The efficiency of a power transformer is _____ at full load.

A. Same

B. Minimum

C. Maximum

D. Fluctuates

Answer

C. Maximum

Explanation

• Power transformers act as a step-up device that operates with maximum efficiency at full load conditions with negligible load fluctuation.
• The efficiency of the transformer is obtained from various experiments conducted on different loads. The efficiency of a power transformer is always greater than 90%. Thus, it can be said highly efficient device.
• Power transformers are operated on full load hence power transformers are designed to have maximum efficiency at full load.
• The efficiency of a power transformer under short-circuit test conditions is approximately zero % because during short circuit test output power of transformer is zero.
• When the load is not connected across the secondary of the transformer, the output power of the transformer is zero. As efficiency is the ratio of output power by input power, the efficiency will be zero at no-load conditions.
• Transformer efficiency is defined as the ratio of its output power to input power
• At light load, hysteresis losses (magnetization and demagnetization of the core of the transformer) and eddy current losses are high compared to output power; Hence, the efficiency is low at this condition.
• When the load on the transformer is further increased, its efficiency increases
• At heavy loads, copper losses are high compared to the output power; Hence the efficiency is low at this condition
• Efficiency is maximum at both copper losses are equal to iron losses
• Transformer efficiency is the ratio of its output power to input power and it depends on both load power-factor and load magnitude.
• At low load, a transformer has low efficiency as hysteresis losses (magnetization and demagnetization of a core of transformer) and eddy current losses dominate over output power.

Power System MCQs With Explanation 

 

• The advantages of high transmission voltage are
• The charging current drawn by the cable is
• The fact that current density is higher at the surface when compared to the center is known as
• In which of the following transmission lines capacitance effect is negligible?
• The distribution constant of the transmission line is
• Proximity effect is more in case of
• If the frequency is increased, then the skin effect will
• Bundled conductors in EHV transmission lines help in
• Which of the following produces radio interference in communication lines?
• Telecommunication lines are transposed to reduce the
• What is the function of economizer in Thermal Power Plant 
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• Corona is accompanied by
• The conductor carries more current on the surface as compared to the core. This is called as
• Critical disruptive voltage is a voltage at which
• Bundled conductors are used for EHV transmission lines primarily for reducing the
• Low power factor is usually not due to
• Bonding is done at both ends of the cable to reduce the
• For Improving power factor
• Stock bridge dampers are used to
• Which of the following insulator is practically used for railway crossings?
• Which of the following decides the insulation level of 400 kV, EHV line?
• When earth fault occurs
• The minimum length of pipe electrode used for earthing should not be less than
• A ground wire is used to
• Earth resistance in typical domestic wiring is
• By which of the following systems electric power may be transmitted?
• Which of the following equipment will be most economical for regulating the voltage in the distribution feeder?

Transformer MCQs With Explanation 

• In a transformer the primary flux is 
• The noise of the transformer is mainly due to
• Buchholz relay is used for the protection
• Iron loss in a transformer can be determined by
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• In a star-delta transformer, the delta side phase voltage leads the star sides phase voltage by an angle
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• The chemical used in the breather of a transformer should have the property of
• The power transformer can be termed as a constant
• In a transformer, which of the following losses are zero?
• Which of the following Transformer can have a tap changer?
• If the supply frequency (f) of a transformer decreases, the effect of frequency on the transformer's secondary output voltage?
• The primary winding of a transformer has a 120 V ac supply. What is the value of secondary voltage if the turn ratio is 10?
• The efficiency of a power transformer is _____ at full load.
• In a transformer the relation between the input frequency and the output voltage on secondary winding is _____.
• In a current transformer, _____ winding is closed.
• A transformer is a _____ device.
• A step-down transformer has _____ number of turns on primary winding and _____ number of turns on the secondary winding.
• A step-up transformer has _____ number of turns on primary winding and _____ number of turns on the secondary winding.
• Transformer works on ______ principle.
• Shell Type Transformer is mainly used for 
• A Magnetic Oil level Guage (MOG) is used in the Transformer to 
• The Function Of Power Transformer is/are
• The Radiators are used in transformers for 

Synchronous Motor MCQs With Explanation 

• In 3 -Φ synchronous motor if one of the phases is short-circuited the motor will
• The speed regulation of a synchronous motor is
• The negative phase sequence in a three-phase synchronous motor exists when the motor is
• What happens if the field winding of the synchronous motor is short-circuited?
• For power factor correction, synchronous motors operate at

Induction Motor MCQs With Explanation 

• In a capacitor start and run the motor the function of the running capacitor in series with the auxiliary winding is to
• A split-phase motor has
• If the capacitor of a single-phase motor is short-circuited
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