127.  A transformer oil must be free from
A. sludge
B. odure
C. gases
D. moisture

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128.  A buchholz relay can be installed on
A. auto-transformers
B. air-cooled transformers
C. welding transformers
D. oil cooled transformers

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129. Gas is usually not liberated due to decomposition of transformer oil unless the oil temperature exceeds
A. 50? C
B. 80? C
C. 100?C
D. 150? C

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130. Distribution transformers are generally designed for maximum efficiency around
A. 90% load
B. zero load
C. 25% load
D. 50% load

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131.  Which of the following property is not necessarily desirable in the material for transformer core?
A. Mechanical strength
B. Low hysteresis loss
C. High thermal conductivity
D. High permeability

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132. Star/star transformers work satisfactorily when
A. load is unbalanced only
B. load is balanced only
C. on balanced as well as unbalanced loads
D. none of the above

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133.  Delta/star transformer works satisfactorily when
A. load is balanced only
B. load is unbalanced only
C. on balanced as well as unbalanced loads
D. none of the above

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