Electrical machines 1 -Transformers

A good voltage regulation of a transformer means

• output voltage fluctuation from no load to full load is least
• output voltage fluctuation with power factor is least
• difference between primary and secondary voltage is least
• difference between primary and secondary voltage is maximum

During open circuit test of a transformer

• primary is supplied rated voltage
• primary is supplied full-load current
• primary is supplied current at reduced voltage
• primary is supplied rated kVA

Hysteresis loss in a transformer varies as CBmax = maximum flux density)

• Bmax
• Bmax1-6
• Bmax1-83
• B max

In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are

• hysteresis and eddy current losses
• friction and windage losses
• copper losses
• none of the above

In a transformer the resistance between its primary and secondary should be

• zero
• 10 Q
• 1000 Q
• infinity

Short circuit test on transformers is conducted to determine

• hysteresis losses
• copper losses
• core losses
• eddy current losses

The magnetising current of a transformer is usually small because it has

• small air gap
• large leakage flux
• laminated silicon steel core
• fewer rotating parts

The main reason for generation of harmonics in a transformer could be

• fluctuating load
• poor insulation
• mechanical vibrations
• saturation of core

The secondary of a current transformer is always short-circuited under operating conditions because it

• avoids core saturation and high voltage induction
• is safe to human beings
• protects the primary circuit
• none of the above

Which of the following is the main advantage of an auto-transformer over a two winding transformer ?

• Hysteresis losses are reduced
• Saving in winding material
• Copper losses are negligible
• Eddy losses are totally eliminated