Description : For protection of rotating machines against lightning surges _______ is used. (1) lightning arrester (2) capacitor (3) combination of lightning arrester and capacitor (4) lightning conductor and arrester
Answer :
For protection of rotating machines against lightning surges combination of lightning arrester and capacitor is used.
asked
Apr 30, 2018
by
anonymous
Description : The friction losses in Real Transformers are : (A) 0% (B) 5% (C) 25% (D) 50%
Answer :
A
asked
May 8, 2018
by
anonymous
Description : The efficiencies of transformers compared with that of electric motors of the same power are?
Answer :
Transformers have high efficiency than the same ratted motors
asked
Mar 19, 2018
by
anonymous
Description : Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in?
Answer :
Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in loading of the transformers not in proportion to their kVA ratings.
Description : The inertia constants of two groups of machines which do not swing together are M1 and M2. The equivalent inertia constant of the system is
Answer :
The inertia constants of two groups of machines which do not swing together are M1 and M2. The equivalent inertia constant of the system is M1M2/M1+M2
asked
May 3, 2018
by
anonymous
Answer :
Winding will be damaged
asked
Mar 19, 2018
by
anonymous
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.
asked
Mar 19, 2018
by
anonymous
Answer :
In case of D.C. machines, mechanical losses are primary function of speed.
asked
Mar 20, 2018
by
anonymous
Description : Define transformation ratio in terms of current and voltage.
Answer :
(i) Transformation Ratio (K) is defined as the ratio of the primary current to the secondary current. (ii) Transformation Ratio (K) is defined as the ratio of the secondary voltage to the primary voltage.
Description : Reduction in core losses and increase in permeability are obtained with transformer employing?
Answer :
Reduction in core losses and increase in permeability are obtained with transformer employing core built-up of laminations of cold rolled grain oriented steel.
asked
Mar 19, 2018
by
anonymous
Description : Compare core type transformer and shell type transformer on the following parameters. (i) Types of winding used, (ii) Application
Answer :
Ans:
Description : Define: (i) Commercial efficiency of a transformer and (ii) All day efficiency of a transformer.
Answer :
(i) Commercial Efficiency : It is the ratio of output power in watt to the input power in watt. (ii) All day efficiency of a transformer: It is the ratio of output energy in kWh to the input energy in kWh in the 24 hours of the day
Description : State any two applications of single phase autotransformer.
Answer :
Applications of single phase auto transformers: 1) Give small boost to distribution cable to correct the voltage drop. 2) As auto transformer starter for induction motors. 3) As furnace supply ... . 5) In control equipment for single phase locomotives. 6) As dimmer in lighting circuits.
Description : State any two conditions for parallel operation of 3-phase transformer.
Answer :
Conditions for Parallel operation of 3 phase transformer 1) Voltage ratings of both the transformers must be identical. 2) Percentage or p.u. impedance should be equal in magnitude. 3) X/R ratio ... between primary & secondary voltages must be same. 6) Phase sequence on both sides must be same.
Description : A 50 KVA transformer has iron loss 2 kW on full load. Calculate its iron loss at 75% of full load.
Answer :
Iron loss is dependent on voltage and independent of load. Hence iron loss at 75% of Load = Iron loss at full load = 2 kW
Description : State any four properties of Ideal transformer.
Answer :
Properties of Ideal transformer: 1) No losses (iron and copper losses), hence no temperature rise. 2) No magnetic leakage i.e (Coefficient of coupling between primary and secondary windings is unity) 3) Zero winding ... drop i.e. E1 = V1, E2 = V2 5) Efficiency 100 %. 6) Regulation 0 %.
Description : Draw the connection diagram of long shunt differential D.C. compound generator.
Answer :
Ans:
Answer :
In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called armature.
asked
Mar 21, 2018
by
anonymous
Description : If the percentage impedances of the two transformers working in parallel are different, then?
Answer :
If the percentage impedances of the two transformers working in parallel are different, then parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load.
asked
Mar 19, 2018
by
anonymous
Description : Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is?
Answer :
Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is approximately equal to 1.
asked
Mar 19, 2018
by
anonymous
Answer :
Distribution transformers are generally designed for maximum efficiency around 50% load.
asked
Mar 19, 2018
by
anonymous
Answer :
Power transformers are generally designed to have maximum efficiency around near full-load.
Description : State advantages of rotating field type alternators.
Answer :
Advantages of Rotating Field Type Alternator: 1) For high-voltage alternator, large space is required to accommodate conductors with insulation, as high voltage is induced in them. If field poles are placed ... is kept rotating. 8) Rotating field is comparatively light and can run with high speed.
asked
May 7, 2020
by
anonymous
Description : UNIT 1 fundamentals of AC rotating machine Contents 1.1 Introduction 1.2 Advantages 1.3 Parts of AC machines 1.4 Synchronous speed 1.5 AC winding 1.6 Winding factor (Coil pitch and distributed winding) 1.7 Distribution factor 1.8 EMF equation of alternator or generator 1.9 Numericals 1.10 Harmonic 1.11 Slot harmonics 1.12 Harmonics minimization
Answer :
1.2 Advantages: In practices most of alternator have rotating magnetic field type construction with stationary armature due to following reason. The generation level of AC voltage may be in the range ... at high speed. Only two Slip rings are required to excited the field by AC supply.
asked
Aug 25, 2018
by
Notes
Description : The slip of 400 V, three phase, 4 -pole induction motor when rotating at 1440 rpm is
Answer :
The slip of 400 V, three phase, 4 -pole induction motor when rotating at 1440 rpm is 4 percent
asked
Apr 29, 2018
by
anonymous
Description : what is mean by rotating transformer ?
Answer :
Induction motor is a rotating transformer
Answer :
Natural oil cooling is used for transformers up to a rating of 3000 kVA.
asked
Mar 19, 2018
by
anonymous
Answer :
Short circuit test on transformers is conducted to determine copper losses.
asked
Mar 19, 2018
by
anonymous
Answer :
Necessary conditions required to be satisfied in order to ensure successful parallel operation of single phase transformers: 1. Only transformers having the same phase displacement between primary and secondary ... . 7. The phase sequence must be followed strictly on HV and LV side connection.
asked
Mar 19, 2018
by
anonymous
Answer :
Natural air cooling is generally restricted for transformers up to 1.5 MVA .
asked
Mar 19, 2018
by
anonymous
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.
asked
Mar 19, 2018
by
anonymous
Description : Why do transformers make noise?
Answer :
Transformers make noise based on it out put if an transformer outputs is 400v maximum than a 398v be apply to that transformer it also make a noise because of that
asked
Dec 17, 2017
by
anonymous
Description : In DC motor iron losses are occurred in?
Answer :
In DC motor iron losses are occurred in the armature.
asked
Mar 26, 2018
by
anonymous
Answer :
Iron losses in a D.C. machine are independent of variations in load.
asked
Mar 20, 2018
by
anonymous
Description : What are the losses in a transmission line?
asked
Mar 10, 2018
by
anonymous
Description : What are the types of power losses in inductor?
Answer :
Copper losses, Eddy current loss, and hysteresis loss are the types of power losses in inductor.
asked
Mar 8, 2018
by
anonymous
Answer :
Iron loss, copper loss and mechanical losses these are the losses in DC machine.
asked
Sep 27, 2017
by
anonymous
Description : In a synchronous motor which losses varies with load?
Answer :
In a synchronous motor, copper losses varies with load.
asked
Mar 18, 2018
by
anonymous
Answer :
Current transformers (CT) : Current transformer (CT) actually step down the high current to low current for the operation of relays. Current transformer is use for measurement of ... use for relay. This is about potential transformer.
asked
Jan 15, 2018
by
James
Description : In dc machines, the armature windings are placed on the rotor because of the necessity for (1) electromechanical energy conversion (2) generation of voltage (3) commutation (4) development of torque
Answer :
3 Commutation
asked
May 1, 2018
by
anonymous
Description : Laminated cores, in electrical machines, are used to reduce?
Answer :
Laminated cores, in electrical machines, are used to reduce eddy current loss.
asked
Mar 25, 2018
by
anonymous
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
asked
Apr 29, 2018
by
anonymous
Description : Explain following techniques related to energy conservation in transmission and distribution system. (i) By balancing phase currents (ii) Variable technical losses (I2R losses).
Answer :
(i) Balancing Phase currents: Proper (healthy balanced) three phase loads always draw equal currents in all lines but single phase loads in the 3 phase 4 wire system or loads connected between two ... . 11) Minimize I2R losses. 12) Balance the load currents. 13) Regulate the system voltages.
asked
Sep 22, 2018
by
anonymous
Answer :
Brushes of D.C. machines are made of carbon.
asked
Mar 20, 2018
by
anonymous
Answer :
Exciters of synchronous machines are d.c. shunt machines.
asked
Mar 20, 2018
by
anonymous
Description : In a transmission line if booster transformers are to be used, preferred location will be (A) At the receiving end (B) At the sending end (C) At the intermediate point (D) Anywhere in the line
Answer :
In a transmission line if booster transformers are to be used, preferred location will be At the intermediate point
asked
May 8, 2018
by
anonymous
Description : Explain how in a 3 phase induction motor to a rotating magnetic field is developed.
Answer :
Production of Rotating Magnetic Field in Three-phase Induction Motor: In three-phase induction motor, the three-phase stator windings are displaced in space by 120° and their three-phase currents are displaced ... time by 120°. Such fluxes give rise to the resultant rotating magnetic field.
Description : Explain the “mitigation of power theft” and “faulty meter replacement” for energy conservation techniques to reduce commercial losses.
Answer :
Energy conservation techniques to reduce commercial losses: 1. Mitigation of Power Theft: Power theft being the most important issue which all of the service providing utilities ... agricultural sector. Prepaid meters may prove effective measures against unauthorized abstraction of energy.
asked
Sep 22, 2018
by
anonymous
Description : Explain the electrical losses of magnetic materials used for the cores of inductors and transformer.
asked
Mar 10, 2018
by
anonymous
Description : Which of the following is the advantage of using CRGO steel in transformers? A) High magnetic flux density B) Low permeability C) Both A and B D) None of these
Answer :
It definitely High Magnetic Flux Density since a crgo steel has always a more around 3% of silicon proportion among the remaining ferrite which make cold rolled grain oriented steel having high flux magnetic ... for more about the crgo core you can learn here https://nicoreindia.com/crgo-core/
asked
Apr 29, 2018
by
anonymous