101. The High-frequency transformer cores are generally made of
- Cast iron
102. Two transformers operating in parallel will share the load depending upon their
- Copper and iron losses
- Turns ratio
- Per unit impedance
103. The source of harmonics in a transformer supplied by a voltage source of the fundamental frequency is
- Poor insulation
- Saturation of core
- Loose laminations
104. In an ideal transformer
- The flux is 180° out of phase with induced emf.
- The applied voltage is in phase with the induced emf.
- The phase angle between the applied voltage and emf is 90°.
- The magnetizing current is in phase with the flux.
105. Due to magnetostriction, which one of the following problems occurs in the transformer?
- Oil leakage
- Humming sound
- Speed destruction
- No problem occurs
106. If the output power of a transformer is 600 W whereas the losses are 200 W, the efficiency of the transformer will be:
- 66.6 %
- 75 %
- 50 %
- 41.1 %
107. The best material for the core of the transformer is
- Mild steel
- Stainless steel
- Soft iron
108. In a step-up transformer
- Np > Ns
- Ns > Np
- Ns + Np
- Varies accordingly
109. Transformers in which, part of the winding is common to both primary and secondary circuits are known as
- Step-up transformers
- Step-down transformers
- Leakage transformer
110. Which of the following statements regarding a shell-type transformer is incorrect?
- It provides a shorter magnetic path.
- Magnetizing current is lesser as compared to a core type.
- Natural cooling is quite good.
- It gives better support against electromagnetic forces between current-carrying transformer.
111. Distribution transformers
- have good voltage regulation
- are designed for a small value of current
Which of these is/are correct?
- 1 only
- 2 only
- Both 1 and 2
- Neither 1 nor 2
112. Transformers are connected in parallel for supplying
- Load in excess of the rating of an existing transformer
- Load less than the rating of an existing transformer
- Load equal to the rating of an existing transformer
- Load less or equal to the rating of an existing transformer
113. A current transformer has a phase error of +3%. The phase angle between primary and secondary current is
114. Two transformers, with an equal rating and negligible excitation current, connected in parallel, share the load in the ratio of their kVA ratings only, if their pu impedances (based on their own kVA) are
- In the inverse ratio of their ratings
- In the direct ratio of their ratings
- Pure reactive
115. A transformer has a turn ratio of 1 : 10. A resistance of 2000 Ω is connected across the secondary terminals. The resistance offered to the current in the primary winding will be
- 20 Ω
- 200 Ω
- 2000 Ω
- 20000 Ω
116. The saving in copper achieved by converting a 2 winding transformer into and auto-transformer into and auto-transformer is determined by
- Voltage transformation ratio
- Load on the secondary
- Iron losses in the transformer
- Permeability of core material
117. A 20 turn iron-cored inductor is connected to a 100 V, 50 Hz source. The maximum flux density (Bm) in the core is 1 Wb/m2. The cross-sectional area of the core is
- 0.345 m2
- 0.152 m2
- 0.0225 m2
- 0.56 m2
118. In core type furnace, the secondary winding has
- No turns
- More number turns
- Less number turns
- Equal to primary turns
119. An isolation transformer has primary to secondary turn’s ratio of
120. A transformer has maximum efficiency at of full load. The ratio of its iron loss (Pi) and full load copper loss (Pe) is