481. Which of the following bus-bar schemes has the lowest cost?
A. Ring bus-bar scheme
B. Single bus-bar scheme
C. Breaker and a half scheme
D. Main and transfer scheme
482. Owing to skin effect:
A. current flows through the half cross-section of the conductor
B. portion of the conductor near the surface carries more current and core of the conductor carries less current
C. portion of the conductor near the surface carries less current and core of the conductor carries more cur¬rent
D. any of the above
E. none of the above
483. By which of the following methods string efficiency can be improved?
A. Using a guard ring
B. Grading the insulator
C. Using long cross arm
D. Any of the above
E. None of the above
484. In aluminium conductors, steel core is provided to____turefalsa
________?
A. compensate for skin effect
B. neutralise proximity effect
C. reduce line inductance
D. increase the tensile strength
485. By which of the following a bus-bar is rated?
A. Current only
B. Current and voltage
C. Current, voltage and frequency
D. Current, voltage, frequency and short time current
486. A circuit is disconnected by isolators when____________?
A. line is energized
B. there is no current in the line
C. line is on full load
D. circuit breaker is not open
487. For which of the following equipment current rating is not necessary?
A. Circuit breakers
B. Isolators
C. Load break switch
D. Circuit breakers and load break switches
488. In a substation the following equipment is not installed?
A. exciters
B. series capacitors
C. shunt reactors
D. voltatre transformers
489. jCorona usually occurs when the electrostatic stress in air around the conductor exceeds?
A. 6.6 kV (r.m.s. value)/cm
B. 11 kV (r.m.s. value)/cm
C. 22 kV (maximum value)/cm
D. 30 kV (maximum value)/cm
490. The voltage drop, for constant voltage transmission is compensated by installing__________?
A. inductors
B. capacitors
C. synchronous motors
D. all of above
E. none of the above
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