Transformer Construction MCQ Quiz in मल्याळम - Objective Question with Answer for Transformer Construction - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Core of a Transformer:

• The core is the part of the transformer which provides a low reluctance path for the flow of magnetic flux.
• Magnetic flux is responsible for inducing the emf in the transformer.
• For providing a low reluctance path, the permeability of core material must be high. Therefore, ferromagnetic materials such as iron and steel must be used.

But silicon steel is preferred over iron because:

1. The addition of silicon steel to iron increases the resistivity of the core by five times. Hence the value of the current decreases.
2. As current decreases, I²R and eddy current losses decrease.
3. The heating of transformer becomes less.
4. Magnetostriction decreases.

Therefore, the best suited magnetic material for the construction of the transformer core is silicon steel.

Important Points Magnetostriction: It is the change in the dimension of the core of the transformer when subjected to a changing magnetic field.

Construction details of a transformer:

• The core of the transformer is made up of soft iron it has high coercivity and low retentivity.
• The primary coil and the secondary coil are wound on the soft iron core.
• The iron core decreases the reluctance of the magnetic path to flow magnetic flux.
• The soft iron core has high permeability and it provides a complete linkage of the magnetic flux of the primary coil with the secondary coil. 

Cold rolled grain oriented steel is used for the construction of large power transformers cores for the following reasons:

1) Low hysteresis loss

2) High permeability

3) High resistance

4) Virtually eliminated aging

5) Lower thickness of the lamination

The differences between core type and shell-type transformers are given below.

Air-Core Transformer:

• Air-core transformers are designed to transfer radio-frequency currents.
• The currents used for radio transmission consist of two or more coils wound around a solid insulating substance or on an insulating coil form.
• Iron-core transformers serve analogous functions in the audio-frequency range.
   

Iron Core Transformer:

• Iron core transformers are most suitable for power frequency applications such as power transformers or distribution transformers.
• It is often operated at 50 Hz and can also operate from the frequency 25 Hz to 400 Hz.
• In iron core transformers Highly permeable iron and Steel alloy are generally used.
• The ability of iron and steel alloy to carry magnetic flux is much greater than it is in air, and this ability to allow magnetic flux to flow is called permeability.
• Most transformer cores are constructed from low carbon steel which can have a permeability in the order of 1500 compared with just 1.0 for air.

The correct answer is option 2):(Primary winding will burn out)

Concept:

• When DC supply is given to the primary of the transformer, The alternating flux cannot be generated
• The primary will have lower resistance
• The winding acts as a short circuit across the terminals of the Direct current t(DC) source that leads to the flow of heavy current through the winding resulting in overheating of the winding.
• Primary winding will burn out when the rated DC supply is given to the primary of the transformer
• The transformer works on the principle of mutual induction. so it only operates on alternating current

The correct option is 2

Concept:

In high voltage A.C. circuits, the measurement cannot be done by using the method of extension of ranges of low range meters by providing suitable shunts.

In such conditions, specially constructed accurate ratio transformers are used. These transformers are used to isolate the instruments from high current and high voltage A.C. circuits.

These are generally classified as

(i) Current transformer - large alternating currents can be measured

(ii) Potential transformer - High voltages can be measured.

Note: The secondary CT or PT is connected to the low-range meter.

Application:

Given, CT ratio = 250/5 = 50

Measured value = 2.7 A

Hence, estimated line current = measured value × CT ratio

Line current = 2.7 × 50 = 135 A

• Power Transfer Capability: Shell-Type Transformers: Known for better short-circuit strength due to the compact design, where windings are surrounded by the core. This makes them more suitable for higher current loads.
• Power Transfer Capability Comparison: Core-Type: Generally used for higher voltage and power ratings. Shell-Type: Often used for lower voltage and power ratings but provides better mechanical protection and improved resistance to external forces. So Power transfer capability is not inherently higher than core-type.

• Maintenance Issues: Shell-Type Transformers: Due to the more complex winding structure (windings surrounded by core), these transformers are indeed more difficult to inspect and maintain compared to core-type transformers.

• Losses: Shell-Type Transformers: Generally they have lower core losses due to better magnetic circuit design and reduced magnetic leakage. The core surrounds the windings completely, providing more efficient flux linkage.

Additional InformationThe differences between core type and shell-type transformers are given below.

Ideal Transformer:

The transformer which is free from all types of losses is known as an ideal transformer. It is an imaginary transformer that has no core loss, no ohmic resistance, and no leakage flux. The ideal transformer has the following important characteristics.

• The resistance of their primary and secondary winding becomes zero
• The core of the ideal transformer has infinite permeability
• The infinite permeable means less magnetizing current requires for magnetizing their core
• The leakage flux of the transformer becomes zero, i.e. the whole of the flux induces in the core of the transformer links with their primary and secondary winding
• The ideal transformer has 100 percent efficiency, i.e., the transformer is free from hysteresis and eddy current loss.

Transformer copper loss:

• Transformer copper loss is mainly due to primary and secondary windings resistance (I²R loss)
• Shell type transformers use less winding than core type transformers
• Therefore, shell-type transformers have a low copper loss when compared to core type transformers.

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Key Points

The differences between core type and shell-type transformers are given below.