a practical time-domain fault current analysis using … · a practical time-domain fault current...

A Practical Time-Domain Fault Current Analysis using EMTP

Ryuya Tanabe, Yasuyuki TadaTokyo Electric Power Company

Yokohama, [email protected]

Abstract - The challenge of this paper is to provide apractical time-domain fault current analysis based on the op-timized fault current calculations for finding the best possibleeconomic balance among the various parameters dependingon the coordination of system protective device settings, in-terrupting equipment, etc. Specifically, this paper presentsthe practical fault current calculations using EMTP (Elec-tromagnetic Transient Program). It can clear the way forthe widespread availability of the time-domain fault currentanalysis. The effectiveness and practicability of the proposedanalysis are demonstrated on typical power system modelsincluding 211-generator bulk power system.Keywords - Large-scale power systems, Time-domain

fault current analysis, EMTP (Electromagnetic Tran-sient Program), Transient DC component identification

1 Introduction

FAULT current is one of key critical issues to improvereliability in power systems. The fault current anal-

ysis is one of the most important tasks of power systemplanning and operation so as to make a study of the de-termination of the system protective device settings, theverification of the adequacy of existing interrupting equip-ment, the selection of the interrupting equipment, etc.

If the margin of fault current calculations can be op-timized more by using a detailed fault current analysis,the fault current capability would be upgraded withoutany capital investment. Especially, since the transient DCcomponents in asymmetrical fault currents have a greatimpact on the interruption capability of circuit breakers,the important issue is to study the fault current analysisfor transient phenomena in power systems.

However, regarding the general fault current evalu-ation, the standards are determined in IEC and IEEE(ANSI) where the fault current calculations are based onthe conventional impedance methods representing the sys-tem at steady state. Since such conventional methodsare approximate calculations, not only the transient DCcomponents cannot be accurately computed, but also theAC components cannot correctly consider the operationalimpedance of generators, which have a great effect on thebehavior of short-circuit currents.

On the other hand, the time-domain fault analysis cancompute fault currents with considerable accuracy as afunction of time from the moment of the fault inception.For large power systems, with many generators contribut-ing to the fault currents, the contributions of many gen-erators have to be taken into account concurrently. It cantherefore be seen that the calculating requirements could

be stupendous, because the problem is reduced to simulta-neously solving a large number of differential equations.Despite its inherent power, the use of time-domain faultanalysis is not very widespread and is only used for spe-cial studies because it is a data-intensive task and it re-quires special software.

The challenge of this paper is to provide a practicaltime-domain fault current analysis based on the optimizedfault current calculations for finding the best possible eco-nomic balance among the various parameters dependingon the coordination of system protective device settings,interrupting equipment, etc.

Specifically, this paper presents practical fault currentcalculations using EMTP, which is not only a more accu-rate calculation method, but also can calculate large-scalepower systems. It can be realized by the application ofpower system data processing function making use of thedatabase (DB) and object-oriented script technologies. Itcan clear the way for the widespread availability of thetime-domain fault current analysis.

Moreover, this paper presents not only a practicalmethod based on the least squares estimation for identify-ing the transient AC and DC components in asymmetricalfault currents, but also the critical information of systemmodeling and parameters on the fault current analysis us-ing EMTP. The effectiveness and practicability of the pro-posed analysis are demonstrated on typical power systemmodels including 211-generator bulk power system.

2 EMTP Fault Current Calculations

2.1 Practical EMTP Data Export Function

The EMTP calculations for large-scale systems havetroubles of making data files because they are data-intensive tasks and need the know-how for system mod-eling such as power flow solutions and control systems.It is necessary to develop a practical EMTP data exportfunction for a practical fault current analysis using EMTP.

The practical EMTP data export function can be re-alized by the application of power system data process-ing function making use of the DB and object-orientedscript technologies. Since it can make data files for 9000-bus large-scale power systems (three-phase circuits), it canclear the way for the widespread availability of the EMTPfault current analysis. The features of EMTP data exportfunction are summarized as follows:

• Depending on the targeted time-domain of analysis,the modeling of power systems can be assembledin combination with adequate line models, machine

16th PSCC, Glasgow, Scotland, July 14-18, 2008

models,control system models and so on.

• The computed initial power flow solutions can beincorporated into EMTP data as initial conditions.

• The initial status of control system models canbe automatically initialized according to the initialpower flow solutions.

Data Processing Function by Script Technology

Power System Model

Database

Make Power Flow Data

Compute Initial

Power Flow Solution

Make Control System model

(TACS/MODELS) Data* excitation systems

* governing systems

Make Line model Data;* π-circuit

* LINE CONSTANTS

* JMARTI SETUP, etc.

Select models;

* line models

* generator models

* control systems

Make Generator Model Data* Synchnonous machine models

* Constant voltage models, etc.

Make Power System Model Class

Make ATP-EMTP Data including

the reflection of the initial power flow solution and

the initialization of the dynamic model status

ATP-EMTP Data

Figure 1: EMTP data export function based on DB and object-orientedscript technologies

Figure 1 shows the procedure for making EMTP datafiles with the script technology, where the modeling ofpower systems can be assembled and initial power flowsolutions and initial status of the dynamic models can beincorporated into EMTP data files.

2.2 DC Components of Asymmetrical Fault Currents

The fault currents in power systems are asymmetri-cal currents including transient DC components depend-ing on current phase at the moment of the fault inception.The time constants of the DC components are being in-creased due to the increased ratio of resistance to reac-tance of transmission lines as a result of adopting a bundleof multiple-conductors with an increased diameter.

Since root-mean-square (rms) values of the asymmet-rical currents increase with the increasing in DC time con-stants, the increased time constants will have great stresseson circuit breakers resulting to the degradation of the inter-ruption capability of the circuit breakers[1]-[3]. The faultcurrents from the viewpoint of the interruption capabilityshould be evaluated by both DC and AC values.

2.3 A Method for Identifying Transient DC Components

In order to examine fault currents, the fault currentsin EMTP should be decomposed into AC and DC compo-nents. This paper presents a practical method for identi-fying the transient DC components of asymmetrical faultcurrents. It is based on the least-square estimation with afault current model, which can directly compute DC time

constants and AC rms values, formulated as follows;

Given:

T , set of time instanttj : time instant for eachj ∈ TIATPj : EMTP fault current for eachj ∈ T

ω0 : angular frequency [rad/s]wj : weighting factor for eachj ∈ T

Variables:

Ij : estimated fault current for eachj ∈ TIACj : estimated AC rms value for eachj ∈ T

θj : phase angle for eachj ∈ TD : initial value of DC componentτ : DC decay time constanta2, a1, a0 : variables of AC rms value functionb2, b1, b0 : variables of phase angle function

Objective:

minIj∈T

∑

j∈T

wj(IATPj − Ij)2 (1)

Subject to:

Ij =√

2IACj sin(ω0tj + θj)

+D exp(−tj/τ) for eachj ∈ T (2)

IACj = a2t

2j + a1tj + a0 for eachj ∈ T (3)

θj = b2t2j + b1tj + b0 for eachj ∈ T (4)

-150000

-100000

-50000

0

50000

100000

150000

200000

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

Current (A)

Time (sec.)

A EMTP

A estimated

A DC

B EMTP

B estimated

B DC

C EMTP

C estimated

C DC

A EMTPA estimated

EMTPestimatedB

B

EMTP

estimatedCC

B DC

C DC

A DC

Figure 2: Numerical example of DC component identification

Since the fault current depends mostly on phase angleat the fault initialization, the coefficients in the phase an-gle function can be treated as decision variables. Since ACrms values and their phase angles are treated as a functionof time, respectively, the above formulation can preciselyidentify the transient AC and DC components. Addition-ally, the method can practically identify the transient ACand DC components with reasonable computation time(e.g. the computation time on 200-generator and 6000-bus class power systems is a few seconds with commonpersonal computer).

Figure 2 shows the plot of EMTP currents and theidentified currents from eq.(1)-(4). As can be seen fromFigure 2, the results of the identification method is in con-sistency with EMTP calculations.


Table 1: A modeling for the fault current analysis using EMTP

Model EMTPFault Current Analysis Conventional Impedance MethodBusvoltage Power flow solution Constantpre-fault voltagesGenerator Constantvoltage behind Xd’, Xd”, X2 model Constantvoltage behind Xd’ or Xd” model

Synchronousmachine (SM) models (Type58, 59) N/ASaturationcharacteristics can be considered. Saturationeffect as safe margin (IEC and IEEE std.)AVR and Gov. control system can be considered.N/A

Transformer Leakageimpedance model Leakageimpedance modelTap ratio is considered. Tap ratio can be considered. (IEC and IEEE std.)Saturationcharacteristics can be considered. Saturationeffect as safe margin (IEC and IEEE std.)

Line PI-equivalent branch model SeriesR-L branch modelLoad Constantimpedance model Constantimpedance model

Induction machine Inductionmachine can be considered. As large induction machine (IEC and IEEE std.)ShR, SC Shuntreactor and capacitor are considered. N/A

Fault impedance Arc impedance characteristics can be considered.Constantfault impedance can be considered.* Note: N/A; not applicable

3 Modeling in EMTP Fault Current Analysis

As can be seen from Table 1, EMTP fault current anal-ysis can apply various models to rigorously simulate dy-namics of generators and power flow condition comparedwith the conventional impedance methods. For example,shunt capacitances of transmission lines are included inthe EMTP solutions. Therefore, the study on the neces-sary and sufficient modeling for fault current analysis isrequired in practical use.

3.1 Generator Models

3.1.1 Synchronous Machine Models

EMTP calculations with the ATP version of the EMTPhave two kinds of Synchronous Machine (SM) models;

- Type58 phase-domain SM model- Type59 dq0-domain SM model

Though both models are based on the dynamics of Park’sequations, each model has merits and demerits dependingon each applied coordinate system. For other EMTP-typeprograms, the synchronous machine for the ATP discussedhere may not apply.

Computation Accuracy:

• Though both models can give reliable results inmost cases, it is known that Type59 model has theproblems in numerical instability caused by the pre-diction of electrical variables and inadequacy of sat-uration modeling[6]-[8].

Computation Time:

• Type58 model has time-variant inductances as afunction of rotor angle. Therefore, the conductancematrix regarding Type58 model in EMTP changesand the triangularization of the conductance matrixis necessary in every time-step. It takes longer com-putation time than Type59 model.

• In the modeling of saturation effects in synchronousmachines, since both models have time-variant in-ductances, computation times rapidly increase as in-crease in scale of power systems.

3.1.2 Constant Voltage Model

Constant voltage model is a simple representationof synchronous machines as a voltage source behindimpedance. This representation is Type14 sinusoidalsource behind an impedanceZG in EMTP (see Figure 3).

Type14 ZG

Figure 3: Constant voltage behindX model

ZG =

Zs Zm Zm

Zm Zs Zm

Zm Zm Zs

(5)

3.1.2.1 Constant voltage behindX ′d or Xd” model:

This model considers positive-sequence component ofZG. The diagonal elementsZs and off-diagonal elementsZm of ZG are formulated as follows:

Zs = Ra + jX ′d

Zm = 0

(6)

Where,Ra is an armature resistance andX ′d is a direct-

axis transient reactance.X ′d can be substituted with sub-

transient reactanceXd” in some cases.

3.1.2.2 Constant voltage behindX2 model (Consid-ering zero-sequence impedances):This model consid-ers zero-sequence component ofZG. The diagonal ele-mentsZs and off-diagonal elementsZm of ZG are formu-lated as follows:

Zs =Z0 + 2Z2

3

Zm =Z0 − Z2

3

(7)

where, Z2 = R2 + jX2 (8)

Z0 = R0 + jX0 (9)


Where,R2 is a negative-sequence resistance,R0 is a zero-sequence resistance,X2 is a negative-sequence reactanceandX0 is a zero-sequence reactance.

4 System Modeling and Parameterson EMTP Fault Current Analysis

G10

G9 G8

G1 G2 G4 G7 G6

G3 G5

L47 L19 L18

L38 L39 L40 L41 L42 L43

L44 L46L45

T47 T19 T18

T45T44 T46

T40T39 T41 T42 T43T38

(947) (919) (918)

(944) (945)

(946)

(940) (941)(939)(938) (942) (943)

SC47 SC19 SC18

SC44 SC45 SC46

SC40SC39SC38 SC41 SC42 SC43

(10) (20) (37) (36)

(47)(18)(19)

(8)(9)

(1)

(11)

(2)

(12)

(4)

(14)

(7)

(17)

(6)

(16)

(3)

(13) (15)

(5)

(21) (23) (25) (26) (28) (29) (31) (32) (35)

(22) (24) (27) (30) (33) (34)

(43)(41) (42)(40)(39)(38)

(46)(45)(44)

Static condenser

Shunt reactor

Auto Transformer

L33

71-bus, 124-branch,

10-generator

Total Load Demand: 6,552MW

Figure 4: IEEJ 10-generator power system model

Kundur’s 4-generator system model[9], IEE of JapanEAST10-generator system model (See Figure 4)[10] and211-generator and 6156-bus bulk power system model arestudied to organize the information of system modelingand parameters on EMTP fault current analysis.

Table 2: EMTP calculation parameters

Fault point & mode 3LS,1LG at each busAC rms value 0.07sec. after fault

DC decay time constant 0.0-0.10sec. after faultTime step size 50µ sec.

Table 2 lists the common simulation conditions for allcases in this paper. The kinds of faults are assumed three-phase fault (3LS) and single-line-to-ground fault (1LG) ateach bus. The AC rms values of fault currents are evalu-ated at 0.07 seconds after faults have occurred. The DCdecay time constants of fault currents are evaluated duringthe period 0.0-0.1 seconds after occurring faults. The timestep size of EMTP calculations is 50µ seconds.

4.1 Effect of Generator Models

The EMTP generator models listed in Table 3 are stud-ied to evaluate the effect of the operational impedance ofgenerators. The power system model and fault conditionsin EMTP calculations are listed in Table 4.

Table 3: EMTP generator models

(Type58)∗ : Synchronous machine (SM) models(Type14+Xd′) : Constant voltage behindXd′ model(Type14+Xd”) : Constant voltage behindXd” model(Type14+X2’) : Constant voltage behindX2 model

* Note: The results of Type58 are same as such of Type59 model.


Power system model IEEJ10-generator systemFault point ateach bus N11-N47 (37 buses)

Fault impedance 0.0Ω

In EMTP calculations of 74 cases (37-fault-points, 2-fault-kinds), the constant voltage models increase AC rmsvalues by about 4%-11% and DC time constants by about0.6%-0.8% compared with Type58 synchronous generatormodel. The constant voltage models especially give pes-simistic results regarding AC components compared withType58 synchronous generator model.

N12_3LS0.0.pl4: c:N0LD2A- FFFFFA Type58 N12_3LS0.0.pl4: c:N0LD2A- FFFFFA Xd' N12_3LS0.0.pl4: c:N0LD2A- FFFFFA Xd" N12_3LS0.0.pl4: c:N0LD2A- FFFFFA X2

0.00 0.02 0.04 0.06 0.08 0.10[s]

- 150

- 125

- 100

- 75

- 50

- 25

0

25

50

[kA]

(Falut point: N12; near-to generator)

Type58

Xd'

Xd"X2

Type58

Xd'

Xd"X2

Fault Current

Time (sec.)

Figure 5: Effect of generator models (Fault point: near-to generator)

N45_1LG0.0.pl4: c:N0NUKA- FFFFFA Type58 N45_1LG0.0.pl4: c:N0NUKA- FFFFFA Xd' N45_1LG0.0.pl4: c:N0NUKA- FFFFFA Xd" N45_1LG0.0.pl4: c:N0NUKA- FFFFFA X2

0.00 0.02 0.04 0.06 0.08 0.10[s]- 150

- 100

- 50

0

50

100

[kA] (Falut point: N12; far-from generator)Fault Current

Time (sec.)

Type58

Xd'

Xd"X2

Figure 6: Effect of generator models (Fault point: far-from generator)

Figure 5 shows fault currents for a case where the ef-fect of the constant voltage models is observed to be sub-stantially different from that of Type58 model. In thiscase, the fault point is near to a generator and the othernear-to generator cases are much the same.

On the other hand, Figure 6 shows fault currents for acase where the effect of the constant voltage models is notobserved to be significantly different from that of Type58model. In this case, the fault point is far from a generatorand the other far-from generator cases are much the same.

As can be seen from Figure 5, the results of(Type14+Xd”) and (Type14+X2) models are found to beapproximate to that of Type58 in the time from the mo-ment of the fault inception to 0.05 seconds. Conversely,the result of (Type14+Xd′) is observed to have the ap-proximate result of Type58 in the time of 0.03-0.07 sec-onds after the fault inception.

The same tendency in Figure 5 can be seen fromFigure 6, but the observed effect is insignificant. Incase where the fault point is far from a generator,(Type14+Xd′) model may be adequate for evaluating theinterruption capability of circuit breakers.

4.2 Effect of Generator Excitation Control Systems

The modeling of generator excitation control systemshave a great impact on transient stability and temporary


over-voltage studies. Since the time frame in fault currentanalysis is several hundred milli-seconds in most cases,the effects of the control systems may be relatively small.However, since the calculating requirements to considerall excitation control systems in large-scale EMTP calcu-lations are stupendous, it is important to evaluate the ef-fects of generator excitation control systems.


Power system model IEEJ10-generator systemFault point ateach bus N11-N47 (37 buses)

Fault impedance 0.0ΩGeneratormodel SM model (Type58)

N19_3LS0.0.pl4: c:N0MQPA- FFFFFA c:N0MQPB- FFFFFB c:N0MQPC- FFFFFC N19_3LS0.0.pl4: c:N0MQPA- FFFFFA c:N0MQPB- FFFFFB c:N0MQPC- FFFFFC

0.00 0.02 0.04 0.06 0.08 0.10[s]- 200

- 150

- 100

- 50

0

50

100

150

200

[kA] (Fault:N19, 3LS)

Fault Current

Time (sec.)

with control systemswithout control systems

Figure 7: Effect of generator excitation control system

In EMTP calculations of 74 cases (37-fault-points, 2-fault-kinds, see Table 5), the modeling of generator excita-tion control systems increase AC rms values by the max-imum 0.2% and the average 0.06% and reduce DC timeconstants by the maximum 0.02% and the average 0.005%compared with no such modeling.

Though Figure 7 shows the plot of fault currents fora case with the maximum effect of generator excitationcontrol systems and a case without generator excitationcontrol systems, the effect of generator excitation controlsystem modeling is substantially small.

4.3 Saturation Effects of Synchronous Machines

In fault current analysis, it is important to study themodeling of saturation effects of synchronous machines,since the machine saturations can have an impact on tran-sient stability and on electromagnetic transients.

2713

17071546

1546

1680

2016

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 500 1000 1500 2000 2500 3000

Field Current [A]

Terminal Voltage [pu]

Suturation characteristics

No suturation effect

Figure 8: Saturation characteristics for generator model

It is very difficult to rigorously model saturation ef-fects of synchronous machines. Because it would requiremagnetic field calculations, e.g. by finite element meth-

ods, which are time-consuming processes and require thedetailed and stupendous data for field calculations. Ap-proximate treatments of saturation effects are, therefore,commonly accepted in most dynamic simulation programsfor power system analysis[8]. The approximate treatmentsuse saturation curve characteristics as shown in Figure 8.The synchronous machine models in EMTP also use thesaturation curve characteristics.


Power system model Kundur’s 4-generator systemFault point & mode Bus2,3LS

Fault impedance 0.0ΩGeneratormodel SM models (Type58, 59)

SM saturation effect Seefig.8

EMTPcalculation parameters listed in Table 6 and thesaturation curve as shown in Figure 8 are used to study thesaturation effects of synchronous machines in the follow-ing cases;

Case1 : All generators have no saturation effect.Case2 : Only Generator G1 has saturation effect.Case3 : Only Generator G2 has saturation effect.Case4 : Only Generator G3 has saturation effect.Case5 : Only Generator G4 has saturation effect.Case6 : All generators have saturation effect.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Terminal Voltage (pu)Gen1: 0.55pu

Gen2: 0.32pu

Gen4: 0.91pu

Gen3: 0.89puFault Point

Figure 9: Kundur’s simple two-area system

Figure 9 shows the profile of bus voltage magnitude ofgenerators during the fault. The terminal voltage magni-tude becomes small as near to fault point.

8700

8750

8800

8850

8900

8950

9000

9050

0.14 0.142 0.144 0.146 0.148 0.15 0.152 0.154 0.156

AC rms value (A)

DC Decay Time Constant (sec.)

Bus2-3L

Bus2-3LS

Bus2-3LS

Bus2-3LS Bus2-3LS

Bus2-3LS

Phase APhase BPhase C

Case1

Case6

Case3

Case2

Case4Case5

1ms

1ms

1ms

Figure 10: Saturation effect of generator model

Figure 10 shows AC rms values and DC time constantsderived from EMTP calculations for the above cases. Theresults are summarized as follows:


• The range of DC time constants is about 1 milli-seconds. The saturation effects have little impact ontransient DC components.

• The range of AC rms values is about 3% of the max-imum AC rms value. The no saturation effect case(Case1) has the smallest AC rms value, and the sat-uration effect case for all generators (Case6) has thelargest AC rms value.

• The saturation effect increases as terminal voltagemagnitude decreases.

Bus2_3LS0.0_agl- a.pl4: t: FFFFFA t: FFFFFB

Bus2_3LS0.0_sat- a.pl4: t: FFFFFA t: FFFFFB t: FFFFFC Case6

0.00 0.02 0.04 0.06 0.08 0.10[s]

- 30

- 20

- 10

0

10

20

30

t: FFFFFC Case1

Fault Current (kA)

Time (sec.)

Case1: without saturation effect

Case6: with Saturation effect

Figure 11: Fault currents (Case1 and Case6)

Figure 11 shows three-phase fault currents for no sat-uration effect case (Case1) and the all generator saturationeffect case (Case6). As can be seen from Figure 11, itis observed little difference in DC components and some-what difference in AC components. These differences canbe negligible in the sense of engineering judgment.

The above results are the calculations using Type58phase-domain SM model. The modeling of Type59 dq0-domain SM model is observed to give substantially differ-ence from such of Type58 model. The results of Type59model calculations in the same conditions may be im-proper, because Type59 model has some problems in sat-uration modeling[6]-[8].

4.4 Effect of Resistance components of Transformer

The resistance components of transformer models canbe neglected in the modeling of most transient stabilitystudies. However in fault current analysis, the transformerresistances can have a great impact on transient DC com-ponents. The modeling of the transformer resistancesshould be carefully considered in fault current studies.

Though the transformer resistances in the original dataof 4-generator system[9] are neglected, it is assumed thateach resistance in the primary and secondary winding ateach phase is0.1Ω. The effect of transformer resistancescan be evaluated on DC decay time constants in EMTPcalculations. EMTP calculation parameters are listed inTable 6.

Table 7 shows the comparison of DC decay time con-stants with or without the transformer resistances. Sincethere are only step-up transformers in this power systemmodel, the effect of resistance components are larger asthe fault points near to generators. The modeling of trans-former resistances decreases DC time constants by from

8% to 12% of no such modeling cases for near-to genera-tor fault point (Bus1, Bus2, Bus3, Bus4) cases.

Since the realistic values transformer resistances arenothing less than the above assumed values, the trans-former resistances are indispensable data for evaluatingtransient DC components in fault currents.

Table 7: Effect of transformer resistance

Fault point DC decay time constant (sec.)Transformer Resistance

(a)R = 0.0Ω (b)R = 0.1Ω (b)/(a)Bus1 0.171 0.015 0.08Bus2 0.147 0.016 0.11Bus3 0.137 0.016 0.12Bus4 0.162 0.016 0.10BusC 0.035 0.021 0.60BusL 0.062 0.018 0.29BusR 0.062 0.018 0.28

4.5 Effect of Arc Impedance at Fault Point


Power system model IEEJ10-generator systemFault point e.g.N12, N45

Fault impedance 0.0,0.02, 0.04, 0.06, 0.08, 0.10ΩGeneratormodel SM models (Type58)

The arc voltage characteristics of high current (50kArms class) fault arcs on 500kV class transmission linesare roughly 1kV/m (voltage gradient of arc)[11]. Con-sequently the expected fault impedances of high currentfaults are roughly from 10mΩto 100mΩ. The effect offault impedances can be evaluated on EMTP fault currentcalculations (see Table 8).

40000

45000

50000

55000

60000

65000

70000

75000

80000

0.05 0.1 0.15 0.2 0.25 0.3

AC rms value (A)

DC Decay Time Constant (sec.)

0.0 0.02 0.04 0.06

0.08

0.10

0.0 0.02 0.04

0.06

0.08

0.10

0.0 0.02 0.04 0.06

0.08

0.10

0.0 0.02 0.04

0.06

0.08

0.10

Phase APhase BPhase C

N12 1LG

N12 3LS

N45 3LS

N45 1LG

Figure 12: Effect of arc resistance at fault point

Figure 12 shows the effect on AC and DC componentsin fault currents by increasing fault impedances. The nu-meric character in Figure 12 indicates arc resistance valuefor each case. As can be seen from Figure 12, the model-ing of arc resistances decreases DC decay time constantseven 10mΩ and has no effect on AC rms values.

In case of lightning faults, the modeling of fault resis-tances are necessary to study DC decay time constants offault currents. However, fault resistances are almost zeroΩ in case of metal contact short-circuits.


4.6 Comparison of Computation Time

The EMTP fault current calculations can calculate9000-bus class systems (three-phase circuits) with highprecision. However, EMTP calculations are time consum-ing operations compared with the conventional impedancemethods.

As we have seen in Section 3.1, the computation timesare influenced a great deal by synchronous machine mod-eling and their saturation modeling in EMTP calculations.Consequently in order to study the guideline for the useof EMTP calculations, the computation times of EMTPcalculations on 6156-bus large-scale power systems with211-generator are evaluated on type of generator models(time period: 0.1 seconds, Time step size: 50µseconds,Computer: Pentium(R)4-3GHz PC).

Table 9: Comparison of computation time

Generatormodel Computationtime(Type58) 1 h. 56 min. 40 sec.(Type58) + saturation effect 1 h. 57 min. 24 sec.(Type59) 72sec.(Type59) + saturation effect 51min. 57 sec.(Type14+Xd’) 51sec.(Type14+Xd”) 50sec.(Type14+X2’) 52sec.*for reference;

Conventional method lessthen 1 sec.

As can be seen from Table 9, the computation time ofType59 model without saturation effect is about 70 sec-onds and approximately 1.4 times of Type14 models. Butthe computation time of Type59 model with saturation ef-fect increases approximately 43 times because of the treat-ment of time-variant inductances.

Since the conductance matrix regarding Type58 mod-els in EMTP changes and the triangularization of the con-ductance matrix is necessary in every time-step, the com-putation time of Type58 models are approximately 2 hoursindependent of with or without saturation effects.

Therefore the practical procedure of EMTP calcula-tions can be recommended as follows:

Step 1: Since the EMTP calculations including Type59models without saturation effect have reason-able computation times (almost the same asType14 models), Type59 model without satu-ration effect should be used in EMTP calcula-tions for the primary analysis.

Step 2: If more detailed analysis is necessary, Type58model with saturation effect should be used inEMTP calculations.

5 Conclusions

This paper presents the practical fault current analysisbased on the optimized fault current calculations, whichcan clear the way for the widespread availability of theEMTP calculations. Specifically this paper provides:

• The EMTP fault current calculations based on DBand object-oriented script technologies

• The transient AC and DC components identificationmethod based on the least-square estimation

• The critical information of system modeling and pa-rameters derived from EMTP calculations on typi-cal power system models including 211-generatorbulk power system

Further research works are studies on EMTP calcula-tions on large-scale systems from practical standpoints in-cluding the effects of load modeling, induction machinesand frequency-dependent transmission lines.

REFERENCES

[1] Standard of the Japanese Electrotechnical Commit-tee, ”Alternating-current Circuit Breakers,” JEC-2300, 1998 (in Japanese).

[2] T.Satou, M.Nishio, et al., ”Influence of the TimeConstant of D.C. Component on Interrupting Dutyof GCB,” IEEE Power Engineering Society WinterMeeting 2001, Vol.1, 28, pp.300-305, 2001.

[3] T.Simato, K.Chiyajo, et al., ”Evaluation of Interrup-tion Capability of Gas Circuit Breakers on LargeTime Constants of DC Component of Fault Current,”39th CIGRE SC13-104 Paris Session, 2002.

[4] IEC International Standard 60909-0-4, ”Short-circuit currents in three-phase a.c. systems,” , 1992-2003.

[5] IEEE Brown book, ”IEEE Recommended Practicefor Industrial and Commercial Power Systems Anal-ysis,” IEEE Std. 399-1997.

[6] J.Lin, J.Mahseredjian, S.Lefebre, ”Improvement ofSynchronous Machine Saturation Simulation in theEMTP,” IEEE TENCON’93 Proceedings, Vol.5,pp.127-132, 1993.

[7] Can/Am EMTP, ”Machinery Saturation Ques-tioned,” Can/Am EMTP News October, Vol.97-4,1997.

[8] X.Cao, A.Kurita, Y.Tada, H.Okamoto ”Type-58 Syn-chronous Machine Model and Related Modifica-tions,” EMTP Journal, Vol.11, pp.78-84, 2006.

[9] Prabha Kundur, ”Power System Stability and Con-trol,” ERPI,1994.

[10] Technical Committee of IEE of Japan, ”JapanesePower System Models,” IEEJ Technical ReportNo.754, 1999.

[11] Y.Goda, M.Iwata, et al., ”Arc Voltage Character-istics of High Current Fault Arcs in Long Gaps,”IEEE Transactions on Power Delivery, Vol.15, Issue2, Apr. 2000, pp.791-795, 2000.


a practical time-domain fault current analysis using … · a practical time-domain fault current...

Documents