IEC SHORT CIRCUIT ANALYSIS CONCEPTS & DATA REQUIRED cy1.0 cy1.0
ETAP ETAP provid provides es two short-c short-circ ircuit uit calcula calculatio tionn me metho thods ds based based on ANSII ANSIIEEE EEE and IE! standards. "ou can select select the calculation method method #rom the Short-!ircuit Study !ase Editor. This section describes the IE! standard standard method o# calculation.
$.0
Standard !o !ompliance ETAP short-circuit calculation per IE! standards #ully complies with the latest IE! documentation as listed below% Standard
Title
IE! &0 &00'& IE! IE! &00$ &00$+$ +$-1 -1 IE! &1/&/
(i)h vo volta)e al alternatin)-cu -current ci circuit-br -brea*ers ,uses uses #or #or volt volta) a)es es ece eceeedin) din) 1000 1000 ac Electrical Installations Installations o# Ships and obile and ,ied ##shore 2nits Appl Applic icat atio ionn )ui )uide de #or #or cal calcu cula latition on o# sho short rt-c -cir ircu cuitit curr curren ents ts in low low volta)e radial systems Shor Shortt-ci circ rcui uitt cal calcu cula latition on in thre threee-ph phas asee ac syst system emss Elec Electr tric ical al e5u e5uip ipme ment nt - dat dataa #or #or shor shortt-ci circ rcui uitt curre current nt cal calcu cula latition onss in accordance with IE! 404 7ow 7ow volt volta) a)ee swit switch ch)e )ear ar and and con contro trol) l)ea ear8 r8 Part Part 1% 1% 9ene 9enera rall rule ruless 7ow volt voltaa)e swi switch) tch)eear and con control trol))ear ear8 Part art $% !irc !ircuuititbrea*ers
IE! IE! &003 &003+1 +1 IE! IE! &004 &00404 04-1 -1 IE! IE! &004 &00404 04-$ -$ IE! IE! &004 &00463 63-1 -1 IE! &00463-$
These standards are #or short-circuit calculation and e5uipment ratin) in ac systems with nominal volta)es up to $60 * and operatin) at '0 (: or &0 (:. They cover ; -
three-phase8 line-to-)round8 line-to-line8 and line-to-line-to-)round line-to-line-to-)round #aults.
IE! 404 and the associated standards classi#y short-circuit currents accordin) to their ma)nitudes ma)nitudes
s subtransient reactance and time constants. This provides provides an accurate evaluation evaluation o# the short-circuit current current #or si:in) protective devices and coordinatin) relays #or isolated systems such as ships and o##-shore plat#orms. /.0 /.0
9ene 9enera rall ?es ?escr crip iptition on o# !alc !alcul ulat atio ionn e eth thod odol olo) o)yy In IE! short-circuit calculations8 an e5uivalent volta)e source at the #ault location replaces all volta)e sources. A volta)e #actor c is applied to ad@ust the value o# the e5uivalent e5uivalent volta)e source #or minimum and maimum current calculations. All machines are represented by their internal impedances. impedances. 7ine capacitances capacitances and static loads are ne)lected. Trans#ormer taps can be set at either the nominal position or at the tapped position8 and di##erent schemes are available to correct trans#ormer impedance and system volta)es i# o##-nominal tap settin) eists.
1 OF 7
IEC SHORT CIRCUIT ANALYSIS CONCEPTS & DATA REQUIRED System impedances are assumed to be balanced three-phase8 and the method o# symmetrical components is used #or unbalanced #ault calculations. !alculations consider electrical distance #rom the #ault location to synchronous )enerators. ,or a #ar-#rom-)enerator #ault8 calculations assume that the steady-state value o# the short-circuit current is e5ual to the initial symmetrical short-circuit current. nly the dc component decays to :ero8 whereas #or a near-to-)enerator #ault8 calculations count #or both decayin) ac and dc components. The e5uivalent B ratios determine the rates o# decay o# both components8 and di##erent values are recommended #or )enerators and motors near the #ault. !alculations also di##er #or meshed and unmeshed networ*s. The #actor *8 which is used to multiply the initial short-circuit current to )et the pea* short-circuit current ip8 is de#ined di##erently #or di##erent system con#i)urations and the methods selected to calculate the B ratios. 6.0
?e#inition o# Terms IE! standards use the #ollowin) de#initions8 which are relevant in the calculations and outputs o# PowerStation. -
Initial Symmetrical Short-!ircuit !urrent
-
Pea* Short-!ircuit !urrent
-
Symmetrical Short-!ircuit Drea*in) !urrent
-
Steady-State Short-!ircuit !urrent
-
Subtransient olta)e
-
,ar-,rom-9enerator Short-!ircuit This is a short-circuit condition durin) which the ma)nitude o# the symmetrical ac component o# available short-circuit current remains essentially constant.
2 OF 7
IEC SHORT CIRCUIT ANALYSIS CONCEPTS & DATA REQUIRED
-
Near-To-9enerator Short-!ircuit This is a short-circuit condition to which at least one synchronous machine contributes a prospective initial short-circuit current which is more than twice the )enerator>s rated current8 or a short-circuit condition to which synchronous and asynchronous motors contribute more than ' o# the initial symmetrical short-circuit current < IC*= without motors.
-
Subtransient eactance
-
inimum Time ?elay
-
olta)e ,actor c This is the #actor used to ad@ust the value o# the e5uivalent volta)e source #or minimum and maimum current calculations accordin) to the #ollowin) table% Vlta!e Fa"tr " Fr $a%i## Fr $ini## S'rt(Cir"it S'rt(Cir"it Crrent Crrent Cal"latin Cal"latin "#in "#a%
N#inal Vlta!e Un
(i)h olta)e %- M /' * to $/0 * edium olta)e %- M 1 * to /' * ther olta)e %- 1000
) OF 7
1.1 1.1
1.0 1.0
1.0'
1.0
IEC SHORT CIRCUIT ANALYSIS CONCEPTS & DATA REQUIRED
'.0
!alculation ethods -
Initial Symmetrical Short-!ircuit !urrent !alculation Initial symmetrical short-circuit current
-
Pea* Short-!ircuit !urrent !alculation Pea* short-circuit current
-
ethod A - 2ni#orm ratio B. The value o# the * #actor is determined #rom ta*in) the smallest ratio o# B o# all the branches o# the networ*. nly branches that contain a total o# +0 percent o# the current at the nominal volta)e correspondin) to the short-circuit location are included. Dranches may be a series combination o# several elements.
ethod D - B ratio at the short-circuit location. The value o# the * #actor is determined by multiplyin) the * #actor by a sa#ety #actor o# 1.1'8 which covers inaccuracies caused a#ter obtainin) the B ratio #rom a networ* reduction with comple impedances.
ethod ! - E5uivalent #re5uency. The value o# the * #actor is calculated usin) a #re5uency-altered B. B is calculated at a lower #re5uency and then multiplied by a #re5uency-dependent multiplyin) #actor.
Symmetrical Short-!ircuit Drea*in) !urrent !alculation ,or a #ar-#rom-)enerator #ault8 the symmetrical short-circuit brea*in) current s initial shortcircuit current to its rated current8 as well as real power per pair o# poles o# asynchronous machines.
* OF 7
IEC SHORT CIRCUIT ANALYSIS CONCEPTS & DATA REQUIRED IE! standards allow you to include or eclude ac decay e##ect #rom asynchronous machines in the calculation. -
?! !omponent o# Short-!ircuit !urrent !alculation The dc component o# the short-circuit current #or the minimum delay time o# a protective device8 is calculated based on initial symmetrical short-circuit current and system B ratio% I dc H I>> * R $ EBP <- $.U.#.t min= < B = V W where # is the system #re5uency8 tmin is the minimum delay time o# the protective device under concern8 and B is the system value at the #aulted bus.
-
Asymmetrical Short-!ircuit Drea*in) !urrent !alculation The asymmetrical short-circuit brea*in) current #or comparison with circuit brea*er ratin)8 is calculated as the rms value o# symmetrical and dc components o# the short circuit current. ,or #uses8 it is the sum o# asymmetrical currents #rom all #irst level contribution branches.
-
Steady-State Short-!ircuit !urrent !alculation Steady-state short-circuit current s ecitation volta)e8 ratio between its initial symmetrical short-circuit current and rated current8 and other )enerator parameters8 and Ir9 is the )enerator>s rated current. The maimum steady-state current re#lects maimum modelin) inaccuracies. This value is used to determine minimum device ratin)s. The minimum steady-state current re#lects minimum modelin) inaccuracies. This value is used #or relay coordination purposes in preventin) the occurrence o# nuisance trips and loadin) deviations.
&.0
!omparison o# ?evice atin) and Short-!ircuit ?uty In the Three-Phase ?evice ?uty calculation8 PowerStation compares the protective device ratin) a)ainst bus short-current duty #or the devices that are chec*ed as complyin) with IE! standard and also have device ratin) entered. In case the short-circuit duty is )reater than the device duty8 PowerStation will #la) the device as underrated in both one-line dia)ram and output reports. The #ollowin) table lists the device ratin)s and short-circuit duties used #or the comparison #or !D8 7 !D8 and #uses%
+ OF 7
IEC SHORT CIRCUIT ANALYSIS CONCEPTS & DATA REQUIRED ?evice Type !D a*in)
?evice !apability S! !urrent ?uty a*in) ip A! Drea*in) Ib8symm Ib8asymm Y Ib8 asymm Idc Y 7 !D a*in) Ip A! Drea*in) Ib8symm Ib8asymm Y Ib8 asymm Idc Y ,use Drea*in) Ib8symm Ib8asymm Y Ib8asymm !omparison o# ?evice atin) and Short-!urrent ?uty Y?evice capability calculated by PowerStation. 3.0
Transient Short-!ircuit !alculation In additional to device duty calculations8 PowerStation also provides transient shortcircuit calculation per IE! standard &1/&/-1. The transient short-circuit calculation presents #ault current wave#orms as a #unction o# time8 considerin) a number o# #actors that a##ect short-circuit current variations at di##erent time a#ter the #ault. These #actors include synchronous machine subtransient reactance8 transient reactance8 reactance8 subtransient time constant8 transient time constant8 and dc time constant. It also considers decay o# short-circuit contributions #rom induction motors. This detailed modelin) provides an accurate evaluation o# the short-circuit current #or si:in) protective devices and coordinatin) relays #or isolated systems such as ships and o##-shore plat#orms. The calculation can be conducted on both radial and looped system with one or multiply sources. As calculation results8 PowerStation provides short-circuit current as #unction o# time up to 0.1 second at 0.001 second time increment. It also presents short-circuit current as #unction o# cycles up to 1 cycle at 0.1 cycle increment. Alon) with the instantaneous current values8 PowerStation also #urnish calculated A! component8 ?! component8 as well as top envelope o# the current wave#orm. In the summary pa)e8 it also provides the subtransient8 transient8 and steady-state #ault current #or each bus.
+.0
!alculation o# IE! ?evice !apability As Shown in the above table8 some o# the dvice capability values are calculated by PowerStation based on capability provided by users and de#ault parameters )iven in IE! standards.
!D ; The asymmetrical brea*in) and dc current ratin)s #or !D are calculated as #ollows8 Ib8 asymm H Ib8 symm R 1 $ EBP <- 6.U.#.t min= < B = V W I dc H Ib8 symm R $ EBP <- $.U.#.t min= < B = V W Lhere # is the system #re5uency8 tmin is the minimum delay time8 and Ib8symm is the A! brea*in) current provided by the user. ,ollowin) IE! Standard '&8 ,i)ure 48 B is calculated based on a testin) P, o# 3 at '0(:.
7 !D ; The asymmetrical brea*in) current ratin) #or 7 !D is calculated as #ollows% , OF 7
IEC SHORT CIRCUIT ANALYSIS CONCEPTS & DATA REQUIRED
Ib8 asymm H Ib8 symm R 1 $ EBP <- 6.U.#.t min= < B = V W Lhere # is the system #re5uency8 tmin is the minimum delay time8 and Ib8symm is the brea*in) current provided by the user. B is calculated based on a testin) P, )iven in IE! Standard 463-$8 Table BI.
,use ; The asymmetrical brea*in) current ratin) #or #use is calculated as #ollows% Ib8 asymm H Ib8 symm R 1 $ EBP <- 6.U.#.t min= < B = V W Lhere # is the system #re5uency8 tmin is assumed to be a hal# cycle8 and Ib8symm is the brea*in) current provided by the user. B is calculated based on the de#ault testin) P,o# 1' .
7 OF 7
