Question 1

Q.1. Explain Bulk Power Grids and Micro-grids.

Accepted Answer

Bulk power grids are the large, interconnected high-voltage transmission networks that transport large blocks of power over long distances from generating stations to load centers, while micro-grids are small, localized networks that can operate connected to or independently (islanded) from the main grid.

Question 2

Q.2. What are the effect of Electric and Magnetic Field in Transmission Line?

Accepted Answer

The electric field around a transmission line causes charging current, capacitive coupling and induced voltages on nearby conductors, while the magnetic field (from load current) induces circulating currents and voltages in nearby conductors and can interfere with communication lines.

Question 3

Q.3. What is the difference between synchronous and asynchronous grid?

Accepted Answer

A synchronous grid is one where all interconnected generators operate at exactly the same electrical frequency and remain in phase synchronism through a common AC network, whereas an asynchronous grid consists of two or more grids operating at independent frequencies/phases, interconnected only through non-synchronous links such as HVDC.

Question 4

Q.4. What you mean by Renewable Energy Sources? Give the example.

Accepted Answer

Renewable Energy Sources are naturally replenishing energy resources that are not depleted by use, such as solar, wind, hydro, biomass, geothermal and tidal energy, as opposed to finite fossil fuels.

Question 5

Q.5. Describe term corona. What are the factors which affect the corona losses?

Accepted Answer

Corona is the localized ionization of air around a high-voltage conductor when the surface voltage gradient exceeds the breakdown strength of air, producing a visible glow, hissing sound and power loss; it is affected by conductor size, spacing, surface condition, atmospheric conditions and system voltage.

Question 6

Q.6. Why fault analysis is needed in power system?

Accepted Answer

Fault analysis is needed to determine the magnitude of fault currents and voltages under various fault conditions, which is essential for correctly rating switchgear, setting protective relays, and ensuring system stability and safety.

Question 7

Q.7. Explain the difference between feeder and distributor.

Accepted Answer

A feeder is a conductor that carries bulk power from a substation to a load area without any direct tapping/loads connected along its length, whereas a distributor has loads (service connections) tapped off at multiple points along its length, causing its current to vary from point to point.

Question 8

Q.8. What is the per unit value?

Accepted Answer

The per unit value of any quantity is its actual value expressed as a fraction (or decimal ratio) of a chosen base value of the same dimension, i.e., p.u. value = actual value / base value.

Question 9

Q.9. Write short note on Distributed Energy Resources.

Accepted Answer

Distributed Energy Resources (DERs) are small-scale power generation or storage units located close to the point of consumption (rooftop solar, small wind, batteries, fuel cells), connected at the distribution level rather than centralized bulk generation.

Question 10

Q.10. Describe single line diagram with voltage levels topologies (meshed and…

Accepted Answer

A single line diagram represents a 3-phase power system using a single line with standard symbols; meshed topology interconnects multiple substations/lines in loops for high reliability (multiple power paths), while ring topology connects loads in a closed loop fed from one or more points, offering better continuity of supply than a simple radial system.

Question 11

Q.1. A 50 km long transmission line supplies a load of 5 MVA at 0.8 power fac…

Accepted Answer

For a 50 km line supplying 5 MVA at 0.8 pf lagging, 33 kV, 90% transmission efficiency, the required aluminium conductor volume for a 3-phase 3-wire system is exactly 0.75 times (75%) the volume required for an equivalent single-phase 2-wire system, since 3-phase transmission needs less conductor material for the same power and loss.

Question 12

Q.2. Explain clearly how the magnetic field energy and the reactive power in …

Accepted Answer

Reactive power in an inductive circuit represents the rate at which energy oscillates into and out of the circuit's magnetic field twice per cycle without net energy transfer; it equals ωL·I² (or equivalently I²X), directly proportional to the peak magnetic field energy stored (½LI²) times twice the angular frequency.

Question 13

Q.3. Discuss the advantages and disadvantages of HVDC transmission system.

Accepted Answer

HVDC transmission offers advantages of lower losses over long distances, asynchronous interconnection capability, no reactive power/stability limits, and reduced right-of-way, but suffers from disadvantages of costly converter stations, harmonic generation, and lack of easy multi-terminal tapping compared to AC.

Question 14

Q.4. Explain the operations of standalone and grid interactive Solar PV syste…

Accepted Answer

A standalone (off-grid) Solar PV system uses a charge controller and battery bank to supply an isolated load independently of the grid, while a grid-interactive system uses a grid-tie inverter to synchronize PV output with the utility grid and export/import power without necessarily needing battery storage.

Question 15

Q.5. What is grounding? Describe about the various methods of neutral groundi…

Accepted Answer

Grounding (earthing) the neutral point of a power system connects it to earth to limit overvoltages and provide a controlled return path for fault current; common methods are solid grounding, resistance grounding, reactance grounding, and resonant (Petersen coil) grounding, each offering different trade-offs between fault current magnitude and overvoltage control.

Question 16

Q.6. Explain the conversion of wind energy into electric energy in a wind pow…

Accepted Answer

A wind power plant converts the kinetic energy of wind into mechanical rotation of turbine blades, which drives a generator (through a gearbox in geared designs) to produce electrical energy, which is then conditioned by power electronics and stepped up via a transformer for grid connection.

Question 17

Q.7. What is nominal π (pi) circuit? Find the ABCD constants for nominal π ci…

Accepted Answer

A nominal π circuit models a medium-length transmission line as a series impedance Z with half the total line shunt admittance (Y/2) lumped at each end; its ABCD constants are A = D = 1+ZY/2, B = Z, and C = Y(1+ZY/4).

Question 18

Q.1. (a) Describe puffer type SF6 circuit breaker with neat and clean diagram…

Accepted Answer

A puffer-type SF6 circuit breaker mechanically compresses SF6 gas in a cylinder during contact separation and directs the resulting high-pressure gas blast axially across the arc to extinguish it at current zero, offering advantages of compact size, minimal maintenance and quiet operation over oil/air-blast breakers, though at higher operating mechanism force requirements; power flow through a transmission line, characterized by ABCD constants, allows direct calculation of active and reactive power at both ends using standard power-flow equations.

Question 19

Q.2. (a) Explain short circuit of synchronous machine. Also describe steady s…

Accepted Answer

A synchronous machine's short-circuit current has three characteristic periods (sub-transient, transient, steady-state) governed by progressively decaying damper-winding and field-winding flux-retention effects, each associated with a distinct reactance (Xd″<Xd′<Xd); shunt compensation uses shunt reactors or capacitors connected across the line to absorb excess reactive power (reducing Ferranti overvoltage on lightly loaded lines) or supply reactive power (supporting voltage on heavily loaded lines).

Question 20

Q.3. Describe the I-V and P-V characteristics of PV panels of solar system wi…

Accepted Answer

The I-V characteristic of a PV panel shows current nearly constant (equal to short-circuit current Isc) over most of the voltage range before dropping sharply near open-circuit voltage Voc, while the P-V characteristic rises to a single maximum power point (MPP) and then falls, with both curves shifting significantly with irradiance and moderately with temperature.

Question 21

Q.4. Why Line Commutated Converters (LCC) used in HVDC transmission system? C…

Accepted Answer

Line Commutated Converters are used in HVDC transmission because thyristor valves are robust, high-power-rated, and can rely on the AC system's own voltage for natural commutation without requiring self-commutating switching devices; compared to AC transmission, DC transmission has lower losses and no stability/reactive-power limits over long distances but requires costly converter stations, making the choice between AC and DC a distance/application-dependent economic and technical trade-off.

Question 22

Q.5. Write note on the followings protection schemes with their application: …

Accepted Answer

Over-current protection trips on excessive current magnitude; directional protection adds current-direction discrimination to distinguish faults in front of vs behind the relay; distance protection measures line impedance (proportional to fault distance) to provide zone-graded protection for transmission lines; and differential protection compares currents entering and leaving a protected zone, tripping instantly on any internal imbalance — each is applied to specific equipment/network configurations.

Power System - I