Electrical Q&A Part-1

1)     Why ELCB cannot work if Neutral input of ELCB does not connect to ground?

  • 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 same 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 will 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.

2)     What is the difference between MCB & MCCB, Where it can be used?

  • MCB is miniature circuit breaker which is thermal operated and use for short circuit protection in small current rating circuit.
  • Normally it is used where normal current is less than 100A.
  • MCCB moulded case circuit breaker and is thermal operated for over load current and magnetic operation for instant trip in short circuit condition. Under voltage and under frequency may be inbuilt.
  • Normally it is used where normal current is more than 100A.

3)     Why in a three pin plug the earth pin is thicker and longer than the other pins?

  • It depends upon R=ρL/A where area (A) is inversely proportional to resistance (R), so if  area (A) increases, R decreases & if R is less the leakage current will take low resistance path so the earth pin should be thicker. It is longer because the The First to make the connection and last to disconnect should be earth Pin. This assures Safety for the person who uses the electrical instrument.

4)     Why Delta Star Transformers are used for Lighting Loads?

  • 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 So delta / star transformer is used for lighting loads.

5)      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 3-4 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.

6)     What is meant by regenerative braking?

  • When the supply is cut off for a running motor, it still continue running due to inertia. In order to stop it quickly we place a load (resistor) across the armature winding and the motor should have maintained continuous field supply so that back e.m.f voltage is made to apply across the resistor and due to load the motor stops quickly. This type of breaking is called as “Regenerative Breaking”.

7)     When voltage increases then current also increases then why we need of over voltage relay and over current relay? Can we measure over voltage and over current by measuring current only?

  • No. We cannot sense the over voltage by just measuring the current only because the current increases not only for over voltages but also for under voltage (As most of the loads are non-linear in nature).So, the over voltage protection & over current protection are completely different.
  • Over voltage relay meant for sensing over voltages & protect the system from insulation break down and firing. Over current relay meant for sensing any internal short circuit, over load condition, earth fault thereby reducing the system failure & risk of fire. So, for a better protection of the system. It should have both over voltage & over current relay.

8)     If one lamp connects between two phases it will glow or not?

  • If the voltage between the two phases 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.

9)     What are HRC fuses and where it is used?

  • HRC stand for “high rupturing capacity” fuse and it is used in distribution system for electrical transformers

10)  Mention the methods for starting an induction motor?

  • The different methods of starting an induction motor
  • DOL:direct online starter
  • Star delta starter
  • Auto transformer starter
  • Resistance starter
  • Series reactor starter

11)  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.

12)  Why most of analog o/p devices having o/p range 4 to 20 mA and not 0 to 20 mA?

  • 4-20 mA is a standard range used to indicate measured values for any process. 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 100 psi or full scale. Due to any problem in instrument (i.e) broken wire, its output reduces to 0 mA. So if range is 0-20 mA then we can differentiate whether it is due to broken wire or due to 0 psi.

13)  Two bulbs of 100w and 40w respectively connected in series across a 230v supply which bulb will glow bright and why?

  • Since two bulbs are in series they will get equal amount of electrical current but as the supply voltage is constant across the Bulb (P=V^2/R).So the resistance of 40W bulb is greater and voltage across 40W is more (V=IR) so 40W bulb will glow brighter.

14)  What happen if we give 220 volts dc supply to bulb or tube light?

  • Bulbs or devices for AC are designed to operate such that it offers high impedance to AC supply. Normally they have low resistance. When DC supply is applied, due to low resistance, the current through lamp would be so high that it may damage the bulb element

15)  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.

16)  What is reverse power relay?

  • Reverse Power flow relay are used in generating stations’ protection.
  • A generating station is supposed to feed 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.

17)  What will happen if DC supply is given on the primary of a transformer?

  • Mainly transformer has high inductance and low resistance. In case of DC supply there is no inductance, only resistance will act in the electrical circuit. So high electrical current will flow through primary side of the transformer. So for this reason coil and insulation will burn out
  • When AC current flow to primary winding it induced alternating flux which also link to secondary winding so secondary current flow in secondary winding according to primary current.Secondary current also induced emf (Back emf) in secondary winding which oppose induced emf of primary winding and thus control primary current also.
  • If DC current apply to Primary winding than alternating flux is not produced so no secondary emf induced in secondary winding  so primary current may goes high and burn transformer winding.

18)  Different between megger and contact resistance meter?

  • Megger used to measure cable resistance, conductor continuity, phase identification where as contact resistance meter used to measure low resistance like relays, contactors.

19)  When we connect the capacitor bank in series?

  • We connect capacitor bank in series to improve the voltage profile at the load end in transmission line there is considerable voltage drop along the transmission line due to impedance of the line. so in order to bring the voltage at the load terminals within its limits i.e (+ or – %6 )of the rated terminal voltage the capacitor bank is used in series

20)  What is Diversity factor in electrical installations?

  • 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. Diversity factor is usually more than one.

21)  Why humming sound occurred in HT transmission line?

  • This 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.

22)  Why frequency is 50 hz only & why should we maintain the frequency constant?

  • We can have the frequency at any frequency we like, but then we must also make our own motors, transformers or any other equipment we want to use.
  • We maintain the frequency at 50 Hz or 60hz because the world maintains a standard at 50 /60hz and the equipments are made to operate at these frequency.

23)  If we give 2334 A, 540V on Primary side of 1.125 MVA step up transformer, then what will be the Secondary Current, If Secondary Voltage=11 KV?

  • As we know the Voltage & current relation for transformer-V1/V2 = I2/I1
    We Know, VI= 540 V; V2=11KV or 11000 V; I1= 2334 Amps.
    By putting these value on Relation-
    540/11000= I2/2334
    So,I2 = 114.5 Amps

24)  What are the points to be considered for MCB (miniature circuit breaker selection)?

  • I(L)x1.25=I(MAX) maximum current. Mcb specification is done on maximum current flow in circuit.

25)  How can we start-up the 40w tube light with 230v AC/DC without using any choke/Coil?

  • It is possible by means of Electronic choke. Otherwise it’s not possible to ionize the particles in tube. Light, with normal voltage.

26)  What is “pu” in electrical engineering?

  • Pu stands for per unit and this will be used in power system single line diagram there it is like a huge electrical circuit with no of components (generators, transformers, loads) with different ratings (in MVA and KV). To bring all the ratings into common platform we use pu concept in which, in general largest MVA and KV ratings of the component is considered as base values, then all other component ratings will get back into this basis. Those values are called as pu values. (p.u=actual value/base value).

27)  Why link is provided in neutral of an ac circuit and fuse in phase of ac circuit?

  • Link is provided at a Neutral common point in the circuit from which various connections are taken for the individual control circuit and so it is given in a link form to withstand high Amps.
  • But in the case of Fuse in the Phase of AC circuit it is designed such that the fuse rating is calculated for the particular circuit (i.e load) only. So if any malfunction happens the fuse connected in the particular control circuit alone will blow off.
  • If Fuse is provided in Neutral and if it is blowout and at the same time Supply is on than due to open or break Neutral Voltage is increase and equipment may be damage.

28)  If 200w, 100 w and 60 w lamps connected in series with 230V AC , which lamp glow brighter? Each lamp voltage rating is 230V.

  • Each bulb when independently working will have currents (W/V= I)
  • For 200 Watt Bulb current (I200) =200/230=0.8696 A
  • For 100 Watt Bulb current (I100) =100/230=0.4348 A
  • For 60 Watt Bulb current (I60) =60/230=0.2609 A
  • Resistance of each bulb filament is (V/I = R)
  • For 200 Watt Bulb R200= 230/0.8696= 264.5 ohms
  • For 100 Watt Bulb R100= 230/0.4348 = 528.98 ohms and
  • For 60 Watt Bulb R60= 230/0.2609=881.6 ohms respectively
  • Now, when in series, current flowing in all bulbs will be same. The energy released will be I2R
  • Thus, light output will be highest where resistance is highest. Thus, 60 watt bulb will be brightest.
  • The 60W lamp as it has highest resistance & minimum current requirement.
  • Highest voltage drop across it X I [which is common for all lamps] =s highest power.
  • Note to remember:
  • Lowest power-lamp has highest element resistance.
  • And highest resistance will drop highest voltage drop across it in a Series circuit
  • And highest resistance in a parallel circuit will pass minimum current through it. So minimum power dissipated across it as min current X equal Voltage across =s min power dissipation

29)  How to check Capacitor with use of Multi meter.

  • Most troubles with Capacitors either open or short.
  • An ohmmeter (multi meter) is good enough. A shorted Capacitor will clearly show very low resistance. A open Capacitor will not show any movement on ohmmeter.
  • A good capacitor will show low resistance initially, and resistance gradually increases. This shows that Capacitor is not bad. By shorting the two ends of Capacitor (charged by ohmmeter) momentarily can give a weak spark. To know the value and other parameters, you need better instruments

30)  What is the difference between Electronic regulator and ordinary rheostat regulator for fans?

  • The difference between the electronic and ordinary regulator is that in electronic regulator power losses are less because as we decrease the speed the electronic regulator give the power needed for that particular speed .But in case of ordinary rheostat type regulator the power wastage is same for every speed and no power is saved. In electronic regulator triac is employed for speed control. by varying the firing angle speed is controlled but in rheostat control resistance is decreased by steps to achieve speed control.

31)  What will happen when power factor is leading in distribution of power?

  • If there is high power factor, i.e if the power factor is close to one:
  • Losses in form of heat will be reduced,
  • Cable becomes less bulky and easy to carry, and very cheap to afford.
  • It also reduces over heating of transformers.

32)  What the main difference between UPS & inverter?

  • Uninterrupted power supply is mainly use for short time. Means according to ups VA it gives backup. Ups is also two types: on line and offline. Online ups having high volt and amp for long time backup with high dc voltage. But ups start with 12v dc with 7 amps. but inverter is start with 12v,24,dc to 36v dc and 120amp to 180amp battery with long time backup

33)  Which type of A.C motor is used in the fan?

  • It is Single Phase induction motor which mostly squirrel cage rotor and are capacitor start capacitor run.

34)  What is the difference between synchronous generator and asynchronous generator?

  • In simple, synchronous generator supplies’ 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.

35)  What is the Polarization index value?

  • Its ratio between insulation resistance (IR)i.e meager value for 10min to insulation resistance for 1 min. It ranges from 5-7 for new motors & normally for motor to be in good condition it should be Greater than 2.5 .

36)  What is Automatic Voltage regulator (AVR)?

  • AVR is an abbreviation for Automatic Voltage Regulator.
  • 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.

37)  Difference between a four point starter and three point starters?

  • The shunt connection in four point starter is provided separately from the line where as in three point starter it is connected with line which is the drawback in three point starter

38)  What happens if we connect a capacitor to a generator load?

  • Connecting a capacitor across a generator always improves power factor, but it will help depends up on the engine capacity of the alternator, otherwise the alternator will be over loaded due to the extra watts consumed due to the improvement on pf.
  •  Don’t connect a capacitor across an alternator while it is picking up or without any other load

39)  Why the capacitors work on ac only?

  • Generally capacitor gives infinite resistance to dc components (i.e., block the dc components). It allows the ac components to pass through.

40)  Why the up to dia 70mm² live conductor, the earth cable must be same size but above dia 70mm² live conductor the earth conductor need to be only dia 70mm²?

  • The current carrying capacity of a cable refers to it carrying a continuous load.
  • An earth cable normally carries no load, and under fault conditions will carry a significant instantaneous current but only for a short time most Regulations define 0.1 to 5 sec before the fuse or breaker trips. Its size therefore is defined by different calculating parameters.
  • The magnitude of earth fault current depends on:
  • (a) the external earth loop impedance of the installation (i.e. beyond the supply terminals)
  • (b) the impedance of the active conductor in fault
  • (c) the impedance of the earth cable.
  • i.e. Fault current = voltage / a + b + c
  • Now when the active conductor (b) is small, its impedance is much more than (a), so the earth (c) cable is sized to match. As the active conductor gets bigger, its impedance drops significantly below that of the external earth loop impedance (a); when It is quite large its impedance can be ignored. At this point there is no merit in increasing the earth cable size
  • i.e. Fault current = voltage / a + c
  • (c) is also very small so the fault current peaks out.
  • The neutral conductor is a separate issue. It is defined as an active conductor and therefore must be sized for continuous full load. In a 3-phase system,
  • If balanced, no neutral current flows. It used to be common practice to install reduced neutral supplies, and cables are available with say half-size neutrals (remember a neutral is always necessary to provide single phase voltages). However the increasing use of non-linear loads which produce harmonics has made this practice dangerous, so for example the current in some standard require full size neutrals. Indeed, in big UPS installations I install double neutrals and earths for this reason.

 

188 Responses to Electrical Q&A Part-1

  1. debasish ghoshal says:

    I am unable to download the softwares from zuddu.com as everytimes it says that the verification word is wrong although I am typing correctly every time. Please help.

    • eswar says:

      Excellent boss …….. thanks a lot … applaud for your good work..
      its very useful for electrical engineers.. once again thanks

      • ramana.d says:

        most of the people afraid about electrical once go through your books question and answers everybody feel we can learn…………….. thank you very much you fill confidence………in me….

  2. debasish ghoshal says:

    Plwease let me know how to download correctly.

  3. Benadict Joshua says:

    Sir I want to meet u I stay in bombay this is my contact number 8097440160 I have hunger for the knowledge u have

  4. santosh says:

    good blog , informative

  5. Jeelani says:

    Excellent Yaar…sorry Sir… Great collection.

  6. thanks sir…if possible up load electromagnetically protective relay…

  7. asha says:

    Extremely good effort.It was really very helpful for me…sir please i need ur help in getting the answers for many more questions…

  8. asha says:

    Excellent work…I am Asha.. I have lot of hunger for knowledge.. It would be very helpful for me in future…. Hats of to u sir…..

  9. asha says:

    Sir please mail me (Asha) the protection required for the distribution transformer and also where actually the fault occurs for which the protection is provided.It would be helpful if the complete detail is shown through the SLD and also explained in detail…… Regards, Asha

  10. srinu says:

    superb work.its really very useful notes.thanks a lot

  11. M P Singh says:

    Sir
    please sent me what is difrence of MCB, MCCB, RCCB, RCCBO whre are used

  12. M P Singh says:

    Sir
    Please tel me what is impdence in Transformer how mutch impedence for 315 KVA Transformer and how mutch transformer oil qty. required.

  13. dhanraj.m says:

    its really very useful………………………..

  14. K.Jothilingam says:

    Most useful informations .thanks for the effort taken to make others to share part of ur knowledge and experence

  15. M P Singh says:

    Sir

    Please tel me how calculate short circuit current of Transformer, HT&LT Cable, MCCB & ACB

  16. dhanraj says:

    sir i want to know what is ieee standards for tan delta testing and ieee standards for sfra testing for transformer testing

  17. pankaj says:

    thanks sir, great job…

  18. kesavan says:

    It is nice thing for all electrical peoples continue this job good for all

  19. Devendra Chavan says:

    Whats the reason for locating HV capacitor banks in a separate bay outside substation building.
    If specified in any standards please let me know.

  20. kesavan says:

    WHAT IS BACK EMF EXPLANE?

  21. kesavan says:

    HOW TO REDUCE THE BACK EMF?

  22. guru bheem rao says:

    why lightening arrestors ( surge arrestors ) fixed for say 11kv transformer is rated for 10kv?

  23. kids bedding says:

    I am currently studying Electrical Engineering at McGill University, however, I needed to take a computer class and because of that I now realize that I am really starting to enjoy programming. My debate is now whether to switch to software engineering or to stick to electrical.
    Note:
    I don’t mind electrical engineering.
    I am really liking my programming class (JAVA).
    It is my first year.
    It is very easy to switch between software, electrical (and computer also) engineering because they are all in the same department (also especially since its my first year).

    My real problem here is that I hear people saying that an Electrical engineer has the opportunity to do a Software engineer’s job, but not vice-versa.

    Help is highly appreciated!

    • kishore says:

      right decision in right time is important. it seems ur details u mentioned , u neither intrest in computer …. nor u dislikes d electrical.so i suggest u if u ri good in computer programing u shift to computers nor u complete degree with present one and go software job.software allways welcomes aweel programmer irrespective of their stream.
      gud luck take a right decision of ur own.

  24. Santosh Kumar says:

    IT IS VERY USEFUL. FOR SPECIFIC USE..I WANT TO ASK ..
    IF IN 33KV SUBSTATION, CT OF ONE PHASE IS BURNT THEN HOW THE POWER SUPPLY CAN MAINTAIN IN EMERGENCY PROVIDED ALL EQUIPMENT SAFE?

  25. very good source of technical information relative to electrical circuits…..
    can I have question? here it is..
    what will happen to my power consumption if 2 of the 3 current transformers used in three phase metering is PURPOSELY shorted, it is in effect using only one current transformer for the said 3 phase metering… IS MY KWH CONSUMPTION REDUCED TO 1/3? WHY?

    THANKS,

    OSCAR A.,MENDOZA

  26. Edward says:

    Pls, i want 2 know d function of a feeder pillar and lighting kiosk for d operation of streetlights and how to calculate the number of streetlights a 60kva generator can take.

  27. Muhammad Aslam Butt says:

    Reasons of high current in power transformer body ground wire ?

  28. Muhammad Aslam Butt says:

    Nice way of sharing technical knowledge. I liked it. Please keep it up & reply my above query

  29. Ashlesha says:

    Can a trasformer of 200 kvA & a DG set of 250 kvA be installed on a single platform? What is the minimum distance to be maintained while installing?

  30. Hemrajsinh D. Chudasama says:

    It is a good attempt to share knwoledge bet’n Engineers. I realy apriciate your knowledge of Electrical Engineering . Very rare persons shares his knowledge with others But You are different Boss!

  31. vijay says:

    practically what amount of flux would be there in induction motors & transformer (or max flux density)

    • Sandeep Kumar Pradhan says:

      I really thankful to him who creat this page. This page not only for me but also for every electrical student is very useful. I want more and more question with answer u share on this page.

  32. vijay says:

    ractically what amount of flux would be there in induction motors & transformer (or max flux density)

  33. raghu m says:

    nice job sir..

  34. vinay kumar says:

    Sir,
    Most useful informations for all the electrical engineers and other,
    i cant’s load “electrical calculation excel sheets’ so,
    sir r u sent all the maximum “electrical calculation excel sheets’
    on
    E-mail: er_vinaykumar123@rediffmail.com
    and…..

    Thanks
    Vinay kumar
    09953036104

    .

    thanks sir, great job…

  35. Patel mitul says:

    It imaginig collecton…and really happy after read i know what is electrical….thanks……

  36. deepak jha says:

    please provide the link of book for electrical equipment testing & commissioning.

    thnx

  37. Mahesh says:

    Extrordinary gesture of knowledge sharing;Indeed beneficial to many Engrs.
    Thanks&Regards
    mahesh

  38. far_east says:

    hello..i try to find what answer function in electrical

  39. Satyanarayana Murthy says:

    We have 63 KVa transformer, Transformer out put is connected 3 * 7.5 HP ans 2*5 Hp water pump Motors,
    Same line we extended ( with 35 sq.mm Alu.conductor ) nearly 2000 meters. At this point we have requirement of 3 * 5 Hp water pump motors.
    Present problem is If we switch on all the three ( 3 * 5 HP ) extended line motors, motors are not running, even near by motors stopped fully also.

    That means we are loading the transformer with 3 * 5 HP motors (with distribution line is extended) only. Please suggest us.

    Can we connect capacitor bank at the end of distribution line or shall we put any other step up transformenr ( nearly 15 to 20 Volts )

    • Please give data of Your Receiving end Voltage before Starting Motors at Tail end and Voltage after Starting Motors.
      Need Data of Voltage Deep.Motor Starter.
      Required to study Voltage Drop Calculation.

      • parameshwar says:

        Dear Jignesh sir,Good Morning… I am working as a electrical engineer…I dont know how to calculate the size of HT cable..I am requesting you to please give me the answer for my question..
        Please send me the answer to mail id: parameshvkr@gmail.com
        I am expecting a positive reply from you..please send me the answer sir..

      • Click the Page of “Electrical Tool” of this Blog. Here You get sheet for Calculation Size of LT/HT Cable.

  40. Nagaraju says:

    Give 2-phase motor power formula

  41. OP KHATRI says:

    Its a very very supportive stuff for electrical personal.
    I treat this a BHAGWAT KATHA on behalf of them.
    with profound regards,

    O.P.KHATRI,Kota (Raj)
    9414393194

  42. neeraj says:

    its awesome question and answers thanx of lot sir.

  43. BASAVARAJ says:

    What is power factor,how to do it calculation for capacitor banks and one capacitor failes what will happen.

  44. mynsiem says:

    how to know the cable size if suppose the carrying current is 400A???? is there any formula???

    • There is no any FORMULA but there is Thumb Rule for Remembering
      For Cu Wire (<300 Sq.mm)=6X wire Size(Sq.mm)
      Ex. For 2.5Sq.mm Cu wire capacity=6X2.5= Appro 13Amp. for 1Sq.mm Wire=6X1= 6Amp
      For Cu Cable=4X Cable Size(Sq.mm)
      Ex For 2.5Sq.mm Cu Cable capacity=4X2.5= Appro 10Amp

      • Wael Haddad says:

        First of all thanks for your reply, but I’d like to add:
        this is in general but for accurate calculation we must go back to cables manufacture catalogs, taking inro account the derating factor for the site condition

        Best Regards

      • jithin says:

        1mm dia conductor carry 4.25 amp then .23 amp conduct 1 amp,,,,, so 400 amp need 400*.23 amp = 92 mm= 9.2 cm dia conductor need to transmitt 400 amp….. is it wright jignesh sir

      • You can not do such type of Mathematical assumption …You have to refer Cable Rating Cataloger for that..
        Transmission of Current (Amp) depend upon not only Size of Cable but mainly
        =Distance
        =Type of Load
        =Type of Medium (Air/Ground)
        For instant memorization of Current Vs Size of cable I normally use one Thumb Rule (don’t apply above Math formula for this):
        (1) For Cu Wire 6 Amp for each Sq.mm Example. 2.5 Sq.mm wire may carry 6X2.5=15 Amp
        (2) For Cable 4 Amp for each Sq.mm Example: 2.5 Sq.mm Cable may carry 4X2.5=9 Amp

      • subasish says:

        I would like to know what should be minimum IR reqmt for 11 kv motor ?

        subasish

      • Bishnu says:

        what is it for the aluminium cable..??

    • jithin says:

      sir mm2 means area na,,, if we want in guage? then how to calculate

  45. DOUBT says:

    WHETHER LIGHTING TX SEC NEUTRAL SHALL BE EARTHED OR NOT

  46. NIRBHAI SINGH SOHI says:

    WHAT SHOULD BE THE EARTH RESISTANCE OF 11 LINE H-POLE ?

  47. Yes it shoud be earthed. Else neutral point shall shaft and cause unbalance in supplies to the repective phases, also leading to harmonics/ dips/ swells in the supply

  48. rerally nice collection

  49. Ashish Chauhan says:

    what is the difference between capacitor and battery

  50. j.k.raman says:

    what is the formula when power factor is neglected when current flows from sub station to destination station

  51. Gilbert says:

    Good work buddy,,,,,must read before going for interview

  52. sandeep desai says:

    what is the impedance of transformer.?

  53. HordHord says:

    Sir,
    Please advise how to do the O/C setting in the Main Switch Board.

  54. Priti says:

    Very nice collection………Pls tell me from where i can get standards for Control Panels ?

  55. Todimi Sreekanth says:

    Thanks for sharing knowledge..

  56. Saurabh says:

    Excellent collection sir

  57. sriramlaxman says:

    boss you did a excellent job

  58. manoj shah says:

    fantastic collection

  59. sunny says:

    really nice collection sir

  60. vamsi says:

    very useful collection for a electrical engineer, excellent work ………………..

  61. lova rajesh says:

    can we operate a d.c machine at less than unity powerfactor?

  62. ghanshyam says:

    thanks sir i proud of you

  63. jithin says:

    interesting tip- 1 kg U235= 4500 TONS OF COAL

  64. Sohel rana says:

    This is a great collection of questions for electrical engineers. I want to study for sub station design.Please sir give me a guideline to go ahead ..Thanks.

  65. kulvinder Singh says:

    what is different between ac &dc

  66. eduard says:

    nice and good

  67. Muhammad Farooq says:

    very informative. hats off!

  68. vinay.k.s says:

    nice and good

  69. santosh says:

    thank you so much

  70. Renu says:

    Please tell me the differences b/w measuring & protection CTs ?

  71. making nice article,its very useful to all indian engineers

  72. please explain p.i test of cable value?

  73. vijay prabhu says:

    Nice Blog & Very informative

  74. What is a double tester?can you explain to me.

  75. moorthykrishna says:

    hats up sir for sharing this.its realy useful for electical engineers.

  76. habeeb says:

    thank u so much for your contribution in Electrical field….we are gaining lots of knowledge through your blog.

  77. Farhan Haddadin says:

    Great job, keep the good work up.

  78. Vijay Kumar A says:

    very very nice blog….. It is very useful for every electrical person to gain more knowledge

  79. robin kumar. please help md to get notes. says:

    electrical notes

  80. aglourdu says:

    i realy ennjay nd knws a lot with dis,,,is realy superb tanx

  81. vasudevan says:

    good. These q and a hols good for basic technical skills

  82. ANWAR says:

    IT IS VERY HELPFUL FOR ELECTRICAL KNOWLEDGE .THANKS

  83. Vineet says:

    Dear Sir,
    Please provide in depth details of tan delta test on transformers, CT, CVT and cables.
    If possible please provide basic to advance working concept of distance protection for transmission line along with relay setting example.

  84. Raja says:

    Thanks a lot… Your blog helps a lot for a growing engineers like me… Our credits goes to you sir…

  85. Vincent sibeko says:

    love the webpage

  86. manikanta says:

    its great collection to gain the subject and very useful…very thanks

  87. balu says:

    sir please provide answer for this question. what happens if the secoundary winding of a 3phase step down transformer is short circuted to ground and what be the current and voltage values

  88. Preeti says:

    Sir please tell me what would happen if two electrical sources are connected in series?

  89. kanugula pradeep says:

    hi.sir i got 1 dought that is the star connection we have the nutral point and retern path also available but in delta connection how it possible plz reply

  90. Harish Rawat says:

    If we dont use fuse on neutral wire, Meter can burn ????

  91. kanugulapradeep says:

    i think that the fuse is safty perpas.shart ckt their is no fuse the meter must burn out in high fault condition only

  92. M.Tayyab says:

    How we can increase our 220 volt up to 3000 as well as frequency from 60 Hz to 2500 Hz.
    I need a detailed answer kindly help me by giving a suitable answer.

  93. Naresh Ahlawat says:

    Dear Sir,
    when stepdown transformer 33KV into 230V input traminal in three R Y B and output traminal is four R Y B N just time cennction of 4th wire

  94. D H Gandhi says:

    What will happen if PVC strip falls on 3ph 11 insulated libe bus ?

    • Just experiment and see what Happen..
      I am here to share Technical knowledge only not for testing of my knowledge/Ability.
      If PVC Material falls on PVC insulated Bus/Cable ..What Happen !!!!!
      Ask question such that every one can gain knowledge rather than wasting of yours,mine and reader’s Time..
      Thanks ..

      • D H Gandhi says:

        It is not wasting time , In our company it was occurred and found PVC strip burnt . WHY ?

  95. Muthu says:

    Nice Work.
    Thank You Sir

  96. yuny says:

    What happen to the electricity in the first socket when Live (L) cable from MCB is cut off? Explain it.

  97. yuny says:

    What happen to the electricity in the ring circuit if we use MCB with a lower current rating? Explain it.

  98. yuny says:

    State the reason why we need to combine the two Live (L) cables into one MCB.

  99. yuny says:

    Give twi different between radial and ring circuit.

  100. dinesh says:

    i would like to learn to design electrical network for high rise building. not like designing socket or switches and lighting. it should be design from db then mdb to Transformer , i searched google but i could net get correct & easiest one. so kindly give any guide or Internet link for that designing electrical network

  101. aaakkkkk says:

    why we should increase power factor of a machine????(mostly asked in viva voice?

  102. kushvendra says:

    Dear sir,

    4 pole 200A MCCB can take 200A current on each pole or it will take current all inclusive 200A.
    Please clear the doubt.

  103. Tripurari Singh says:

    Sir i want to know what changes occure in 3phase distribution transformer no load loss after using it 2 to 3 years. Thanks

  104. Manivannan says:

    why neutral busbar size is same of the phase busbar size upto 200A ,Any Reasons kindly clarify my doubt

  105. PRABHAT KUMAR ROUT says:

    Hai, dude you did a great job.The information you are collect is very useful to me. “thanks” keep it up.

  106. PRABHAT KUMAR ROUT says:

    Dear sir, you did a great job.The information you are collect is very useful to me. “thanks” a lot.

  107. Varatharajan.V says:

    How to size the neutral cable of Distribution transformer. Transformer is 11/433V ang NGR is 330ohms, 750mA.

  108. pervez says:

    dear sir, why a three phase transformer ht/lt coils burnt on no load

  109. kapil says:

    Why we should disconnect the neutral if the load is fed through RCCB/ELCB ???

  110. Manan says:

    can’t understand armature and field winding

  111. Praful says:

    Very very good question and answer

  112. Ramu says:

    i need the answer for the following question.,
    What happens when a phase has been cut off in a 3Phase transformer.will it supply three phase supply or what happens(delta to star transformer)

  113. Stephen N Kimathi says:

    I really like this.Please be inboxing me this kind off stuff.Just a request.

  114. amjad shakikh says:

    DIFFERENCE BETWEEN 4 POLE & TPN MCB ?

  115. Venkat says:

    Great job ,I can’t say single word for thanks………after that

  116. Abhinav says:

    tnkuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu sirrrrrrrrrrr
    for this…………..

  117. Misrak says:

    what is minimium clerance distance b/n 132kv powerline and aircraft flight path on air?

  118. lalit says:

    Good Morning Sir, i prajapati from Surat. Can you give brief description calculating HT vs LT circuit breaker current
    countion. If supply is 11KV or 33KV and transformer can be 4to 5 mva..Expedite soon..thanks

  119. iqbal says:

    M.iqbal ,Pakistan, your work is very good for workers of power plant and electrical family.pl you are increse the solutions of many other problums of turbo generator
    thanks

  120. Jatin Patel says:

    What is the standard value of PI for Transformer??

  121. eswar varma says:

    Thanks & usefull for all electrical engineers. and one thing to ask u sir.
    i need to learn schematic drawings plant give me suggetions boss.
    waiting for ur reply sir.
    Regards
    Eswar varma.

  122. yagnik says:

    Dear sir,
    In our country/world ,There r many types of Transmission pole for transmit the energy.
    so how can we understand that voltage rating regarding its type of transmission pole.

  123. Neeraj Yadav says:

    Thanks alot

  124. lakshmireddy says:

    please explain about building wire estimation foe single phase and three phase systems

  125. husen says:

    thank you sir its splendid job pls sent me on my email address multitester useing method fault finding with multitester sir you better know about multitester its same our electric like taparia tester but looking just diffrent shape
    best regards

  126. Sagar says:

    sir i’m unable to point out the difference between line voltage and phase voltage whenever its given in any powe electronics or machine or system subjects.. i still have doubt about where to use line voltage and where to use phase voltage..

  127. What is the standard time to run any electrical motor from star to delta time?.

  128. It is useful to all of us who need to learn every time.

    One of the question related is what is the maximum time limit to convert from star to delta feeder.
    Application is to run the 3phse squirrel cage induction motor on star-delta feeder.

    The timing is not as per tailor made or may very as per industry opinion. we ask as per standard or may have rule.

  129. k siva says:

    dear sir,
    i am siva
    three phase AC motor no load current how to calculate and if any formula available please give me

  130. k siva says:

    dear sir
    how to calculate required cable size suitable current. if any formula available please give me sir

  131. harikrishna says:

    very good interesting detailed subject

  132. kesar singh says:

    Sir tell me at what direction of current should be kept in directional over current relay ( micom P442 relay) when current is following from 400kv to 220kv or vice versa

  133. david says:

    how to find the earthing will work properly how will check it

  134. Sagar says:

    Hello sir..
    I have a question regarding protection scheme of power system..
    Q) why are we providing only 80 % protection in zone 1 and only 20% in zone 2?
    Q) what is overlapping phenomena in this protection scheme?

  135. SIR,

    WHETHER THE MCB SHOULD TRIP, IF MAINs (LINE) IS SHORTENED WITH EARTH WIRE.

  136. dear sir please get me know about how capacitor and inductor work in dc circuits ? whats the response by capacitor and inductor in dc supply?

  137. sabariprakash says:

    Sir, currently we have changed Bearing on Drive side & Non drive side in one motor 160KW LT .
    after that we are facing problem of Earth leakage fault frequently but this motor is delta connected one.

  138. sabariprakash says:

    what is mean by dynamic braking resistance??

  139. sabariprakash says:

    I need to Replace DC MCB with AC MCB?
    please tell the selection of AC MCB for DC supply.
    For example IF 24V DC with 2A current DC MCB to be replace with AC MCB??

  140. D H Gandhi says:

    pl open motor there will be some thing metal part between rotor and stator
    There will be mimimum clearance between live cable/link to motor body

  141. saravanan says:

    Nice job.
    I want to know Why we are mentioning the transmissions as 110 kv,66kv,33,kv,… like that.. Apart from standard Is there any other reason…

  142. Austin says:

    what will happen when
    100 watt, 60 watt, and 40 watt bulbs
    are connected in series when the
    following is done. 1)when 100watt
    bulb is remove?, 2) when 60 watt bulb
    is remove?, 3) when 40watt bulb is
    remove? 4) When you interchange any
    of the two bulbs?

  143. Ronald Quadros says:

    Excellent Jignesh Sir

  144. jaspreet says:

    Sir
    I want to know how to calculate Total productivity in watt of a 125 kva dg. If we are using following
    3 phase energy meter
    200/5 CT
    Then what is the formula to calculate thr KWH of dg

    • dear,,,,
      3 Phase energy meter is used for measuring KWH (Unit) and you written that You are using 3 phase energy meter(which measured KWH) than Why you need formula to measure KWH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

  145. raza haider says:

    dear sir
    how the increased diameter of conductor reduces the electrostatic stresses b/w the conductors, which in turn reduces the corona effect in power transmission lines?

  146. Avdhesh Kumar says:

    Dear Sir,
    Why we use double run cable in 3-phase, star delta starter type motor for feeding it.

  147. Rohit Ramteke says:

    Thanks Sir…for sharing such motivational things related to electrical.

  148. bramhanand dhawas says:

    sir capacitor bank of 2400 kvar , 3.3 kv i.e (400×6 kvar ) in delta fashion gives current of 398 amps per phase and line current is also same . but we provided the fuse rating of 270 amps 7.2 kv per phase.. my question is that why fuses are not blown out as current exceeded the fuse current level?

  149. surya says:

    What is the lux levels(area wise lighting) in oil&gas, power projects.

  150. SANDEEP RAWAT says:

    HOW TO CALCULATE SHORT CIRCUIT CURRENT FOR MCB IN HVAC

  151. milan rana says:

    Induction motor showing 4amp in star and 40 amp in multimeter when connected in delta why?

  152. R.Srinivasa Rao says:

    Sir,you are giving very valuable notes to all useful for career and personal devolopement.Thank you sir.

  153. Mistu Ghosh says:

    Why Transformer making sound during operation ?

  154. Rajesh says:

    What would happen if we connect a test lamp between earth & phase and is ckt is protected by ELCB?

  155. umesh rajpal says:

    How to calculate rating of mccb and contractors in three Phase unbalanced load.ie 80A, 50A and 65A

  156. gaurav khandelwal says:

    sir,
    how can we control power factor in industries where 2 phase machines are installed

  157. gaurav khandelwal says:

    sir can any circuit with components like capacitor, contactor, mcb or mccb be used in homes ……and what effect will it produce..

  158. Amrish Suthar says:

    With taking of maximum load of outgoing with margin of 20%.

  159. Prakash says:

    any one can share CCC of ACSR and AAAC conductors

  160. afsal says:

    Very thanks sir.. This paper is more helpfull for all electrical engineering students and also all electrical engineers.. again thank you sir.. may God bless you. .

  161. Keshav Sain says:

    Dear Parmar Sir,

    You have excellent storage of mind set for Electrical Fundamental and Engineering.

    I need your notes,

    How I can pay which is showing on blog.

    Regards,

    Keshav Sain
    Barmer , Rajasthan

  162. SAB says:

    what happen if we short the phase of the 230V,ac glowing bulb to the ground?

    NOTE: phase and neutral supply is connected to the bulb and the bulb is glowing….
    post ur ans soon….

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