# Chapter 12 Transformers. Chapter 12 Transformers.

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Chapter 12 Transformers

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. Â© 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. Â© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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

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

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

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

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

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

Transformer Power (Cont.)
Find power in primary Find power in secondary PS = IS Ã— ES IS Ã— ES = IP Ã— EP = 900 VA Â© 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 Â© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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

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

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

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

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

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

Glossary Copper loss Current ratio
Heat loss in motors, generators, and transformers as result of resistance of wire. Sometimes called the I2R loss. Current ratio The ratio between the currents in the primary and secondary windings in a transformer. Â© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Glossary Eddy current loss High leg
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. Â© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Glossary Hysteresis loss Impedance
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. Â© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

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

Glossary Megohmmeter Mutual induction
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. Â© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Glossary Primary Secondary Self induction
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. Â© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Glossary Step-down transformer Step-up transformer Tap
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. Â© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.

Glossary Transformer Turns ratio
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. Â© 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. Â© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.