Transformer Questions and Answers (1)

Question and Answer Electrical Power Transformers

 

1. What is an Air Cooled transformer?

A transformer uses "air" as the cooling medium. This term is abbreviated with the ANSI designation AA, indicating open, natural draft ventilated construction.


2. What is Ambient Noise Level?
The noise level of the surrounding area, measured in decibels (dB).


3. What is Ambient Temperature?
It is the inherent or existing temperature of the atmosphere surrounding a transformer into which its heat is dissipated.


4. What is an Ampere?
It is the unit of measurement for electric current flow.


5. What does ANSI stand for?
The American National Standards Institute Inc. - one of the recognized organizations that specify the standards for transformers.


6. What is an Autotransformer?
It is a transformer that has only one winding per phase, part of which is common to both the primary and secondary circuits.


7. What does the term Banked describe?
Two or more single-phase transformers connected together to supply a three-phase load.


8. What does the term BIL mean?
Basic impulse level is a means to express the ability of the insulation system to withstand high voltage surges.


9. What is a Buck Boost transformer?
It is a two winding, single-phase transformer with low voltage secondary windings, which can be connected as an autotransformer. Used to raise or lower single and three phase line voltages by 10 - 20%.


10. What is a Cast Coil transformer?
A transformer with coils solidly cast in epoxy resin under vacuum in a mold. Also called cast resin or epoxy cast coil transformers.


11. What is a Center Tap?
It is a reduced capacity tap at the midpoint in a winding.


12. What makes up a Coil?
Turns of electrical grade wire or strip conductor material wound on a form, referred to as a winding.


13. What is Coil Hot-Spot Temperature?
It is the absolute maximum temperature present in the transformer. This number is equal to the sum of the ambient temperature, temperature rise and a variable.
T Hot Spot = T ambient + T rise + (10-20) °C.


14. What is Common Mode?
An electrical noise or voltage disturbance, that occurs between all of the line leads and the common ground, or between the ground plane and either line or the neutral.


15. What is a Compensated Transformer?
It is a transformer with a turn's ratio that provides a higher than rated voltage at no load, and rated voltage at rated load. These transformers CANNOT be used for reverse feed.


16. What is the term Continuous Rating?
The constant load which a transformer can carry its rated primary voltage and frequency, without exceeding its specified temperature rise.


17. What is a Control Transformer?
A transformer is designed to supply good voltage regulation characteristics when low power factor or high inrush current is drawn. Usually referred to as an Industrial Control Transformer.


18. What is the Core of a transformer?
It is the electrical grade steel laminations, which carry the magnetic flux.


19. What is Core Loss?
Losses in watts caused by magnetization of the core and its resistance to magnetic flux when excited or energized at rated voltage and frequency. Also referred to as excitation loss or no-load loss.


20. What is a Current Transformer?
It is a transformer generally used in control or instrumentation circuits for measuring current.


21. What is a Delta connection?
The delta connection is a standard three phase connection with the ends of each phase winding connected in series to form a closed loop with each phase 120 degrees from the other.


22. What is a Delta-Wye connection?
A Delta Wye is when the primary is connected in delta and the secondary in Wye when pertaining to a three-phase transformer bank or three-phase transformer.


23. What are "Dielectric Tests"?
These tests consist of the application of a voltage higher than the rated voltage for a specified time, for the purpose of determining the adequacy against breakdowns of insulating materials and spacing under normal conditions.


24. What is a "Dry Type" transformer?
A dry type transformer is one in which the transformer core and coils are not immersed in a liquid.


25. What is a "Dual Winding"?
A winding consisting of two separate parts, which can be connected, in series or parallel. Also referred to as dual voltage or series-multiple winding.


26. What is the "Efficiency" of a transformer?
The percentage of power transferred from the input of equipment to the output of equipment in Watts. (power out/power in x 100)


27. What is an "Electrostatic Shield"?
It is Copper or other conducting material placed between the primary and secondary winding and grounded to reduce electrical interference and to provide additional protection.


28. What is "Exciting Current (No-Load Current)"?
Current which flows in any winding used to excite the transformer when all other windings are open-circuited. It is usually expressed in percent of the rated current of a winding in which it is measured.


29. What does the term "Encapsulated" describe?
A transformer with its coils either encased or cast in an epoxy resin or other encapsulating materials.


30. What does the abbreviation FCAN stand for?
"Full Capacity above Normal." This designates that a transformer will deliver its rated kVA when connected to a voltage source that is higher than the rated voltage.

31. What does the abbreviation FCBN stand for?
"Full Capacity Below Normal." Same as FCAN except that the taps are below rated voltage.


32. What is a Fan Cooled transformer?
A transformer cooled mechanically to maintain its rated temperature rise, typically using auxiliary fans to accelerate heat dissipation.


33. Describe a Flexible Connection?
A non-rigid connection used to reduce transmission of noise and vibration.


34. Describe Flux Density?
The magnetic field strength in the core, typically measured in Telsa or Gauss.


35. Explain Frequency?
On AC circuits, designates the number of times the polarity alternates from positive to negative and back again . . . such as 60 cycles per second. Measured in Hertz.


36. What is a Full Capacity Tap?
A full capacity tap is one through which the transformer can deliver its rated kVA output without exceeding the specified temperature rise.


37. What is a Grounding Transformer?
It is a special three-phase autotransformer for establishing a neutral on a 3-wire delta secondary. Also referred to as a 'Zigzag' transformer.


38. Describe Grounds or Grounding?
Connecting one side of a circuit to the earth through low resistance or low impedance paths.


39. What is a Harmonic?
A Harmonic is a sinusoidal component of a periodic wave having a frequency that is a multiple of the fundamental frequency. For example, a component whose frequency is twice the fundamental frequency is referred to as the second harmonic, (120 Hz is the second harmonic of 60 Hz).


40. What does the term Hertz (Hz) mean?
It is a term for AC frequency in cycles per second.