Protection IV

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PRT4701/101/0/2016

Tutorial letter 101/0/2016

Protection Technology IV (Theory)

PRT4701

Year Module

Department of Electrical and MiningEngineering

IMPORTANT INFORMATION:

This tutorial letter contains important informationabout your module.


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CONTENTS

Page

1 INTRODUCTION........................................................................................................................... 3

2

PURPOSE OF AND OUTCOMES FOR THE MODULE ............................................................... 3

2.1 Purpose ........................................................................................................................................ 3

2.2 Outcomes ..................................................................................................................................... 3

3 LECTURER(S) AND CONTACT DETAILS ................................................................................... 3

3.1 Lecturer(s)..................................................................................................................................... 3

3.2 Department ................................................................................................................................... 3

3.3

University ...................................................................................................................................... 4

4 MODULE-RELATED RESOURCES ............................................................................................. 4

4.1 Prescribed books .......................................................................................................................... 4

4.2 Recommended books ................................................................................................................... 4

4.3 Electronic Reserves (e-Reserves) ................................................................................................. 4

5 STUDENT SUPPORT SERVICES FOR THE MODULE ............................................................... 4

6 MODULE-SPECIFIC STUDY PLAN ............................................................................................. 4

7

MODULE PRACTICAL WORK AND WORK-INTEGRATED LEARNING ..................................... 4

8

ASSESSMENT ............................................................................................................................. 4

8.1 Assessment plan ........................................................................................................................... 4

8.2 General assignment numbers ....................................................................................................... 5

8.2.1 Unique assignment numbers ......................................................................................................... 5

8.2.2 Due dates for assignments ............................................................................................................ 5

8.3

Submission of assignments ........................................................................................................... 5

8.4

Assignments ................................................................................................................................. 7

9 OTHER ASSESSMENT METHODS ........................................................................................... 18

10 EXAMINATION ........................................................................................................................... 18

11 FREQUENTLY ASKED QUESTIONS ......................................................................................... 18

12 SOURCES CONSULTED ........................................................................................................... 18

13

CONCLUSION ............................................................................................................................ 18

14

ADDENDUM ............................................................................................................................... 18


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1 INTRODUCTION

Dear Student

Welcome to the subject Protection Technology IV (Theory) (PRT4701)at UNISA. Thistutorial letter serves as a guideline to this subject. It provides you with general administrativeinformation as well as specific information about the subject. Read it carefully and keep itsafe for future reference. We trust that you will enjoy this course.

2 PURPOSE OF AND OUTCOMES FOR THE MODULE

2.1 Purpose

The purpose of this subject is for the student to study the calculation of fault currents (three

and/or single phase) to form an integral part of application of the field of ProtectionTechnology.

2.2 Outcomes

The ability to calculate fault currents theoretically (three and single phase as well assymmetrical and unsymmetrical faults) by using the Zbus- and other methods.

3 LECTURER(S) AND CONTACT DETAILS

3.1 Lecturer(s)

Your Lecturer for Protection Technology IV is Mr E Naud Pr Eng. He can be contacted atthe following number for any theoretical questions:

Tel nr : 0828067717

e-mail: [email protected]

Contact Times: Mondays to Fridays18h00 20h00

3.2 Department

Department of Electrical and Mining Engineering: electrical&[email protected]


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3.3 University

If you need to contact the University about matters not related to the content of this module,please consult the publication My studies @ Unisa that you received with your studymaterial. This brochure contains information on how to contact the University (e.g. to whomyou can write for different queries, important telephone and fax numbers, addresses anddetails of the times certain facilities are open).Always have your student number at hand

when you contact the University.

4 MODULE-RELATED RESOURCES

4.1 Prescribed books

Grainger & Stevenson. Power System Analysis. Mc Graw-Hill. ISBN 0071133380

4.2 Recommended books

There are no recommended books for this module.

4.3 Electronic Reserves (e-Reserves)

There are no electronic reserves for this module.

5 STUDENT SUPPORT SERVICES FOR THE MODULE

Important information appears in your my Studies @ Unisabrochure.

6 MODULE-SPECIFIC STUDY PLAN

Use your my Studies @ Unisabrochure for general time management and planning skills.

7 MODULE PRACTICAL WORK AND WORK-INTEGRATED LEARNING

The practical part of this module will be covered in the module PRTPRA4.

8 ASSESSMENT

8.1 Assessment plan

You will find your assignments for this subject in this Tutorial Letter. Assignment 1,2 and 3 are compulsory and all assignments will be used in the calculation of youryear mark. Please send the completed assignments to UNISA before the closingdates stated in this section.

Assignment 1 must be completed on a mark reading sheet.

The mark for Protection Technology IV (Theory) (PRT4701) is calculated as follows:

The year mark contributes to 20%.


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The examination mark contributes to 80%

The year mark is based on all the assignment marks obtained and their contribution towardsthe final year mark are as shown in the table below:

ASSIGNMENTNUMBER

CONTRIBUTIONTOWARDS YEAR

MARK1 (Compulsory) 10%

2 (Compulsory) 45%

3 (Compulsory) 45%

TOTAL = 100 %

8.2 General assignment numbers

Assignments are numbered consecutively per module, starting from 01.

8.2.1 Unique assignm ent numbers

Assignment 1: 852091



8.2.2 Due dates for assig nments

THE CUT-OFF SUBMISSION DATES FOR THE ASSIGNMENTS ARE :

Assignment 1:Assignment 2:Assignment 3:

20 May 201618 July 2016

5 September 2016

8.3 Submission of assignments

ALL ASSIGNMENTS (submitted) HAVE TO BE ATTEMPTED!!!!!!!

THE SUBMISSION OF AN EMPTY ASSIGNMENT COVER IS UNACCEPTABLE.

IT IS VERY IMPORTANT TO CONSIDER THE FOLLOWING POINTS :

NO LATE ASSIGNMENT SUBMISSIONS WILL BE ACCEPTED.

KEEP A CLEAR COPY OF THE ASSIGNMENT FOR YOUR OWNREFERENCE.THIS IS IMPORTANT, AS ASSIGNMENTS DO GET LOST.

SUBMISSIONS OF ASSIGNMENTS MUST BE IN ACCORDANCE WITH MYSTUDIES @ UNISA.


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Please note that model answers for the assignments will be dispatched to all

students within 1 week of the closing date of the assignment. This implies that

you cannot submit your assignment later than the stipulated submission date.

For detailed information and requirements as far as assignments are concerned, see

the brochure my Studies @ Unisathat you received with your study material.

To submit an assignmentvia myUnisa:

Go to myUnisa.

Log in with your student number and password.

Select the module.

Click on assignments in the menu on the left-hand side of the screen.

Click on the assignment number you wish to submit.

Follow the instructions.


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8.4 Assignments

THE CUT-OFF SUBMISSION DATES FOR THE ASSIGNMENTS ARE :

Assignment 1: (Compulsory)Assignment 2: (Compulsory)Assignment 3: (Compulsory)

20 May 201618 July 2016

5 September 2016

ASSIGNMENT 1

Choose the correct answer for the questions below:

1. Examine the three phasor diagrams of a short transmission line: (All diagrams are drawnfor the same magnitudes of VRand IR)

Diagram 1. is for a:

1. load power factor of 70% lagging

2. load power factor of 70% leading

3. load power factor of 100%

4. None of the above

2. Diagram 2. from the diagrams in question 1 above is for a:.1. load power factor of 70% lagging




3. Diagram 3. from the diagrams in question 1 above is for a:.1. load power factor of 70% lagging





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4. The shunt admittance, usually __________, is included in the calculations for a line ofmedium length.

1. pure resistive

2. pure capacitive

3. pure inductive

4. All of above

5. If, in a medium length line, the total shunt admittance of the line is divided into two equalparts placed at the sending and receiving ends of the line, the circuit is called ______.

1. an independent circuit

2. a symmetrical circuit

3. a nominal circuit

4. a capacitive circuit

6. For a long transmission line, ZCis called:1. capacitive impedance

2. characteristic impedance

3. long line impedance

4. shunt admittance

7. For a long transmission line, is called the propagation constant. The real part of thisconstant is called ___________.

(1) attenuation constant(2) impedance constant(3) termination constant(4) instantaneous constant

8. The real part of the propagation constant mentioned in question 7 above, is measuredin ________:

(1) ohms per meter(2) Siemens(3) F/m(4) nepers per unit length.

9. The quadrature part of the propagation constant mention in question 7 above, is called______________.

(1) propagation voltage(2) impedance constant(3) rotation constant


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(4) phase constant

10. The impedance elements of Zbuson the principal diagonal are called ______________ ofthe buses.

1. characteristic impedances

2. phasor impedances

3. driving point impedances

4. mutually coupled impedances

11. The impedance elements of Zbuson the off-diagonal elements are called _________ ofthe buses

1. resistive impedances

2. characteristic impedances

3. transfer impedances

4. coupled impedances

12. Circuit breakers have rating determined by:1. minimum instantaneous current which the breaker must withstand

2. maximum instantaneous current which the breaker must withstand

3. minimum instantaneous voltage that which a breaker must withstand

4. 1. and 3. above

13. A transformation of network variables which preserves power is said to be _______.1. power variant

2. power invariant

3. power network

4. power relationships

14. The interrupting rating of a circuit breaker is specified in:1. kVA

2. kVAr

3. kW

4. kWh


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15. Subtransient currents are ___ than transient and steady state currents.1. larger

2. smaller

3. equivalent

4. negligible

16. Experience has shown that between 70% and 80% of transmission lines faults are______ faults.

(1) single line to line(2) single line to ground(3) two phase(4) three phase

17. Reclosing of circuit breakers usually restore the voltage on the transmission line. Ifreclosing is unsuccessful, the fault on the line is usually a _______ fault.

(1) line to line(2) permanent(3) three phase(4) None of the above

18. In an auto transformer, the three windings are called primary, secondary and ______windings.

1. tertiary;

2. impedance;

3. phasors ;

4. None of above

19. Roughly 5% of all faults are three phase faults. These are so-called ________ threephase faults.

1. permanent

2. transient

3. symmetrical

4. unsymmetrical

20. The bus impedance matrix is most often used for _____ calculations.1. positive-sequence current

2. negative-sequence current

3. fault current

4. sequence and system current (20)


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ASSIGNMENT 2

QUESTION 1:

A single line diagram of a synchronous generator feeding a synchronous motor isshown in the figure below:

1.1 Use the one step at a time method to construct Zbusfor the two bus network. (15)

1.2 Add a new branch with Zb= j0.4pu between busses 1 and 2 for this network.Construct the new bus matrix assuming Zb is not mutually coupled to theexisting line. (10)

[25]

QUESTION 2:

A single Study the following single line diagram (Figure 1) of a reactance network andanswer questions 2.1 to 2.5. The magnitude and angle of each of the generatedvoltages may be assumed to remain constant.

Figure 1


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2.1 Determine the Zbusby direct formulation. (10)

2.2 Determine the voltage at each bus. (4)

2.3 The current drawn by a capacitor having a reactance of 4.0 per unitconnected from bus 3 to neutral; (3)

2.4 The change in voltage at each bus when the capacitor is connected at bus 3; (3)2.5 The voltage at each bus after connecting the capacitor. (3)

[23]

QUESTION 3:

A single line diagram of a power system is shown in the figure below where negative

and zero sequence reactances are also given. The neutrals of the transformers aresolidly earthed whilst the neutral of the motor is grounded via zero's pu reactance.

3.1 Using a base of 100MVA and 13.8kV, determine and draw the pu zero,positive and negative sequence network for the system. (9)

3.2 Reduce the sequence network to their Thevenin equivalent (draw theThevenin's circuits). Pre-fault the sub-transient fault current is Vp = 1.05 0

0

pu. Ignore pre-fault load current and any transformer phase shifts. (9)

3.3 Calculate the sub-transient fault current in per unit and actual value for abolted single phase line to ground short circuit from phase a and ground atbus 2. (6)

3.4 Calculate the per unit line to ground voltage at the faulted bus 2 mentioned inproblem 3.3 above. (6)

[30]


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QUESTION 4:

Study the following one-line diagram:

A 1MVA generator with Xd = 0.2 per unit is connected to a bus through a circuitbreaker. Connected through circuit breakers to the same bus are three synchronousmotor rated 200kW, 6.6kV, 1.0 power factor, 92% efficiency with Xd = 0.2 per unit.The motors are operating at full load, unit power factor and rated voltage with theload equally divided among the machines. Neglect the resistance of the lines.

4.1 Draw the impedance diagram with the impedance marked in per unit on abase of 1MVA, 6.6kV. (6)

4.2 Find the symmetrical short-circuit current in Amps, which must be interruptedby breakers A and B for a three phase fault at point P. Simplify thecalculations by neglecting the pre-fault current. (12)

4.3 Repeat 4.2 for a three phase fault at point Q. (2)4.4 Repeat 4.2 for a three phase fault at point R. (2)

[22]

TOTAL:100


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ASSIGNMENT3

QUESTION 1:

A 30MVA, 13.8kV, 3 phase alternator has a sub transient reactance of 15% and negativeand zero sequence reactance of 15% and 5% respectively. the alternator supplies twomotors over a transmission line having transformers at both end as shown in the figure

below. The motors have rated inputs of 20MVA and 10MVA both 12.5kv with 20% subtransient reactance and negative and zero sequence reactance of 20% and 5%respectively. Current limiting resistors of 2 each are in the neutral of the alternator andlarger motor. The three phase transformers are rated 35MVA, 13.2/115kV Y with leakagereactance of 10%. Series reactance of the line is 200.

1.1 Determine and draw the three sequence networks. (15)

1.2 Determine the fault current when a L-L to ground fault occurs at point P.Assume Vf = 120kV. (10)

[25]

QUESTION 2:

Study the following single line diagram of an unloaded system:

Reactances of the two sections of the transmission line are shown in the diagram. Thegenerators and transformers are rated as follows:

G1 20MVA, 13.8kV, X"d= 0.2 per unit


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G2 30MVA, 18kV, X"d= 0.2 per unit

G3 30MVA, 20kV, X"d= 0.2 per unit

T125MVA, 220Y/13.8 kV, X = 10%

T2 single phase units, each rated 10MVA, 127/18kV, X = 10%

T3 35MVA, 220Y/22Y kV, X = 10%

2.1 Draw the negative and zero sequence impedance networks. Mark all thevalues of all reactances in per unit on a base of 50MVA, 13.8kV in the circuit ofgenerator 1. Letter the networks to correspond to the single diagram. Theneutrals of generator 1 and 3 are connected to ground through current limiting

reactors having a reactance of 5% each on the base of the machine to which itis connected. Each generator has negative and zero sequence reactances of20% and 5% respectively, on its own rating as base. The zero sequencereactance of the transmission line is 210 ohm from B to C and 250 ohm from Cto E. Shown all relevant calculations. (10)

2.2 Determine the zero-sequence Thevenin impedance seen on bus C of thesystem if transformer T3has

(i) one ungrounded and one solidly grounded neutral and (5)(ii) both neutrals are solidly grounded. (5)

[20]

QUESTION 3:

3.1 The currents flowing in the lines towards a balanced load connected in are:Ia= 100 0

Ib= 141.4 225

Ic= 100 90

(a) Find the symmetrical components of the given line currents and drawphasor diagrams of the positive - and negative sequence line andphase currents. (4)

(b) Determine Iabin amperes. (5)(c) Assume that the current specified above are flowing towards a load

from lines connected to the Y-side of a -Y transformer rated10MVA, 13.2 /66YkV. Determine the currents flowing in the lines onthe side by converting the symmetrical components of the currents


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to per unit on the base of the transformer rating and by shifting thecomponents according the following rules: (6)

Check the results by computing the currents in each phase of the windingin amperes directly from the currents on the Y-side by multiplying by the turnsratio of the windings. Complete the check by computing the line currents fromthe phase currents on the side.

3.2 The voltages at the terminals of a balanced load consists of three 10

resistors connected in Y are Vab= 10000

, Vbc= 80.8-121.40

and Vca =901300. Assuming that there is no connection to the neutral of the load,draw the phasor diagrams of the positive and negative sequence voltagesand find the line currents from the symmetrical components of the given linevoltages. (10)

[25]

QUESTION 4:

4.1 One conductor of a three phase line is open as shown in the figure below:

The current flowing to the delta connected load through the line R is 10A.

With the current in line R as reference and assuming that B is open,determine the symmetrical components of the line currents. (15)


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4.2 For the system below, determine 4.2.1 and 4.2.2:

4.2.1. Determine the earth fault current for a fault at F. (9)

4.2.2. Determine the current in the delta winding of the transformer. (6)

[30]

TOTAL: 100


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9 OTHER ASSESSMENT METHODS

None

10 EXAMINATION

Use your my Studies @ Unisabrochure for general examination guidelines and examinationpreparation guidelines.

11 FREQUENTLY ASKED QUESTIONS

The my Studies @ Unisa brochure contains an A-Z guide of the most relevant studyinformation.

12 SOURCES CONSULTED

None

13 CONCLUSION

Please ensure that you have all the tutorial letters and prescribed book available before

starting with your studies.

14 ADDENDUM

None

Documents

Protection IV