Library

Symbols

Symbol	Meaning	Unit	Topic
$3 I_{0}$	symmetrical earth fault current	kA	Grid current
$a$	Wenner spacing	m	Two-layer soil
$A$	minimum cross-section of the conductor	mm²	Conductor sizing
$A$	area of the mat	m²	Grid resistance and GPR
$A$	height of the protected level	m	Masts and shield wires
$α_{r}$	thermal coefficient of resistivity at 20 °C	1/°C	Conductor sizing
$c$	plan point of the sphere's centre		Masts and shield wires
$c$	voltage factor, $c_{\max}$ or $c_{\min}$		Short-circuit currents by IEC 60909-0
$C_{s}$	surface layer derating factor		Step voltage
$C_{s}$	surface layer derating factor ([[surface-layer]])		Tolerable body current
$C_s$, $\rho_s$, $t_s$	derating factor and resistivity of the surface layer, shock time ([[surface-layer]])		Mesh voltage and touch voltage
$d$	diameter of the mat's conductor	m	Mesh voltage and touch voltage
$d$	plan distance of the element from $c$	m	Masts and shield wires
$D$	spacing between parallel conductors	m	Mesh voltage and touch voltage
$D_{f}$	decrement factor		Grid current
$e$	the base of the natural logarithm		Direct stroke shielding by the rolling sphere
$E$	driving voltage, the maximum system voltage line to neutral	kV	Short-circuit duty by IEEE C37.010
$E (P)$	lowest height the sphere reaches at $P$	m	Masts and shield wires
$E_{0}$	corona inception gradient	kV/m	Direct stroke shielding by the rolling sphere
$E_{m}$	mesh voltage	V	Mesh voltage and touch voltage
$E_{step}$	tolerable step voltage	V	Step voltage
$E_{step50}$	tolerable step voltage for a person of 50 kg	V	Step voltage
$E_{\mathrm{touch50}}$, $E_{\mathrm{step50}}$	tolerable touch and step voltage for a person of 50 kg	V	Tolerable body current
$E_{s}$	step voltage of the mat	V	Step voltage
$f$	system frequency	Hz	Short-circuit duty by IEEE C37.010
$h$	burial depth of the mat	m	Grid resistance and GPR
$h$	depth of the upper layer	m	Two-layer soil
$h$	height of the protected conductor above the ground	m	Direct stroke shielding by the rolling sphere
$H$	height of the site above the {{clear.altitude_220.alt_std}} the clearances hold for, 0 below it	m	Electrical clearances
$H (c)$	lowest height of the sphere's centre over $c$	m	Masts and shield wires
$h_{s}$	depth of the surface layer	m	Step voltage
$I$	rms fault current	kA	Conductor sizing
$I_{k}^{''}$	initial symmetrical short-circuit current	kA	Peak current and thermal equivalent current
$I_{k 1}^{''}$	initial symmetrical current of a line-to-earth fault	kA	Short-circuit currents by IEC 60909-0
$I_{k 1 Q}^{''}$	single-phase fault level of the grid at the remote bus	kA	Symmetrical components
$I_{k 2}^{''}$	initial symmetrical current of a line-to-line fault	kA	Short-circuit currents by IEC 60909-0
$I_{k 2 E L 2}^{''}$	current in phase L2 of a line-to-line-to-earth fault (phase L3 with $\underline{a}^2$)	kA	Short-circuit currents by IEC 60909-0
$I_{k 3}^{''}$	initial symmetrical current of a three-phase fault	kA	Short-circuit currents by IEC 60909-0
$I_{k E 2 E}^{''}$	current to earth of a line-to-line-to-earth fault	kA	Short-circuit currents by IEC 60909-0
$I_{k Q}^{''}$	three-phase fault level of the grid at the remote bus	kA	Short-circuit currents by IEC 60909-0
$I_{0}$	zero-sequence current	A	Symmetrical components
$I_3$, $I_1$	symmetrical three-phase and line-to-ground currents	kA	Short-circuit duty by IEEE C37.010
$I_{B}$	body current that a person of 50 kg tolerates	A	Step voltage
$I_{B,50}$, $I_{B,70}$	body current a person of 50 kg or 70 kg tolerates	A	Tolerable body current
$I_{G}$	maximum grid current	kA	Grid current
$I_{G}$	maximum grid current ([[grid-current]])	A	Grid resistance and GPR
$I_{close}$	rated closing and latching current, peak	kA	Circuit breakers and isolators
$I_{NGR}$	rated current of the neutral grounding resistor	A	Earthing of the neutral
$I_{th}$	thermal equivalent short-circuit current	kA	Peak current and thermal equivalent current
$i_{p}$	peak short-circuit current	kA	Peak current and thermal equivalent current
$I_{s}$	allowable stroke current	kA	Direct stroke shielding by the rolling sphere
$I_{sc}$	rated short-circuit current of the breaker, r.m.s. symmetrical	kA	Circuit breakers and isolators
$k$	striking distance factor		Direct stroke shielding by the rolling sphere
$K$	reflection factor of the interface		Two-layer soil
$k_{0}$	ratio of the transformer's zero-sequence to positive-sequence impedance		Short-circuit currents by IEC 60909-0
$K_{0}$	$1/\alpha_0$, the inverse of the coefficient at 0 °C	°C	Conductor sizing
$K_{a}$	atmospheric correction factor for altitude		Electrical clearances
$κ$	peak factor		Peak current and thermal equivalent current
$κ_{b}$	peak factor by [[#eq-kappa]] from the R/X ratio at the fault location		Peak current and thermal equivalent current
$K_{h}$	correction for the burial depth, with $h_0$ = 1 m		Mesh voltage and touch voltage
$K_{i}$	irregularity factor		Mesh voltage and touch voltage
$K_{ii}$	correction for the inner meshes, 1 with electrodes on the perimeter		Mesh voltage and touch voltage
$K_{m}$	spacing factor for mesh voltage		Mesh voltage and touch voltage
$K_{s}$	spacing factor for step voltage		Step voltage
$K_{S}$	correction factor of a power station unit with an on-load tap changer		Per-unit quantities
$K_{T}$	correction factor of a network transformer		Short-circuit currents by IEC 60909-0
$l$, $n$	length of the line, number of parallel circuits	km,	Short-circuit currents by IEC 60909-0
$L_{C}$	total length of horizontal conductor	m	Step voltage
$L_C$, $L_R$	total length of horizontal conductor and of electrodes	m	Mesh voltage and touch voltage
$L_{M}$	effective length for mesh voltage	m	Mesh voltage and touch voltage
$L_{P}$	perimeter of the mat	m	Mesh voltage and touch voltage
$L_{r}$	length of one electrode	m	Mesh voltage and touch voltage
$L_{R}$	total length of electrodes	m	Step voltage
$L_{S}$	effective length of conductor and electrodes for step voltage	m	Step voltage
$L_{T}$	total buried length, conductor and electrodes	m	Grid resistance and GPR
$L_x$, $L_y$	length and width of the mat	m	Mesh voltage and touch voltage
$m$	exponent of the correction, which the design takes as 1		Electrical clearances
$m$	factor for the heat effect of the DC component		Peak current and thermal equivalent current
$BIL$	basic lightning impulse insulation level of the protected level	kV	Direct stroke shielding by the rolling sphere
$GPR$	rise of earth potential of the mat	V	Grid resistance and GPR
$TCAP$	thermal capacity per unit volume	J/(cm³·°C)	Conductor sizing
$M F$	duty factor on the symmetrical current		Short-circuit duty by IEEE C37.010
$n$	geometry factor of the mat		Mesh voltage and touch voltage
$n$	order of the reflection		Two-layer soil
$n$	factor for the heat effect of the AC component, {{sc.peak_220.n}} far from a generator		Peak current and thermal equivalent current
$n_a$, $n_b$	factors of the geometry factor for a rectangular mat		Mesh voltage and touch voltage
$ω$	angular frequency, $2\pi f$	rad/s	Grid current
$P$	protected point, in plan		Masts and shield wires
$P$	plant capacity	MW	Reactive power equipment
$π$	the ratio of a circle's circumference to its diameter		Soil resistivity and Wenner readings
$Q_{\mathrm{SVG}}$, $Q_{\mathrm{STATCOM}}$	total rating of the reactive power device, plus and minus	Mvar	Reactive power equipment
$r$	radius of the protected conductor	m	Direct stroke shielding by the rolling sphere
$R$	resistance the earth tester reads	Ω	Soil resistivity and Wenner readings
$R / X$	ratio of the resistance to the reactance of the positive-sequence impedance at the fault location		Peak current and thermal equivalent current
$R_1$, $X_1$	positive-sequence resistance and reactance of a line circuit	Ω/km	Short-circuit currents by IEC 60909-0
$R_{B}$	resistance of the body	Ω	Step voltage
$R_{c}$	corona radius	m	Direct stroke shielding by the rolling sphere
$R_{f}$	contact resistance of one foot on the surface layer	Ω	Step voltage
$R_{g}$	grid resistance	Ω	Grid resistance and GPR
$ρ$	resistivity of the soil	Ω·m	Grid resistance and GPR
$ρ$	apparent resistivity of the soil	Ω·m	Soil resistivity and Wenner readings
$ρ$	resistivity of the soil below the surface layer	Ω·m	Step voltage
$ρ$	resistivity of the soil below the layer	Ω·m	Surface layer and Cs
$\rho_1$, $\rho_2$	resistivity of the upper and the lower layer	Ω·m	Two-layer soil
$ρ_{a}$	apparent resistivity at spacing $a$	Ω·m	Two-layer soil
$ρ_{r}$	resistivity of the conductor at 20 °C	µΩ·cm	Conductor sizing
$ρ_{s}$	resistivity of the surface layer	Ω·m	Step voltage
$R_{NGR}$	resistance of the neutral grounding resistor	Ω	Earthing of the neutral
$R_{NGR}$	resistance of the neutral earthing resistor	Ω	Symmetrical components
$S$	distance between successive electrodes	m	Soil resistivity and Wenner readings
$S$	radius of the rolling sphere of the protected level	m	Masts and shield wires
$S$	striking distance, the radius of the rolling sphere	m	Direct stroke shielding by the rolling sphere
$S$	rated asymmetrical capability of the breaker per unit of its rated short-circuit current, at $t$		Short-circuit duty by IEEE C37.010
$S_{f}$	split factor		Grid current
$t$	contact parting time	ms	Short-circuit duty by IEEE C37.010
$t$	ratio of the MV to the HV nominal voltage		Earthing of the neutral
$T_{a}$	ambient temperature	°C	Conductor sizing
$τ$	DC time constant of the fault current, which IEEE 80-2013 writes $T_a$	s	Grid current
$τ$	DC time constant of the fault	ms	Short-circuit duty by IEEE C37.010
$t_{c}$	duration of the current	s	Conductor sizing
$t_{f}$	duration of the fault	s	Grid current
$T_{k}$	duration of the short-circuit current	s	Peak current and thermal equivalent current
$T_{m}$	maximum allowable temperature	°C	Conductor sizing
$t_{r}$	rated ratio of the generator transformer, HV over LV		Per-unit quantities
$t_{s}$	duration of the shock current	s	Step voltage
$u_{k r}$	rated short-circuit voltage of the transformer	%	Short-circuit currents by IEC 60909-0
$U_{n}$	nominal voltage of the MV system	kV	Earthing of the neutral
$U_n$, $U_{nQ}$	nominal voltage of the faulted bus, of the grid bus	kV	Short-circuit currents by IEC 60909-0
$a$	rotation operator, $e^{j2\pi/3}$		Short-circuit currents by IEC 60909-0
$U_{n Q}$	nominal voltage of the HV bus	kV	Per-unit quantities
$U_r$, $S_r$	rated voltage and rated apparent power of the equipment	kV, MVA	Per-unit quantities
$U_{rG}$, $S_{rG}$	rated voltage and rated apparent power of the generator	kV, MVA	Per-unit quantities
$U_{rT}$, $S_{rT}$	rated voltage on the HV side, rated apparent power	kV, MVA	Short-circuit currents by IEC 60909-0
$U_{rT}$, $S_{rT}$	rated voltage of the transformer on the side considered, rated apparent power	kV, MVA	Per-unit quantities
$U_{rTHV}$, $U_{rTLV}$	rated voltages of the generator transformer, HV and LV side	kV	Per-unit quantities
$φ_{r G}$	phase angle of the generator at its rated power factor		Per-unit quantities
$x_{d}^{''}$	subtransient reactance of the generator, per unit of its rating		Per-unit quantities
$X / R$	ratio of reactance to resistance of the fault path		Grid current
$X_1$, $R_1$, $X_0$, $R_0$	positive- and zero-sequence reactance and resistance at the fault, from the separate reductions	Ω	Short-circuit duty by IEEE C37.010
$x_{T}$	relative reactance of the transformer, $X_T$ per unit of $U_{rT}^2/S_{rT}$		Short-circuit currents by IEC 60909-0
$x_{T}$	relative reactance of the transformer		Per-unit quantities
$z$	height of a wire, tower or mast	m	Masts and shield wires
$Z_{0, MV}$	zero-sequence impedance of a MV section	Ω	Earthing of the neutral
$Z_1$, $Z_2$, $Z_0$	positive-, negative- and zero-sequence impedance at the fault location	Ω	Short-circuit currents by IEC 60909-0
$Z_{b}$	base impedance, $U_r^2/S_r$	Ω	Per-unit quantities
$Z_{G}$	impedance of the generator	Ω	Per-unit quantities
$Z_Q$, $R_Q$, $X_Q$	impedance, resistance and reactance of the network feeder	Ω	Short-circuit currents by IEC 60909-0
$Z_{Q1}$, $Z_{Q0}$	positive- and zero-sequence impedance of the grid feeder	Ω	Symmetrical components
$Z_{s}$	surge impedance of the conductor under corona	Ω	Direct stroke shielding by the rolling sphere
$Z_{S}$	impedance of the power station unit, referred to the HV bus	Ω	Per-unit quantities
$Z_T$, $X_T$	impedance and reactance of the transformer	Ω	Per-unit quantities
$Z_{T 0}$	zero-sequence impedance of the ICT, seen from the HV side	Ω	Earthing of the neutral
$Z_{T H V}$	impedance of the generator transformer, referred to its HV side	Ω	Per-unit quantities