Ans: – A transformer is a static device which transfers electric power from one circuit to another circuit at same frequency but voltage level is usually changed.
Ans: – When the voltage level is raised on the output side, the transformer is called step-up transformer, whereas, the transformer in which the voltages is lowered on the output side, is called a step-down transformer.
Ans: – Primary and secondary windings
Ans: – There is no rotating part in the transformer, therefore, it is called static electrical machine.
Ans: – In provides additional insulation and protects the insulation from dirt and moisture and it carries away the heat generated in the cores and coils.
Ans: – To ensure a high permeability of the magnetic circuit. Because of high permeability, the magnitude of exciting current necessary to create the required flux in the core is small. The presence of steel core also causes hundred per cent of magnetic flux.
Ans: – An isolation transformer has equal turns in primary and secondary windings. These transformers are employed for isolating the load from supply.
Ans: – No-load current is transformers ranges from 2 to 5 per cent of full-load primary current.
Ans: – By interleaving the primary and secondary windings.
Ans: –The ratio of secondary voltage to primary voltage is called a transformation ratio. It is denoted by capital letter K.
Ans: – According construction point of view, the transformers are divided into two types: (i) Core type and (ii) Shell type.
Ans: – Frequency.
Ans : – To reduce eddy current loss, the core of the transformer is laminated.
Ans: – Transformer oil’s primary functions are to insulate and cool a transformer.
Ans: – In a transformer, noise occurs mainly due to loosening of stampings and mechanical forces developed during operation.
Ans: – Short circuit test.
Ans: – Tap changers are usually employed on H.V. side because, the high voltage side has a large number of turns which allows smoother variation of voltage. It is easily accessible physically and above all, it has to handle low currents.
Ans: – The power transformers are designed to operate at 50 Hz. On the other hand, if the primary is connected to a source of 5 Hz frequency, the primary winding will have an insufficient inductive reactance (XL = 2πfL). The result will be that, the primary will have excessive current producing considerable copper losses. There is every possibility that the transformer may start to smoke.
Ans: – The power transformers are designed to operate at a particular frequency, generally at 50 Hz. If the frequency of the supply will be high, it will result greater inductive reactance. This high inductive reactance of the winding will prevent the primary from drawing sufficient power. Moreover, the iron losses i.e. hysteresis and eddy current losses will be excessive.
Ans: – Silica gel is placed in the transformer breather. The function of the silica gel is to absorb the moisture so that the life of the transformer can be increased.
Ans: – 0.35mm to 0.5mm
Ans: – Silicon content exceeding 5% makes the sheet steel brittle and so causes in punching.
Ans: – Placing of LV winding near the core and HV winding around the LV winding in a core type transformer reduces the amount of insulation material required.
Ans: – Circular coils are preferred for winding a transformer as they can easily wound on machines, conductors can easily be bent and winding does not bulge out due to radial forces developing during operation.
Ans: – Yes, no load primary current.
Ans: – Since the induced primary ampere-turns and secondary ampere-turns always neutralize one another, the flux in the core on load is the same as the flux on no-load. Hence, the iron losses are constant and are independent of load.
Ans: –In shell type core, both the windings are wound on the central limb. This type of core is used for those transformers which work on poor power factor.
Ans: – The efficiency of a transformer is always determined by open-circuit and short-circuit tests due to the following reasons: (i) The power required to carry out these tests is very small. (ii) The tests give the core loss and copper loss separately.
Ans: – (i) Porcelein insulator bushing (ii) Oil filled bushing (iii) Capacitor bushing
Ans: – It is due to the fact that the ranges of the meter at the high voltage (HV) side at the short circuit condition of the low voltage (LV) side is much more suitable.s
Ans: – A tapped transformer is one whose windings are fitted with special taps for changing in voltage or current ratio.