ELECTRICAL MACHINE - 1

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

A transformer can have zero voltage regulation at

• leading power factor
• lagging power factor
• unity power factor
• zero power factor

D.C. generators are installed near the load centres to reduce

• iron losses
• line losses
• sparking
• corona losses

D.C. generators are normally designed for maximum efficiency around

• full-load
• rated r.p.m.
• rated voltage
• all of the above

D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration We will select the

• series motor
• shunt motor
• compound motor
• any of the above

D.C. series motors are used

• where load is constant
• where load changes frequently
• where constant operating speed is needed
• in none of the above situations.

D.C. shunt motors are used for driving

• trains
• cranes
• hoists
• machine tools

Differentially compound D.C. motors can find applications requiring

• high starting torque
• low starting torque
• variable speed
• frequent on-off cycles

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

For a D.C. shunt motor if the excitation is changed

• torque will remain constant
• torque will change but power will remain constant
• torque and power both will change
• torque, power and speed, all will change