Power Systems Interview Questions

Power Systems Interview Questions

  • Anuj Awasthi
  • 17th Apr, 2021

Power Systems Interview Questions

1) What is a Power System?

An electric power system is a network of electrical components deployed to supply, transfer, and use electric power. An example of an electric power system is the grid that provides power to an extended area.

2) What are P-V curves?

P-V curves are used to assess voltage security and to compute the real power margin. The process of P-V analysis involves using a series of load flow solutions for incremental power transfers at constant power factor to obtain the voltage to MW transfer relationship.

3) What is synchronous condenser?

A synchronous condenser is a DC-excited synchronous motor, whose shaft is not connected to anything but spins freely. Its purpose is not to convert electric power to mechanical power or vice versa, but to adjust conditions on the electric power transmission grid.

4) What is difference beteen fuse and circuit breaker?

A fuse and circuit breaker both of them protect an overloaded circuit by disrupting the current continuity. The way they disrupt the current flow is dissimilar. A fuse is a simple piece of metal that melts down when overheated because of excessive flow of current whereas a circuit breaker has a switching mechanism that is activated when unsafe current flows through the circuit. Fuses are faster to disrupt the current flow but they must be replaced after a piece of metal melts down, whereas circuit breakers can be reset and used multiple times.

The most significant distinguishing factor between fuse and circuit breaker lies in their operational mechanism. The fuse functions at the base of thermal as well as electrical characteristics of the conducting metal which is utilized in the fuse, whilst a circuit breaker functions on the base of electro-mechanical principles.

5) What is electricity tariff?

The amount of money frame by the supplier for the supply of electrical energy to various types of consumers is known as an electricity tariff. In other words, the tariff is the method of charging a consumer for consuming electric power. The tariff covers the total cost of producing and supplying electric energy plus a reasonable cost.

The actual tariffs that customer pay depends on the consumption of electricity. The consumer bill varies according to their requirements. The industrial consumers pay more tariffs because they use more power for longer times than domestic consumers.

6) What is Transmission and distribution line?

Transmission lines are a high voltage line that carries electricity from power plant to the substation from it is further distributed to various areas for different purposes.

Distribution lines are low voltage lines that carry electricity from the substations to the end-users for residential and commercial use.

7) Enlist different sources of energy?

Different sources of energy are

  • Solar Energy
  • Wind Energy
  • Geothermal Energy
  • Hydrogen Energy
  • Tidal Energy
  • Wave Energy
  • Hydroelectric Energy
  • Biomass Energy
  • Nuclear Power
  • Fossil Fuels (Coal, Oil and Natural Gas)

8) What is a Relay?

A relay is an electrically operated switch. It consists of a set of input terminals for a single or multiple control signals, and a set of operating contact terminals. The switch may have any number of contacts in multiple contact forms, such as making contacts, break contacts or combinations thereof.

9) What is nuclear power plant?

A nuclear power plant is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a generator that produces electricity.

10) What do you mean by grading of cables?

Grading of cable is the process of achieving uniform distribution of dielectric stress or voltage gradient in a dielectric of cable.

11) What are pumped storage plant?

Pumped-storage plants provide a way for Duke Energy to store the potential energy of water. A pumped-storage plant is designed with two reservoirs – upper and lower. Like every other hydroelectric plant, a pumped-storage plant generates electricity by allowing water to fall through a turbine generator.

12) What is CT Analyzer?

The CT Analyzer is the most complete and easy-to-use test system for protection and metering CTs according to IEEE and IEC standards. It combines the highest safety standards with CT tests and assessment features.

13) What is expanded ACSR?

Expanded ACSR are conductors composed of. larger diameter individual strands for a given cross-section of the aluminum strands, the larger diameter of central steel strands for a given overall diameter of the conductor.

14) Explain what is Ferranti effect?

The effect in which the voltage at the receiving end of the transmission line is more than the sending voltage is known as the Ferranti effect. Such type of effect mainly occurs because of light load or open circuit at the receiving end.

15) List different types of faults in Electrical Power Systems?

Different types of faults in Electrical Power Systems are

Symmetrical faults: These are very severe faults and occur infrequently in the power systems. These are also called as balanced faults and are of two types namely line to line to line to ground (L-L-L-G) and line to line to line (L-L-L).

Unsymmetrical faults : These are very common and less severe than symmetrical faults. There are mainly three types namely line to ground (L-G), line to line (L-L) and double line to ground (LL-G) faults.

16) What is Electrical Grounding and Earthing?

Electrical grounding: It is a backup pathway that provides an alternating route for the current to flow back to the ground if there is a fault in the wiring system. It facilitates a physical connection between the ground and the electrical equipment and appliances in your home.

Electrical Earthing: The process of transferring the immediate discharge of the electrical energy directly to the earth by the help of the low resistance wire is known as the electrical earthing. The earthing provides a simple path to the leakage current.

17) What do you understand by Sag?

Sag word is related to transmission line in electrical engineering. Sag is defined as the difference between the highest point of the tower where the conductor is connected, to the lowest point of conductor between the tower. From the view of safety the conductor between to tower not fully stretched, but it has some sag. If the sag is not provided and the conductor fully stretched then the wind exert pressure on it hence the conductor has more chance to be broken.

18) How does the over voltage surge affect the power system?

Over voltage caused by surges can result in spark over and flashover between phase and ground at the weakest point in the network, breakdown of gaseous/solid/ liquid insulation, failure of transformers and rotating machines.

19) What is Bus Bar Protection?

A busbar is a strip or bar of copper, brass or aluminum that conducts electricity within a switchboard, a substation or a battery bank. The busbar protection relay is intended for use in high-impedance-based applications within utility substations and industrial power systems.

20) What can electrical faults cause?

An electrical fault is an abnormal condition, caused by equipment failures such as transformers and rotating machines, human errors and environmental conditions. Theses faults cause interruption to electric flows, equipment damages and even cause the death of humans, birds, and animals.

21) What is a bundle conductor?

A bundle conductor is a conductor made up of two or more sub-conductors and is used as one phase conductor. For voltages greater than 220 kV it is preferable to use more than one conductor per phase which is known as Bundle conductor.

22) What is Critical disruptive Voltage?

Critical Disruptive Voltage is defined as the minimum phase to the neutral voltage required for the Corona discharge to start. Basically corona discharge is the current discharge in the air.

23) What are the various states of operation in power system?

The various states of operation in the power system are Normal state, Alert state, Emergency state, Extremis state, and Restorative state.

24) What is Slack Bus?

In electrical power systems a slack bus, defined as a bus, is used to balance the active power |P| and reactive power |Q| in a system while performing load flow studies. The slack bus is used to provide for system losses by emitting or absorbing active and/or reactive power to and from the system.

25) When Directional relays are used?

Directional overcurrent relays are normally used on incoming line circuit breakers on buses which have two or more sources. They are connected to trip an incoming line breaker for fault current flow back into the source so that a fault on one source is not fed by the other sources.

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