Power network analysis using ERACS

8/9/2019 Power network analysis using ERACS

1/41

Student Name/ID: Muhammad Ali Qaiser/26561999 Module: Power Systems Analysis ELEC6114Coursework Title: PSA ERACS Date: 03-Dec-2013

EXECUTIVE SUMMARY

This network modelling assignment in ERACS was performed as part of Power Analysiscoursework by the student at University of Southampton 1 (fall semester 2013, Masters degreein Energy and Sustainability). ERACS is an advance electrical power analysis simulation softwaredeveloped by ERA Technology, UK.

The work comprised building up a typical plant power network, which is fed by 11 kV grid and 3.3kV synchronous generators. Consumption load is made up of group of induction motors at

different voltage levels (3.3 kV and 415 V), which are regulated by a multitude of transformersseparating various busbar sections. All equipment parameters were preset (PSA Library Keys) .

In first part of simulation, normal loadflow was assessed for the baseline network. Additionalloads were then added at a pre-determined busbar (Point D) in form of heavy induction motorand a stationary shunt with similar consumption rating. Comparison loadflows were re-simulatedto compare with baseline configurations. Findings have been tabulated and commented upon tobring out the various power flow aspects of generation, consumption and losses. In doing so,focus was kept on real power (P), reactive power (Q), current (I), load angle and power factor.Relevant observations were also documented for cable loading and voltage drops. Every findingis backed up by technical reasoning.

In the second part of assignment, fault scenarios were created at a pre-determined busbar (PointB) for the basic and upgraded networks. Four types of faults were investigated, namely 3-phase,phase to phase, 2-phase to earth and 1-phase to earth. Qualitative and quantitative evaluationshave been made to compare the different types of faults (for example, in terms of severity andsymmetry), as well as the different network configurations (for example, to see if additional


2/41

symmetry), as well as the different network configurations (for example, to see if additional


Table of ContentsA. INTRODUCTION ..................................................................................................................................... 1

A.1. Aims of Coursework ...................................................................................................................... 1

A.2. Network Element Assumptions .................................................................................................... 1

A.3. Note to Instructor on Value-Sets .................................................................................................. 1

B. Part 1: OPERATIONAL LOADFLOW ANALYSIS ....................................................................................... 2

B.1. Basic Network Loadflow................................................................................................................ 3

B.2. Rotational Load Incremental Loadflow ......................................................................................... 5

B.3. Non-Rotational Load Incremental Loadflow ................................................................................. 6

B.4. Economic Aspects of Network Loading ......................................................................................... 7

C. Part 2: FAULT ANALYSIS ........................................................................................................................ 8

C.1. General Observations on all Faults ............................................................................................. 10

C.2. 3 Phase Faults ............................................................................................................................. 11

C.3. Phase to Phase Faults ................................................................................................................. 11

C.4. Two Phases to Earth Faults ......................................................................................................... 11

C.5. Single Phase to Earth Faults ........................................................................................................ 12

C.6. Manual Fault Calculation ............................................................................................................ 12

C.7. Comparison of Manual Result with ERACS ................................................................................. 14

D. CONCLUSION ....................................................................................................................................... 14

References ..................................................................................................................................................... i

Appendix 1: ERACS Loadflow Schematics ..................................................................................................... ii


3/41


A. INTRODUCTIONElectrical network systems are in a process of continual evolution. This is especially true over thepast decade, where the concept of conventional generation and transmission are being challengedby the concepts of non-dispatchable generation and smart grid distributions. While the first evergenerating stations supplied local specialized loads at DC, electricity system matured quickly into adecentralized scheme of interconnecting stations known as the Grid in Britain [1]. In recent times,focus on network losses and greenhouse emissions would continue to push the development ofpower generation and transmission systems.

In real-life systems, often generation levels and points are at a considerable distance from theconsumption levels and points, and a number of transmission cables, regulation transformers andinterconnecting busbars are required to complete a feasible power network. In addition to this is thefact that loads can be reactive (generally rotating) or resistive (such as heating and lighting). Thecomplexity of interwoven elements therefore means that a careful modelling of operating andpotential fault characteristics is needed before a system can be commissioned.

A.1. Aims of CourseworkThe purpose and goals of this coursework are understood by the student as follows:

To gain an understanding of normal operational loadflows of a real-life network To observe how addition of rotating and non-rotating loads interfere with system

characteristics, and require modifications for protection and continued operation To model different types of faults and their effect on a network To supplement software modelling by manual fault calculations for comparison

A.2.

Network Element AssumptionsThe power network was constructed according to the given schematic. For individual elements, thespecialized library with rating parameters already provided by supervisor was used; any missingcomponents were imported from ERACS standard reference keys as required. Any other default


4/41


B. Part 1: OPERATIONAL LOADFLOW ANALYSISHere I shall comment on my observations from running load flow simulations on the normal network,with basic and loaded configurations. Throughout this section, the reader should refer to 0 Appendix1: ERACS Loadflow Schematics) . The basic equations demonstrating relationship between powerflows and busbar voltages are as follows (assuming R is negligible compared to X ) [1]:

= and =2

where

PG generated real powerQG generated reactive powerV G generated voltageV L load voltage

X equivalent reactance between source and sink load angleERACS uses more complex version that accounts for resistive components R; hence Xwill be replaceby Z, where Z = R + jX . For easy reference during qualitative comments that will now be given onloadflows run in ERACS, a selected summary of the results from these three loadflow scenarios istabulated below.

Network Component Quantity Meaning Units LF1: Basic LF2: Rot. Load LF3: Stat. LoadGrid PG Generated real power MW 0.469 1.293 1.292Grid QG Generated reactive power MVAr 0.096 0.825 0.825Grid I Current kA 0.025 0.081 0.080Grid pf Power factor - 0.980 0.843 0.843

Generators PG Generated real power MW 2.280 2.280 2.280Generators QG Generated reactive power MVAr 1.680 1.680 1.680


5/41


B.1. Basic Network LoadflowA loadflow was conducted on the basic network constructed (without the additional test-point loadsor induced fault conditions). It was noted that no errors were reported by ERACS at this stage (see

Appendix 1: ERACS Loadflow Schematics . Some major observations are as follows.

1. Power Losses: In all, the grid and generators now supply 2.749 MW and 1.78 MVAr to thenetwork, of which the vast majority comes from plant generators (2.28 MW). The systemloads absorb in all 2.72 MW and 1.73 MVAr 2. Therefore 0.03 MW (1% of total) real power islost primarily due to cables and 0.05 MVAr (2.8% of total) reactive power is lost mainly due

to transformers. This is also confirmed by the results as we move across the network afterloadflow display (see Figure 1 ).2. Reactive Gain: It is seen that cables add small quantity of reactive power to the system3. Fault Levels: The maximum fault levels with full plant connected and operating in basic

configuration gives a pattern that corresponds with general understanding that higher buslevels carry higher fault levels [1] as we move from 11 kV to 415 V (see Figure 3 ).

4. Voltage Drops: The phase voltage (pV) starts at 1 p.u. on intake busbar (11 kV) but dropsslightly to between 0.988 p.u. and 0.999 p.u. on the 3.3 kV busbars; generally it is seen thatpresence of a nearby transformer raises the value slightly by introduction of reactivecomponent, whereas long cable transmission and/or loads tend to decrease it by reductionof real component. A similar pattern is seen on 415 V busbars, where the transformers tendto increase voltage profile to above 1.0 p.u. possibly due to voltage tap regulation (see Figure2), as well as the fact that library keys used for these transformers raise secondary side to 433V (even though the busbars are rated at 415 V). It is therefore to be noted that ERACS preferstransformer output to busbar capacity when performing per-unit calculations. However,

nowhere is overvoltage limit of 10% crossed [3].5. Driving-point Impedance: The transfer function driving through-source (current) into

network from the across-source, known as Z s or driving-point impedance, is seen to be lowfor higher voltage busbars and vice versa This is logically explained by the fact that current


6/41


8. Power Factor: The induction motors operate in p.f. average range of 0.9 with the exceptionof IM2 (0.75); this is because it is the motor with lowest ratio between real power capacityand rated MVA, leading to a greater reactive component during its fully loaded operation. Toa lower extent, this same behaviour is seen in motor IM8.

It is seen from library data that the busbars in ERACS are floating kind, with voltage specified but anylosses accounted for purely by power sources (grid and generators).

Note: Observe the loss in real powerbut gain in reactive power from take-

off (1) to destination (2) of cable

Note: Observe the loss in reactive powerfrom primary (1) to secondary (2) oftransformer


7/41


B.2. Rotational Load Incremental LoadflowAn additional 0.8 MW induction motor at 3.3 V (rated 2 MVA) was added at point D, and loadflowperformed again. It was noted that power flow through the respective busbar rose from 0 to 0.8 MWand 0.69 MVAr (see Appendix 1: ERACS Loadflow Schematics . The added motor draws 191 A at powerfactor 0.75; this appears to be significantly lower than other motors, which operate around 0.89. Onereason could be the higher power rating causing it to draw larger current and therefore a greaterVAr component.

Although the network remains stable leading to the conclusion that the system is big enough to

absorb this addition, a few differences from the basic configuration are indeed seen.1. Power Changes: In all, the grid and generators now supply 3.573 MW and 2.505 MVAr to the

network; this time however, the component from grid makes a greater percentage of the piethan before, as the generators are already working at full capacity (0.76 MW). The systemloads absorb in all 3.52 MW and 2.403 MVAr, which aligns neatly with the P/Q componentsintroduced by the motor, taking into account a slight raise in losses (0.053 MW PLO being1.4% of total). The real losses can be confirmed by moving across the network cables and

reactive losses by moving across transformers.2. Cable Loading: The percentage current loading increases significantly bilaterally around the

busbar 3.3-4, which is point D of induction motor attachment. This is because current flowsin from both sides of the network in an attempt to deliver the requisite power flow. Althoughno over-current is seen, the maximum loading is observed around 84% for cable L3connecting busbars 3.3-2 and 3.3-3; this is the cable which was earlier commented upon tosupply 3 induction motors as well. It may be the case that during summer time, this networkconfiguration if left unchanged could result in excessive heating of the cable (as carriagecapacity decreases with temperature). It may therefore be recommended that a parallel cableof same size be installed to take half the current, and return loading to around 45%, whichwould be in the same range as basic configuration. The length of this cable is only 100 m, and


8/41


5. Power Factor: While the plant generating units retain their power factors without observablechange, the grid supply experiences a loss of power factor from 0.98 to 0.84; this hasimplications for compensatory equipment which shall be further discussed in economicsection. The reason for this fall is that now a significant portion of power is being drawn fromgrid as referred earlier, due to addition of motor group; with the real power also comes thereactive component required by the system.

On the contrary, a very slight power factor gain is seen in nearly all of the induction motors in theoverall system; this corresponds to a very small rise in current; this however, appears to be asoftware iterative differential, because there is no practical reason why introduction of a largeinductive load should encourage greater current flows in other parallel loads. It could well be that ifground-neutral paths are not correctly set up that current unbalances can swirl in the network, butthis does not appear to be the reason in this network, which has all its neutral points earthed.

(load angle)

Figure 4 Formation of load angle swing


9/41


system where distortion may become a problem at distributed loads, especially if the motors arevariable speed drives, requiring installation of cleaning filters.

B.4. Economic Aspects of Network LoadingFrom above load-flow analysis and load additions, a few considerations arise on economical side ofnetwork design and planning. These are as below:

1. Current Loading: It is important that system links, especially cables being the weakest link

normally, be not loaded near 100% current value at normal load flow. This is because withhotter weather it could well lead to overcurrent. We have seen from the stability flows above,that cable L3 carries 84% loading (at 402 A) with addition of load at point D. It is thereforerecommended that it be supplemented with one in parallel (240 mm2, 3 core). This will proveto be minimal in terms of cost.

2. Reactive Power: Introduction of additional loads draws out VArs that pose several problems.Firstly, and increase in reactive power causes a rise in overall system current as is immediatelyevident by comparing current flows at grid feeder. As current rises, so do I2R losses,translating into greater voltage drops, system heating and need for bigger transmissioncomponents such as thicker cables.


10/41


two-part tariff containing a portion proportional to maximum kVA, then the plant will facehigher consumption charges without any increase in real consumption.Thirdly, larger kVA rating also means a greater equipment kVA capacity in terms of design,planning and purchase, without achieving real increase in power efficiency.Fourthly, reactive power can cause a bad power factor on the grid feeder, which in someparts of the world is penalized. This requires installation of corrective capacitors, incurringcapital cost.

3. Harmonics: Having variable speed drives and advanced electronic loads on a network canalso inject undesirable pollutants (harmonics), which need to be cleaned up with expensiveRLC filters.

4. Generation Capacity: By introducing extra induction loads, greater generation capacity isoften required to compensate for the greater VAr drawn with respect to real power beingadded into the system. This consideration must be kept in mind when introducing such loadsto evaluate whether any benefit can be derived from such addition, or whether existing

system should be optimized to improve ratio of real to inductive power components.

C. Part 2: FAULT ANALYSISFour fault types were simulated at Point B on each of the 3 networks denoted basic, additional motor(Xm) 3 and additional shunt (Xnr) 4, giving a total of 12 fault scenarios. These faults were:

a. 3 phase (3P)b. Phase to phase (P-to-P)c. 2 phase to earth (2P-to-E)d Single phase to earth (1P to E)


11/41


Page | 9

Point B: Bus3.3-2 Ip (kA) Ip (deg) In (kA) Iz (kA) IL1 (kA) IL2 (kA) IL3 (kA) VL1 (kV) VL2 (kV) VL3 (kV) MVA

3P: Basic 13.742 -79.4471 0 0 13.742 13.742 13.742 0 0 0 78.5464

3P: Xm 15.0765 -80.6103 0 0 15.0765 15.0765 15.0765 0 0 0 86.17393P: Xnr 13.6295 -79.8034 0 0 13.6295 13.6295 13.6295 0 0 0 77.9033

P-to-P: Basic 6.7181 -79.3402 6.7181 0 0 11.636 11.636 1.9285 0.9642 0.9642 N/AP-to-P: Xm 7.3891 -80.5327 7.3891 0 0 12.7983 12.7983 1.8906 0.9453 0.9453 N/AP-to-P: Xnr 6.6647 -79.6874 6.6647 0 0 11.5436 11.5436 1.8947 0.9474 0.9474 N/A2P-to-E: Basic 6.744 -78.4473 6.6952 0.2114 0 11.946 11.329 2.8828 0 0 N/A2P-to-E: Xm 7.4134 -79.7362 7.3673 0.2073 0 13.1027 12.4963 2.8275 0 0 N/A2P-to-E: Xnr 6.691 -78.8052 6.6414 0.2077 0 11.8476 11.2426 2.8322 0 0 N/A1P-to-E: Basic 0.4089 -5.1256 0.4089 0.4089 1.2266 0 0 0 3.1448 3.3161 7.01071P-to-E: Xm 0.4026 -5.5806 0.4026 0.4026 1.2079 0 0 0 3.1045 3.2551 6.90421P-to-E: Xnr 0.4017 -5.8928 0.4017 0.4017 1.205 0 0 0 3.0908 3.2572 6.8876

Table 2 Summary of fault values for 12 scenarios

Figure 7 Comparison of various faults

Legend1P to E: Single phase to earth2P to E: Two phase to earthP to P: Phase to phase3P: Three phaseXm: Additional rotating loadXnr: Additional shunt load

0 2 4 6 8 10 12 14 16

3P: Basic3P: Xm3P: Xnr

P to P: BasicP to P: Xm

P to P: Xnr2P to E: Basic

2P to E: Xm2P to E: Xnr

1P to E: Basic1P to E: Xm1P to E: Xnr

kA (through 3.3 kV bus)

T y p

e o

f F a u

l t

Positive Sequence Fault Currents at Point B


12/41


C.1. General Observations on all Faults

In all fault situations, the total current flowing through all network elements increasesdrastically compared to normal loadflow. This leads to a very high cable loading. In all fault situations, the busbar voltages drop compared to respective normal loadflow,

by nearly the same order as current rises. This is because voltage levels will go down inshort-circuit situation when current inrush increases over shorted terminals (i.e. powerconversion from potential to kinetic electricity); this is also in part due to powerlimitations imposed by upstream components 5 (such as generators).

The phase lines experiencing the fault show 0 V on busbar if fault flow is toward earth orneutral, since that is 0 potential point; this is true in all 4 types of faults except P-to-P.

Conversely to the above, the phase(s) not experiencing fault show 0 A current; this meansall fault current is being routed through failing phases. Again, the inverse relationbetween V and I holds as discussed above.

It can be seen that in general for the 4 types of faults, the fault current levels in descendingorder are:i. Highest for 3Pii. Medium for 2P-to-E and P-to-P, which are nearly equal to each otheriii. Lowest for 1P-to-EThe above order can be deduced from noting the fact that as more phases of the systemare involved in a fault, the severity increases as current is produced from increasingpotential difference. More lines/cables of a system also get affected.

By method of symmetrical components, we can see from Table 2 that phase resolutionbecomes more complex as we proceed in this order:

i. 3P only positive sequence-components, which equal phase currentsii. P-to-P positive and negative-sequence components equal, but different from phase

currents due to swing angle; no zero-sequence componentsiii 2P t E g f ll t th t k f diff


13/41


because fault flows show current surge being supplied by induction motors (outgoing

flow). This occurs because induction motors store flywheel energy, momentarily actingas generators at time of fault. Non-rotating loads continue to consume power during fault; they do not supply as

confirmed by direction on ERACS fault-flow diagrams. In view of large current faults, it may be recommended that fault current limiters be

installed in some of the interconnecting busbar cables for system protection. To test the role of NGR values in fault situation, the 2P-to-E scenario was retested for

basic network by setting NGR to 0 instead of 6 ; it was seen that fault currents increased.This is further discussed below (see Section C.4).

C.2. 3 Phase Faults(Appendix 2: ERACS Fault-flow Schematics to FF1.3)The 3-phase fault currents in all 3 network configurations were, as expected, symmetrical in 3phases (compare IL1, IL2, IL3 in Table 2 above) in terms of current level. The level of currents,whether taken per phase total or just the positive sequence component, were also the highest in

this type of fault compared to all other types. Between the 3 network scenarios, the one withadded rotating load produces highest current components as explained above.

The positive sequence component is equal to individual phase fault level, whereas negative andzero-sequence components have 0 value. This keeps the system completely symmetrical withoutneed for further phasor resolution.

C.3. Phase to Phase Faults(Appendix 2: ERACS Fault-flow Schematics to F2.3)The P to P simulation in ERACS was achieved on phases L2 and L3 of the busbar, and it wasobserved that both phases showed an equal current flow between them, whereas there was 0flow on L1. Also, the voltage level on non-fault phase was higher than the levels on faulted lines,


14/41


15/41


The reader is advised to refer to Appendix 3 : Manual Fault Calculation for circuit reduction, and

Appendix 3: Manual Fault Calculation

B for calculated values table. The steps and underlyingassumptions are detailed hereunder.

1. All circuit components were considered as inductive reactances; any resistance orcapacitive effects including NGRs were ignored. This may lead to over-simplification ofelement models.

2. Only rotating machinery (generators, motors) and transmission equipment (grid,transformers, cables) were modelled; shunt loads were not included as their presence is

assumed to be similar to an open circuit.3. Neutral points of all rotating machinery (motors, generators) and grid source wereassumed to be common; this is not actually the case in software network.

4. Parameters for modelling equivalent (p.u.) inductance of each component were takenfrom ERACS library keys as follows:

Component Key Parameter (p.u.) ExplanationGenerator X ttd sub-transient reactanceTransformer X zero-sequence reactanceInduction Motor X s + Xrr stator reactance + running rotor reactanceCable X0 zero-sequence reactance per km

so Xeq = X0 * l / Z b where l is length (km) and is Z b = Vb2 / S b

Grid X eq Sb / S R where S R is rated power of gridTable 3 Equivalent inductance parameters from library keys

5. Network base power S b was set at 100 MVA, and V b was taken as rated voltage of eachbusbar in question.

6. Each elements equivalent resistance was converted to adjusted p.u. value by comparing


16/41


C.7. Comparison of Manual Result with ERACSThe phase fault current in ERACS for the basic network 3-phase fault at Point B is 13.74 kA. Thisreasonably comparable within limits, to manual result of 15.41 kA. Upon review, several reasonsemerge as possible candidates for causing this decrease of actual fault current when comparedwith manual calculation, as discussed here:

1. Detailed equivalent circuits of network elements are not taken; therefore resistive,capacitive and even additional sub-inductive items are ignored. For example, a cable is

assumed to be simply an inductor whereas in reality it possesses a resistance in series toinductance and a capacitive shunt in parallel. Similar argument holds for all othercomponents. Such oversimplification in manual calculation leads to a difference, becauseERACS considers each components detailed circuit model (i.e. decreasing actual currentflow due to introduction of further impedance).

Figure 9 Detailed equivalent model of cable

2. Busbar pre-fault base voltage is taken as 1 p.u. in final calculation, whereas in reality it isslightly lower at 0.99. Again this will lead to a lower Isc.

3. No pre-fault current is considered in manual calculation, whereas in reality it exists by


17/41


Addition of rotating loads can cause deterioration of power factor, as is seen for lower pf

at busbars with more induction motors attached. Driving-point impedance of connected network as seen by a busbar, is inverselyproportional to busbars voltage ra ting. This is because current flows increase at feed-inpoints of network (where V is higher), and decrease at consumption points (where V islower), whereas impedance follows a converse relation to current.

Load angles are greater at low voltage busbars; this is because the load components existat such points, where greater current flows (whereas higher busbars are involved intransmission at lower currents). A large current component naturally causes a greaterphasor swing due to IX .

For addition into a system, a stationary load having same P, Q rating as a rotating load,will not cause any reasonable loadflow differences but offers superior harmonicimpedance. Additionally, during fault scenarios, the stationary load seems to limit currentbetter than rotating one.

Upgrade Economics

When adding loads into a network, care must be taken to check how the incrementalreactive component distorts power factor, as this poses several problems e.g. rise incurrent causing I2R losses, greater voltage drops and cable overloading by heating.

Rise in peak kVA can lead to a higher fixed annual bill or penalty, without an increase ofreal work done.

Fault Analysis Under fault, busbar voltages drop compared to respective normal loadflow, by nearly the

same order as current rises (i.e. potential drop is converted into kinetic energy). The phase lines experiencing the fault show 0 V on busbar if fault flow is toward earth orneutral. Conversely, any phase not experiencing fault shows 0 A current as all fault currenti b i d h h f ili h


18/41


References

[1] B. M. Weedy, B. J. Cory, N. Jenkins, J. B. Ekanayake and G. Strbac, Electric Power Systems, Sussex:John Wiley & Sons, 2012.

[2] A. R. Sultan, M. W. Mustafa and M. Saini, Ground fault currents in unit generator -transformer atvarious NGR configur ations, IEEE Symposium on Industrial Electronics and Applications (ISIEA), pp.136-140, 2012.

[3] European Parliament, D irective 2006/95/EC on Electrical Harmonisation, Council of Dec -2006,Strasbourg, 2006.


19/41

ii

Appendix 1: ERACS Loadflow SchematicsERACS Schematics from Loadflow Studies (x3)

Student Name/ID: Muhammad Ali Qaiser/26561999 Diagram LF1Loadflow at Basic ConfigurationCoursework Title: PSA Coursework ERACS(Dec-2013)

Module: Power Systems Analysis ELEC6114


20/41

iii

Student Name/ID: Muhammad Ali Qaiser/26561999 Diagram LF2Loadflow with Rotating Load (induction motorgroup) at Point D (bus 3.3-4)

Coursework Title: PSA Coursework ERACS(Dec-2013)



21/41

iv

Student Name/ID: Muhammad Ali Qaiser/26561999 Diagram LF3Loadflow with Non-rotating Load (PQ shunt) atPoint D (bus 3.3-4)




22/41

v

Appendix 2: ERACS Fault-flow SchematicsERACS Schematics from Fault-flow Studies (x12)

Student Name/ID: Muhammad Ali Qaiser/26561999 Diagram FF1.13-Phase Fault in Basic Network at Point B (bus 3.3-

2)

Coursework Title: PSA Coursework ERACS(Dec-2013)Module: Power Systems Analysis ELEC6114


23/41

vi

Student Name/ID: Muhammad Ali Qaiser/26561999 Diagram FF1.23-Phase Fault at Point B (bus 3.3-2) , with additional

Rotating Load at Point D (bus 3.3-4)



24/41

vii

Student Name/ID: Muhammad Ali Qaiser/26561999 Diagram FF1.33-Phase Fault at Point B (bus 3.3-2) , with additionalNon-rotating Load at Point D (bus 3.3-4)



25/41

viii

Student Name/ID: Muhammad Ali Qaiser/26561999 Diagram FF2.1

Phase-to-Phase Fault in Basic Network at Point B(bus 3.3-2)



26/41


27/41

x

Student Name/ID: Muhammad Ali Qaiser/26561999 Diagram FF2.3Phase-to-Phase Fault at Point B with Non-rotatingLoad at Point D



28/41

xi

Student Name/ID: Muhammad Ali Qaiser/26561999 Diagram FF3.12 Phase-to-Earth Fault in Basic Network at Point BCoursework Title: PSA Coursework ERACS(Dec-2013)



29/41

xii

Student Name/ID: Muhammad Ali Qaiser/26561999 Diagram FF3.22 Phase-to-Earth Fault in Basic Network at Point B,with NGR values set to 0 instead of 6




30/41

xiii

Student Name/ID: Muhammad Ali Qaiser/26561999 Diagram FF3.32 Phase-to-Earth Fault at Point B, with additionalRotating Load at Point D



31/41

xiv

Student Name/ID: Muhammad Ali Qaiser/26561999 Diagram FF3.42 Phase-to-Earth Fault at Point B, with additional

Non-rotating Load at Point D



32/41


33/41


34/41

xvii

Student Name/ID: Muhammad Ali Qaiser/26561999 Diagram FF4.31 Phase-to-Earth Fault at Point B, with additionalNon-rotating Load at Point D



35/41


36/41


37/41


38/41


39/41


40/41

Appendix 3B: Manual Fault Calculation ParametersSbase (MVA) = 100

Device Zb X/km (km) Xeq Xs Xrr Old X p.u. Comments Rated MVA New X p.u.

G1 0.161 Xttd 1.863 8.64198G2 0.161 1.863 8.64198

G3 0.161 1.863 8.64198Grid 1.21 1.344444 Xeq / Zb 1.11111

L1 0.1089 0.069 0.8 0.0552 (X per km) * l / Zb 0.50689

L2 0.1089 0.069 0.3 0.0207 l is 0.6 but 2 in // so eff 0.3 0.19008L3 0.1089 0.069 0.1 0.0069 0.06336L4 0.1089 0.069 0.15 0.01035 0.09504

L5 0.1089 0.069 0.1 0.0069 l is 0.2 but 2 in // so eff 0.1 0.06336L6 0.1089 0.068 0.175 0.0119 0.10927L7 0.1089 0.068 0.175 0.0119 0.10927T1 0.03234 X 3.5 0.92400T2 0.02363 0.75 3.15067T4 0.02405 1.25 1.92400T6 0.02405 1.25 1.92400IM1 0.1 0.15 0.25 Xs + Xrr 0.76 32.89474IM2 0.1 0.15 0.25 1.5 16.66667IM3 0.1 0.15 0.25 0.76 32.89474IM4 0.092 0.191 0.2828 0.196 144.28571IM5 0.092 0.191 0.2828 0.119 237.64706IM6 0.092 0.191 0.2828 0.142 199.15493

IM7 0.092 0.191 0.2828 0.142 199.15493IM8 0.115 0.111 0.2263 0.13 174.07692


41/41

Circuit reduction is done as follows:1 Only inductive reactances are considered (X L); resistive effects are ignored2 Shunt loads are ignored as open circuits3 Effective inductance in parallel is 1/X eff = 1/X 1 + 1/X2...4 Effective inductance in series is X eff = X1 + X25 to Y conversion is done as X A = X1X3 / (X1 + X2 + X3) etc.

Step 1: Reduction of left half of circuit Step 2: Reduction of bottom right half of circuitXa = G1 // G2 // G3 = 2.8807 Xg = IM1 // IM2 // IM3 = 8.2781Xb = IM4 + T2 = 147.43638 X h = IM5 // IM6 // IM7 = 70.1737Xc = Xa // X b = 2.825454 X i = T4 + Xh 72.09770Xd = L6 // L7 = 0.0546 X2 = Xg // X i = 7.425555Xe = Xc + Xd = 2.8801Xf = Grid + T1 = 2.03511X1 = Xe // X f = 1.192485

Step 3: to Y conversion of top-left triangle of reduced circuitBranch 1 X1 1.1924851 Branch A 1.1810812

Branch 2 T6 + IM8 176.00092 Y Branch B 0.5020396Branch 3 L1 0.50689 Branch C 0.0034015

Step 4: Addition of Y components in series of existing circuitGiving A 1.181081

C + L2 0.19348B + L4 + L5 0.66044

Step 5: to Y conversion of top triangle of further reduced circuitBranch 1 A 1.1810812 Branch A' 0.9463807

Branch 2 X2 7.42555 Y Branch B' 0.529201Branch 3 B + L4 + L5 0.66044 Branch C' 0.0841727

Step 6: Addition of new Y components in series of existing circuitGiving C' + C + L2 0.27766 = X j

B' + L3 0.59256 = X kStep 7: Final equivalent resistance (p.u.) as seen from point of fault

Xeq = (X j // X k) + XA'= 1.135447And Isc (p.u.) = 1/X eq = 0.880711Since I b (kA) = 17.49546 Isc (kA) = 15.40844

Documents

Power network analysis using ERACS