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Chapter 12 Transformers © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Explain the operation of a.

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Presentation on theme: "Chapter 12 Transformers © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Explain the operation of a."— Presentation transcript:

1

2 Chapter 12 Transformers

3 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Explain the operation of a transformer. Discuss the relationship between mutual induction and transformers. Describe the effect of self induction. Calculate the various values of currents and voltages in transformer circuits.

4 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives List three types of transformer losses. Identify delta and wye transformer connections. Discuss grounding an electrical circuit. Explain troubleshooting procedures for transformers. Describe several special transformer applications.

5 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. TransformerTransformer Theory Induction Turns ratio principleTurns ratio Transformer power Transformer losses Impedance Phase relationship Taps

6 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Transformer Theory (Cont.) Primary and secondary windingsPrimarysecondary

7 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Transformer Theory (Cont.) Core- and shell-type construction

8 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Induction Voltage can be induced on a conductor with motion and a magnetic field With a coil, motion, and a magnetic field, an emf is produced

9 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Induction (Cont.) Mutual induction –No physical motion in transformer –Rising and collapsing magnetic field produces motion

10 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Induction (Cont.) Self induction –Separate fields combine to form an overall magnetic field –EMF produced in direction opposite to force generating magnetic field

11 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Turns Ratio Principle To increase or decrease a voltage, increase or decrease number of turns on the secondary winding

12 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Turns Ratio Principle (Cont.) Primary of a transformer connects to the source Secondary of a transformer connects to the load

13 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Turns Ratio Principle (Cont.) Relationship between primary and secondary voltages and current values

14 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Turns Ratio Principle (Cont.) Voltage ratio Current ratio

15 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Turns Ratio Principle (Cont.) Step-up transformers Step-down transformers

16 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Transformer Power Power on primary side equals power on secondary side P P = P S Expressed in VA (volt-amps) or kVA (kilovolt-amps)

17 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Transformer Power (Cont.) Find power in primary Find power in secondary –P S = I S × E S –I S × E S = I P × E P = 900 VA

18 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Transformer Power (Cont.) Power companies raise voltage to supply cities with electricity Wires of least resistance capable of carrying strong current

19 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Transformer Losses Copper losses Eddy current losses Hysteresis losses

20 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Impedance Combination of conductor resistance and the self induction Total resistance value

21 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Phase Relationship in Transformers Output voltage should be in phase or 180 degrees out of phase with primary voltage Polarity of induced voltage is opposite to voltage producing it

22 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Taps In secondary winding Allow a transformer to provide different voltages

23 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is a transformer? Device used to transfer energy from one circuit to another using electromagnetic induction

24 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is the ability to produce electrical energy in a conductor without making physical contact with the conductor? Induction

25 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review How is voltage induced on a conductor? With motion and a magnetic field

26 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What produces an emf? A coil, motion, and a magnetic field

27 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review If two coils are coupled together by a rising and collapsing field, what kind of induction are they using? Mutual induction

28 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What does increasing or decreasing the number of turns on the secondary winding affect? It increases or decreases the voltage

29 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is the current ratio? Ratio between currents in secondary and primary, inversely proportional to turns ratio

30 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What unit is used to express power in a transformer? Volt-amps (VA) or kilovolt-amps (kVA)

31 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What are three types of transformer losses? Copper losses, eddy current losses, and hysteresis losses

32 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is impedance? Total opposition to current in an ac circuit, a combination of the conductor resistance and self induction

33 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is a tap? Fixed electrical connection made to a winding at a point other than its terminals

34 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Typical Distribution Systems Power generated at plant, voltage stepped up Energy is routed onto transformers, voltage stepped down Residential areas have lower voltage distribution systems

35 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Typical Distribution Systems (Cont.) High voltage results in lower current values Less current means less power lost

36 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Delta and Wye, Three-Phase Power Systems Similar to generators Windings connected in series are delta connected Windings connected in parallel are wye connected

37 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Delta and Wye, Three-Phase Power Systems (Cont.) Only two lines of delta connection are equal to 120 V, the other is equal to 200 V High leg

38 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Grounding Provides safe path for fault current If one conductor is not connected to earth, a conductor-to-ground voltage reading will behave similarly to an open circuit

39 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Troubleshooting Transformers Megohmmeter Disconnect load, insulate secondary leads, fuse primary with small value fuse

40 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review How are delta and wye connections made in transformers? Delta connections are in series, and wye connections are in parallel

41 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is the function of a ground? Provides a safe path for fault current

42 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is a megohmmeter? An ohmmeter that uses higher than normal voltages and accurately reads resistance into the megohm values

43 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Special Transformer Applications Autotransformers Induction circuit breakers Lighting ballasts Coupling transformers Isolation transformersIsolation Automobile ignition coils

44 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Autotransformers Isolation for transformers One winding without isolation Used in low-voltage applications

45 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Induction Circuit Breakers Inductor triggers a switch to shut off current Strength of magnetic field breaks circuit Used to protect equipment or prevent fires

46 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Lighting Ballasts Start lamp by producing voltage Limit current through lamp Use capacitors to reduce power loss

47 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Coupling Transformers Separate sections of an amplifier system Impedance matching Make sections compatible with one another

48 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Isolation Transformers Used to separate commercial power systems from sensitive equipment power supply systems Transient voltages

49 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Automobile Ignition Coils Type of autotransformer High turns ratio develops 30,000 V or more

50 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Electric Resistance Welding When electrical current passes through metal, friction caused by resistance heats the metal Includes spot welding, projection welding, seam welding, and upset welding Welding current can be ac or dc, but resistance spot welding typically uses ac

51 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What does isolation of a transfer refer to? The electrical separation between the primary and secondary windings

52 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review How does an induction circuit breaker function? An inductor triggers a switch to shut off current

53 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review Which transformer starts a lamp by producing a voltage? Lighting ballast

54 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What kind of transformer is used to separate the sections of an amplifier system? Coupling transformer

55 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. For Discussion Discuss why power companies use high voltage in power lines. Explain the differences between step-up transformers and step-down transformers. Discuss how electricity might be distributed in the future.

56 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Copper loss –Heat loss in motors, generators, and transformers as result of resistance of wire. Sometimes called the I 2 R loss. Current ratio –The ratio between the currents in the primary and secondary windings in a transformer.

57 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Eddy current loss –Heat loss resulting from eddy current flowing through resistance of a core. High leg –The hot conductor in a delta-connected transformer bank that is not common to the neutral. The high leg exhibits a higher voltage to ground than the other hot conductors.

58 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Hysteresis loss –Energy loss in a substance as molecules or domains move through the cycle of magnetization. Loss is due to molecular friction. Impedance –Total resistance to the flow of an alternating current as a result of resistance and reactance.

59 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Induction –The ability to produce electrical energy in a conductor without making physical contact with the conductor. Isolation –Electrical separation between two locations.

60 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Megohmmeter –An ohmmeter that uses higher than normal voltages and accurately reads resistance into megohm values. Mutual induction –Two coils located so the magnetic flux of one coil can link with turns of the other coil. The change in flux of one coil will cause an emf in the other.

61 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Primary –The input winding in a transformer. Secondary –The output winding in a simple transformer. Self induction –EMF is self-induced when it is induced in a current-carrying conductor.

62 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Step-down transformer –Used to lower a voltage. Step-up transformer –Used to raise a voltage. Tap –Connection made to a coil at a point other than its terminals.

63 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Transformer –Device that transfers energy from one circuit to another by electromagnetic induction. Turns ratio –The number of turns of the primary winding of a transformer compared to the number of turns of the secondary winding.

64 © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Voltage ratio –The ratio between the voltages of the primary and secondary windings.


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