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How eddy current is produced in a transformer?

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Description : How eddy current can be minimized?

Description : Which of the following can reduce the Eddy current losses? A) By making the core of a stack of plates electrically insulated from each other B) By making the core of solid block C) By increasing the applied voltage  D) None of these

Answer : Which of the following can reduce the Eddy current losses? A) By making the core of a stack of plates electrically insulated from each other B) By making the core of solid block C) By increasing the applied voltage  D) None of these

Description : A ferrite core has less eddy current loss than an iron core because?

Answer : A ferrite core has less eddy current loss than an iron core because ferrites have high hysteresis.

Description : What is the difference between eddy current and hysteresis loss?

Answer : Loss occurred by magnetising and demagnetising process is called histerisis loss and the current flowed due to the magnetic field produced by the electric field applied is called eddy current losses

Description : what is eddy current ?

Answer : In magnetic circuits when we supply current to coil which wound on some core( of iron cast iron, ferrite ) material it produce magnetic field but there is small amount of flux which also ... heat and losses in magnetic circuits..for good working conditions we always try to minimize eddy current

Description : The eddy current loss in a dc generator is 400 W at 40 Hz frequency of reversal and constant flux density. When frequency is increased to 50 Hz., eddy current loss is :  (A) 256 W (B) 320 W (C) 500 W (D) 625 W

Answer : The eddy current loss in a dc generator is 400 W at 40 Hz frequency of reversal and constant flux density. When frequency is increased to 50 Hz., eddy current loss is : 625 W

Description : Give two applications of each : 1) Eddy current sensor 2) Optical sensor.

Answer : Eddy current sensor : 1. Detection of non-magnetic but conductive materials. 2. Displacement sensing 3. Position sensing Optical sensor : 1. Position Detection 2. Velocity Detection 3. Acceleration Detection 4. Direction Detection

Description : Eddy current damping cannot be used for moving iron instrument because

Answer : Eddy current damping cannot be used for moving iron instrument because the presence of a permanent magnet required for such purpose would affect the deflection and hence the reading of the instrument

Answer : The disc of an instrument using eddy current damping should be of conducting and non-magnetic material.

Description : Explain hysteresis loss, eddy current loss and skin effect limitations with reference to magnetic material.

Answer : Hysteresis loss: Hysteresis loss is a loss which occurs due to the friction of magnetic domain due to the change in magnetic field in ferromagnetic material like iron. Hysteresis loss causes power loss ... loss in transformer is given by, We=Kef2Kf2Bm2watts Skin effect limitations:

Description : Step-down transformer converts high voltage and low current into:  (A) How voltage and high current (B) High voltage and low current (C) Low voltage and high current (D) None of the above

Answer : Step-down transformer converts high voltage and low current into: Low voltage and high current

Description : How eddy currents are generated?

Description : In a single-phase transformer, the magnetizing current is (A) in phase with the no-load current (B) in quadrature with the no-load current (C) the product of no-load current and power factor (D) in phase with the flux in the core

Answer : In a single-phase transformer, the magnetizing current is in phase with the flux in the core

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

Description : The operating point of a protective current transformer is near the

Answer : The operating point of a protective current transformer is near the Ankle point

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

Answer : The inverse definite mean time relays are used for over current and earth fault protection of transformer against internal short-circuits.

Description : When secondary of a current transformer is open-circuited its iron core will be?

Answer : When secondary of a current transformer is open-circuited its iron core will be hot because of heavy iron losses taking place in it due to high flux density.

Description : The secondary of a current transformer is always short-circuited under operating conditions because it?

Answer : The secondary of a current transformer is always short-circuited under operating conditions because it avoids core saturation and high voltage induction.

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.

Description : A transformer at 25 Hz develops 20 W hysteresis loss and 50 W eddy current loss. If the applied voltage and frequency are doubled, the new core losses are (A) 140 W (B) 180 W (C) 240 W (D) 480 W

Answer : A transformer at 25 Hz develops 20 W hysteresis loss and 50 W eddy current loss. If the applied voltage and frequency are doubled, the new core losses are 240 W

Description : Eddy currents are induced in the pole shoes of a D.C. machine due to?

Answer : Eddy currents are induced in the pole shoes of a D.C. machine due to relative rotation between field and armature.

Description : The noise produced by a transformer is termed as?

Answer : The noise produced by a transformer is termed as hum.

Description : Heat in a conductor is produced on the passage of electric current due to?

Answer : Heat  in  a   conductor  is  produced   due  to  frictional  collision  of  electrons   flow  as  they  conduct  current.

Description : The kVA rating of Three-phase transformer with Voltage = 200V and Current = 100A will be :  (A) 34.64 kVA (B) 75 kVA (C) 20 kVA (D) None of the above

Answer : The kVA rating of Three-phase transformer with Voltage = 200V and Current = 100A will be : 34.64 kVA

Description : About trnsformer

Answer : Acc to Ohms law V=IR but it is only applicable when our resistance R is constant, as in case of transformer we take impedence which is equivalent to resistance is not constant it varies with system parameters that why Ohms law not applicable in case of transformer

Description : Define: 1) voltage ratio, 2) current ratio, 3) transformation ratio of transformer.

Answer : 1) Voltage ratio: The voltages in primary and secondary winding is proportional to number of turns in primary and secondary respectively. So, the voltage ratio is same as transformation ratio. V2/V1 = N2 ... as transformation ratio of transformer. It is denoted by K. K = N2/N1

Description : Details of current flowing direction to clear concept

Description : A charge of 0.1 C moves past a given point every 0.01 s. How much is the current?

Answer : The current is 10.0A.  1ampere = 1 Coulomb per 1 second.  0.1Coulombs ÷ 0.01seconds = 10.0amperes.

Description : How to find total impedance Z, current I and Impedance angle ?

Answer : How to find total impedance Z, current I and Impedance angle ?

Description : How does AC current change direction?

Answer : This  is  because  the  angle  at  which  the   magnetic  fields  cuts  across  a  winding  changes  its  poles  thus  current  has  to  change  dirention  .

Description : How can we increase the induced current?

Answer : Induced  current  can  be  increased by  reducing  no  of   windings  on  the  secondary  part   compared   to   primary.

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

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

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

Answer : The magnetising current of a transformer is usually small because it has small air gap.

Description : What is a transformer and how does it work?

Answer : A transformer is an electrical apparatus designed to convert alternating current from one voltage to another. It can be designed to step up or step down voltages and works on the magnetic ... or voltage ratio) between the primary and secondary depends on the turns ratio of the two coils.

Description : If a 5-bus test system contains 6 transmission lines and one transformer, how many non-zero elements are there in the system Y-bus ? (A) 25 (B) 12 (C) 11 (D) 19

Answer : If a 5-bus test system contains 6 transmission lines and one transformer, 19 non-zero elements are there in the system Y-bus.

Description : Eddy current losses in transformer cores can be reduced by the use of  1. Solid cores  2. Laminated cores  3. Ferrites  Select the correct answer using the codes given below : (a) 2 and 3 only (b). 1 and 2 only (c) 1 and 3 only (d) 1, 2 and 3

Answer : Eddy current losses in transformer cores can be reduced by the use of  1. Solid cores  2. Laminated cores  3. Ferrites  Select the correct answer using the codes given below : (a) 2 and 3 only (b). 1 and 2 only (c) 1 and 3 only (d) 1, 2 and 3

Description : How can a magnetic field be used to generate an electric current?

Answer : Magnetic  field  can  be  used  to  generate  electric  current  on  a  condition  that  it  is  on  a  rate  of  changing  magnetic  flux.  (Faraday's  law)

Description : What is the back E.M.F in Transformer ?

Answer : Back emf in transformer is when apply voltage in primary side of transformer. This voltage produce flux according to Faraday law electro magnetic induction. This flux called mutual flux and this ... secondary flux oppos the applied voltage according to lenz law. its called back emf of transformer

Description : State the advantages of instrument transformer in using for extension of range of meters. 

Answer : Advantages of instrument transformer: 1. Extension of instrument range is possible. 2. Isolation of instruments from high voltage side. 3. Power loss is less as compared to shunts and multipliers. 4 ... measurement. 5. It is economical method of range extension. 6. Increases in safety of operator.

Description : The rating of transformer may be expressed in ____________.  (A) kVAR (B) kW (C) kVA (D) Horse power

Answer : The rating of transformer may be expressed in kVA . 

Description : Which of the following does not change in a transformer?  (A) Current (B) Voltage (C) Frequency (D) All of the above

Answer : Which of the following does not change in a transformer?  (A) Current (B) Voltage (C) Frequency (D) All of the above

Description : A certain transformer has 200 turns in the primary winding, 50 turns in the secondary winding and 120 volts applied to the primary. What is the voltage across the secondary?  (A) 30 Volts (B) 480 Volts (C) 120 Volts (D) 60 Volts

Answer : A certain transformer has 200 turns in the primary winding, 50 turns in the secondary winding and 120 volts applied to the primary. What is the voltage across the secondary?  (A) 30 Volts (B) 480 Volts (C) 120 Volts (D) 60 Volts

Description : The main purpose of using core in a transformer is to (A) decrease iron losses (B) eliminate magnetic hysteresis (C) reduce reluctance of the common magnetic circuit (D) prevent eddy current loss

Answer : Reduce Relucatnce of the common magnetic circuit.

Description : Transformer generally rated in KVA

Answer : The power of transformer is apparent power because it has no power factor and it is the product of voltage and current.

Answer : Transformer noise is generated due to vibration of core and winding this is because of magnetostriction and magnetomotive force.

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