I did not get selected but, still, I am sharing my overall experience of BARC interview OCES/DGFS 2019 for the reference or help of aspirants in the future.
Be patient in reading as a really long post follows but it’s worth your time. Trust me.
So, let’s get started.
This is a precise yet detailed account of my overall experience in the off-campus recruitment process of the prestigious organization named Bhabha Atomic Research Centre (BARC) under the Department of Atomic Energy (DAE), India in the discipline of Electrical Engineering (EE) for the post of OCES (Orientation Course for Engineering Graduates and Science Postgraduates).
BARC recruitment process
BARC recruitment broadly involves two steps:-
1. Screening through GATE Score or Online Examination Score conducted by BARC generally in the month of March in slots (my slot was on 9 March, 2019 3-5 pm). The Online Examination consists of 100 MCQ single-option correct questions with 4 options having 3 marks each and a penalty of -1 for wrong answers with a time limit of 2 hrs. Since I got screened on the basis of this, getting 170.5/300 after normalization where cutoff was 158/300 in 2019 for EE, a suggestion would be to make a proper selection of questions that are to be attempted since not all questions can be attempted and high accuracy is required. A candidate is just needed to clear the cutoff (independent of category) for that discipline to be shortlisted for the BARC interview.
2. Upon getting shortlisted for interview and seeing one’s name in the Discipline wise list PDF uploaded on their website, a candidate has to proceed in preparing for the BARC interview after choosing his scheduled interview slot from the slots available for that discipline – 8:30 and 11 am slots (that indicate reporting time) are generally available for a consecutive period of 10-12 days barring holidays for a particular discipline by logging in on the website and choosing from the allotted dates in the coming week after the display of registration numbers with name of those shortlisted for interview in Discipline wise PDF format on first-cum-first-serve basis. One can request for changing the BARC interview slot by citing genuine reason and sending it through Help Desk and generally as in my case, they help as there are plenty of slots allotted and a large number of students.
Once shortlisted for the BARC interview, only the performance in the interview matters and the weightage is fully on the interview and NOT on screening test criteria like Online Examination Score or GATE Score.
The interview is held in the BARC Training School Hostel, Anushaktinagar, Mumbai and candidates are required to reach the venue on time and report in the Multipurpose Hall of the same building for document verification after which an introduction (green) slip is issued, followed by biometric verification, giving of refreshment packet and waiting for one’s turn in the waiting room beside the classrooms where the interviews are held. Candidates are called in serially according to the serial number written on the introduction slip while issuing it.
My BARC interview experience was as follows:
Reported around 8:30 am on 21 May, 2019 (actual slot was on 13 May 2019 8:30 am but had got it shifted due to ongoing semester exam upon request), had serial number 17 on introduction slip issued around 10:30 am but after a patient wait, turn for interview came at 2:40 pm in Electrical Committee-4.
There were five members in the interview panel seated around a round table that included a male chairman C, three male members M1-M3 and a lady member L. On entering, I greeted “Good afternoon” to the members and was asked for the introduction slip by C. Then I was asked to hand over my document file to M1 as a custom just for verification and C started asking about some technical subjects of interest.
I mentioned the subjects in the order: Network Theory, Power Systems, Signals and Systems, Control Systems upon which C said and other members supported that since I have applied in the discipline of Electrical, I should mention core subjects upon which I said that I have not got enough time to revise the subjects properly as final semester exam ended last week. So they considered me as a fresher and thought that I had got my BARC interview slot rescheduled but still insisted on choosing core subjects and offered a choice between Machines and Power Electronics at which I replied that I will be more comfortable with Electrical Machines as I have dealt with it more than Power Electronics in the course.
Then some member, probably M1, asked which subject to start with. I told Power Systems, which they approved of and said that they would start with Power Systems, then ask from Machines and Control Systems and also touch upon Networks.
M1 started asking from Power Systems. What is a power system and there are so many devices around that deal with power, so are all of them are a part of the power system?
Answered that to be a part of the electrical power system, a device needs to operate and supply or receive power above a specified voltage level which is generally high voltage and not low voltage application like electronic devices, chargers, etc.
Next, what is the specified voltage level to be called high voltage?
Answered that voltages above 1 kV at which M1 looked satisfied and said that it is so as specified by Indian Standards.
Since Power Systems is too vast a core subject, M1 asked if I am thorough with Protection and when I said that I have studied it but not revised properly due to the shortage of time due to final semesters, I was asked which part I have revised and prepared. I answered confidently Power System Stability and this led to a discussion on the topics in Power System Stability.
M1: How many types of Power System Stability are there?
Answered Rotor Angle Stability, Voltage Stability, etc. upon which M1 had to say that what about the three types – Steady-state, transient and dynamic?
Answered that those are also the types of stability study when looking from a different aspect.
M1: How to distinguish and depending on what are these three different types required and based?
Answered that upon the type of disturbance or fault that occurs to the power system – the time or duration for which it affects the system and also its severity.
M1 did not look quite convinced and following this asked:
M1: What are the methods to determine Power System Stability?
Answered that by studying the variation of rotor angle or power angle delta with time after the occurrence of the disturbance graphically we can get an idea about if the power system remains stable or becomes unstable.
M1 asked about the analytic methods to check stability.
Seeing me unable to answer and pausing to think, he gave the subtle hint – Equal Area Criterion to which I agreed and was asked to explain the concept of determining stability graphically using Equal Area Criterion using a pencil on an A4 sheet of paper.
Answered by first stating the equal area criterion – that decelerating area should be greater than accelerating area for power system to remain stable and supported it by drawing a simple single line diagram with a single generator such that fault occurs in any one of the lines connecting it to the bus and cleared by the circuit breaker (CB).
When I started drawing the P-delta curve, I referred to Delta as rotor angle or power angle, upon which C asked why two names for the same quantity I explained by stating the definition of rotor angle as angle between rotor and synchronously rotating air-gap flux and power angle as phasor angle between terminal voltage and generated or excitation emf, then answered terminal voltage when asked which one is taken as reference, followed by answering “No” when senior member M2 questioned if rotor angle can be measured physically, and then proceeded with explaining equal area criterion upon which I used notations Pm for mechanical power then M1 questioned then what will be used to denote maximum power output (electrical) upon which I changed mechanical power input notation to Pmech and M1 objected saying that standard notations should be used. I made another mistake of not taking electrical power output as zero during fault but a very low non-zero value in place of that so was rectified as I also noticed that Pe=0 during fault as there is a single generator to supply power.
Further explained by taking a certain Pmech and holding it constant during the period of stability study, drawing pre and during fault P-delta curves and shading the decelerating and accelerating area and supporting it by saying that if decelerating area<accelerating area alternator rotor will accelerate continuously and lose synchronism with rest of the generators in the system so stability will be lost else if, decelerating area>=accelerating area, nothing as such will happen and the power system remains stable.
Then, M1 had to say that I am presenting an inequality then why the name Equal Area, to which I retorted that equal area is the limiting case in going from instability to stability and it comes in the form of equality so it is important to be considered.
M1 looked satisfied and continued asking about critical clearing angle – its definition, expression and position on the Delta axis on the P-delta curve.
I marked critical clearing angle, deltac on the graph and replied that I do not remember the exact expression but can derive it by solving the integration but M1 told that a simple expression exists that I should have remembered.
Then I defined deltac as the maximum time within which the circuit breaker should operate to keep the power system stable.
M1 asked operation means open or reclose in this case, I answered open and was asked to think again at which I got confused and after contemplating a while on this, I answered reclose and then again open, so was asked to think about it later. That was it from Power Systems.
Going on to Machines, the members wanted to know if I was okay with transformers and I said yes.
C asked the principle of operation of the transformer.
Answered it after drawing the core, primary and secondary winding, the marked direction of the current, core flux and voltage polarity. When voltage is applied to the primary winding, core flux circulates and links with the secondary winding.
C asked why does the flux circulate and get linked and it implied as if they were looking for a keyword which was the electromagnetic law that governs it and so I replied Faraday’s law of electromagnetic induction.
C said alright and to continue with the explanation and when I proceeded to polarity of emf induced due to time-varying flux (in between M1 asked me to clearly specify which kind of alternating voltage source connected at the primary to which I said it is, of course, a sinusoidal waveform at which M1 said it can mean square waveform as well unless otherwise specified) I had to state Lenz law – the statement – the effect of emf induced emf will oppose its cause, the applied voltage.
C asked if voltage or current was responsible for core flux upon which I said, the current – magnetizing current sets up the core flux and M1 asked how did I mark the direction of flux and I answered using Right-Hand Thumb Rule.
Next, M2 asked what would happen if a load is connected at the secondary.
Answered that due to emf induced in the secondary winding and as the circuit is closed, a current will flow that will circulate a flux that will oppose the original flux.
C and other members asked whether that flux will always oppose the primary flux or can be additive as well.
I said the flux due to the flow of current in secondary winding cannot be additive in accordance with Lenz law. Then was asked what would happen after that. I answered that a component of this secondary current would be reflected into primary winding and more current will be drawn from the source to maintain the core flux, as on connecting a load at the secondary, the core flux would reduce momentarily due to oppositely directed flux due to the current flowing in the secondary winding.
Then, M2 and other members demanded the answer to what would make the core flux remain almost constant upon which repeated my earlier answer and then looked clueless, a subtle hint was given by M2 that which electrical parameter will change instantly on connecting load and when I could not catch this hint, they said induced emf will change which would change the difference between applied primary voltage V1 and primary induced emf E1 (said by M1) and I cheerfully started answering that as E1 is almost equal to V1 by KVL and it cannot change instantaneously so core flux will also not change and they confirmed that this is indeed the reason but in practice there is also a voltage drop which is the difference between V1 and E1, and I continued that then also, if core flux reduces instantaneously, induced emf will reduce and that would increase the difference between V1 and E1 leading to drawing of more primary current and in this way, the core flux gets restored gradually to its initial value.
Other members thought about wrapping up the interview at this stage but C decided to give more chance and test my basics further.
So, C asked which is the core material used in the transformer and the reason for using it.
Answered that CRGOS primarily because of its high permeability to magnetic flux and low leakage.
C: What would happen to the magnetizing current, emf induced in the secondary and core flux if I remove a small portion of the core material and space gets occupied by air?
Answered incorrectly at first after thinking for a while that magnetizing current and hence, core flux will increase but soon after C rectified and told me to think of the analogy between magnetic and electric circuits. I could figure what he was implying and I corrected myself and said that an air path is of high reluctance and analogous to an open electrical circuit, so the magnetic circuit will offer overall high reluctance to the path of core flux and hence, it will reduce to a small value and that would decrease the secondary emf.
C was glad to hear this answer but a bit disappointed to see that I was not very clear and contradicted my earlier answer.
Around this time about 40 minutes were already over and lady member L took her turn to ask questions from Control Systems.
L had already written three open loop transfer functions of the form K(s+1)/s(s^2+2s+2) (other two I did not solve and do not remember) and to simplify it added another pole at s=-2, asked to draw the root locus and the asymptotes.
I was on the verge of completing to draw when probably C asked about the other techniques used to determine stability in Control Systems in the frequency domain.
Answered that Nyquist plot, Bode plot, etc. Then was asked the simplest method of determining stability if pole-zero location is known.
Answered Routh criterion can be applied after forming the Routh array. C then asked if Routh criterion can be applied to check stability, what is the use of other frequency analysis methods like Bode plot, etc.
Answered numbly that Bode plot gives additional information like magnitude and phase spectrum in frequency domain but C asked how is it related to stability and seeing me think over it, gave a subtle hint that it gives information of gain and phase margin. I nodded and C further asked to explain the gain and phase margin and its importance.
Answered by drawing the simple polar plot and explaining that gain margin is the gain by which the system gain has to be multiplied to reach the verge of instability and it is calculated at phase crossover frequency while phase margin is the angle that the polar plot makes with negative real axis with the point (-1,0) on it. Then L asked why (-1,0) is the point of consideration on Nyquist or polar plot.
Answered that characteristic equation is GH+1=0 or G=-1 for unity negative feedback system, that is why so and also it is called the magnitude and angle criteria.
Control Systems questions got over with this, followed by questions on Network Theory from M3 who was almost silent till now.
M3: Have you studied Two-Port Networks?
Answered that yes, I have.
M3: What is a two-port network?
Answered that it is a network that consists of two ports or two pairs of terminals characterized by a set of two independent variables and two dependent variables, the variables being voltages and currents at the two ports.
M3: Which are taken as the dependent and independent variables?
Answered that depending on the application, two are taken as independent and the other two are expressed in terms of them. Depending on the selection of the two independent variables, six such parameters are possible – Z, Y, ABCD or transmission parameters used in transmission line modeling, inverse ABCD, hybrid parameters H, and G.
Then M3 further asked why so many parameters are there and are they at all needed for different applications.
Answered that all the parameters are not suitable to convey information for a particular application and in fact, not of them can be defined for specific applications.
M3 somewhat accepted this answer and got inclined towards asking about a practical application of what I had just stated. He asked me to draw a series resistor open on both ends and to do two-port network analysis of it, which parameter will be suitable, etc.
Answered by writing the Z parameters and M3 told to write the equations and the conditions to find the parameters at which I wrote V1=Z11*I1+Z12*I2 and V2=Z21*I1+Z22*I2 so, Z11=V1/I1|I2=0, Z12=V1/I2|I1=0, Z21=V2/I1|I2=0, and Z22=V2/I2|I1=0 and as resistor is open on both sides, each of the Z parameters cannot be defined and tend to infinite simply implying open circuit. Instead, the equations can be written in terms of Y parameters I1=Y11*V1+Y12*V2 and I2=Y21*V1+Y22*V2 so, Y11=I1/V1|V2=0 =1/R, Y12=I1/V2|V1=0 =-1/R, Y21=I2/V1|V2=0 =-1/R and Y22=I2/V2|V1=0 =1/R will definitely imply that a resistor open on both ends is connected and give its value R.
The questions on Networks concluded with this followed by the last question from senior member M2.
M2: For connecting a 3-phase 10 hp motor to the supply, what all things are required?
Answered that an overcurrent relay with a setting a little higher than the starting current and a fuse with a rating several times the normal rated current would be required for protection and the type of load that the motor will drive also needs to be known.
With this question, my interview ended and while leaving M1 asked me if I had appeared for the Engineering Services exam. I said that I had appeared for ESE 2019 prelims but could not clear it, missing the cutoff by about 15-20 marks at which M1 smiled and said that he came to know about my appearing by going through my document file.
In this way, the panel members greeted me and announced an official end to my BARC interview and I came out to realize that my interview went on for about an hour as the time at which it got over was recorded as 3:37 pm by the person seated outside, which was comparable to the average interview time of 40-50 min for each candidate on that day.
Hence, I got a great experience of my first off-campus at BARC that was indeed a purely technical one (of a much better standard than campus technical interviews!) and enjoyed it as I got to learn a lot – my areas of weakness in the basic concepts and how to improve and rectify mistakes.
Though I did not get selected (with results being declared in the last week of June) as I fumbled in the basic things but could catch their hints and rectify many a time, this one hour of BARC interview experience will be a valuable asset to carry and cherish in the future.
Tips for BARC Interview
A suggestion or tip with regard to this BARC interview would be to keep calm, be thorough with the basics of the subjects that the candidate is going to tell the panel members to ask questions from, be mentally present and suggest one’s approach to the questions asked, irrespective of thinking too much whether they are correct or not and hesitating, as hints or clues are provided by the members to help and comfort the candidate, admit if one does not know about something and not act over-smart as the panel members are veterans, ask questions or doubts from their side if any and not go with the flow every time.
I tried to include all of the details about the selection process and questions that were asked but regret having missed any because of forgetfulness and mistakes that I may have committed unknowingly while writing this. Lastly, all the best for the whole process from screening until the interview and have an enriching and wonderful experience at BARC regardless of whether you get selected or not.