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An ideal transformer will have maximum efficiency at a load such that copper loss equal to iron loss.

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Description : For a transformer, operating at constant load current, maximum efficiency will occur at?

Answer : For a transformer, operating at constant load current, maximum efficiency will occur at unity power factor.

Answer : Generators for peak load plants are usually designed for maximum efficiency at 50 to 75 percent full load.

Description : The maximum load that a power transformer can carry is limited by its?

Answer : The maximum load that a power transformer can carry is limited by its voltage ratio.

Answer : Transformer efficiency is maximum when copper losses are equal to iron losses.

Description : A transformer operates 24 hours day at full -load. It's full -load efficiency is :  (A) equal all day efficiency (B) more than all -day efficiency (C) less than all -day efficiency (D) equal to maximum efficiency

Answer : A transformer operates 24 hours day at full -load. It's full -load efficiency is : equal all day efficiency 

Description : State why a transformer always have an efficiency of more than 90%.

Answer : As transformer is static device with no moving parts, the losses due to friction & windage are completely absent. Hence transformer has efficiency of more than 90%.

Answer : An ideal transformer is one which has no losses and magnetic leakage.

Description : The efficiency of two identical transformers under load conditions can be determined by?

Answer : The efficiency of two identical transformers under load conditions can be determined by back-to-back test.

Description : If a transformer is continuously operated the maximum temperature rise will occur in?

Answer : If a transformer is continuously operated the maximum temperature rise will occur in windings.

Answer : The efficiency of a power transformer is of the order of 98 percent.

Description : The efficiency of a transformer, under heavy loads, is comparatively low because?

Answer : The efficiency of a transformer, under heavy loads, is comparatively low because copper loss becomes high in proportion to the output.

Answer : D.C. generators are normally designed for maximum efficiency around full-load.

Answer : The condition for maximum efficiency for a D.C. generator is variable losses equal to constant losses.

Description : The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as?

Answer : The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as pull-in torque.

Description : The synchronous motor will develop maximum power when the load angle is?

Answer : The synchronous motor will develop maximum power when the load angle is 900.

Answer : In an actual transformer the iron loss remains practically constant from no load to full load because core flux remains practically constant.

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

Answer : In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are hysteresis and eddy current losses.

Description : In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of?

Answer : In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of less than 15A.

Description : Transformer efficiency

Answer : Transformer efficiency

Answer : The efficiency of transformer is Greater than electrical Machine because there is no rotational losses in transformer and there is no air gap losses in transformer so losses is less in transformer compare to electrical machine so efficiency is higher in case of transformer.

Description : A 40 kVA transformer has a core loss of 400 W and a full load copper loss of 800 W. The proportion of full load at maximum efficiency is

Answer : A 40 kVA transformer has a core loss of 400 W and a full load copper loss of 800 W. The proportion of full load at maximum efficiency is 0.707

Description : A transformer has negative voltage regulation when its load power factor is   (1) Zero (2) Unity (3) Leading (4) Lagging

Answer : Leading

Answer : The maximum efficiency of a distribution transformer is at 50% full load.

Answer : The full-load copper loss of a trans¬former is 1600 W. At half-load, the copper loss will be 400 W.

Description : An ideal voltage source should have?

Answer : An ideal voltage source should have zero source resistance.

Answer : An ideal traction system should have easy speed control, high starting tractive effort, equipment capable of with standing large temporary loads.

Answer : An ideal transformer has infinite values of primary and secondary inductances. The statement is false.

Description : Even at no-load, a transformer draws current from the mains. Why?

Description : A simple phase transformer has a maximum efficiency of 90% at full load and unity power factor. Efficiency at half load at the same power factor is  (A) 86.7% (B) 88.26% (C) 88.9% (D) 87.8%

Answer : A simple phase transformer has a maximum efficiency of 90% at full load and unity power factor. Efficiency at half load at the same power factor is 87.8%

Description : For a constant load current, transformer maximum efficiency occurs at   (a) any power factor (b) zero power factor leading (c) zero power factor lagging (d) unity power factor 

Answer : For a constant load current, transformer maximum efficiency occurs at unity power factor 

Answer : The no load current in a transformer lags behind the applied voltage by an angle of about 75°.

Description : The inrush current of a transformer at no load is maximum if the supply voltage is switched on  (1) at peak voltage value (2) at zero voltage value (3) at half voltage value (4) at 0.866 time voltage value

Answer : At 0.866 time voltage value

Description : The internal resistances of an ideal current source, and an ideal voltage source are, respectively, (A) 0, ∞ (B) ∞, ∞ (C) ∞, 0 (D) 0,0

Answer : The internal resistances of an ideal current source, and an ideal voltage source are, respectively, ∞, 0

Description : The gain of an ideal amplifier must be

Answer : The gain of an ideal amplifier must be infinity

Description : An ideal voltage source has?

Answer : An ideal voltage source has zero internal resistance.

Answer : Power plant having maximum demand more than the installed rated capacity will have utilisation factor more than unity.

Answer : In a transformer, routine efficiency depends upon load current and power factor of load.

Description : The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as?

Description : Negative voltage regulation is indicative that the load is?

Answer : Negative voltage regulation is indicative that the load is capacitive.

Answer : No-load current in a transformer lags behind the voltage by about 75°.

Answer : No-load current of a transformer has small magnitude and low power factor.

Description : A no-load test is performed on a transformer to determine?

Answer : A no-load test is performed on a transformer to determine magnetizing current and loss.

Description : Which motor have more efficiency, synchronous motor or induction motor?

Answer : Synchronous motor has more efficiency.

Answer : For given maximum axle load tractive efforts of AC. locomotive will be more than that of D.C. locomotive.

Answer : The efficiency of a properly designed synchronous motor will usually fall in range 85 to 95%.

Description : "Maximum power output is obtained from a network when the load resistance is equal to the output resistance of the network as seen from the terminals of the load". The above statement is associated with?

Answer : "Maximum power output is obtained from a network when the load resistance is equal to the output resistance of the network as seen from the terminals of the load". The above statement is associated with Maximum power transfer theorem.

Description : A network contains linear resistors and ideal voltage sources. If values of all the resistors are doubled then the voltage across each resistor will

Answer : A network contains linear resistors and ideal voltage sources. If values of all the resistors are doubled then the voltage across each resistor will not change

Answer : For any type of consumer the ideal tariff is three part tariff.

Description : What should be the ideal resistance of ammeter ?

Answer : Ideal resistance of ammeter should be zero.

Description : What are the desirable characteristics of ideal switch?

Answer : Desirable characteristics of the ideal switch: It is desirable to have power switches characteristics closer to ideal switch. The ideal switch should have the following characteristics. Zero resistance when ... . 100% efficiency. Able to control power flow with zero power dissipation.

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