Transformers Objectives Part 04
61 . Auto transformer is used when the transformer ratio is small
62 . In an auto transformer effective saving on copper and core losses will occur when the transformer ratio is near to 1
63 . An auto transformer has only one winding
64 . Percentage impedance, polarities and voltage rating should same for parallel operation of the transformer
65 . If the transformer core is made of copper then the eddy current losses will be same
66 . If the ohmic resistance of windings of a transformer is zero then the copper copper loss will be zero
67 . The efficiency of two identical transformers under load condition can be determined by back to back test
68 . Three to three phase transformer connection possible for parallel operation is delta-Y to delta-Y
69 . Three to three phase transformer connection nor feasible for parallel operation is Y-delta to delta-delta
70 . When a Three to three phase transformer connection possible for parallel operation is delta-Y to delta-Y operates under no load condition the current will lag the applied voltage by about 75
71 . If a transformer core is made of copper and coils are made up of steel wire then copper losses in the windings will be more.
72 . Friction loss in a transformer is zero even at full load
73 . In a step up transformer the emf per turns on primary windings is the same as the emf per turns of winding on secondary windings
74 . 1 Tesla is the same as 1 weber/m^2
75 . As a general rule the KVA rating ratio of transformer operating in parallel should be within 3:1
76 . Maximum value of flux in involved in the emf equation of the transformer
77 . Harmonic current in a transformer cause increased I^2R losses and core losses and magnetic interference with protective relay
78 . Core saturation is most likely sources of harmonics in a transformer
79 . In Scott connection the main transformer has center tap on both primary and secondary windings.
80 . In Scott connections the teaser transformer operates on 0.8666 of its rated voltage
