Campus Recruitment – Technical Interview – Electrical and Electronics Engineering
Electrical and Electronics Engineering
1) Explain the working principle of a battery. List the batteries used in cell phones, laptops and electric vehicles with their voltage ratings and operating characteristics.
2) Classify various types of storage cells. Explain the working principle of lead acid battery.
3) Define operating and restraining torques. Write the expression for operating and restraining torques of an admittance relay.
4) List the different protections used for motors. What is the main function of an over load protective device to protect the motors?
5) What is meant by single phasing? How to detect single phasing in a motor?
6) What are the effects of single phasing of a squirrel cage motor? During single phasing, maximum to nominal torque ratio drops to?
7) Explain operation of balanced voltage longitudinal differential protection. Draw how the secondaries of CTs are connected in a balanced voltage longitudinal differential protection of transformer.
8) What are the required properties of CTs when using for indicating, metering and protection purpose?
9) What is meant by accuracy limit factor of current transformer? List out standard accuracy limiting factors.
10) Classify voltage transformers. List out the limits of errors in VT for measuring and protection purpose.
11) Draw the equivalent circuit diagram and vector diagram of potential transformer. Explain the causes of phase angle error and ratio error.
12) Define instrument security factor. Explain its significance.
13) What is meant by rated short time thermal current of a current transformer? List out the factors on which it depends.
14) Name different types of CTs used for protection and their purpose.
15) Define burden on CT and state the factors on which it depends.
16) What is the burden on the CT secondary with 1A compared to the CT with 5A secondary?
17) Explain the behavior of CT under transient fault condition. Explain the effect of CT saturation on impedance and overcurrent protection.
18) Explain the working principle of negative sequence relay. List out the functions of negative sequence current protection.
19) Differentiate between power transformer and distribution transformer. State the reasons for excessive flux densities in power transformers.
20) Explain how a thermal relay works. Draw thermal withstand curves for electric motor and thermal relay.
21) Explain the working principle of differential feeder protection scheme. Will the differential feeder protection scheme provides protection under double¬end power supply conditions?
22) Define a drive and state advantages of electric drive over other conventional drives.
23) Why do we need to consider rise in temperature in an electrical drive? What are the assumptions made for calculating rise in temperature in electrical drive systems?
24) Define a torque and differentiate between speed- torque characteristics of single cage and double cage motors.
25) Draw the typical performance characteristics of LV induction motor. List out the factors affecting the losses.
26) What is meant by commutation? Compare D.C series motor and D.C shunt motor in terms of commutating properties.
27) Explain the working principle of linear motor and state its applications.
28) Explain the working principle of air blast circuit breaker. Explain why resistance switching is never used with air blast circuit breakers.
29) What will happen if secondary winding of current transformer is kept open? Explain the reasons for the cause.
30) Classify different-types of measuring instruments based on working principles. Which of these principles is not used to design a wattmeter and which type of the instruments can’t be used for the measurement of both D.C and A.C?
31) List out the methods used for testing cables for short circuits, ground faults and open circuits.
32) Classify null detectors and state the main features of electronic null detectors.
33) Why do we use bridge measurements? Explain how
to reduce the errors due to thermal e.m.f in bridge measurements.
34) Why do we use arm ratios in bridge method of measurements? Explain how to decide the upper and lower limits for it.
35) Define installed capacity of a generating plant. What is the total installed electrical power generation capacity in India?
36) List the different standard voltages used for generation, transmission and distribution systems.
37) What is the approximate useful life span of a j transmission lines according to Indian standards?
38) Define load factor and state the order of normal residential or domestic load factor.
39) Explain the working principle of synchronous motor. Explain the effect of reversal of field current on the direction of rotation of the machine.
40) What is meant by plugging? Explain how plugging is done for synchronous motors.
41) Is the power developed in a salient pole machine is always greater than or lesser than the power developed by smooth rotor machine? Explain the reasons for it.
42) Define fractional pitch. Why do we prefer to have fractional pitch type of A.C machines?
43) Explain the working principle of repulsion motor. Explain what will happen if the load on a repulsion motor is increased beyond a certain value under which the reluctance torque cannot maintain the synchronous speed?
44) Out of synchronous machine, double cage induction machine, slip ring induction machine and D.C shunt machine, which machines is costlier for the same power output and state the reasons for it.
45) Explain the working principle of a D.C motor. What will happen if A.C supply is applied to D.C motor and explain the reasons for its effects?
46) How do you choose a rating of a pump? What eventually happen if we switch on a pump (induction motor) with 25% lower than its rated voltage?
47) What is the significance of reactive power in electrical power transmission system? Explain the methods used to inject the reactive power into transmission systems.
48) Classify electrical power transmission and distribution systems. What are the main criteria used for designing feeders and transmission lines?
49) Why do we need to maintain the power transmission system voltage within the limits? Where do we have to place the booster transformers to increase/decrease the voltage in a transmission lines?
50) Why and where do we prefer to use underground cabling? What is the general distance beyond which we don’t prefer to go for underground cabling?
51) Define the zero sequence impedance of a transformer. Draw zero sequence network circuits for different three phase transformers connections.
52) Classify different protection schemes used for : electrical distribution system & compare them.
53) List the methods of checking the instant of synchronization. What is the condition for maximum synchronizing power in the parallel operation of alternators?
54) What is hydrograph and mass cure? Explain their importance.
55) Classify hydro turbines and draw the operating characteristics of water turbine.
56) What is the main function of turbine? Differentiate between impulse and reaction turbines.
57) Classify hydro electric power plants. List out the factors on which the hydro electric power plant output depends.
58) Explain the basic working principle of magneto hydro dynamic power generation.
59) What is an inter-connector? State the factors on which the power transmitted through the interconnector depends.
60) What are the advantages of combined operation of power plants? Explain how reactive power is controlled in an inter-connected system.
61) State the necessary conditions for connecting alternators in parallel. Explain how the total kW load is divided between alternators connected in parallel.
62) What are the factors on which the amount of excitation of an alternator mainly depends? Explain the effect of increasing the excitation of one of the alternators operating in parallel for sharing the load equally.
63) Explain the working ^principle of synchronous generator. Draw salient pole alternator phasor diagrams when it is operating under steady state, transient and sub-transient conditions.
64) Explain the effect of increasing the driving torque of one of the alternators operating in parallel.
65) Explain the effect of changing speed of one of the two alternators connected in parallel.
66) Explain the effects of varying the excitation of a synchronous machine connected to infinite bus-bars.
67) Explain the effects of varying the torque of the prime-mover of the synchronous machine connected to infinite bus-bars.
68) Define synchronous capacity and short circuit ratio.
69) What is the condition for economical loading of alternators operating in parallel? Explain how is an alternator made to share the load after synchronizing?
70) Why do we use a synchroscope? Name the motor used in synchroscope.
71) Define incremental losses and penalty factor. Explain their significance.
72) What is a heat rate curve? Draw typical heat rate
curves for a steam plant and hydro power plant.
73) Explain the co-relation between economic load dispatch of power systems and load frequency control.
74) What do you understand about penalty factors and B-coefficients of economic operation of power systems?
75) Why do we need to maintain power system frequency and voltage remains constant or within the limits?
76) Explain flat frequency control and tie line frequency control methods.
77) Name the type of frequency control system suitable for an interconnection of a small system and a large system.
78) What is the purpose of a national power grid and state its tasks.
79) What are the objectives of automatic generation control? Draw the steady state load frequency
80) characteristics of a speed governor system, i 80) What are the functions of reactors in power systems and where do we locate the reactors in power systems?
81) Differentiate between isolator and circuit breaker and explain the sequences of operations used for opening and closing a circuit using isolator.
82) Distinguish between resistance earthing and solid
earthing. What are the disadvantages of isolated ‘ neutral system?
83) What are the advantages of neutral grounding? What do you understand about Peterson coil earthing and arcing grounds in an overhead line?
84) What do you understand by depreciation of the equipment? Graphically differentiate different methods of determination of depreciation.
85) What information could you get out of integrated load duration curve and load curves?
86) What is meant by tariff? Why two part tariff is normally used for industries?
87) Differentiate chronological load curve and load curve.
88) Why do we use A.C.S.R conductors for transmission lines? Write the formulae to find the no. of wires in a standard conductor having n layers.
89) What is the significance of maximum prospective short circuit value? How do you calculate the value in a circuit?
90) Draw positive, negative and zero sequence networks for an unloaded generator with solidly grounded neutral.
91) If Za, Zb, Zc are the impedances of the load between phases a, b ,c to the neutral, then the sequence impedances are.
92) Define and classify stability of a power system. Explain why the transient stability limit is lower than the steady state limit?
93) Define steady state and transient stability limit of a power system. List out the methods to improve steady state and transient stability.
94) State and explain equal area criteria. What are the limitations and advantages of equal area criteria?
95) Draw the diagrams to illustrate the application of equal area criteria to study transient stability for fault and subsequent circuit isolation & study of sudden increase in input of the generator.
96) Explain the effect of change of excitation on steady state stability of a synchronous generator feeding an infinite bus bar?
97) What are the main causes for the study of transient stability problems?
98) Differentiate between transient and dynamic stability. List out the factors that affect power system transient stability.
99) List out the typical values of standard parameters of salient pole machines in p.u with stator base values equal to the corresponding machine rated values.
100) Explain how does auto-reclosing of circuit breakers affects stability of power transmission systems?
101) What is a swing equation? What are the assumptions made in deducing the swing equation?
102) What is meant by synchronizing power coefficient? For what values of synchronizing coefficient the system remains stable?
103) Differentiate between a weak and a robust power system.
104) Write the swing equations for machines swinging coherently and non-coherently.
105) Explain the importance of reactive power in power systems. List out the components of power systems which absorb / generate reactive power.
106) What are the advantages of reactive power
compensation? Explain the principle of operation of static VAR compensator. –
107) What are the drawbacks in voltage control using generator excitation and series capacitors?
108) Compare synchronous capacitors and static capacitors.
109) What is off-nominal transformer ratio? Explain the working principle of booster transformer.
110) What do you understand about loss of excitation and pole slipping of synchronous machines?
111) Explain the effects of frequency and voltage changes on impedance load.
112) Define load flow or power flow. Why do we need to study load flows?
113) What are the practical applications of static load flow studies? Explain how you represent a three winding transformer and phase transformer in load flow studies.
114) What are the different types of buses used in power systems? Explain significance of swing bus.
115) List the different equality and inequality constraints imposed in load flow studies.
116) When do we have to treat a generator bus as a load bus in load flows? Explain the reason for it.
117) Explain how the approximation is performed Newton-Raphson method.
118) What are the advantages and disadvantages of Newton-Raphson method?
119) Compare G-S and N-R methods.
120) What are the properties of Y bus? Why do we prefer to use Y bus than a Z bus in load flows?
121) What is the significance of base values? What are the advantages of p.u systems?
122) What are the approximations made in constructing reactance diagram? Explain how you represent different loads in reactance diagram.
123) What are symmetrical components? Draw the positive, negative and zero sequence current vectors for negative sequence protection relay under operation.
124) List out the characteristics of harmonics in power systems. Explain the impact of harmonics on electrical equipment.
125) Differentiate between characteristic and non characteristic harmonics.
126) Express the unbalanced voltages V , Vb, Vc in terms of symmetrical components V j, Va2, Vao and vice-versa.
127) Classify synchronous machines. Draw the equivalent circuit diagram of synchronous motor and generator.
128) Classify different types of power systems faults. Why do we need to study fault analysis at all?
129) Explain the methods used to reduce the short circuit currents.
130) How do you represent a power system in load flows and short circuit studies?
131) Rank the different types of faults in the order of severity if the fault is taken place at a given distance.
132) Explain how to determine the synchronous, transient and sub-transient reactances from oscillogram of the short circuit current.
133) What are symmetrical components? Explain the
significance of transient reactance in short circuit studies. .
134) Draw the connection diagram of the sequence networks for a double line to ground fault, line-line faults in a power system.
135) What do you understand about short, medium and long lines? How do you represent them?
136) Draw the schematic diagram of an isochronous governor and the response of generating unit with isochronous governor.
137) What is a stringing chart and sag template? Explain their significance in transmission lines.
138) Explain the method of determining the values Cc and Cs of three-core belted cables.
139) Justify the need for distance protection of transmission lines in an integrated power system.
140) What do you understand by string efficiency? Why it is very low for ordinary insulators strings?
141) Explain the working principle of differential relay. Explain the reasons for providing large bias settings in transformers differential relays.
142) Classify circuit breakers. List the pre¬commissioning tests carried on circuit breakers.
143) Explain the routine tests carried out on circuit breakers.
144) Define R.R.R.V and list the factors on which R.R.R.V depends.
145) Explain the effects of power factor and armature reaction on recovery voltage.
146) What do you understand about field emission and thermal emission?
147) Explain the phenomenon of auto-reclosing. What are the advantages of single shot re-closing and multi¬shot reclosing?
148) What is meant by Basic Insulation Level of equipment? Explain its significance in power system studies.
149) Define corona. What is the advantage of corona in A.C as well as D.C lines?
150) What is meant by surge impedance and surge impedance loading? Explain its significance in transmission lines. What is the range of surge impedance for an overhead line and underground line?
151) What is equivalent spacing of a three phase lines and state its significance. Explain how you can calculate the inductance of bundled conductors.
152) What do you understand about infinite bus-bars? What is the surge impedance value of infinite bus bar?
153) What is electromagnetic interference between communication lines and power lines? Explain its effects and the methods to reducing it.
154) What are the advantages and limitations of adopting high voltage for transmission?
155) What are the practical limitations to apply Kelvin’s law for economic size of the conductor?
156) What is meant by skin effect and proximity effect? What are the factors on which these depend?
157) List the properties of SFft and state the draw backs of SF, circuit breakers.
158) List out different types of faults that occur in stator and rotor of an alternator.
159) What do you understand about insulation resistance? What is the order of insulation resistance of HV circuit breaker?
160) Draw and explain voltage and current traveling wave forms of a transmission line if surge impedance of the line is equal to load.
161) W’hat do you understand by a zone of protection? Explain how do we decide the protective zones in the electrical transmission systems?
162) Explain the working principle of undervoltage relay and state its applications.
163) Differentiate between belted and screened types of cables. Explain capacitance grading of cables.
164) Differentiate between a fuse and an overcurrent relay.
165) Define fusing current. State the factors on which
the fusing current depends.
166) Explain the working principle of HRC fuse. Draw current cut-off and recovery voltage characteristics of HRC fuse.
167) Explain the working principle of a plain oil circuit breaker. State the factors on which the performance of a plain oil circuit breaker depends.
168) What do you understand about counterpoises? Draw different arrangements of counterpoises.
169) Explain the working principle of surge arrester. Where and how do we connect a surge arrester?Draw ideal characteristics of surge arrester.
170) What is the function of spillways? List the commonly used spillways.
171) Explain how precipitation, evaporation and run¬off are inter-related?
172) List the special features of an alternators used in hydro-electric power plants.
173) Differentiate between a jet condenser and a surface condenser.
174) Classify different coals used for thermal power plant and specify their ash contents. What are the factors on which the selection of coal for thermal power plant depends?
175) Which public sector company is associated with erection and commissioning of thermal power plants in India? What is its current total installed capacity?
176) Which public sector company is associated with manufacturing thermal power plant equipment in India?
177) Define load factor. What is the average load factor of steam power plants in India?
178) What is natural draught? What are the factors on which magnitude of natural draught depends
179) What is load shedding? When the load shedding and restoring is done?
180) Classify different insulators used in power system. State the causes of failure of insulators.
181) What do you understand about transposition of lines? Explain how the’Uansposition is done.
182) List the different types of laying the underground cable and state the drawbacks of direct laying of underground cables.
183) Classify the insulating material based on temperature. What are the main characteristics required for the insulating materials used for underground cables?
184) Explain the principle of operation of buchholz relay and state its limitations.
185) Name the different types of faults that usually occur in cables. How do we localize them? ’
186) Distinguish between Varley loop test and Murray loop test.
187) Why do we use to express the reactances of various elements in percentage values for short circuit calculations?
188) Explain why the neutral grounding impedance Zn appears as 3Zn in the zero sequence equivalent circuit?
189) Show that the positive and negative sequence currents are equal in magnitude but out of phase by 180° in a line to line fault.
190) Classify protective relays. What do you understand about time setting and current setting in relays?
191) Write universal torque equation. Obtain directional relay characteristics from it.
192) Draw the loadability characteristics of transmission line. Explain its significance.
193) What is field suppression of alternator? Why do we use to suppress the field of the alternator immediately after disconnecting from the faulty system?
194) Explain the working principle of harmonic restraint relay.
195) What do you understand about incipient and through faults?
196) Explain the working principle of IDMT relay. Explain why IDMT relays are most suitable for radial feeders?
197) What do you understand about zones of protection and unit type of protection?
198) Explain Merz-price protection. Why it is not suitable beyond 33 kV?
199) What is the difference between surge absorber and surge diverter?
200) Explain working principle of lightning arrester. Define the impulse ratio of lightning arrester.
201) Define symmetrical breaking current and asymmetrical breaking current. Explain why symmetrical breaking current is lower than the asymmetrical breaking current in a circuit breaker?
202) Define sag and list the factors that affecting the sag in a transmission lines.
203) Define string efficiency. Why distribution of voltage across the discs in an insulator string is not uniform?
204) Draw the typical characteristics of receiving end voltage, current and power as a function of load demand for a simple radial system.
205) What do you understand about power circle diagrams and list the information that can be obtained from.
206) Distinguish between power circle diagram and universal power circle diagram.
207) What do you understand about tuned power transmission lines?
208) What do you understand about hollow, bundled and ACSR conductors?
209) Distinguish between high resistance and low resistance methods of arc extinction.
210) Explain the working principle of carrier current protection. Explain why it is suitable for interconnected lines.
211) Explain the working principle of biased circulating current protection and state its advantages.
212) Compare HVDC&HVAC transmission systems.
213) Write the sending end and receiving end power expressions in terms of A, B, C and D parameters for a transmission with 2 bus system.
214) Write A, B, C and D parameters for two transmission lines connected in series and parallel.
215) From the +ve, -ve and zero sequence phasors obtain the resultant phase phasors.
216) Explain the principle of operation of electromagnetic type distance relay.
217) Explain the working principle of a DC circuit breaker.
218) Draw the schematic diagram and explain operating characteristics of an impedance relay.
219) Draw the contact circuit of a 3 zone impedance protection and explain its operating characteristics.
220) What is meant by polarizing coil? Why do we use polarizing coil in protective relays?
221) Differentiate between mho relay and offset mho relay characteristics.
222) Explain the working principle of differential protection. Explain the difficulties to implement practically.
223) Explain how % basic setting and % pickup value is set for differential relays.
224) What do you understand about % age of winding protected and % age of winding is unprotected.
225) Explain the working principle of transverse percentage differential protection for multi-winding generators.
226) State the factors governing the selection of a particular pilot protection scheme. Explain the working principle of carrier pilot protection scheme.
227) Define sub-transient, transient and steady state reactances of an alternator.
228) Draw zero sequence networks of loads connections for star ungrounded neutral, star grounded neutral, star grounded neutral with an impedance Zn and delta connected loads.
229) Explain formulation of Ybug using nodal method and singular transformation method,
230) Define sparsity. What is the value of sparsity of Ybus for a practical power system?
231) What are the assumptions made to develop ,relation between bus voltages and bus currents in load flow studies?
232) Define voltage regulation and efficiency of a transmission line. Explain the effect of load power factor on regulation and efficiency.
233) Draw phasor diagrams and write A, B, C and D parameters for nominal T and n circuit of transmission line.
234) Derive A, B, C and D parameters for nominal T and n methods.
235) Explain how to determine A, B, C and D parameters of a transmission lines practically.
236) Explain how to determine +ve, -ve and zero sequence impedances of transformers practically.
237) Explain how to determine +ve, -ve and zero sequence impedances of alternators practically.
238) Explain phenomenon of current chopping in vacuum circuit breakers. State the properties of contact materials used for vacuum interrupters.
239) Define switchgear and differentiate between low voltage switchgear and high voltage switchgear.
240) Define coefficient of earthing and state the significance of it in selection of voltage rating of surge arrester.
241) Explain about single frequency transient and double frequency transients.
242) Explain the working principle of current limiting reactors and explain why we need these reactors in power systems.
243) Explain the principle of directional element. Draw and explain impedance relay characteristics with directional element.
244) What do you understand about power swings and explain its affects on distance relays.
245) Define reach and under-reach of distance relay. Explain the effect of arc resistance in distance relays.
246) Draw voltage characteristics of surge arrester and define residual voltage, impulse spark over voltage and power frequency voltage of a surge arrester.
247) Draw the phasor diagrams of synchronous generator feeding constant active power into infinite bus bars as excitation is varied.
248) What do you understand about insulation coordination, protective margins and protective ratio?
249) Explain the N-R method of load flow studies. Explain the reasons for the order of Jacobian in N-R method using polar coordinates is smaller than in N-R method using rectangular coordinates.
250) What is traveling wave? Explain the concept of standing wave and voltage standing wave ratio.