reference iec61363

8/9/2019 Reference IEC61363

1/26

IEC_6 363 FAULT Study

This chapter examines the short-circuit current calculation procedures used in the

IEC_61363 Short Circuit Study.

The IEC_61363 Study follows the specifications of theInternational Electrotechncal

Commission (IEC) International Standard 61363: Electrical installations of ships and

mobile and fixed offshore units Procedures for calculating short-circuit currents in

three-phase a.c.

This guide includes:

Engineering Methodology

Terminology and Symbols

Assumptions and Equations

PTW Applied Methodology

Examples

IN

T

H

IS

C

H

A

P

T

E

R

IEC_61363 FAULT STUDY

1.1 What is the IEC_61363 Study? 2

1.2 Engineering Methodology 2

1.3 PTW Applied Methodology 171.4 Application Example 24

SKM Power*Tools for Windows


2/26

IEC_FAULT 2 Reference Manual

1.1 What is the IEC_61363 Study?

The IEC_61363 Short Circuit Study (referred to hereafter as IEC363) models the current

that flows in the power system under abnormal conditions and determines the prospective

fault currents in an electrical power system. These currents must be calculated in order toadequately specify electrical apparatus withstand and interrupting ratings. The Study

results are also used to selectively coordinate time current characteristics of electrical

protective devices.

IEC363 represents conditions that may affect typical marine or offshore installations more

significantly than land-based systems, including more emphasis on generator and motor

decay.

1.2 Engineering Methodology

IEC Standard 61363 describes a detailed method for calculating three-phase short circuit

duties for marine or offshore installation. The Standard contains 9 chapters. Individual

paragraphs are referred to as articles or clauses, and sub-paragraphs are referred to as sub-

clauses.

1.2.1 IEC Standard 61363The IEC 61363 standard outlines procedures for calculating short-circuit currents that may

occur on a marine or offshore a.c. electrical installation.

The calculation methods are intended for use on unmeshed three-phase a.c. systems

operating at 50 Hz or 60 Hz; having any system voltage specified in IEC 60092-201 table

2; having one or more different voltage levels; comprising generators, motors,

transformers, reactors, cables and converter units; having their neutral point connected to

the ships hull through an impedance (designed to limit the short-circuit current flowing to

the ships hull; or having their neutral point isolated from the ships hull.

The IEC 61363 standard is intended for three-phase symmetrical short circuit conditions

over the first 100 ms of the fault. The effects of voltage regulators are not considered.

The primary reasons for performing the IEC 61363 short circuit calculations include:

1) obtain the short-circuit current magnitude at each point in the power system;

2) compare the calculated fault current to the ratings of installed equipment to verify

the equipment ratings are adequate to handle the short circuit current;

3) support proper selection of circuit protection equipment.

Note that marine and offshore electrical systems typically have large generating capacities

confined in a small area resulting in high short circuit values with low power factors.

Special attention is required if the calculated power factor during fault conditions is below

the power factor used to test the circuit breakers.

3/26/2006


3/26

IEC_61363 FAULT Study IEC_FAULT 3

1.2.2 DefinitionsShort circuit

accidental or intentional connection, by a relatively low resistance or impedance, of two or

more points in a circuit which are normally at different voltages. [61363-1 IEC:1998]

Short circuit current

over-current resulting from a short circuit due to a fault or an incorrect connection in and

electric circuit. [61363-1 IEC:1998]

Prospective current

Short-circuit current that would flow in the circuit if each pole of the device were replaced

by a conductor of negligible impedance. [61363-1 IEC:1998]

Symmetrical short-circuit current

r.m.s. value of the a.c. symmetrical component of a prospective short-circuit current, the

aperiodic component of current, if any, being neglected. [61363-1 IEC:1998]

Initial symmetrical short-circuit current Ik

r.m.s. value of the a.c. symmetrical component of a prospective short-circuit current

applicable at the instant of short circuit if the impedance remains at zero-time value.

[61363-1 IEC:1998]

Current

Theoretical maximum

Peak at 1/2 cycle

(DC decay)

Bottom envelope

Top envelope

Decaying (aperiodic) component i

Time

2

2

I"

i

k

p

2 2 I k

dc Asymmetrical valuesincluding motor contributions

Steady state value(no motor contributions)

dc

i

Subtransient short-circuit current Ikdin the direct axis

r.m.s. value of the short-circuit current flowing through a circuit with rotating machines

having an impedance equal to the transient impedance of the circuit. [61363-1 IEC:1998]

Transient short-circuit current Ikdin the direct axis

r.m.s. value of the short-circuit current flowing through a circuit with rotating machines

having an impedance equal to the transient impedance of the circuit. [61363-1 IEC:1998]

Steady-state short-circuit current Ikdin the direct axis

r.m.s. value of the short-circuit symmetrical current flowing through a circuit with

generators witch remains after the decay of the transient phenomena. [61363-1 IEC:1998]

Aperiodic (d.c.) component of the short-circuit current IdcComponent of current in a circuit immediately after it has been suddenly short-circuited,

all components of fundamental and higher frequencies being excluded. [61363-1

IEC:1998]

Peak short-circuit current Ip



4/26


Maximum possible instantaneous value of the prospective short-circuit current [61363-1

IEC:1998]

Direct-axis subtransient short-circuit time constant Td

Time required for the rapidly changing component, present during the first few cycles in

the direct-axis shrot-circuit current following a sudden change in operating conditions, to

decrease to 1/e, i.e. 0.368 of its initial value, the machine (or equivalent machine) runningat rated speed. [61363-1 IEC:1998]

Direct-axis subtransient open-circuit time constant Tdo

Time required for the rapidly changing component present during the first few cycles of

the open-circuit primary winding voltage which is due to direct-axis flux following a

sudden change in operation, to decrease to 1/e i.e. 0.368 of its initial value, the machine

running at rated speed. [61363-1 IEC:1998]

Direct-axis transient short-circuit time constant Td

Time required for the slowly changing component of the direct-axis short-circuit primary

current following a sudden change in operating conditions, to decrease to 1/e ie.e 0.368 of

its initial value, the machine running at rated speed. [61363-1 IEC:1998]

Direct-axis transient opencircuit time constant Tdo

Time required for a slowly changing component of the open-circuit primary voltage,

whish is due to the direct-axis flux, follwing a sudden change in operating conditions, to

decrease to 1/e i.e. 0.368 of its initial value, the machine running at rated speed. [61363-1

IEC:1998]

DC time constant Tdc

Time required for the d.c. component present in the short-circuit current, following a

sudden change in operating conditions, to decrease to 1/e i.d. 0.368 of its initial value, the

machine running at rated speed. [61363-1 IEC:1998]

Direct-axis subtransient reactance Xd (saturated)

Quotient of the initial value of a sudden change in that fundamental a.c. component ofprimary voltage, which is produced by the total direct-axis primary flux, and the value of

the simultaneous change in fundamental a.c. component of direct-axis primary current, the

machine running at rated speed. [61363-1 IEC:1998]

Direct-axis transient reactance Xd (saturated)

Quotient of the initial value of a sudden change in that fundamental a.c. component of

primary voltage, which is produced by the total direct-axis primary flux, and the value of

the simultaneous change in fundamental a.c. component of direct-axis primary current, the

machine running at rated speed and the high decrement components during the first cycles

being excluded. [61363-1 IEC:1998]

Direct-axis synchronous reactance Xd

Quotient of the steady-state value of that fundamental a.c. component of primary voltagewhich is produced by the total direct-axis primary flux, and direct-axis primary current

after the decay of the transient phenomena. [61363-1 IEC:1998]

Stator resistance of a generator Ra

Resistance of the stator of a synchronous machine, measured at d.c. current. [61363-1

IEC:1998]

Short-circuit impedance Z

3/26/2006


5/26


Quotient of the sinusoidal voltage per phase on a balanced a.c. system and the same

frequency component of the short-circuit current in that system. [61363-1 IEC:1998]

Voltage source

Active element which can be represented by an ideal voltage source independent of all

currents and voltages in the circuit, in series with a passive circuit element. [61363-1

IEC:1998]

Nominal system voltage Un

Voltage (line-to-line) by which a system is designated and to which certain operating

characteristics are referred. [61363-1 IEC:1998]

Subtransient voltage of a rotating machine E

r.m.s. value of the symmetrical internal voltage of a machine which is active behind the

subransient impedance Z at the moment of short circuit. [61363-1 IEC:1998]

Transient voltage of a rotating machine E

r.m.s. value of the symmetrical internal voltage of a machine which is active behind the

transient impedance Z at the moment of short circuit. [61363-1 IEC:1998]

Nominal value (n)

Suitable approximate quantity value used to designate or identify a component, device or

equipment. [61363-1 IEC:1998]

Rated value (r)

Quantity value assigned, generally by a manufacturer, for a specified operating condition

of a component, device or equipment. [61363-1 IEC:1998]

Equivalent generator

Fictitious generator having characteristics which will produce the same short-circuit

current at any point on an electrical installation, as would be produced by a combination

of generators having different ratings and different characteristics, which are connected to

the system. [61363-1 IEC:1998]

Equivalent motor

Fictitious motor having characteristics which will produce the same short-circuit current at

any point on an electrical installation, as would be produced by a combination of motors

having different ratings and different characteristics, which are connected to the system.

[61363-1 IEC:1998]



6/26


1.2.3 IEC 61363 Symbols

PTWs Reports and documentation conform to IEC 61363 notation, including:

f phase Angle

Eq subtransient q-axis voltage of a generator (r.m.s.)

Eq transient q-axis voltage of a generator (r.m.s.)EM subtransient voltage of a motor (r.m.s.)

f frequency

fe lowest frequency of a shaft generator

fr rated frequency of a network

I* subtransient short-circuit current of the equivalent generator (r.m.s.)

I* transient short-circuit current of the equivalent generator (r.m.s.)

I* current of the equivalent generator (r.m.s.)

IM* subtransient short-circuit current of the equivalent motor (r.m.s.)

Ikd subtransient initial short-circuit current of a synchronous machine (r.m.s.)

Ikd transient initial short-circuit current of a synchronous machine (r.m.s.)

I current (r.m.s.)

Iac a.c. component of the short-circuit current of a synchronous machine (r.m.s.)

IacM symmetrical short-circuit current of an asynchronous motor (r.m.s.)ILR asynchronous motor locked rotor current

idc d.c. component of the short-circuit current of a synchronous machine

(instantaneous).

idcM d.c. component of the short-circuit current of an asynchronous motor and an

equivalent motor (instantaneous).

ik upper envelope of the short-circuit current.

I* steady-state short-circuit current of an equivalent generator (r.m.s.)

Ikd steady-state short-circuit current of a synchronous machine (r.m.s.)

iM upper envelope of the short-circuit current of an asynchronous motor.

ip peak value of the short-circuit current of a synchronous machine.

ipM peak value of the short-circuit current of an asynchronous motor.

Ir rated current (r.m.s.)

IrM rated current of an asynchronous motorR resistance

R* resistance of an equivalent generator

Ra stator resistance of a synchronous machine

RC cable resistance

Rdc d.c. resistance

RM motor resistance

RR rotor resistance of an asynchronous motor

RR* rotor resistance of an equivalent asynchronous motor

RS stator resistance of an asynchronous motor

RS* stator resistance of an equivalent asynchronous motor

RT resistance of a transformer

t time duration from the beginning of a short circuit

Td subtransient time constant of a synchronous machineTd transient time constant of a synchronous machine

Td* subtransient time constant of an equivalent generator

Td* transient time constant of an equivalent generator

Te subtransient time constant of a synchronous machine including the non-active

components

Te transient time constant of a synchronous machine including the non-active

components

TM subtransient time constant of a an asynchronous motor

3/26/2006


7/26


TMe subtransient time constant of a an equivalent asynchronous motor including

connecting cables.

Tdc d.c. time constant of a synchronous machine

Tdc* d.c. time constant of an equivalent generator

Tdce d.c. time constant of a synchronous machine including the non-active

components.

TdcM d.c. time constant of an asynchronous motorTdcM* d.c. time constant of an equivalent asynchronous motor

TdcMe d.c. time constant of an asynchronous motor including the connecting cables.

U0 prefault voltage (line-to-line)

Un nominal voltage (line-to-line)

Ur rated voltage (line-to-line)

UrM rated voltage of a motor (line-to-line)

X* subtransient reactance of an equivalent generator

X reactance

Xd subtransient reactance of a synchronous machine in the d-axis

Xd transient reactance of a synchronous machine in the d-axis

XM subtransient reactance of an asynchronous motor

Z impedance

Z* equivalent impedance

1.2.4 MethodologyThe Conventional or Comprehensive short circuit analysis procedure involves reducing

the network at the short circuit location to a single Thevenin equivalent impedance,

determining the associated fault point R/X ratio calculated using complex vector algebra,

and defining a driving point voltage (assuming the effect of transformer taps on bus

voltage). The initial symmetrical short circuit current can be calculated and, given the

fault location R/X ratios, the asymmetrical short circuit current at various times during the

onset of the fault can be calculated.

Conventional short circuit analysis techniques do not satisfy IEC Standard 61363

methodology. IEC363 requires a time-dependent calculation divided into active and non-

active components with separate AC and DC calculations. Active components, such as

generators and motors, are combined to form equivalent motors and generators. The

equivalent motors and generators are combined with non-active components, such as

cables and transformers, to further adjust the impedance and time constants of the

equivalent components.

Short-Circuit Study Procedure

The general study procedure outlined in the IEC 61363 standard includes:

1. prepare a system one-line diagram;

2. define component characteristics;

3. calculate the time-dependent short-circuit currents at the major points in the system

using the equations and methods described in the IEC 61363 standard;

4. prepare a short-circuit summary and document study conclusions.



8/26


1.2.5 IEC 61363 Assumptions

IEC 61363 standard outlines procedures for calculating short-circuit currents that may

occur on a marine or offshore a.c. electrical installation. The calculation methods are for

use on unmeshed three-phase alternating current systems, operating at 50 Hz or 60 Hz.

The following assumptions are applied

- All system capacitance are neglected

- The short-circuit arc impedance is neglected

- The short circuit occurs simultaneously in all three phases (three phase fault)

- Unmeshed systems

When calculating short-circuit currents, it is important to understand the difference

between

- The short-circuit current generated by an individual piece of equipment

- The short-circuit current which results when several pieces of equipment are

connected in a system.

When an isolated machine is being considered, only the electrical parameters of the

machine affect the short-circuit current generated. In a system, however, this current is

limited by the impedance of the non-active components, for example, cables, transformers,

etc., forming the system, changing both the transient and steady-state values of the

resulting short-circuit current.

3/26/2006


9/26


1.2.6 IEC 61363 Equations

Generators

Three-phase short-circuit current calculation

The upper envelope of the maximum values of the three-phase short-circuit current of agenerator can be calculated as

)()(2)( titIti dcack +=

The a.c. component

kd

Tt

kdkd

Tt

kdkdac IeIIeIItI dd ++=

'" /'/'" )()()(

2"2

"

0

"

"

0"

da

q

d

q

kd

XR

E

Z

EI

+==

2'2

'0

'

'0'

da

q

d

q

kd

XR

E

Z

EI

+==

="

0qE 000 cos3

IRU

a+ 2 + 0

"

00 sin3

IXU

d+ 2

=' 0qE 000 cos3

IRU

a+ 2

+ 0'00 sin3

IXU

d+ 2

The d.c. component

dcTt

kddc eIIti/

00

" )sin(2)( =

The peak value

)2()2(2)2(

T

i

T

I

T

ii dcackp +==

for 60 Hz system

msT

33.82*60

1000

2==



10/26


Effects of non-active components connected in series with Generators

Impedance changes

[ ] 2/12"2" )()( XXRRZ dae +++=

[ ]2/12'2'

)()( XXRRZ dae +++=

Time-constant changes

[ ] "'"2"'2"2

"

))(()(

)()(

ddda

ddda

eXXXXXRR

TXXXRRT

++++

+++=

[ ] ''2'2'2

'

))(()(

)()(

ddda

ddda

eXXXXXRR

TXXXRRT

++++

+++=

a

adc

dce

RR

fRXT

T +

+

= 1

2

Motors

General motor parameter

)()( statorRrotorRR SRM +=

)()(" statorXrotorXX SRM +=

Rr

SR

MR

XXT

+=

"

Sr

SR

dcMR

XXT

+=

General data for large motors ( > 100 kW)

..16.0" upZM =

..15.0" upXM =

..034.0 upRS=

..021.0 upRR=

msTmsTat dcMM 73.1167.18Hz,60"

==


==

3/26/2006


11/26


General data for small motors

..2.0" upZM =

..188.0

"

upXM=

..043.0 upRS=

..027.0 upRR =


==


==


The upper envelope of the maximum values of the three-phase short-circuit current of anasynchronous motor can be calculated as

)()(2)( titIti dcMacMpM +=

The a.c. component

"/")( M

Tt

MacM eItI =

22

"

"

"

"

MM

M

M

MM

XRE

ZEI

+==

='"

ME rMMMrM IR

U+cos

32

+ rMMMrM IX

U 'sin3

+ 2

The d.c. component

dcMTtMrMMdcM eIIti

/" )sin(2)( =

The peak value

)2

()2

(2)2

( T

iT

IT

ii dcMacMkp +==

for 60 Hz system at cycle



12/26


msT

33.82*60

1000

2==

Effects of non-active components connected in series Motors

Impedance Changes

RRRR SRMe ++=

XXXX SRMe ++="


Rr

Me

MeR

XT

""

=

)(

"

RR

XT

Sr

Me

dcMe+

=

Equivalent generator

*

/

*

'

*

/'

*

"

**

'*

"* )()()( k

TtTt

ac IeIIeIItI dd ++=

*

/

*

/

**

'*

"*)( k

TtTt

ac IeNeMtI dd ++=

*/"

** 2)( dcTt

dcM eItI =

where we defined the following variables,nn

"

*I = +"

kdiI"

MjIii

n

'

*I ='

kdiI

i

n

*kI = kdiI

i

)( '*"

** IIM =

)( *'

** kIIN =

3/26/2006


13/26


Equivalent generator time constant

For generator:

'/'"""

)()( kdTt

kdkd IeIItK d +=

For motor:

"/"" )( MTt

MeItK

=

Thus,n n

= +*" )(tK )(" tKi

MTt

jMeI"/"

i i

*

'

**

""*

)(ln

)(

M

ItKttT

x

xxd

=

*

*

/

**

'

*)()(

ln

)( "*

N

IeMtI

ttT

k

Tt

xac

xxd

dx +

=

"

*

**

2

)(ln

)(

I

ti

ttT

xdc

xxdc

=

Equivalent generator impedance

"

*

0"

*3I

UZ = ,

'

*

0'

*3I

UZ = ,

*

0*

3I

UZ =

)()()( "** 3 tXtctR = , )(2

1)(

*3 tfT

tcdc

=

2

3

"

*"

*1)( c

Z

tX +=

2

*

2'

*

'

* )( RZtX =

2

*

2

** )( RZtX =



14/26


Effects of non-active components connected in series with Equivalent Generators

Impedance changes

[ ] 2/12"2" )()( XXRRZ dae +++=

[ ]2/12'2'

)()( XXRRZ dae +++=

[ ] 2/122' )()( XXRRZ dae +++=


[ ] "'"2"'2"2

"

))(()(

)()(

ddda

ddda

eXXXXXRR

TXXXRRT

++++

+++=

[ ] ''2

'2'2

'

))(()(

)()(

ddda

ddda

e XXXXXRR

TXXXRRT

++++

+++=

a

adc

dce

RR

fRXT

T+

+

=1

2


The upper envelope of the maximum values of the three-phase short-circuit current of an

equivalent generator can be calculated as

)()(2)( titIti dcack +=

The a.c. component

e

kd

e

kd

e

kdZ

UI

Z

UI

Z

UI 0

'

0'

"

0" ,, ====

kd

Tt

kdkd

Tt

kdkdac IeIIeIItI dd ++=

'" /'/'" )()()(

The d.c. component

dcTt

kddc eIti/" )(2)( =

Equivalent motor

3/26/2006


15/26


"*/"

**)( MTt

MacM eItI =

*/"

** 2)( dcMTt

MdcM eItI

=

where we defined the following variables,

=n

j

MjM II""

*

Equivalent motor time constant

="/"" )( MTtMM eItK

= dcMTt

MdcM eItK/"2)(

"

*

"

"

*)(

ln

)(

M

xM

xxM

I

tKttT =

"

*

*

2

)(ln

)(

M

xdcM

xxdc

I

tK

ttT

=

Equivalent motor impedance

)()( " *1* tXctR MR = , )()()("

*2* tXtctR MS =

)(2

1)(

"

*

1tfT

tcM

= ,)(2

1)(

*

2tfT

tcdcM

=

"

*

0"

*3 M

MI

UZ = or

2"

*

2

**

"

* )( MSRM XRRZ ++=

2

21

"

*"

*

))()((1)(

tctc

Z

tX M

M

++=



16/26


Effects of non-active components connected in series Equivalent Motors

Impedance Changes

RRRR SRMe ++=

XXXX SRMe ++="


Rr

Me

MeR

XT

"

"=

)(

"

RR

XT

Sr

Me

dcMe+

=

Three-phase short-circuit current calculationThe upper envelope of the maximum values of the three-phase short-circuit current of an

equivalent asynchronous motor can be calculated as

)()(2)( titIti dcMacMM +=

The a.c. component

"

0"

e

kdZ

UI =

"/")( dTt

kdac eItI =

The d.c. component

dcTt

kddc eIti/" )(2)(

=

3/26/2006


17/26


1.3 PTW Applied Methodology

PTW applies the methodology described in Section 1.2. Section 1.3 describes how to run

the IEC_363 Study, including explanations of the various options associated with the

Study.

1.3.1 Before Running the IEC 61363 Fault StudyBefore running the IEC 61363 Fault Study, you must:

Define the system topology and connections.

Define feeder and transformer sizes.

Define fault contribution data.

1.3.2 Running the IEC61363 Fault StudyYou can run the Study from any screen in PTW, and it always runs on the active project.

To run the IEC 61363 Study

1. From the Run menu, choose Analysis.

2. Select the check box next to Short Circuit and choose the IEC 61363 option button.

3. To change the Study options, choose the Setup button.

4. Choose the OK button to return to the Study dialog box, and choose the Run button.

The Short Circuit Study runs, writes the results to the database, and creates a report.

1.3.3 IEC 61363 Study OptionsThe IEC_FAULT Study dialog box lets you select options for running the Study.



18/26


Following is a list of the available Study options.

Report and Study Options

These boxes allow you to customize the breadth of the Study and its Report. You can

choose between a summary report, standard report or a detailed report

Faulted Buses: All or SelectedYou can report a fault at a single bus, a group of buses or all buses. If a fault is to be

reported at a single bus or selected group of buses, then the faulted bus(es) must be

specified using the Select button. The default is to report the fault current at all buses.

System Modeling

These options further customize the Study.

System Frequency

The system frequency must be defined for the time-dependent calculations. The

system frequency is set in the Project>Options>Application menu.

Model Transformer Tap

You may model the transformer taps by selecting this check box.

Time Varying Setup

The time varying setup allows you to specify times to report Iac and Idc time-dependent

short circuit currents.

1.3.4 Component Modeling

Fault Contribution Data

Contribution data must be defined for synchronous generators, synchronous motors, and

asynchronous motors.

Synchronous Generators and Motors

Synchronous generator and motor short circuit current contributions are defined in the

Component Editor as shown in the following figures:

3/26/2006


19/26


ANSI Contribution Format

IEC Contribution Format

The IEC 61363 calculations requires entry of the following values: Xd, Xd, Xd, Ra,

Td, Td and Tdc. For definitions of these values refer to section 1.2.2. Since the IEC

61363 calculations are for 3-phase faults only, the negative sequence, zero sequence and

neutral impedance values are not used. However values for these fields are still required

since the IEC60909, ANSI and Comprehensive fault calculations use them.

PTW calculates the machine kVA and voltage base using the data you enter in the first

subview of the Component Editor. The motor rated size is in mechanical units of work(output) when entered as horsepower, but in equivalent electrical units of work (input)

when entered as electrical quantities of kVA, MVA or kW. Motor efficiency is used to

convert horsepower to electrical units of work, and power factor is used to convert kW to

kVA. If the rated kVA base in the IEC Contribution subview is zero, then PTW calculates

the equivalent kVA base from the machine rated size shown in the first subview of the

Component Editor. If the rated kVA base is not zero, PTW will not change it, even if you

enter a revised rated size in the motors first subview. Also, if the rated voltage is not zero,

PTW will not change it. Therefore, you may need to modify the rated machine kVA and

kVA base together; if you do not modify them together, the kVA base will remain



20/26


unchanged, even if you change the rated size on the first subview of the Component

Editor.

In order to fully model a synchronous machine, the rated size of the machine must be

defined, along with the power factor. Motors can be defined in the Component Editor as

either a single motor (the default) or as multiple motors. PTW will calculate the power for

multiple motors modeled at the bus.

Asynchronous Induction Motors

Asynchronous motor short circuit currents should be modeled in IEC 61363 calculations.

The Component Editor ANSI and IEC contribution data boxes are shown in the following

figures:

ANSI Format

IEC Format

The fields added specifically for the IEC 61363 calculations are the ratio of Stator

Resistance to Rotor Resistance, Td, and Tdc. Either entry format can be used.

3/26/2006


21/26


The motor rated size is in mechanical units of work (output) when entered as horsepower,

but is in equivalent electrical units of work (input) when entered as electrical quantities of

kVA, MVA or kW. Motor efficiency is used to convert horsepower to electrical units of

work, and power factor is used to convert kW to kVA. If the rated kVA base is zero, then

PTW calculates the equivalent kVA base using the machine rated size as defined in the

first subview of the Component Editor. The number of pole pairs, combined with the rated

kW of asynchronous machines, is used to calculate the breaking current duty. If multiplemotors are modeled in a single motor object, PTW will model the MW/pp of each of the

individual motors that comprise the group. Asynchronous motors are modeled as delta-

connected. If specific motor data is not available, the following typical data can be used

for the IEC 61363 calculations:

Large motors ( > 100 kW)

..16.0" upZM =

..15.0"

upXM =

..034.0 upRS=

..021.0 upRR =


==


==

Small motors (


22/26


Transformers also are modeled with a positive sequence impedance value. Zero sequence

impedance values are not used in the IEC 61363 calculations and therefore transformer

earthing impedance is also not used.

Transformer taps may be modeled. A negative primary tap raises the secondary voltage.

Taps will only be considered if the IEC 61363 Study Setup dialog box is set to model

them. The driving point voltages are defined by the generators and are not modified by thetransformer tap settings.

Transformer off-nominal voltage ratios, as compared to the primary and secondary bus

system nominal voltages, are modeled when the Model Transformer Taps check box is

selected in the Study setup dialog box. Essentially, PTW will create a fictitious primary

and/or secondary tap to ensure that the voltage ratios are properly matched.

1.3.5 Error MessagesPTW examines the entered data for the IEC 61363 Study. If PTW finds missing or

incomplete information, it sends an error message to the Study Message dialog box. The

Study Messages dialog box will report both fatal and warning messages. The Study will

attempt to run to completion even if fatal errors are detected, in order to identify any other

errors. The error messages are shared between all fault studies even though each has

slightly different data requirements.

A somewhat common error is:

The calculated zero sequence impedance is negative.

It involves the entry of single-line-to-easrth short circuit contribution data. PTW uses the

three-phase fault data and the single-line-to-earth fault data to calculate the positive-,

negative- and zero-sequence impedances from the following per-unit equations:

Z Z

Z1.0

I

I3 1.0

Z Z Z

Z3

IZ Z

1 2

1f

f1 2 0

0f

1 2

3

sle

sle

=

=

=

+ +

=

b g

b g

Utilities often report available single-line-to-earth fault duties on an equivalent three-

phase rating apparent power basis, using the equation:

kVA 3 I kV3 fsle= LL

However, the actual apparent power of a single-line-to-ground fault is:

kVA = IkV

31 fsle

where

kV line-to-line voltage.

3/26/2006


23/26


You cannot use the three-phase equivalent rating of a single-line-to-ground short circuit

contribution. If you do, PTW may attempt to calculate the zero-sequence impedance as a

negative value. The actual apparent power to be entered into PTW is the utility equivalent

single-line-to-earth duty divided by three. Enter the single-line-to-ground fault current

X/R ratio, not the zero sequence impedance X/R ratio.

1.3.6 ReportsFor each fault location, IEC_363 reports:

Iac at 1/2 Cycle, 3 Cycles, 5 Cycles, and one user-defined time, T4

Idc at 1/2 Cycle, 3 Cycles, 5 Cycles, and one user-defined time, T4

Iac for each branch and source feeding the fault at 1/2 Cycle, 3 Cycles, 5 Cycles, and

one user-defined time, T4

Idc for each branch and source feeding the fault at 1/2 Cycle, 3 Cycles, 5 Cycles, and

one user-defined time, T4

Ipeak for each bus and branch

*FAULT BUS: B1Voltage: 4.200 kV Ipeak: 38583.56 A x(peak factor): 1.615

TIME (Cycles) 0.0 0.5 3.0 5.0 12.5================================================================================Iac(A) 16893.27 14520.23 9684.34 8743.52 7935.77Idc(A) 22907.14 18048.85 9065.28 6133.30 1573.11



24/26


1.4 Application Example

1. 4. 1 Sample Project in IEC 61363 Standard

The following example was included in the IEC 61363 1996 Standard:

B1

4200 V

T2

S 2000.0 kVAR 1.150 %X 6.400 %

T4

S 2500.0 kVAR 1.050 %X 6.410 %

B5

600 V

B2

600 V

MB4/5

2000.0 kW (Output)X"d 0.1880 puTd" 18.67 msTdc 11.73 msRs/Rr 1.5926

M2

2000.0 kW (Output)X"d 0.1500 puTd" 18.67 msTdc 11.73 ms

Rs/Rr 1.6190

T7

S 250.0 kVAR 1.780 %X 6.770 %

B7120 V

B2BEC

46.0 MetersR 0.164 Ohms/kmX 0.096 Ohms/km

B2B3C


BE

600 V

B3

600 V

E1

500 kWX"d 0.12 puX'd 0.18 puXd 2.60 puRa 0.01 puTd" 20.00 msTd' 320.00 msTdc 64.00 ms

G4

2000 kWX"d 0.17 puX'd 0.29 puXd 2.75 puRa 0.01 puTd" 26.00 msTd' 420.00 msTdc 93.00 ms

G1 3500 kWX"d 0.17 puX'd 0.29 puXd 2.75 puRa 0.01 puTd" 26.00 msTd' 420.00 msTdc 93.00 ms



T2C


T2B5C


T4C


T4B2C


G4C

11.0 MetersR 0.069 Ohms/km

X 0.092 Ohms/k

E1C 10.0 MetersR 0.110 Ohms/km

X 0.095 Ohms/km

MB2/3

1700.0 kW (Output)X"d 0.1880 puTd" 18.67 msTdc 11.73 msRs/Rr 1.5926

3/26/2006


25/26


A portion of the output report is shown:

*FAULT BUS: B1Voltage: 4.200 kV Ipeak: 38406.35 A x(peak factor): 1.616

TIME (Cycles) 0.0 0.5 3.0 5.0 12.5================================================================================Iac(A) 16806.57 14453.94 9663.52 8732.21 7930.09

Idc(A) 22784.53 17965.39 9036.90 6119.38 1571.28

TIME-DEPENDENT SHORT-CIRCUIT CURRENTS AT THE MAJOR POINTS:

Bus Name:B1 Voltage: 4.200 kVTIME(Cycles) 0.0 0.5 3.0 5.0 12.5================================================================================- M2 Ipeak: 3127.69 A.Iac(A) 1884.71 1206.14 129.47 21.72 0.03Idc(A) 2893.48 1421.95 40.76 2.38 0.00

- G1 Ipeak: 9382.70 A.Iac(A) 3838.60 3454.88 2608.89 2419.96 2221.24Idc(A) 4918.30 4496.76 2872.92 2007.53 523.52



- MB4/5 (Eq. Motor) Ipeak: 2004.50 A.Iac(A) 1047.51 775.94 173.05 52.10 0.58Idc(A) 1800.69 907.16 29.44 1.90 0.00

- B2 (Eq. Gen.) Ipeak: 5126.06 A.Iac(A) 2358.54 2107.21 1534.33 1398.52 1265.76Idc(A) 3335.47 2146.01 347.95 92.52 0.72



26/26


Datablock results for the same faulted bus are displayed on the following one-line:

B1

AC (0.5cy) 14520 AAC (3cy) 9684 ADC (0.5cy) 18049 ADC (3cy) 9065 AIp 38584 AT2

S

T4

S

B5

B2

MB4/5

M2

AC (0.5cy) 1206 AAC (3cy) 129 ADC (0.5cy) 1422 ADC (3cy) 41 AIp 3128 A

T7

S

B7

B2BEC B2B3C

BE B3

E1 G4

G1

AC (T0) 3842 ADC (T0) 4924 AIp 9392 A

G2

AC (T0) 3842 ADC (T0) 4924 AIp 9392 A

G3

AC (T0) 3842 ADC (T0) 4924 AIp 9392 A

T2C

AC (0.5cy) 831 AAC (3cy) 185 AIp 2136 A

T2B5C

T4C

AC (0.5cy) 2108 AAC (3cy) 1535 AIp 5143 A

T4B2C

G4CE1C

MB2/3

Note that the contributions from MB4/5 Equivalent and Equivalent Generator EG are

slightly different in PTW than the hand calculation example shown in the IEC 61363

standard. These slight differences are due to neglecting motor pre-load condition in PTW

and inconsistent rounding in the hand calculation. The contributions from G1, G2, G3

and M2 match as expected.

reference iec61363

Documents