Recent questions in Electrical Engineering

Description : List any four advantages of 3-phase systems over 1 -phase systems.

Last Answer : .if you miss one phase u get the remaining two .3phase machines are an added advantage . expensive but reliable .More output

Description : Define power factor. State its significance. What is the condition for unity power factor ? 

Last Answer : Definition of Power factor: Power factor is cosine of angle between voltage and current.  OR Power factor is the ratio of active power to the apparent power .  Significance of Power factor:  ... When cosine of angle between voltage and current is zero. When R = Z  When KW = KVA 

Description : Calculate the equivalent resistance between A & B using star-delta conversion

Last Answer : Solution :  Converting Inner star in to delta-  Resistances 4 and 6 are in parallel in all branch so

Description : State different types of power in ac circuits. Write the expression and units for the same. Draw the power triangle. 

Last Answer : i) Active Power (P):- The active power is defined as the average power Pavg taken by or consumed by the given circuit.   ii) Reactive Power (Q):-  The reactive power is defined as the product of ... values of voltage (v) and current (I) it is given by    iv) Power Triangle: 

Description : Draw and explain the circuit diagram for measurement of single phase power using dynamometer type wattmeter. 

Last Answer : Circuit diagram for measurement of single phase power using dynamometer type wattmeter: Explanation: It consists of two stationary coils, called current coils and one moving coil, called voltage or ... i.e. power. The meter can be calibrated directly to indicate the power in watts. 

Description : Draw series R-L-C circuit and describe resonance. 

Last Answer : Series R-L-C circuit:  Explanation of Series R-L-C Resonance circuit: A series circuit containing resistance, inductance and capacitance, is said to be resonant when the circuit power ... , and as we are analyzing a series RLC circuit this resonance frequency produces a Series Resonance.

Description : Explain the working of resistance split phase induction motor with a neat diagram.

Last Answer : Circuit diagram of resistance split single phase induction motor:   * Working of resistors split single phase induction motor: To make a single phase induction motor self-starting, we ... function is to automatically disconnected the starting winding from the supply Once motor is started. 

Description : State the necessity of fuse. 

Last Answer : Necessity of fuse in the circuit: The fuse is provided in an electric circuit to protect the apparatus connected to it from being damaged due to excessive current. If no fuse is provided in the ... case of fault a heavy current flows through the apparatus which may damage due to excessive current. 

Description : State working principle of electric welding. 

Last Answer : Working principle of Electric welding: In resistance welding, sufficiently heavy current at low voltage is passed directly through two metals in contact to be welded. Heat is produced due to I2R ... industry. 15. For fabrication and repair work. 16. In other metal processing industries.

Description : Applications of multimeter

Last Answer : Applications of multimeter:  1. Voltage Measurements * High and low value DC measurement * Peak to Peak and DC average measurement 2. Current Measurements * DC current measurement ... resistance with constant current 5. Time and Frequency measurement * frequency * Time measurement

Description : State the types of heating and welding.

Last Answer : a) Types of heating :  1) Power frequency electric heating:  i) Resistance heating:  a) Direct resistance heating  b) Indirect resistance heating  ii) Arc Heating:  a) Direct arc ... shielded welding b) unshielded welding  2) Metal Arc Welding: a) shielded welding b) unshielded welding

Description : Name any two electrical machines used in electro agro system.

Last Answer : Electrical machines used in electro agro system:  1) Three phase induction motor for pumping of water 2) Single phase induction motors for cutting purpose 3) PMDC motor for insecticide spraying machines

Description : Define rotating magnetic field of an induction motor. 

Last Answer : Rotating magnetic field of an induction motor: A rotating magnetic field is a magnetic field that has moving polarities in which its opposite poles rotate about a central point or axis.

Description : Application of Universal Motor

Last Answer : Application of Universal Motor :  1) Mixer 2) Food processor 3) Heavy duty machine tools 4) Grinder 5) Vacuum cleaners 6) Refrigerators 7) Driving sewing machines 8) Electric Shavers ... ) Small Fans 11) Cloth washing machine 12) portable tools like blowers, drilling machine, polishers etc

Description : Prove N = Ns (1 — S).

Last Answer : Prove N = Ns (1 — S).

Description : Explain process of electroplating. 

Last Answer : Process of Electroplating:-  A DC current passed through a solution of chemical compound then the solution can be dissociated into its constituent's parts & deposition of metal takes place ... its salt. Again it dissociates & process is continued till pure metal goes into solution. 

Description : Advantages of LED over CFL.

Last Answer : Advantages of LED over CFL. 1) Efficiency: LED bulbs use close to a third of the amount of power CFL bulbs would use to produce the same amount of light. This makes them ... decorative to heavy duty industrial applications.  6) Maintenance: Smooth light and low maintenance compared to CFL

Description : Define following terms used in A.C. circuits : (i) Cycle (ii) Rms value (iii) Phase difference (iv) Average value

Last Answer : (i) Cycle:   A complete set of variation of an alternating quantity which is repeated at regular interval of time is called as a cycle. OR  Each repetition of an alternating quantity ... charge as is transferred by the alternating current during the same time under the same conditions. 

Description : electrical machines used in electro-agro system. 

Last Answer : Electrical machines used in electro agro system: 1) Three phase induction motor for pumping of water 2) Single phase induction motors for cutting purpose 3) PMDC motor for insecticide spraying machines

Description : State types of enclosures for electric motors. 

Last Answer : Types of enclosures for Electric Motor:  i) Open type enclosure:-  ii) Screen Protected enclosure  iii) Drip proof (moisture) enclosure:  iv) Flame (Fire) proof enclosure:-  v) Totally enclosed type enclosure:-  vi) Pipe ventilated totally enclosed type enclosure:

Description :  types of tarrifs used in electricity billing. 

Last Answer : Types of Tariff:- ( Any Four Types expected: 1/2 each, Total 2 Marks) 1) Flat-demand Tariff 2) Simple-demand Tariff or Uniform Tariff 3) Flat-rate Tariff 4) Step-rate Tariff 5) ... availability based tariff. As its name suggest it is a tariff system which depends on the availability of power. 

Description : Name safety devices used in electric wiring. 

Last Answer : i) Spirit Level:- * It is used to check the level. * It is a common instrument to test or adjust horizontal surface. ii) Growler:- * It is a equipment used for finding shorted turns of ... main or supply verification  (xii) Wire Stripper: To cut the wire & remove the insulation of the wire. 

Description : Application of DC Series Motor

Last Answer : 1. Electric traction 2. Cranes, 3. Passenger elevators, 4. Continuous conveyors, 5. Grinders, 6. Polishers,

Description : Define: 1) Electrode 2) Electrolyte

Last Answer : Electrode: An electrode is a small piece of metal or other substance that is used to take an electric current to or from the source of power.  Electrolyte: The substance which is ... electric current to pass through it, resulting in the chemical decomposition, is known as an electrolyte.  

Description : Coolers used during summers at homes do they need voltage stabilizers ?

Last Answer : I don't think voltage fluctuations will affect cooler. So cooler don't need voltage stabilizers they are not sensitivity load like computers, television etc.

Description : Why in electric motor or generator heating due to current involves dissipation of electrical energy?

Last Answer : In electric motor or generator heating due to current involves dissipation of electrical energy because as the current increases there will be I2R losses. More current flow means more the heat will be generated and as the temperature of conductor increase its resistance increases.

Description : Will there be infinite energy when we connect electric motor and electric generator to a cycle?

Last Answer : No, because they both don't have 100% efficiency practically, so there will be losses.

Description : What happens insulators when high voltage passes through transmission lines whether it breaks or lose it's insulating property?

Last Answer : I think it will breaks when it crosses breakdown voltage .

Description : Briefly explain how an electrical generator converts mechanical energy into electrical energy.

Last Answer : Working principle of DC generator: * Working principle of DC generator is the principle of dynamically induced emf or electromagnetic induction. * According to this principle, when flux is cut by a conductor, an ... , the flux is cut by the armature winding and an emf is dynamically induced in it. 

Description : Briefly explain how the power factor of an inductive circuit can be improved.

Last Answer : As we know that power factor should be corrected to ensure that the current supplied is cost friendly. Meaning the power factor should be around one but not greater than one(0.8-0.9) in a ... an inductive circuit due to the inductive reactance which oppose the change of current in the ac circuit. 

Description : State significance of earthing. Draw and explain pipe earthing. State the values of earth resistances for : (i) Substation (ii) Residential wiring (iii) H.T. Line (iv) L.T. Line

Last Answer : Significance of earthing:  * Earthing means connecting the body of the electrical equipment (it means the part which does not carries current under normal condition) to the earth. For example electrical equipment' ... surrounded by charcoal and salt.  the values of earth resistances for: 

Description : State failure phenomena observed in insulating material. State four reasons for failure of gaseous and solid dielectric materials. 

Last Answer : Failure phenomena in insulating material means the dielectric property fails :  The dielectric failure mean the dielectric strength of insulating material reduces due to high voltages or high ... 6. Due to poor maintenance of insulating material there may be possibility dielectric failure 

Description : State Magneto-striction. Draw Hysteresis loop for : (i) High silicon steel (ii) Copper (iii) Soft iron (iv) Wood

Last Answer : Magneto-striction: It is the change in dimensions of ferro magnetic material when it is magnetized for eg. Silicon steel, iron or any ferromagnetic material.  i) Hysteresis loop for High silicon steel :  ... loop for Soft iron :  iv) Hysteresis loop for Copper and Wood : 

Description : State the procedure for testing of earth pit resistance with necessary diagrams.

Last Answer : Following procedure (Method) for testing of earth pit resistance with necessary diagrams. 1) Earth Tester : i) Three point method ii) Four point method 2) By Potential drop method 3 ... of that earthing pit. In this test the accuracy is less but electrical rods are not required. 

Description : State the procedure for laying / installation of underground cable.  

Last Answer : 1) Direct laying Cable: or Trench laying method: Procedure: * For laying of a cable trench about 1.5m deep and 0.5m wide is made along the cable route. * A ... over. * Cables laid in this manner are usually plain lead covered because troughing affords good mechanical protection. 

Description : State the insulating materials used in motor. Write temperature class and withstand temperature ranges for them. 

Last Answer : The insulating materials used in motor are as belows: 1. Cotton, 2. Silk, or paper, 3. Press board, 4. Resins 5. PVC 6. Cellulose-Fiber, 7. Enameled coating, etc  ... Over 180° Mica, porcelain, ceramics, glass quartz, asbestos, treated glass fiber or treated asbestos. etc.

Description : Explain HRGO and CRGO. State benefits of CRGO for manufacturing of core. 

Last Answer :  i) HRGO ( Hot -rolled grain oriented steel):  * To minimize the size of machine flux density should be high with small magneto motive force (MMF). Due to this iron loss will ... percentage of silicon which in turn increases the resistance compared to regular steel which reduces eddy currents. 

Description : State any two advantages of MCB over Fuse. State the standard specifications of MCB available in the market.  

Last Answer : Following advantages of MCB over Fuse: 1. No need of replacement of fuse wire. 2. Manually restore of supply is simple. 3. Fault understanding by visual inspection 4. More safe than fuse The standard specifications of ... 6A, 10A,16A,20A, 25A, 30A, 32A, 40A, 50A, 60A and 63A 6. 250V and 450 v

Description : Application one lamp controlled from two places

Last Answer : Application one lamp controlled from two places: 1. For Stair case wiring 2. Hospital Wiring ( For operating the lamp in room and nursing station) 3. Bedroom Lighting. 

Description : State two applications of : (i) PVC paper (ii) Porcelain with type of class based on withstand temperature is insulating material. 

Last Answer :  (i) Application of PVC paper : 1. It is used in slot lining or motor winding insulation purpose 2. For Insulation of Transformer winding (ii) Application of Porcelain : 1. Mainly used for manufacturing ... on withstand temperature : * H' & C' Class of insulation i e. 180° and above 180°C 

Description : Explain MCB and ELCB with connection diagram supplying single phase load. 

Last Answer : OR OR Explanation: * MCB provides short circuit protection. * MCB provides overload protection * ELCB provides earth fault protection. * MCB is in series with ... occurs, the ELCB cuts off the power within the time of 0.1 sec. automatically to protect the personnel. 

Description : Compare casing capping wiring with concealed wiring.

Last Answer : Compare casing capping wiring with concealed wiring: 

Description : Select insulating materials for following parts : (i) Insulation between heating element and base plate of electric iron. (ii) Insulation used over copper or aluminium conductor used for making coils. (iii) Transformer bushings. (iv) Insulation between transmission line and pole.

Last Answer : Parts Insulating Materials  Insulation between heating element and base plate of electric iron. Mica Insulation used over copper or aluminium conductor used for making coils.  ... Transformer bushings Porcelain  Insulation between transmission line and pole. Porcelain

Description : Explain the suitability of aluminium as an electrical conductor with respect to its mechanical and electrical properties. 

Last Answer : Following are requirements of conductor:- i) High conductivity :  Material should have high conductivity, So that * cross section of conductor (size) reduces, * Copper losses reduces, * So Efficiency ... . Boiling point is 1820°C 9. Specific gravity is 2.7 10. High resistance to corrosion. 

Description : State any Four lE Rules regarding electric safety. 

Last Answer :  lE Rules regarding electric safety: 1. IE Rule 3 : Authorization 2. IE Rule 29 : Construction and maintenance of electrical supply line and apparatus 3. IE Rule 30: Service line and apparatus on ... 26. IE Rule 60: Test for resistance of insulation 27. IE Rule 61: Connection with earth 

Description : Define earthing. State its types.  

Last Answer : Definition of earthing: * Earthing means connecting the metal body of electrical device to the general mass of earth by a wire of negligible resistance. OR * Earthing means connecting the metal body of ... ii) Pipe type earthing iii) Rod type earthing iv) Strip earthing v)Water main earthing

Description : State the type of insulating materials under Class Y and Class B.

Last Answer : The type of insulating materials under Class Y : 1. Cotton  2. Silk 3. Paper 4. Rubber 5. PVC The type of insulating materials under Class B: 1. Backelite 2. Impregnated varnish 3. Mica 4. Fiber glass 5. Asbestos 

Description : State gaseous and liquid insulating material.

Last Answer : i) Gaseous insulating material : 1. Air 2. Nitrogen 3. Hydrogen 4. SF6 ii) liquid insulating material: 1. Transformer oil 2. Capacitor oil 3. Cable oil 4. Pyranol 5. Savotal 6. Savol 7. Vegetable oil 8. Silicon liquids

Description : State the material used for making (1) Magnetic Core (2) Fuse element  

Last Answer : The material used for making of:  (1) Magnetic Core : Iron, cobalt, Nickel, CRGO, HRGO , silicon steel  (2) Fuse Element: Tin- lead wire, Tinned copper wire 

Description : State the types of protections provided by MCB. 

Last Answer : The types of protections provided by MCB: 1. MCB provides short circuit protection. 2. MCB provides overload protection