030303a - Introduction to Transformers

Obj. 1 - What is induction?

Induction is generating electromotive force (EMF) through the interaction of magnetic fields and conductors, either by moving a conductor through a magnetic field or vice versa.

Obj. 1 - What is mutal induction?

Mutual induction is the phenomenon where a change in current in one coil induces voltage in another nearby coil due to their magnetic fields interacting.

Obj. 1 - What is transformer action?

Transformer action is another term for Mutual Induction

Obj. 1 - Whats the difference between induction and inductance?

inductance is the property of a circuit that opposes changes in current, while induction refers to the process in which a voltage is produced by the interaction of a conductor and a magnetic field.

Obj. 1 - How are primary and secondary coils determined?

Primary coils connect to the input voltage source, while secondary coils deliver the output voltage.

Obj. 1 - What happenes when there is no relative motion between a magnetic and coil?

No voltage is induced. Voltmeter reads 0V.

Obj. 1 - What is needed for self- or mutually induced voltage to occur?

Self- or mutually induced voltage only occurs when the current is changing.

Obj. 1 - What type of induction occurs on a primary and secondary coil?

Self-induction occurs in a primary coil, whilst mutual induction is applied in the secondary.

Obj. 1 - What is the relationship between the number of turns on a coil and the voltage it induces?

The voltage induced in a coil is directly proportional to the number of turns; more turns result in higher induced voltage.

Obj. 2 - What is a transformer?

A transformer is an electrical device that transforms alternating current (AC) energy from one circuit to another through electromagnetic induction. It consists of two or more coils of wire wound on a common soft iron core.

Obj. 2 - How are transformers so efficient?

Transformers are efficient due to low reluctance materials and absence of air gaps, and a lack of moving parts.

Obj. 2 - What are the types of power losses seen on transformers? Electrical and Mechanical.

Electrical Losses inlcude:

1) Copper losses also known as (I²R)
2) Iron losses, which include hysteresis and eddy current, and small amounts of flux leakage
Mechanical losses include:

1) Friction
2) Windage losses associated with moving parts, although most transformers are static devices.

Obj. 2 - What is Eddy Currents, and whats a solution to reduce it?

Eddy currents cause heating in the core due to changes in the magnetic field. Ways to reduce eddy currents are by adding thin layers of insulating material to the core or using laminated cores, which restrict the flow of these currents.

Obj. 2 - What is Hysteresis, and whats a solution to reduce it?

Hysteresis - Is the molecular friction due to fast and constant changes in polarity in a material. A solution to reduce hysteresis is using materials with good magnetic quality, such as silicon steel.

Obj. 2 - What are three basic types of transformer constructions?

Core type, shell type, and multi-winding type.

Obj. 2 - What are transformers rated in?

Transformers are rated Apparent Power (VA)

Obj. 2 - What type of information can be listen on a transformer nameplate?

The transformer nameplate typically lists:

1. Primary voltage

2. Secondary voltage

3. kVA rating

4. Frequency

5. Temperature rise

6. Percent Impedence (%Z)

7. Type of insulation oil

8. Serial Number (S/N)

9. Type Number

10. Transformer Phase

Obj. 2 - What are 4 things that determine a transformers impedence (%Z)?

1. Amount and type of core material

2. Winding wire size

3. number of winding turns

4. Degree of magnetic coupling

Obj. 2 - What type of test is performed on a transformer to determine its percent impedence (%Z)?

A short-circuit test is performed on a trnasformer to determine its percent impedence (%Z).

Obj. 2 - What are the 3 functions fo a single phase transformer?

1. to step up voltage

2. To step down voltage

3. To isolate one circuit from another

Obj. 2 - Whats the primary use of a step up voltage transformer?

To increase voltage levels when transferring power over long distances, reducing energy losses.

Obj. 2 - Whats the primary use of a step down voltage transformer?

To decrease voltage levels for safe distribution and use in residential and commercial applications.

Obj. 2 - Whats the primary use of an isolation transformer?

Isolation transformers isolates the conductors on the output side from groundand provides protection against electrical shock and noise, ensuring safe operation of sensitive equipment. In addition, the outpuyt voltage to the load equals the input voltage from the source.

Obj. 2 - What are the markings for high and low voltage terminals based on ANSI standars?

High voltage terminals are marked with "H", while low voltage terminals are marked with "X"

Obj. 2 - How are flexible leads on Tx windings identified?

Leads are identified with tags, tape or markings on insulation

Obj. 3 - What does a Transformers kVA rating mean?

The rating is an expression of the ability of ther transformer to supply the rated current at the rated voltage without overheating.

Obj. 4 - Describe transformer polarity.

Transformer polarity refers to the directional relationship between primary and secondary windings, where one winding is positive and the other negative. Leads marked with even numbers must be the same polarity.

Obj. 4 - Where is the H1 terminal located, as required by ANSI Standards?

H1 terminal is located on the top left hand corner.

Obj. 4 - What kind of transformer polarity is present when H1 and X1 leads are diagonally opposite to each other?

Additive polarity, indicating that the voltages are in phase, resulting in a higher output voltage when combined.

Obj. 4 - What kind of transformer polarity is present when H1 and X1 leads are directly opposite to each other?

Subtracting polarity, indicating that the voltages are out of phase, resulting in a lower output voltage when combined.

Obj. 5 - What the purpose of transformer voltage taps?

Taps are arranged in high voltage windings so that the proper secondary voltage is obtained.

Obj. 5 - When are taps installed on a primary winding?

On a step down transformer, taps are installed in on a primary winding to compensate for slightly higher or lower primary voltages so that rated secondary voltages can be obtained.

Obj. 5 - When are taps installed on a secondary winding?

Taps are taken off the secondary windings at different points to access secondary voltages.

Obj. 5 - What are the 4 types of Tx Tap labellings?

1. Full Capacity Above Normal (FCAN); +5%

2. Full Capacity Below Normal (FCBN) -5%

3. Regular Capacity Above Normal (RCAN) +2.5%

4. Regular Capacity Below Normal (RCBN) -2.5%

Obj. 5 - What needs to be done before taps are changed on transformers?

Ensure the transformer is de-energized prior to tap changes.

Obj. 5 - What are 3 types of ways that a tap can be changed on a transformer?

1. Manually changing the leads ona transformer

2. Moving connecting bars

3. Installing a mechanic device such as a rotary switch