$ | Substitution coefficient u | |
| $U_{buried}$ | OHTC of fully buried pipe | W/(K.m$^2$) |
| $U_{d}$ | Constant U for cables in ducts | K.m/W |
| $U_{e}$ | Line-to-ground voltage | kV |
| $U_{exposed}$ | OHTC of part of pipe in contact with water | W/(K.m$^2$) |
| $U_{ground}$ | OHTC of part of pipe in contact with ground | W/(K.m$^2$) |
| $U_{inwall}$ | OHTC of inside film and pipe wall | W/(K.m$^2$) |
| $U_{m}$ | Highest voltage for equipment | kV |
| $U_{n}$ | Rated line-to-line voltage | kV |
| $U_{o}$ | Operating voltage | kV |
| $U_{OHTC}$ | Overall heat transfer coefficient | W/(K.m$^2$) |
| $U_{partially}$ | OHTC of partially buried pipe | W/(K.m$^2$) |
| $U_{ti}$ | Circumference of inner rectangular tunnel wall | m |
| $U_{wall}$ | OHTC of pipe wall | W/(K.m$^2$) |
| V | $v_{4}$ | Ratio thermal resistivity dry/moist soil | |
| $V_{air}$ | Air velocity | m/s |
| $V_{comp}$ | Gas volume | m$^3$ |
| $V_{d}$ | Constant V for cables in ducts | K.m/W |
| $V_{drop}$ | Voltage drop | V/A/km |
| $V_{fluid}$ | Velocity of fluid | cm/s |
| $V_{gas}$ | Volume percentage of second gas | % |
| $V_{m}$ | Molar volume | m$^3$/mol |
| $V_{w}$ | Velocity of water | cm/s |
| 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 |
| $W_{p}$ | Losses in pipe | W/m |
| $w_{p}$ | Weight correction factor | |
| $W_{rad_{ce}}$ | Radiation heat transfer conductor-enclosure | W/m |
| $W_{rad_{ext}}$ | Radiation heat transfer tube-air | W/m |
| $W_{rad_{int}}$ | Radiation heat transfer surface-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 |
| $W_{t}$ | Total losses per phase | W/m |
| $W_{T}$ | Trench width in multi-layer backfill | 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 | |
| $Z_{c}$ | Self impedance of phase conductor | $\Omega$/m |
| $z_{c}$ | Factor z to calculate skin effect coefficients for conductor | |
| $z_{encl}$ | 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$^3$ |