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TRANSFORMERS

TRANSFORMERS. “MORE THAN MEETS THE EYE”. TRANSFORMERS. Definition: An electromagnetic device that transfers electrical energy from one circuit to another circuit through mutual inductance. Construction of Transformers Two sets of windings wrapped on a common core

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TRANSFORMERS

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  1. TRANSFORMERS “MORE THAN MEETS THE EYE”

  2. TRANSFORMERS Definition: An electromagnetic device that transfers electrical energy from one circuit to another circuit through mutual inductance.

  3. Construction of Transformers Two sets of windings wrapped on a common core • Primary Windings: connected to the source • Secondary Windings: connected to the load

  4. Transformers are rated in kva Not all loads consume power, kw ,but still draw current from the transformer

  5. Turns Ratios Voltage in the primary,divided by Voltage in the secondary is equal to Number of turns in the primary divided by the Number of turns in the secondary, is equal to Current in the secondary divided by the Current in the primary

  6. VP/VS=NP/NS=IS/IP • Practice

  7. Before Wiring Transformers • Check the job blueprints, and specifications • Check the manufacturer’s specifications • Check the nameplate on the transformer

  8. Other important items to consider • The source voltage matches the primary windings • The secondary voltage of the transformer matches the load requirements • The kva rating of the transformer is equal to, or greater than, that required by the load

  9. Five factors that reduce the efficiency of a Transformer Copper Losses Eddy Currents Hysteresis Flux Linkage Saturation

  10. Six steps to prevent noise of transformers from interfering with the normal activities of people

  11. 1. Select a transformer which has a sound level of the area in which it is installed

  12. 2. Install the transformer as far away from the activities of people as possible

  13. 3. Locate the transformer where the normal acoustics of the room do not amplify its sounds. The least desirable location is in a corner near the ceiling

  14. 5. Use noise absorbent mounts.

  15. 6. Use flexible couplings and flexible wire for the installation.

  16. The neutral of a 240/120 volt, single-phase system shall be grounded. There are four purposes for which a grounding system is provided for transformers.

  17. 1 To keep the non-current carrying metallic parts of an electrical system at zero potential with the earth

  18. 2 To limit excessive voltages

  19. 3 To stabilize the voltage with respect to ground.

  20. 4 To facilitate the operation of overcurrent protection devices

  21. High Potential test are used to test the insulation quality of the coils at room temperature

  22. Three Phase Systems • Three phase voltages are displaced from each other by 120 electrical degrees • The chief advantage of using three-phase transformer, instead of a bank of single-phase units occurs in the case of

  23. Faults

  24. Three-phase transformers require about______ % less copper than single-phase systems to deliver the same amount of power to all loads

  25. 25

  26. Advantages of using single unit 3-phase transformers, as opposed to using 3 single-phase transformers

  27. 3-phase transformers are easier to install because they are already internally wired

  28. 3-phase transformers require less core material for the same kva and therefore are less expensive

  29. 3-phase transformers have a higher efficiency

  30. 3-phase transformers weigh less and require less space

  31. WYE WIRED Winding Current is the same as Line Current. WC=LC Winding Voltage= Line Voltage divided by 1.73 (square root of 3) WV=LV/1.73

  32. To carry any unbalanced loads in between the 3-phases of the transformer a neutral is required for WYE connections WYE connections require 4 wires unless the transformer is feeding a balanced load

  33. PRACTICE Single voltage connections Low voltage connections 3-phase High voltage connections 3-phase

  34. DELTA WIRED Winding Voltage is the same as Line Voltage WV=LV Winding Current=Line Current divided by 1.73 (square root of 3) WC=LC/1.73

  35. PRACTICE Single voltage connections Low voltage connections 3-phase High voltage connections 3-phase

  36. BUCK-BOOST • A transformer can be wired so that the primary and secondary voltages can either add together to provide a higher voltage to the load, or the secondary voltage can subtract from the primary voltage to lower the load. • When it is additive it is a boost • When it subtracts it is a buck

  37. PRACTICE BUCK connected BOOST connected

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