# Sample Paper of Electrical Technology

Sample Paper of Electrical Technology mentioned here students of the Electrical Engineering need to adopt this Questions and Answer for their Examination preparation that will help very efficiently.The Sample Paper of Electrical Technology will help to gain knowledge about Electrical Technology weather how the Electrical Technology boosting in this era.

Electrical technology

1  Explain Ohm’s law.

Ans: Ohm’s law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance one arrives at the usual mathematical equation that describes this relationship:

I=V/R

2 Explain Kirchhoff’s laws.

Ans: Kirchhoff’s Current Law states that: ‘the algebraic sum of currents at a node is zero’.

The second of Kirchhoff’s Laws, the Voltage Law, states that: ‘the algebraic sum of voltages around a closed circuit loop is zero’.

3  Explain average value of an ac waveform in general and find out average value of sinusoidal wave.

AnsDirect Current or D.C. as it is more commonly called, is a form of current or voltage that flows around an electrical circuit in one direction only, making it a “Uni-directional” supply. Generally, both DC currents and voltages are produced by power supplies, batteries, dynamos and solar cells to name a few. A DC voltage or current has a fixed magnitude (amplitude) and a definite direction associated with it. For example, +12V represents 12 volts in the positive direction, or -5V represents 5 volts in the negative direction.

4 Explain behaviour of pure inductance in ac circuit.

Ans: Inductors do not behave the same as resistors. Whereas resistors simply oppose the flow of electrons through them (by dropping a voltage directly proportional to the current), inductors oppose changes in current through them, by dropping a voltage directly proportional to the rate of change of current. In accordance with Lenz’s Law, this induced voltage is always of such a polarity as to try to maintain current at its present value.

5  Explain Thevenin’s theorem.

Ans: Thevenin’s Theorem states that it is possible to simplify any linear circuit, no matter how complex, to an equivalent circuit with just a single voltage source and series resistance connected to a load. The qualification of “linear” is identical to that found in the Superposition Theorem, where all the underlying equations must be linear (no exponents or roots).

6 Explain Superposition theorem.

Ans: The superposition theorem for electrical circuits states that for a linear system the response (Voltage or current) in any branch of a bilateral linear circuit having more than one independent source equals the algebraic sum of the responses caused by each independent source acting alone, while all other independent sources are replaced by their internal impedances.

7 Explain series resonance in detail.

Ans: In a series RLC circuit there becomes a frequency point were the inductive reactance of the inductor becomes equal in value to the capacitive reactance of the capacitor. In other words, XL = XC. The point at which this occurs is called the Resonant Frequency point, ( ƒr ) of the circuit, and as we are analysing a series RLC circuit this resonance frequency produces a Series Resonance.Series Resonance circuits are one of the most important circuits used electrical and electronic circuits

8 Explain balanced star circuit.explain relation between phase and line voltages amd currents.

Ans: The three-phase ac systems are considered as a balanced circuit, made up of a balanced three-phase source, a balanced line, and a balanced three-phase load. Therefore, a balanced system can be studied using only one-third of the system, which can be analyzed on a line to neutral basis.The star-delta (Y-Δ) or delta-star (Δ-Y) conversion  is required in three-phase ac systems to simplify the circuits and ease their analysis. If a three-phase supply or a three-phase load is connected in delta, it can be transformed into an equivalent star-connected supply or load. After the analysis, the results are converted back into their original delta equivalent.

9 Explain phasor diagram of actual transformer on land for different types of load.

Ans: A high-voltage, direct current (HVDC) power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses. For underwater power cables, HVDC avoids the heavy currents required to charge and discharge the cable capacitance each cycle. For shorter distances, the higher cost of DC conversion equipment compared to an AC system may still be warranted, due to other benefits of direct current links.

10  Explain different types of dc generator.

Ans: The magnetic field in a d.c. generator is normally produced by electromagnets rather than permanent magnets. Generators are generally classified according to their methods of field excitation. On this basis, d.c. generators are divided into the following two classes:
(i) Separately excited d.c. generators
(ii) Self-excited d.c. generators

11 Explain working principles of three phase induction motor and three phase synchronous motor.

Ans: An induction or asynchronous motor is an Ac motor in which all electromagnetic energy is transferred by inductive coupling from a primary winding to a secondary winding, the two windings being separated by an air gap. In three-phase induction motors, that are inherently self-starting, energy transfer is usually from the stator to either a  short circuited squirrel cage motor. Three-phase cage rotor induction motors are widely used in industrial drives because they are rugged, reliable and economical. Single-phase induction motors are also used extensively for smaller loads. Although most AC motors have long been used in fixed-speed load drive service, they are increasingly being used in (VFD) service, variable-torque centrifugal fan, pump and compressor loads being by far the most important energy saving applications for VFD service.