+ Electrical Machines Interview Questions and Answers, Question1: What is the general system requirements of alternator? Question2: Will the alternators. Lap winding is suitable for high current and low voltage generators while wave winding is suitable for high voltage and low current generators. >Lap winding is. Basic Electrical Interview Questions and Answers Pdf ebook for Job. synchronous machines have capability to work on different power.
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EEE_ Technical Interview Questions. 1. Why star delta How can you relate power engineering with electrical engineering? . punches, coal cutter and winding machines etc. . amplifying circuitry rejects it being a common mode signal. Electrical Interview Questions & Answers visit aracer.mobiya. Answer: Stepper motor is the electrical machine which act upon input pulse applied to aracer.mobi is one. Electrical interview questions from AC & DC motor principle and working Synchronous machines have capability to work on different power factor (or say.
Poles and pole shoes. Armature core and Armature winding.
Commutator and brushes Here you are reading electrical machines interview questions and answers pdf free download. I will advise you to bookmark this page and share with your friends. Ans: In any Electrical Machine, rotating part is known as rotor and stationary part is called as stator. Ans: Electrical transformer is a static device which transforms electrical energy from one circuit to another without any direct electrical connection.
You can read this article for Electrical Transformer Interview Questions. According to this, When the current in the primary coil is changed the flux linked to the secondary coil also changes. By this, an EMF is induced in the secondary coil. What is the function of transformer oil in a transformer?
It provides good insulation 2. Can the voltage regulation goes —ive? If so under what condition? Yes, if the load has leading PF. Power transformers have very high rating in the order of MVA. They are used in generating and receiving stations. Sophisticated controls are required. Voltage ranges will be very high. Distribution transformers are used in receiving side.
Voltage levels will be medium. Power ranging will be small in order of kVA. Complicated controls are not needed. Name the factors on which hysteresis loss depends?
Volume of the core 3.
Maximum flux density Why the open circuit test on a transformer is conducted at rated voltage? The open circuit on a transformer is conducted at a rated voltage because core loss depends upon the voltage. This open circuit test gives only core loss or iron loss of the transformer.
What is the purpose of providing Taps in transformer and where these are provided? In order to attain the required voltage, taps are provided, normally at high voltages side low current. What are the necessary tests to determine the equivalent circuit of the transformer? Open circuit test 2. Short circuit test Define efficiency of the transformer? In core type, the windings surrounded the core considerably and in shell type the core surround the windings i.
Full load copper loss in a transformer is W. What will be the loss at half load? List the advantage of stepped core arrangement in a transformer? To obtain reduce length of mean turn of the winding 3. To reduce I2R loss. Explain parallel operation of single phase transformer. Explain the working and construction of auto transformer in detail. Draw and explain the equivalent circuits of transformer 16 4.
Explain all the three phase transformer connections.
Explain a transformer on ON load 8 b transformers on NO load conditions. State the principle of electromechanical energy conversion? The mechanical energy is converted in to electrical energy which takes place through either by magnetic field or electric field 2. Distinguish between statically induced emf and dynamically induced emf?
When emf induced in a conductor is stationary in a magnetic field then we call it statically induced emf. If emf is induced in a conductor due to relative motion between conductor and the field then it call it as dynamically induced emf.
What does speed voltage mean? It is that voltage generated in that coil, when there exists a relative motion between coil and magnetic field 4.
Give example for single and multiple excited systems? Single excited system-reluctance motor, single phase transformer, relay coil Multiply excited system-alternator, electro mechanical transducer 5. Why do all practical energy conversion devices make use of the magnetic field as a coupling medium rather than electric field? When compared to electric field energy can be easily stored and retrieved form a magnetic system with reduced losses comparatively.
Hence most all practical energy conversion devices make use of magnetic medium as coupling 6. State necessary condition for production of steady torque by the interaction of stator and rotor field in electric machines?
Airgap between stator and rotor should be minimum 3. Reluctance of iron path should be negligible 4. Mutual flux linkages should exist between stator and rotor windings 7. Write the application of single and doubly fed magnetic systems? Singly excited systems are employed for motion through a limited distance or rotation through a prescribed angle Whereas multiply excited systems are used where continues energy conversion take place and in ease of transducer where one coil when energized the care of setting up of flux and the other coil when energized produces a proportional signal either electrical or mechanical 8.
Explain the following with respect to rotating electrical machines 1. Pole pitch 2. Charding angle 1. Pole pitch is that centre to centre distance between any two consecutive poles in a rotating machine, measured in slots per poles 2.
Chording angle is that angle by which the coil span is short of full pitched in electrical degrees 9. Why energy stored in a magnetic material always occur in air gap In iron core or steel core the saturation and aging effects form hindrance to storage Built in air gap as reluctance as well permeability is constant, the energy storage takes place linearly without any complexity. Hence energy is stored in air gap in a magnetic medium What is the significance of co energy?
When electrical energy is fed to coil not the whole energy is stored as magnetic energy. Field energy 2. Coenergy Write the equation which relates rotor speed in electrical and mechanical radians per second? Relate co energy density and magnetic flux density? Short advantages of short pitched coil? Hormonics are reduced in induced voltage 2. Saving of copper 3. End connections are shorter What is the significance of winding factor?
What is the necessity to determine the energy density in the design of rotating machines? Derive the relation between co energy and the phase angle between the rotor and stator fluxes of the rotating machines? F1, f2 are the rotor and stator flux peak values respectively Write the energy balance equation for motor?
What is excitation? Excitation is applying an external voltage to DC shunt coil in DC motors. In three pin plug 6 Amp. Because Current flow in the conductor is inversely proportional to the conductor diameter. So if any short circuits occur in the system first high currents bypassed in the Earthling terminal.
Difference between megger test equipment and contact resistance meter test instruments? Megger test equipment used to measure cable electric resistance, conductor continuity, phase identification where as contact resistance meter test instruments used to measure low resistance like relays ,contactors.
When we connect the large capacitor bank in series? So in order to bring the voltage at the load terminals within its limits i. What is electrical diversity factor in electrical installations? Electrical diversity factor is the ratio of the sum of the individual maximum demands of the various subdivisions of a system, or part of a system, to the maximum demand of the whole system, or part of the system, under consideration.
Electrical diversity factor is usually more than one. Why field rheostat is kept in minimum position while armature rheostat at maximum position? In motors at the time of starting the armature resistance is introduced to reduce the high starting current and the field resistance is kept minimum to have high starting torque.
Why computer humming sound occurred in HT transmission line? This computer humming sound is coming due to ionization breakdown of air into charged particles of air around transmission conductor. This effect is called as Corona effect, and it is considered as power loss. Explain What is rated speed? At the time of motor taking normal current rated current the speed of the motor is called rated speed.
It is a speed at which any system take small current and give maximum efficiency. What is different between resistance grounding system and resistance earthing system? Resistance grounding system means connecting the neutral point of the load to the ground to carry the residual current in case of unbalanced conditions through the neutral to the ground whereas resistance earthing system is done in an electric equipment in order to protect he equipment in occurrence of fault in the system.
Why should be the frequency 50 Hz 60Hz only why not others like 45, 95 56 or anything , why should we maintain the frequency constant if so why it is only 50 Hz 60Hz? We can have the frequency at any frequency you like, but than you must also make your own motors,high voltage transformers or any other equipment you want to use.
How to determine alternating current frequency? Zero crossings of the sine wave to trigger a monostable pulse generator is a way to determine alternating current frequency.
A fixed width pulse is generated for each cycle. The more pulses there are per second, the more the energy. The pulses are integrated filtered or averaged to get a steady DC voltage which is proportional to frequency. This voltage can then be displayed on an analogue or digital voltmeter, indicating frequency.
This method is more suitable than a direct counter, as it can get good accuracy in a second or so. Why electricity in India is in the multiples of 11 like 11kv, 22kv, 33kv? Transformer Induced voltage equation contains 4. So always transmission voltage is multiple of 11 Why we use ac system in India why not dc?
Secondly it is much easier to change the voltage of AC electricity for transmission and distribution. When a fault on the network occurs, a large fault current occurs. In an AC system this becomes much easier to interupt, as the sine wave current will naturally tend to zero at some point making the current easier to interrupt.
Which type of motor is used in trains, what is the rating of supply used explain Working principal? Dc series is in the trains to get high starting torque while starting of the trains and operating voltage is v dc. Battery banks are in connected in series or parallel and why? Battery banks are always connected in series in order to get a multiplied voltage where the AH or current capacity remaining same.
Ex : 24 nos. What is inrush current? Inrush current is the current drawn by a piece of electrically operated equipment when power is first applied. It can occur with AC or DC powered equipment, and can happen even with low supply voltages. In a Tap changing transformer where is the tap connected, is it connected in the primary side or secondary side?
Tapings are connected to high voltage winding side, because of low current. If we connect tapings to low voltage side, sparks will produce while tap changing operation due to high current.
Why transformer ratings are in kva? Since the power factor of transformer is dependent on load we only define VA rating and does not include power factor. In case of motors, power factor depend on construction and hence rating of motors is in KWatts and include power factor.
Define what is difference between fuse and breaker? Fuses are burned at the time of over current flows in the circuit but breakers are just open not burn at the time of over current flow. Fuses are used in only one time but breakers are used by multiple number of times. What is the difference between delta-delta, delta-star transformer?
Delta-star is a distribution kind of transformer where from secondary star neutral is taken as a return path and this configuration is used for Step down voltage phenomena. Capacitor is load free component but why ampere meter shows current when capacitor bank breaker close? As we know that Electrical is having two type of load, Active and Reactive. Traction implies with the electric power for traction system i. Now a day, magnetic traction is also utilised for bullet trains.