Learner Workbook Version 1 - VETRES - Vocational … · · 2013-07-25Learner Workbook Version 1. ... Parallel Operation of Transformers ..... 91 Review Questions - Answers ... construction

Learner Workbook

Version 1

Training and Education SupportIndustry Skills Unit

Meadowbank

Product Code: 5634

Single & Three Phase Transformers

SAMPLE


© TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012

Table of ContentsIntroduction ................................................................................... 5

Section 1. Transformer Construction .............................................. 7

Section 2. Transformer Operation ................................................ 17

Section 3. Transformer Losses, Efficiency and Cooling ................. 35

Section 4. Transformer Voltage Regulation and Impedance ......... 51

Section 5. Transformer Auxiliary Equipment and Tap-Changers ... 61

Section 6. Auto-Transformer and Instrument Transformers ......... 69

Section 7. High Voltage Safety Procedures ................................... 77

Section 8. Transformer Connections & Harmonics ........................ 81

Section 9. Parallel Operation of Transformers .............................. 91

Review Questions - Answers ...................................................... 103

Sample Theory Test 1 ................................................................. 115

Sample Theory Test 2 ................................................................. 120

Sample Practical Test 1 .............................................................. 129

Sample Theory Test 1 - Answers ................................................ 133

Sample Theory Test 2 - Answers ................................................ 135

A Glossary of Transformer Terms ............................................... 139

Appendix ............................................................................... 141

Resource Evaluation Form .......................................................... 153SAMPLE

© TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012 Page 7 of 156


Section 1. Transformer Construction

PurposeIn this topic you will develop knowledge of the construction of single and three phase transformers.

Objectives

At the end of this topic you should be able to:

• Describe the principle of mutual induction of a transformer

• Describe the construction of the various types of lamination style and core construction used in single phase, three phase, auto and instrument transformers

• Identify the different winding styles used in transformers

• Describe the construction of transformer tanks for distribution transformers

• List the types of information stated on transformer nameplates

• Describe the methods used to insulate low and high voltage transformers

• Performbasicinsulationresistance,continuityandwindingidentificationtests.

References• Jenneson, J.R., 2010, Electrical Principles for the Electrical Trades, 6th Edition,

McGraw-Hill, Sydney

• Hampson, J., 2011, Electrical Trade Principles - A Practical Approach, 2nd Edition, Pearson Education, Sydney

• Phillips, P., 2012, Electrical Principles, 2nd Edition, Cengage Learning, Melbourne.

SAMPLE

Page 8 of 156 © TAFE NSW (Training & Education Support, Industry Skills Unit Meadowbank) 2012


Student exercise 1

Calculate the induced voltage in a coil of 433 turns which is connected to a 50 Hz supply,whenthemaximumfluxis2.5milliwebers.

Student exercise 2

A single phase transformer is wound with 200 turns on the primary and 60 turns on the secondary.Themaximumvalueofcorefluxis12.5mWbandthefrequencyis50Hz.

Determine:

(a) The primary voltage

(b) The secondary voltage.SAMPLE



Student exercise 3

How many turns are required on each winding of a 11 000:415 volt 50 Hz single phase transformerifthecorefluxis0.03weber.

Student exercise 4

A 300/32 volt, 50 Hz single phase transformer has 600 turns on the primary winding. Determinethemaximumvalueofcoreflux.

SAMPLE



Practical exercise: Transformer identification and testing

Task

• Given a double wound single phase transformer conduct a continuity test to identify the separate windings

• Test the insulation resistance of a double wound single phase transformer

• Identify the windings of different types of double wound transformers.

Equipment

• 1 Insulation resistance tester Type ______________________________

• 1 Voltmeter Type ____________ Range ____________

• Unmarked double wound transformer Type ____________ Ratio _____________

• Three types of double wound step-down transformers, each randomly labeled as X, Y and Z

• Connecting leads

Risk Assessment

Identify any hazards, list the supervision level (D, G or B), list the risk class (A, B or C) and list control measures required in the table below:

Hazard Identification Supervision Level Risk Class Control Measures

Procedure

1. Select and name an appropriate instrument to conduct the continuity test:

2. Mark each terminal of the transformer A, B, C and D.

3. Using the winding markings below, conduct the continuity test and indicate each continuity readings as either low resistance (LR) or open circuit (OC).

SAMPLE



TABLE 1.1

Winding marking Test resultsA-BA-CA-DB-CB-DC-D

4. From the above test results, which of the winding markings have connections as a coil?

5. From their conductor cross sectional area, identify the low tension and high tension windings, assuming the transformer is used to step down the voltage. To answer, choose from the winding markings in Step 4.

Low tension winding: _____________________

High tension winding: _____________________

6. Select and name an appropriate instrument to conduct an insulation resistance test on the transformer.

7. Conduct an insulation resistance test:

• Betweenthetransformerwindings

• Betweenbothwindingsandthecore(earth).

Record your test results as ohmic values in Table 1.2 below.

TABLE 1.2

Winding marking Test resultsCoil to coil

Primary coil to coreSecondary coil to core

8. From the test results, state whether this transformer complies with AS/NZS 3000 for connection to the supply.

Circle: Yes or No

SAMPLE



9. Place the three different transformers side by side, inspect the leads, identify each transformer by the letter X, Y, or Z using tags, then write X, Y and Z opposite the corresponding transformer type below:

• Doublewoundwithouttapping:_____________________________

• Doublewoundcentertapped:_______________________________

• Doublewounddualsecondaries:____________________________

10. For each transformer X, Y and Z, use a continuity tester and the diagrams to:

• Identifyeachcoil

• TagandmarkeachcoilendasindicatedonthediagramsA,BandC.

Figure 1.1

11. Visually inspect the coil leads of the three transformers. On the transformers place a tag on each winding to identify the primary and secondary coils.

12. Brieflyexplainwhyresistancemeasurementusinganohmmetertoidentifyprimary and secondary voltage windings would be likely to give incorrect results on large and well designed transformers.

13. Ask your teacher to check the completed practical exercise.

SAMPLE



Review questionsThese questions will help you revise what you have learnt in this topic.

1. Transformer laminations are manufactured from:

(A) Copper

(B) Corrosion resistant steel

(C) Silicon steel

(D) Iron.

2. Transformer laminations are prevented from shorting out by:

(A) An oxide layer on each lamination

(B) Using spacing blocks to provide air gaps

(C) Sandwiching PVC sheets between laminations

(D) Painting the sides of the laminations.

3. The material most commonly used for transformer windings is:

(A) Aluminium

(B) Copper

(C) Silicon steel

(D) Iron.

4. The cross-sectional shape most commonly used for high power transformer winding conductors is:

(A) Circular

(B) Flat strip

(C) Hexagonal

(D) Square.

5. The lid of a transformer tank is secured to the main tank by:

(A) Welding

(B) Bolting

(C) Hinging

(D) Clamping.

SAMPLE



6. Most high-voltage transformers operate in a medium of:

(A) Synthetic oil

(B) Air

(C) Mineral oil

(D) Solid insulant.

7. The most common insulation used for the conductors of oil-immersed transformer is:

(A) Glassfibre

(B) Cotton

(C) Mica

(D) Asbestos.

8. What are the main parts that make up a high-voltage transformer?

9. Does hot-rolled or cold-rolled silicon sheet provide a better material for transformer laminations? Why?

10. What is the ideal cross-sectional shape for a transformer core?

11. How does the practical cross-sectional shape of laminations differ from the ideal one and why is it used?

SAMPLE

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Learner Workbook Version 1 - VETRES - Vocational … · · 2013-07-25Learner Workbook Version 1. ... Parallel Operation of Transformers ..... 91 Review Questions - Answers ... construction