JIET SETG. EEE_ Technical Interview Questions How can you relate power engineering with electrical engineering? . Apparent power = V I and basic unit of. Basic Electrical Interview Questions and Answers Pdf ebook for Job. ELECTRICAL Engineering Interview Questions with Answers free. Download as PDF, TXT or read online from Scribd. Flag for Electrical interview question: Why is the starting current high in a DC motor? Answer: In DC motors, .. Electrical interview question: Give two basic speed control scheme of DC.
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20 Electrical Engineering Interview Questions & Answers This is a must know question for any good Electrical Engineer Download PDF. Electrical Interview Questions & Answers visit macawebsrilni.ga Page | .. Give two basic speed control scheme of DC shunt motor? Answer: 1. By using flux. We have hope by these PDF Electrical aspirants who are going to face Government or Private It have all possible Technical interview questions and answers which have mostly asked in previous interview. Basic Electrical.
Arc is extinguished by the Arc Quenching media like air, oil, vacuum etc. Electrical interview question: How many types of cooling system it transformers? ONAF oil natural, air forced 3. OFAF oil forced, air forced 4. ODWF oil direct, water forced 5. OFAN oil forced, air forced Electrical interview question: What is the function of anti-pumping in circuit breaker? Answer: when breaker is close at one time by close push button he anti pumping contactor prevent re close the breaker by close push button after if it already close.
Electrical interview question: what is stepper motor. What is its uses? Answer :Stepper motor is the electrical machine which act upon input pulse applied to it. It is important part in Synchronous Generators; it controls the output voltage of the generator by controlling its excitation current.
Thus it can control the output Reactive Power of the Generator. Electrical interview question: What is an exciter and how does it work?
Answer: There are two types of exciters, static exciter and rotary exciter. Purpose of exciter is to supply the excitation dc voltage to the fixed poles of generator. Rotory exciter is an additional small generator mounted on the shaft of main generator. K is the ac generator whose field winding are stationary and armature rotates. It gives the starting torque to the generator. Electrical interview question: Difference between a four point starter and three point starter?
Answer: The shunt connection in four point starter is provided separately from the line where as in three point state it is connected with line which is the drawback in three point starter Electrical interview question: Why use the VCB at High Transmission System?
Why can't use ACB? Answer: Actually the thing is vacuum has high arc quenching property compare to air becoz in VCB ,the die electric strength is equal to 8 times of air. That y always vacuum used as in HT breaker and air used as in LT.
Electrical interview question: What is the difference between surge arrestor and lightning arrestor? Answer: LA is installed outside and the effect of lightning is grounded, where as surge arrestor installed inside panels comprising of resistors which consumes the energy and nullify the effect of surge. Electrical interview question: Why syn. Answer: synchronous machines have capability to work on different power factor or say different imaginary power varying the field emf.
Hence syn. Answer: In simple, synchronous generator supply's both active and reactive power but asynchronous generator induction generator supply's only active power and observe reactive power for magnetizing. This type of generators is used in windmills. Electrical interview question:1 ton is equal to how many watts? Electrical interview question: why syn. Answer: synchronous machines have capability to work on differentpower factor or say different imaginary pow varying the field emf.
Electrical interview question: Enlist types of dc generator? Answer: D. Generators are classified into two types 1 separately excited d. Electrical interview question: Give two basic speed control scheme of DC shunt motor? By using flux control method: in this method a rheostat is connected across the field wdg to control the field current. Electrical interview question: what is the principle of motor? K Answer: Whenever a current carrying conductor is placed in a magnetic field it produce turning or twisting movement is called as torque.
Define What is the function of anti-pumping in circuit breaker? What is stepper motor. Stepper motor is the electrical machine which act upon input pulse applied to it.
How to calculate capacitor bank value to maintain unity power factor with some suitable example? Tell me in detail about c. T means current transformer,and the term P. T means potential transformer. In circuit where measurements of high voltage and high current is involved they are used there. Particularly when a measuring device like voltmeter or ammeter is not able to measure such high value of quantity because of large value of torque due to such high value it can damage the measuring device.
They work on the same principle of transformer, which is based on linkage of electromagnetic flux produced by primary with secondary. They work on the ratio to they are designed. There are a Transformer and an induction machine. Those two have the same supply. For which device the load current will be maximum? And why? The motor has max load current compare to that of transformer because the motor consumes real power..
What is power factor? Power factor should be high in order to get smooth operation of the system. Low power factor means losses will be more. What is the difference between Isolator and Circuit Breaker?
Isolator is a off load device which is used for isolating the downstream circuits from upstream circuits for the reason of any maintenance on downstream circuits. But circuit breaker is onload automatic device used for breaking the circuit in case of abnormal conditions like short circuit, overload etc. Boucholz relay is a device which is used for the protection of transformer from its internal faults, it is a gas based relay.
What is SF6 Circuit Breaker? SF6 is Sulpher hexa Flouride gas.. What is frantic effect? Output voltage is greater than the input voltage or receiving end voltage is greater than the sending end voltage. What is meant by insulation voltage in cables? It is the property of a cable by virtue of it can withstand the applied voltage without rupturing it is known as insulation level of the cable.
Why we do 2 types of earthing on transformer ie: The two types of earthing are Familiar as Equipment earthing and system earthing. In Equipment earthing: In this neutral of the supply source Transformer or Generator should be grounded. With this,in case of unbalanced loading neutral will not be shifted.
We can protect the equipment also. With size of the equipment transformer or alternator and selection of relying system earthing will be further classified into directly earthed,Impedance earthing, resistive NGRs earthing.
Electrical engineering Interview Questions and Answers
MCB is miniature circuit breaker which is thermal operated and use for short circuit protection in small current rating circuit. MCCB moulded case circuit breaker and is thermal operated for over load current and magnetic operation for instant trip in short circuit condition. Normally it is used where normal current is more than A. Where should the lighting arrestor be placed in distribution lines? Near distribution transformers and out going feeders of 11kv and incomming feeder of 33kv and near power transformers in sub-stations.
Define IDMT relay? It is an inverse definite minimum time relay. In IDMT relay its operating is inversely proportional and also a characteristic of minimum time after which this relay operates. It is inverse in the sense ,the tripping time will decrease as the magnitude of fault current increase.
What are the transformer losses? Copper losses are caused by the resistance of the wire I2R.
Magnetic losses are caused by eddy currents and hysteresis in the core. Copper loss is a constant after the coil has been wound and therefore a measurable loss. Hysteresis loss is constant for a particular voltage and current. Eddy-current loss, however, is different for each frequency passed through the transformer.
What is the count of hvdc transmission lines in India? At present there are three hvdc transmission lines in india. What is meant by regenerative braking? When the supply is cutt off for a running motor, it still continue running due to inertia.
In order to stop it quickly we place a load resitor across the armature winding and the motor should have maintained continuous field supply. 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? The main advantage of using the star delta starter is 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 motor in systems are reduced. For lighting loads, neutral conductor is must and hence the secondary must be star winding. To minimize the current unbalance in the primary we use delta winding in the primary.
Why in a three pin plug the earth pin is thicker and longer than the other pins? It is longer because the The First to make the connection and Last to disconnnect should be earth Pin.
This assures Safety for the person who uses the electrical instrument.
Why series motor cannot be started on no-load? Series motor cannot be started without load because of high starting torque. Series motor are used in Trains, Crane etc. ELCB is used to detect earth leakage fault. Once the phase and neutral are connected in an ELCB, the current will flow through phase and that much current will have to return neutral so resultant current is zero.
Once there is a ground fault in the load side, current from phase will directly pass through earth and it will not return through neutral through ELCB. That means once side current is going and not returning and hence because of this difference in current ELCB wil trip and it will safe guard the other circuits from faulty loads. If the neutral is not grounded, fault current will definitely high and that full fault current will come back through ELCB, and there will be no difference in current.
How electrical power is generated by an A. C Generator? For the generation of elect power we need a prime mover which supplies mechanical power input to the alternator, can be steam turbines,or hydro turbines. When poles of the rotor moves under the armature conductors which are placed on the stator ,field flux cut the armature conductor ,therefore voltage is generated and is of sinusoidal in nature…due to polarity change of rotor poles i,e N-S-N-S.
Why an ac solenoid valve attract the plunger even though we interchanges the terminal? Will the poles changes? Yes because the poles changes for every half-cycle of ac voltage so the polarity of AC voltage is continuously changing for every half cycle. What is derating? The current currying of cables will change depending upon the site temperature location of site , type of run it will run through duct, trench, buried etc.
Considering this condition actual current currying capacity of cable reduce than current currying capacity which given to cable Catalogue this is called derating. Why temperature rise is conducted in bus bars and isolators? Bus bars and isolators are rated for continuous power flow, that means they carry heavy currents which rises their temperature. When voltage increases then current also increases then what is the need of over voltage relay and over current relay?
Can we measure over voltage and over current by measuring current only? So, for a better protection of the system. If one lamp connects between two phases it will glow or not? If the voltage between the two phase is equal to the lamp voltage then the lamp will glow. When the voltage difference is big it will damage the lamp and when the difference is smaller the lamp will glow depending on the type of lamp.
At first calculate the electrical current of the load, after that derate the electrical current considering derating factor depending on site condition and laying of cable after choose the cable size from cable catalog considering derating electrical current.
After that measure the length of cable required from supply point of load to load poin. What are HRC fuses and where it is used? Which power plant has high load factor? All base load power plants have a high load factor. If we use high efficiency power plants to supply the base load,we can reduce the cost of generation. Mention the methods for starting an induction motor? The different methods of starting an induction motor.
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? At no load Synchronous Impedance of the alternator is responsible for creating angle difference. So it should be zero lagging like inductor.
Explain How to determine capacitor tolerance codes? In electronic circuits, the capacitor tolerance can be determined by a code that appears on the casing. The code is a letter that often follows a three-digit number such as Z. The first two are the 1st and 2nd significant digits and the third is a multiplier code. Most of the time the last digit tells you how many zeros to write after the first two digits and these are read as Pico-Farads.
The reason that 4ma is chosen instead of 0 mA is for fail safe operation. For example- a pressure instrument gives output 4mA to indicate 0 psi, up to 20 mA to indicate psi, or full scale.
Due to any problem in instrument i. So if range is mA then we can differentiate whether it is due to broken wire or due to 0 psi. Two bulbs of w and 40w respectively connected in series across a v supply which bulb will glow bright and why? What is meant by knee point voltage? Knee point voltage is calculated for electrical Current transformers and is very important factor to choose a CT.
It is the voltage at which a CT gets saturated. CT-current transformer. What is reverse power relay? A generating stations is supposed to fed power to the grid and in case generating units are off,there is no generation in the plant then plant may take power from grid. To stop the flow of power from grid to generator we use reverse power relay. What will happen if DC supply is given on the primary of a transformer?
Mainly transformer has high inductance and low resistance. So high electrical current will flow through primary side of the transformer. So for this reason coil and insulation will burn out. What is bus-bar? Isolators are mainly for switching purpose under normal conditions but they cannot operate in fault conditions. Actually they used for isolating the CBs for maintenance. Whereas CB gets activated under fault conditions according to the fault detected.
Bus bar is nothing but a junction where the power is getting distributed for independent loads. What are the advantage of free wheeling diode in a Full Wave rectifier? It reduces the harmonics and it also reduces sparking and arching across the mechanical switch so that it reduces the voltage spike seen in a inductive load.
What is the function of interposing current transformer? The main function of an interposing current transformer is to balance the currents supplied to the relay where there would otherwise be an imbalance due to the ratios of the main current transformers.
Interposing current transformer are equipped with a wide range of taps that can be selected by the user to achieve the balance required. What are Motor Generator Sets and explain the different ways the motor generator set can be used? Motor Generator Sets are a combination of an electrical generator and an engine mounted together to form a single piece of equipment. Motor generator set is also referred to as a genset, or more commonly, a generator.
The motor generator set can used in the following different ways:. Define what is power quality meter? Power Quality meters are common in many industrial environment. Small units are now available for home use as well. They give operators the ability to monitor the both perturbations on the power supply, as well as power used within a building, or by a single machine or appliance.
In some situations, equipment function and operation is monitored and controlled from a remote location where communication is via modem, or highspeed communication lines. So we can understand the importance of power measurement through power quality meters. What is the different between digital phase converter and ordinary phase converter?
Digital phase converter are a recent development in phase converter technology that utilizes proprietary software in a powerful microprocessor to control solid state power switching components. This microprocessor, called a digital signal processor DSP , monitors the phase conversion process, continually adjusting the input and output modules of the converter to maintain perfectly balanced three-phase power under all load conditions.
Explain the operation of variable frequency transformer? A variable frequency transformer is used to transmit electricity between two asynchronous alternating current domains.
A variable frequency transformer is a doubly-fed electric machine resembling a vertical shaft hydroelectric generator with a three-phase wound rotor, connected by slip rings to one external ac power circuit. A direct-current torque motor is mounted on the same shaft. Changing the direction of torque applied to the shaft changes the direction of power flow; with no applied torque, the shaft rotates due to the difference in frequency between the networks connected to the rotor and stator.
The variable frequency transformer behaves as a continuously adjustable phase-shifting transformer. It allows control of the power flow between two networks.
What is the main use of rotary phase converter?
Rotary phase converter will be converting single phase power into true balanced 3 phase power,so it is often called as single phase to three phase converter. Often the advantages of 3 phase motors, and other 3 phase equipment, make it worthwhile to convert single phase to 3 phase so that small and large consumers need not want to pay for the extra cost of a 3 phase service but may still wish to use 3 phase equipment.
Use of switch mode power converter in real-time basis? Switch mode power converter can be used in the following 5 different ways.
Which type of oil is used as a transformer oil? Transformer oil, or insulating oil, is usually a highly-refined mineral oil that is stable at high temperatures and has excellent electrical insulating properties. It is used in oil filled transformers, some types of high voltage capacitors, fluorescent lamp ballasts, and some types of high voltage switches and circuit breakers.
Its functions are to insulate, suppress corona and arcing, and to serve as a coolant. Well into the s, polychlorinated biphenyls PCB s were often used as a dielectric fluid since they are not flammable. They are toxic, and under incomplete combustion, can form highly toxic products such as furan. Starting in the early s, concerns about the toxicity of PCBs have led to their banning in many countries.
Today, non-toxic, stable silicon-based or fluoridated hydrocarbons are used, where the added expense of a fireresistant liquid offsets additional building cost for a transformer vault. Combustion-resistant vegetable oil-based dielectric coolants and synthetic pentaerythritol tetra fatty acid C7, C8 esters are also becoming increasingly common as alternatives to naphthenic mineral oil. Esters are non-toxic to aquatic life, readily biodegradable, and have a lower volatility and higher flash points than mineral oil.
If we give A, V on Primary side of 1. Mcb specification are done on maximum current flow in circuit. What is the full form of KVAR?
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 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.
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.
Essentially dc motors are utilized for electric traction systems.
Pu stands for per unit in power system. Define stepper motor. What is the use of stepper motor? The motor which work or act on the applied input pulse in it, is called as stepper motor. This stepper motor is under the category of synchronous motor, which often does not fully depend of complete cycle.
It likes to works in either direction related to steps. What is a differential amplifier? Also, explain CMRR. Differential Amplifier: The amplifier, which is used to amplify the voltage difference between two input-lines neither of which is grounded, is called differential amplifier. This reduces the amount of noise which is injected into the amplifier, because any noise appearing simultaneously on both the input-terminals as the amplifying circuitry rejects it being a common mode signal.
It can be defined as the ratio of differential voltage-gain to common made voltage gain. If a differential amplifier is perfect, CMRR will be infinite because in that case common mode voltage gain would be zero. What is use of lockout relay in ht voltage? This relay is powered by the same electrical source as the control power which is operated by a key lock switch.
What types domain of Laplace transforms? What behavior can Laplace transform predict how the system work? Types domain of Laplace transforms is s-domain, Laplace transforms provide a method to find position, acceleration or voltage the system will have.
In the magnetic fluxes, what is the role of armature reaction? The armature flux has an important role for the running condition.
This armature flux can oppose the main flux or it may support the main flux for better running condition. This effect of supporting and opposing of main flux to armature flux is called armature reaction. Explain thin film resistors and wire-wound resistors Thin film resistors- It is constructed as a thin film of resistive material is deposited on an insulating substrate.
Desired results are obtained by either trimming the layer thickness or by cutting helical grooves of suitable pitch along its length. During this process, the value of the resistance is monitored closely and cutting of grooves is stopped as soon as the desired value of resistance is obtained. Wire wound resistors — length of wire wound around an insulating cylindrical core are known as wire wound resistors.
These wires are made of materials such as Constantan and Manganin because of their high resistivity, and low temperature coefficients. The complete wire wound resistor is coated with an insulating material such as baked enamel. What are the operation carried out in Thermal power station? The water is obtained in the boiler and the coal is burnt so that steam is obtained this steam is allowed to hit the turbine, the turbine which is coupled with the generator generates the electricity.
What is the difference between Electronic regulator and ordinary rheostat regulator for fans? The difference between the electronic and ordinary regulator is the fact that in electronic reg. In electronic regulator triac is employed for speed control. A two phase motor is often a motor with the the starting winding and the running winding have a phase split. What does quality factor depend on in resonance?
Quality factor q depends on frequency and bandwidth. What are the types of power in electrical power?
There are normally three types of power are counted in electrical power. They are,. What are the advantages of VSCF wind electrical system?
Advantages of VSCF wind electrical system are:. What is slip in an induction motor? Slip can be defined as the distinction between the flux speed Ns and the rotor speed N. Speed of the rotor of an induction motor is always less than its synchronous speed. State the difference between generator and alternator?
Generator and alternator are two devices, which converts mechanical energy into electrical energy. Both have the same principle of electromagnetic induction, the only difference is that their construction. Generator persists stationary magnetic field and rotating conductor which rolls on the armature with slip rings and brushes riding against each other, hence it converts the induced emf into dc current for external load whereas an alternator has a stationary armature and rotating magnetic field for high voltages but for low voltage output rotating armature and stationary magnetic field is used.Electrical interview question: What will happen when power factor is leading in distribution of power?
Particularly when a measuring device like voltmeter or ammeter is not able to measure such high value of quantity because of large value of torque due to such high value it can damage the measuring device. Why field rheostat is kept in minimum position while armature rheostat at maximum position?
K Answer: Whenever a current carrying conductor is placed in a magnetic field it produce turning or twisting movement is called as torque. These are located in the interpolar region of the main poles and therefore influence the armature coils only when these undergo commutation.
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