Electrical machines interview questions and answers pdf

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    + 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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    Electrical Machines Interview Questions And Answers Pdf

    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 daifiteresua.gaya. Answer: Stepper motor is the electrical machine which act upon input pulse applied to daifiteresua.ga is one. Electrical interview questions from AC & DC motor principle and working Synchronous machines have capability to work on different power factor (or say.

    Series reactor starter What is the difference between earth resistance and earth electrode resistance? Only one of the terminals is evident in the earth resistance. In order to find the second terminal we should recourse to its definition: Earth Resistance is the resistance existing between the electrically accessible part of a buried electrode and another point of the earth, which is far away. The resistance of the electrode has the following components: A the resistance of the metal and that of the connection to it. B the contact resistance of the surrounding earth to the electrode. Explain What is use of lockout relay in ht voltage? A lock-out relay is generally placed in line before or after the e-stop switch so the power can be shut off at one central location. This relay is powered by the same electrical source as the control power and is operated by a key lock switch. The relay itself may have up to 24 contact points within the unit itself. This allows the control power for multiple machines to be locked out by the turn of a single key switch. What is the power factor of an alternator at no load?

    Why are not 4 or something else?

    Answer: 3 phase power generating and delivering is more efficient than 2 phase which in turn is more efficient than 1 phase. Similarly, going up in the number of phases result in increased efficiency as well, i. The increase of efficiency as the number of phases increase is attributed to that power delivery becomes more continuous as the number of phases increases and It affects the Installation cost of transmission of Transmission towers.

    Why is the starting current high in a DC motor? At starting, Eb is zero. What are the advantages of star-delta starter with induction motor? Answer: The main advantage of using the star delta starter is the reduction of current during the starting of the motor. Starting current is reduced to times Of current of Direct online starting. Hence the starting current is reduced; the voltage drops during the starting of the motor in systems are reduced.

    Answer: For lighting loads, neutral conductor is must and hence the secondary must be star winding. And this lighting load is always unbalanced in all three phases. To minimize the current unbalance in the primary we use delta winding in the primary. Why can series motor not be started on no-load? Answer: Series motor cannot be started without load because of high starting torque.

    Series motor is used in Trains, Crane etc. What is 2 phase motor? Answer: A two-phase motor is a motor with the starting winding and the running winding have a phase split. This type of generators is used in windmills.

    It is important part in Synchronous Generators, it controls the output voltage of generator by controlling its excitation current. Thus it can control the output Reactive Power of the Generator. Why the capacitors work on ac only? Answer: Generally, capacitor gives infinite resistance to dc components i. Alternating current AC to direct current DC 2. DC to AC 3.

    DC at one voltage to DC at another voltage 4. AC at one frequency to AC at another harmonically-related frequency. 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.

    In thermal power plants dc motors are employed for certain control and critical emergency operations which are supplied by dedicated batteries. DC motors operate as backup drives for normal ac drive systems when ac power supply to the plant is lost. In thermal power plant, the dc motors finds applications for performing control functions such as Turbine governor motor Governor limit setting Motor operated rheostats Emergency lubrication for the turbines main, boiler feed pumps Generator H2 oil seal.

    DC motor operated valves DC motors employed in thermal plants are classified in to two types based on the type of application. This category consists of the turbine governor motor, governor limiting setting, motor operated rheostats, etc. They are operated quite infrequently for short duration.

    Emergency functions: This category consists of turbine-generator emergency lubrication bearing oil pumps and emergency seal oil pumps. Such pumps may also be provided for steam turbine drives of feedwater pumps, fans, and other large loads.

    The lack of lubrication during a shutdown without ac power will ruin the linings of the bearings and damage the shaft.

    400 TOP ELECTRICAL ENGINEERING Interview Questions and Answers Pdf- EEE

    Hydrogen seal oil pump is provided to prevent the escaping of hydrogen for large turbine-generators hydrogen cooling is provided for efficient cooling from the casing by providing a tight seal with high pressure oil. Advantage or Merits: One of the major advantage of using synchronous motor is the ability to control the power factor.

    An over excited synchronous motor can have leading power factor and can be operated in parallel to induction motors and other lagging power factor loads thereby improving the system power factor. In synchronous motor the speed remains constant irrespective of the loads. This characteristics helps in industrial drives where constant speed is required irrespective of the load it is driving. It also useful when the motor is required to drive another alternator to supply at a different frequency as in frequency changes.

    Synchronous motors can be constructed with wider air gaps than induction motors which makes these motors mechanically more stable. In synchronous motors electro-magnetic power varies linearly with the voltage. Synchronous motors requires dc excitation which must be supplied from external sources. Synchronous motors are inherently not self starting motors and needs some arrangement for its starting and synchronizing. The cost per kW output is generally higher than that of induction motors.

    These motors cannot be used for variable speed applications as there is no possibility of speed adjustment unless the incoming supply frequency is adjusted Variable Frequency Drives. Synchronous motors cannot be started on load.

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    Its starting torque is zero. When loading on the synchronous motor increases beyond its capability, the synchronism between rotor and stator rotating magnetic field is lost and motor comes to halt. Collector rings and brushes are required resulting in increase in maintenance. Synchronous motors cannot be useful for applications requiring frequent starting or high starting torques required.

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