Can a transformer be used to transform direct voltage and direct current? Justify your answer.

The transformer cannot be used for dc supply system (dc voltage & current). According to working principle of the transformer, it works on Faraday laws of Electromagnetic Induction. Therefore, induced emf e = (-dφ/dt). The changing rate of magnetic flux is responsible for e.m.f generation, which opposes the change of magnetic flux that is indicated by negative sign. But in case of dc supply system (d.c Voltage & Current), there is no change of magnetic flux, d φ = 0, so that induced emf at secondary side of transformer is zero. Therefore,...

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Why are starters used for starting 3-phase induction motors?

Starters for three phase induction motors: For starting of 3-φ induction motor, we need Y-∆ (star – delta) starter. These starters are useful for safe running of induction motor by applying 1/√3 times of voltage in Y- mode for safety of induction motor. When motor gets 80% of speed we apply full voltage Vph=VL in ∆ mode; during this time sufficient back e.mf is developed to limit the input current.  ...

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What are the Applications of Induction Motors?

Applications of Induction Motors: The squirrel cage induction motors with single or double pole changing windings are available as follows:              CLASS   APPLICATIONS (1)  Variable torque, power output α N2 Fans, centrifugal pumps. (2) Constant –torque power output α N. Conveyors, stokers, reciprocating, Compressors, printing presses. (3) Inverse torque ...

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The three phase system has only two types of connections viz. star connection and delta connection. Why?

In the three phase system, the three phases should be so connected that we get a system that has equal line voltages displaced 120 degrees electrical from one another and acting simultaneously in the circuit. Only star and delta connections can satisfy these conditions. Any attempt made to connect the three phase in a manner other than these two schemes will result in a system of line voltages which are neither equal nor 120 degree displaced. Such a system will not serve the function as if three phase circuits being connected. -V....

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What are the criteria for the classification of transmission lines as short, medium and long lines?

Classification of transmission lines (Power): The network of transmission lines is formed by three phase AC system. This is required for Bulk power transfer from large group of generating stations to main transmission network. Short power transmission line:  Short distance power transmission lines has voltage ≤  11000 volts. These lines are required to carry power from main sub-station to local distribution area. Further power supply is distributed through pole mounted sub- station or plinth mounted sub-station. Medium...

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Give a list of the factors involved for selecting a factory drive.

Factors involved in selection of factory drives:    - Supply system      :  DC or AC   - Rating                :  kW, MW   - Drive                 :  constant speed, Variable speed   - Special Condition  :  High starting torque, Hazardous location, Traction duty etc.   - User’s requirement : Duty cycle, noise level, load characteristics etc off load, load condition        ...

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What are the essential differences between H.V. and L.V. switchgears?

H.V. switch gears:  Circuit breaker: Switching during normal and  abnormal conditions, interrupt the fault currents.  Isolators: It is disconnecting switch to disconnect the system from line parts under no load condition.  Earth switch: This is used to discharge the voltage on the lines to earth after disconnecting them.  Surge arrester: This is used to divert the high voltage surge to earth and maintaining continuity during normal voltage.  Current Transformer: To step down the...

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What do you understand by electric heating? State its advantages over other methods of heating.

Electric heating: Electric heat is provided by use of a high temperature wire, which is resistant to electric flow with more heat being produced by more electric current being fed into the heating element, creating more resistance and more heat. This method of producing heat is called electric heating.  Advantage of electric heating:  Cleanliness  Absence of flue gases, soot. …etc Accurate control of temperature.  Low maintenance cost  Quicker operation  Higher efficiency  Uniform...

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Discuss the criterion for choice of voltage for transmission and distribution.

Criterion For Choice Of Voltage For Transmission And Distribution: We know that the power  P =VI, so for the same power if voltage is increased then current will decrease. If suppose power required is 500 W and voltage is 250V then current I will be equal to 500/250 =2A.  Now if voltage is increased from 250V to 500V and the power required is same then I = 500/500 =1 A  Now, if the voltage is still increased to say 1000V for the same power  then I = 500/1000 =0.5 A  From the above examples,...

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List out the advantages of nuclear power plants over conventional thermal power plants.

Advantage of Nuclear Power Plants: 1. Nuclear Power station reduces the demand for oil coal and gases. 2. Weight of nuclear fuel required for a given station capacity is negligible compared to that required for a conventional thermal power station. As a result the problems of transport and resulting costs are avoided.  3. The area and volume need for a nuclear power station is less in comparison to a conventional power plant of equal capacity.  4. In addition to producing large amount of power, a nuclear power...

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Compare the induction motor with a transformer.

Comparison of induction motor with a transformer: Figure: Sketch showing similarity between transformer and induction motor The transfer of energy from stator to the rotor of an induction motor takes place entirely inductively with the help of flux mutually linking the two. Hence an induction motor is essentially a transformer with stator forming the primary and rotor forming the rotating secondary. Transformer Induction...

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List out the important advantages of HVDC transmission.

Important advantages of HVDC transmission :  Economical in long distance high power transmission. HVDC transmission line has only two conductors. Reactive power losses do not occur in HVDC.  ...

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State the various applications of synchronous motor.

Various applications of synchronous motor :  It is capable of being operated under a wide range of power factors, both lagging and leading. Hence, it can be used for power factor correction purpose.  In textile industry high speed drives are necessary with wide range of control. Variable frequency drives with synchronous motors are used for speed control.  In chemical industry, rubber industry and petrochemical industry, many processes require compressor drives in which direct coupled synchronous motors supplied...

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What are the applications of DC motor?

Applications of DC motors: Type of motor                 Applications Series Motor                    For traction work, i.e electric locomotives, Rapid transit system, trolley cars etc Cranes and hoists Conveyors Shunt motor                      ...

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What are the two advantages of stepper motors? Give a few applications of them .

Advantages of stepper motors: They can be directly controlled by computers, micro-processors and programmable controllers. Precision control of speed without using closed loop feedback.  Applications:  i) Operation control: Such motors used for operational control in computer peripherals, textile  industries, IC fabrications and robotics etc. ii) Incremental motion:  Applications requiring incremental motion are typewriters, line printers, tape drivers, floppy disk drivers, numerically controlled machine tools, process-control systems and X-Y plotters. iii)...

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Why does a practical transformer draw some current when its secondary winding is open?

Transformer practically draws some current when its secondary winding is open due to primary circuit and this current will produce core losses. ...

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What is a Stepper Motor? What are the application of stepper motor?

Stepper Motor The stepper motor is a motor which takes input pulses and then takes proportional steps to input these signals. You can use for positioning and/or speed control for most any applications. Stepper motor with cable The stepper motor needs a power circuit and a sequence circuit for changing phase. Applications Medical: Infusion Pump, Brad Test, X-ray, Dialysis, DNA Extraction, Pump  Semiconductor: Masking, Etching,...

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