30 electrical engineering interview questions and answers

Part 1   Part 2   Part 3   Part 4   Part 5   Part 6 1.Why star delta starter is preferred with induction motor? 2. State the difference between generator and alternator 3. Why AC systems are preferred over DC systems? 4. How can you relate power engineering with electrical engineering? 5. What are the various kind of cables used for transmission? 6. Why back emf used for a dc motor? highlight its significance. 7. What is slip in an induction motor? 8. Explain the application of storage batteries. Why star delta starter is preferred with induction motor? Star delta starter is preferred with induction motor due to following reasons: • Starting current is reduced 3-4 times of the direct current due to which voltage drops and hence it causes less losses. • Star delta starter circuit comes in circuit first during starting of motor, which reduces voltage 3 times, that is why current also reduces up to 3 times and hence less motor burning is caused. • In addition, starting torque is increased and it prevents the damage of motor winding. 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. Why AC systems are preferred over DC systems? Due to following reasons, AC systems are preferred over DC systems: a. It is easy to maintain and change the voltage of AC electricity for transmission and distribution. b. Plant cost for AC transmission (circuit breakers, transformers etc) is much lower than the equivalent DC transmission c. From power stations, AC is produced so it is better to use AC then DC instead of converting it. d. When a large fault occurs in a network, it is easier to interrupt in an AC system, as the sine wave current will naturally tend to zero at some point making the current easier to interrupt. How can you relate power engineering with electrical engineering? Power engineering is a sub division of electrical engineering. It deals with generation, transmission and distribution of energy in electrical form. Design of all power equipments also comes under power engineering. Power engineers may work on the design and maintenance of the power grid i.e. called on grid systems and they might work on off grid systems that are not connected to the system. What are the various kind of cables used for transmission? Cables, which are used for transmitting power, can be categorized in three forms: • Low-tension cables, which can transmit voltage upto 1000 volts. • High-tension cables can transmit voltage upto 23000 volts. • Super tension cables can transmit voltage 66 kV to 132 kV. Why back emf used for a dc motor? highlight its significance. The induced emf developed when the rotating conductors of the armature between the poles of magnet, in a DC motor, cut the magnetic flux, opposes the current flowing through the conductor, when the armature rotates, is called back emf. Its value depends upon the speed of rotation of the armature conductors. In starting, the value of back emf is zero. What is slip in an induction motor? Slip can be defined as the difference 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. It is usually expressed as a percentage of synchronous speed (Ns) and represented by the symbol ‘S’. Explain the application of storage batteries. Storage batteries are used for various purposes, some of the applications are mentioned below: • For the operation of protective devices and for emergency lighting at generating stations and substations. • For starting, ignition and lighting of automobiles, aircrafts etc. • For lighting on steam and diesel railways trains. • As a supply power source in telephone exchange, laboratories and broad casting stations. • For emergency lighting at hospitals, banks, rural areas where electricity supplies are not possible. Part 1   Part 2   Part 3   Part 4   Part 5   Part 6 Write your comment - Share Knowledge and Experience Discussion Board Electrical engineering It''s the best site for increasing our knowledge in electrical field ,so I''m satisfied in this site. Pabitra Pradhan 09-9-2018 03:50 AM basic knowledge in power system, we analysis only ac fault current why? balram bhati 08-23-2018 03:17 AM electrical quction g.k sunanda jena 11-1-2017 02:23 AM Electrical work question How ,can make, in Electrical current in personal house in 5 kva sushil kumar kushwaha 09-14-2017 05:38 PM Electrical work question How ,can make, in Electrical current in personal house in 5 kva Name sushil kumar kushwaha 09-14-2017 05:35 PM electrcal machine there are two types of machine.1.rotating 2.stationary .stationary machine are transformer,no rotating part transfer enegy from one circuit to another.2.rotating machine are generator and motor,which convert energy from mechanical to electrical and vice versa. haridass 08-26-2017 07:57 AM ac This comment is for answering vanitha p Resistance is the measure of opposition to the current flow offered by the material.Usually denoted by R. Reactance is the resistance offered to the ac currents by inductors and capacitors only. Usually denoted by X. Preethi 06-9-2017 03:18 AM Electrical If it is short circuited what will be the value of current?? Preethi 06-9-2017 03:08 AM ac what is the difference between resistance and reactance? vanitha p 03-31-2017 07:59 AM cables jointing methods question;can anyone explain POT AND LADLE CABLE JOINTING METHOD.also give I.E.E. regulations requirement regarding joints and terminations.please githuka james 10-27-2016 03:49 AM Electrical What are the disadvantages of low frequency? Hamid raza 10-5-2016 03:31 PM eee which one is better in powersystem AC or DC? MAHA 08-30-2016 04:22 AM thanks this infomation really work, thank you guys for making this page ezile 08-20-2016 02:19 PM Neutral and Earth Neutral - It is used as a return path for AC systems to complete the circuit for current to flow. Earth - It is used for safety purposes. Earthing wire is directly connected to the actual earth so that fault current can flow straight to earth without harming the person. RISHABH SRIVASTAVA 08-4-2016 01:20 PM rpm wide open my generator runs wide open , should idle until tool is using power. why ? Eric Sheffer 07-24-2016 05:47 AM Electrical world It's very useful question and answers. And also update more information about the circuit calculation karthick N 07-10-2016 10:40 AM electrical what is neutral and earth? pls explain sir k m samy 07-8-2016 02:14 AM power generation using aircompressor i am thinking of how to generate electrical power and distributing it without wire and transformer. the ideas is to have air compressor power by turbine or diesel engine. the compress air will be transported by pipe to houses where pneumatic winch will be used to rotate smaller alternator that will generate electricity at home. just as we have water system in cities. will this be more expensive than the convectional wire system and building of transmission line? case of electrocution will also reduce. can any one sugest a better way? temiaro godfrey 03-13-2016 12:44 PM Question Why sub stations are rated as 11kw and 22kw why not as 10 kw or 13kw...? Nik 02-28-2016 11:09 AM answer total load is 250 watts, if it is taken through each 13 A socket outlet . k.viswanathan 02-24-2016 07:35 AM verified the questions very useful saranya.T 02-11-2016 12:27 AM Machine Transformer ac and dc motor and others Shivam 01-30-2016 04:25 AM how to solve this please help 5.no 50w halogen lights 5. No. 13A socket outlets Whats is the load? Single line diagram? sky 01-19-2016 03:53 AM how to connected load generator. how to connected load generator?we are used ups 60+60kva,air condisnor 40 no, lighting and fans load total 50 amper per leg.how to connect generator in kva? saad 12-18-2015 05:39 AM emf An emf (electromotive force ) is the potential difference developed or that emanate from the source of electrical energy, say battery , which is capable of driving an electric current in a circuit .. akinremi 11-21-2015 04:36 AM really awesome Thnx for remembering to me ,, my college time and it is really awesome ... rahul 10-31-2015 06:45 AM electrical Sense vineesh 10-23-2015 05:38 AM machines it is really useful... shanthi 09-20-2015 04:31 AM express educating site akshay naravaade. 08-15-2015 10:42 AM transformer which connection of transformer is mostly preffered. Kishor Babasaheb Phasale 08-7-2015 06:12 AM Electrical Engineering what happens when 2 ideal dc voltage source of unequal magnitude are connected in parallel? This question wad asked to me in BAARC interview. Chandan 08-6-2015 06:01 AM Ac n dc motor Mr. Sunil ac is generate a flux and frequency and in a dc not play Flux because dc is play on a strat Akshay kumar gupta 07-13-2015 09:24 AM electrical what is e m f sushil kumar kushwaha ee 07-12-2015 07:42 AM electrical quastion what is frequency in d c motor sushil kumar kushwaha 07-12-2015 07:38 AM demand factor hi guys.. Can help me to determine the demand factor for 6 chillers, each on has 60 kw? azad 06-30-2015 09:28 AM eee What is frequency in DC voltage? sanni 06-22-2015 03:34 PM Electrical machine I m writing this comment in reference to question no. 1 ... Here the ans. Is not clearly explained... actually by using star-delta starter for starting induction motor... at the time of starting motor start with star connection and the starting voltage is reduced to root of one third... now as we know that the torque is proportional to the square of the voltage therefore the starting torque is reduced to one third...and as the current is directly proportional to the torque, it is also reduced to one third... and thus the motor is protected from heavy starting current at time of starting and the motor is prevented from getting damage... when the motor reaches its steady state speed, the motor then works with delta connection... hence the name is star-delta. Mohammed Hamza Shaikh 06-3-2015 09:16 AM electrical nice Question Answer Darpan patel 05-28-2015 10:57 AM Elec engg Interview question for electrical engg Aman 05-26-2015 11:48 PM Electrical Very super Bhogeswaran 05-22-2015 06:11 AM Reforming of VFD What is reforming of VFD? why we are doing that reforming on VFD's? please explain Shamz 05-21-2015 01:18 AM electrical I am very interested to read it.. uzzal et 05-19-2015 04:01 PM Wiring diagram There are two water pumps with a capacity of 5.5KW/3ph each.. I need to design a panel board with an electric water float. Function of it is: when water level goes down, Pump No 1 will start automatically and immediately till adjusted water level reaches. When water level decreases second time around, pump No 2 should start automatically and immediately. And this should be constant. Please can someone draw a wiring diagram for this. Thanks kamil 04-19-2015 02:15 PM regenerative surge protectors. Please excuse me for taking up your valuable time. I have been searching for an answer on line for several hours and cannot find any discussion of this subject. The telephone company has been using regenerative surge protectors for over forty years. I understand that these are low voltage DC circuits. Why is there no common over the counter equivalent for household AC circuits. That is; surge protectors that turn the current back on when the surge is over. You might ask why would I want such a device? I live in a high lighting area that commonly gets surges. I am often out of town for several days at a time and my refrigerator stays on. If I put it on a surge protector and then have a surge you can guess what happens. I come home and the frig. has been off for days and I have a huge mess. So back to my original question why are there no inexpensive devices over the counter to turn the current back on. Thank you Deryck Deryck Clark 03-27-2015 11:37 AM transformer tell me about transformer Amiya ranjan sethy 03-19-2015 07:47 PM capacitor Sir I satisfy ur answer..but sir I want to know one thing when power is supply One place to other place then is it necessary that there are producing capacitor between line power transmission? wasim ahmad 03-18-2015 04:50 AM why star delta starter is used? i am writing with reference to question no 1.... here the current is greatly reduced and hence it protects us from heavy starting current and it too costs us for less starting torque hence we get a reduced torque but have a safe value of current so as to protect the armature winding. prashant verma 03-16-2015 02:14 AM electrical in answer of first question u wrote voltage reduce 3 times then current reduce 3 times. u r in false because voltage actually reduce by root 3 i.e. 1.723. write this answer clearly . plz rashed 02-20-2015 08:26 AM ( difference between grounding and earthing.... pradeep 02-17-2015 01:26 PM eee why we r using power factor? Megavath krishna naik 02-9-2015 11:16 AM electrical shot question electrical knowlege intrested sagar mahapatra 02-7-2015 09:18 PM power system the lamp will strike i n R and Y phases ? GOWRISHANKAR 02-4-2015 05:28 AM hi I satisfy sudheer 12-30-2014 10:49 AM general question If we touch the single phase of HT line what will the for humans? boovalingam 12-29-2014 08:49 AM ee very use full q shekhar kashiwar 12-21-2014 10:50 AM plz teacher about electrical engineers things plz plz can any one teacher me about electrical engineers thing and other musa rashaunshe 12-21-2014 05:49 AM explain the application of storage batteries how can you relate power engineering and electrical engineering musa rashaunshe 12-21-2014 05:38 AM electrical engg electrical engg Q:why rating of transformer in KVA and for motor rating isi n hp or KW. A: Transformer losses depends on current (CU loss) & Voltage (Iron loss) (VA). So its rated in KVA. Also TFR is independent from load PF. But in motor the losses depends of load power factor. That's why motor rated in KW. boopathi 12-17-2014 09:22 PM electrical engg Rating of the motor is also depends of PF. P=Root3 V*I*PF. So PF increase the power of the motor is also increases. Boopathi 12-17-2014 09:17 PM electrical motor Ans: DC Motor used in high torque application. Boopathi 12-17-2014 09:13 PM electrical motor Q: which application DC motor preffer on AC motor? 1)variable speed operation 2)high speed 3)low speed 4)fixed speeed plz give ans sapna 12-17-2014 08:37 AM EEE define Lenz law. at application m.prasanth 12-16-2014 01:52 AM gate sir can you send electrical subject gate questions sandeep kumar 12-9-2014 11:53 PM electrical motor sir can u post the subject relating sunchronous speed its related small problems and the brief description about the motor parts and about the stuff related to feeders. gajula sampath kumar 11-4-2014 12:11 AM electrical engg how rating of motor depeds on power factor gaurav singh rajwar 11-1-2014 03:28 AM electrical engg why rating of transformer in KVA and for motor rating isi n hp or KW. gaurav singh rajwar 10-21-2014 01:53 AM Electrical outlets We have an electrical fireplace. Whenever it is on one of my outlets get hot in the kitchen. Can you give me some answers? Thank you. 8 Pat 10-13-2014 04:19 PM Neural This is a very good for an electrical engineer i have question what will happen if i am using ground as a return path instead of neutral Rahul prajapat 10-12-2014 09:49 PM EE Thanks Sir. It isvery much usefull. Priya Ranjan Panigrahi 10-12-2014 12:27 PM nice Sir it is very usefull.i need many q&a from u. kasinath rout 10-3-2014 06:21 AM eee its very knowledgeful satyendra kumar 09-30-2014 07:42 AM Qfactor What is a Qfactor? Er.vijay nayee 09-6-2014 11:45 PM electrica maintenance sensitivity of elcb pwr. about mcb ratings pwr. earth resistance and earth compounds pwr. what is earth ldr pwr? transformer and related formulas pwr. what is the nature of electrons pwr? use of ballast tube light pwr. cable size and ampere ratings pwr. lesole kabo modise 08-29-2014 06:07 AM Electrical How can we know supply line is ac or dc????? Pragnesh 08-16-2014 02:37 AM hi Plz explain the protections of alternator Pramod 07-4-2014 09:41 AM electrical eng why use earthig and neutral use for earthing replace neutral. gajendra 06-25-2014 08:02 AM Electrical Eng. Why a single -phase induction motor not an inherently self -starting machine? indrajeet 06-15-2014 01:48 AM eee Pls give a quastions as per topic.like circuits basics t/f induction motors power system syam 06-8-2014 01:19 PM eee Pls give a quastions as per topic.like circuits basics t/f induction motors power system syam 06-8-2014 01:19 PM electricl engnearing vpo bhadwar teh nurpur distt kangra hp manoj kumar 02-9-2014 02:05 AM commentment of the interview question this type of question can easily solved by the 1st year student. plz give a hard question ok tata. amiya 06-27-2013 03:40 PM