Saturday, December 7, 2013

Transformer Questions and Answers (2)

Question and Answer Electrical Power Transformers







1. What are High Voltage and Low Voltage windings?
These terms are used to distinguish the winding having the greater voltage rating from that having the lesser in two winding transformers.


2. Describe Hi Pot?
It is a high potential dielectric test impressed on the windings to check insulation materials and clearances.


3. What is Impedance?
It is the apparent resistance in a circuit to the flow of an alternating current analogous to the actual resistance to a direct current.


4. What is an Impulse Test?
It is a dielectric test that determines the BIL capability by applying high frequency, steep wave-front voltage between windings and ground.


5. What is an Induced Potential Test?
It is a standard dielectric test that verifies the integrity of insulating materials and electrical clearances between turns and layers of a transformer winding.


6. What is Inductance?
It is a property that opposes a change in current flow.


7. What is Inrush Current?
It is an abnormally high transient current, caused by residual flux in the core, which maybe drawn when a transformer is energized.


8. What are Insulating Materials?
Those materials used to electrically insulate the transformer's windings, turn-to-turn or layer-to-layer, and other assemblies in the transformer such as the core and busswork.


9. What is an Isolation Transformer?
It is a transformer that insulates the primary circuit from the secondary circuit. Also referred to as a two-winding or insulating transformer.


10. What is the abbreviation KVA stand for?
"Kilovolt Ampere Rating" designates the output that a transformer can deliver for a specified time at rated secondary voltage and rated frequency without exceeding the specified temperature rise. (1 kVA = 1000 VA, or 1000 volt amperes)


11. What are Knockouts and what are they used for?
They are easily removable circle of metal in an enclosure that eliminates the need for punching holes for conduit.


12. What is a Lamination?
Thin sheets of special steel used to make the core of a transformer.


13. What is a Line Reactor?
It is an electrical device whose primary purpose is to introduce a specific amount of inductive reactance into a circuit, usually to reduce or control current.


14. What is the term Load?
The load of a transformer is the power in kVA or volt-amperes supplied by the transformer.


15. What are Load Losses?
They are losses in a transformer, which are incident to load carrying. Load loses include I2R loss in the windings due to load current, stray loss due to stray fluxes in the windings, core clamps, etc., and to circulating currents (if any), in parallel windings.


16. What is a Mid-tap?
It is a reduced capacity tap midway in a winding. Also referred to as a 'Center tap'. Usually it is in the secondary winding.


17. Describe Moisture Resistance?
Materials or equipment constructed or treated so that it will not be harmed readily by exposure to a moist atmosphere.


18. What does the abbreviation NEC?
National Electric Code


19. What does the abbreviation NEMA?
National Electrical Manufacturers Association.


20. What are No-Load Losses (Excitation Losses)?
It is the loss in a transformer that is excited at rated voltage and frequency, but without a load connected to the secondary. No-load losses include core loss, dielectric loss, and copper loss in the winding due to exciting current.


21. What is Overload?
When a transformer is overloaded, excessive heat develops and the insulation system begins to breakdown. Life expectancy of the transformer is decreased due to heat exceeding the rating of the insulation system.


22. What is Parallel Operation?
Single and three phase transformers may be operated in parallel by connecting similarly marked terminals, provided their ratios, voltages, resistances, reactance and ground connections are designed to permit parallel operation. Current and voltage angular displacements are also required to be the same in the case of three phase transformers.


23. Explain the term Phase?
It is a type of AC electrical circuit; usually single phase 2-wire or 3-wire, or three-phase, 3 or 4 wire.


24. What is Polarity?
It designates the instantaneous direction of voltages in the primary compared to the secondary.


25. What is a Potential (Voltage) Transformer?
A transformer generally used in instrumentation circuits for measuring or controlling voltage.


26. What is Power Factor?
It is the relation of watts to volt amps in a circuit.


27. What are Primary Taps?
Taps added to the primary winding. (See Taps)


28. What is Primary Voltage Rating?
Designates the input circuit voltage for which the primary winding is designed.


29. What is a Primary Winding?
The primary winding is the winding on the energy input (supply) side.


30. Describe the term Rating?
It is the design characteristics such as primary and secondary voltage, kVA capacity, temperature rise, frequency, etc.


31. What is Ratio in terms of Voltage?
It is a reference to either the primary to secondary winding turns ratio or to the voltage ratio of the transformer.


32. What is a Ratio Test?
It is a standard test of transformers to determine the ratio of the primary to secondary voltage.


33. What is Reactance?
It is the impedance component due to inductance and/or capacitance.


34. What is a Reactor?
A single winding device with an air or iron core which, produces a specific amount of inductive reactance into a circuit, usually to reduce or control current.



35. What is a Rectifier Transformer?
A transformer designed to supply AC input to a rectifier to obtain the desired DC output and have the ability to withstand the heating effects caused by rectifier commutation or ripple.


36. What is RCBN - Reduced Capacity Below Normal?
It is taps that carry full-rated winding current only, thus reducing available power because of lower output voltage.


37. Define Regulation?
Usually expressed as the percent change output voltage when the load goes from full load to no load at a given power factor.


38. What is a SCR?
It is a silicon-controlled rectifier.


39. Describe Saturation?
Saturation is a natural condition in which an increase in current results in a decrease in inductance.


40. What is a Scott Connection?

It is a connection for polyphone using two special single-phase transformers. Usually used to change from two-phase to three-phase or three-phase to two-phase.
  

1 comment:

  1. It is a job exclusive to the contract personnel only. Transformers are dangerous, specially if it connects a lot of pannels from it. https://www.electriciansouthauckland.kiwi/papakura/

    ReplyDelete