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UNIT -
Introduction to Electrical Engineering & Network Analysis
1. State KVL and KCL. KVL: kirchhoff’s voltage law states that the algebraic sum of all branch voltages around any closed path in a circuit is always zero at all instants of time. KCL: kirchhoff’s current law states that the sum of the current entering into any node is equal to the sum of the currents leaving that node. 2. State Ohm’s law It states that at constant temperature, potential difference ‘V’ across the ends of a conductor is Proportional to the current ‘I’ flowing through the conductor ,i.e
3. What are the different types of induced emf’s? a. Statically induced emf. b. Dynamically induced emf.
4. State superposition theorem. Is superposition theorem is applicable to power calculations? In a linear network response in a particular branch when all the sources acting simultaneously is equal to the linear sum of individual responses. It is not applicable for power calculations why because power is a non linear. 5. State maximum power transfer theorem. What is the percentage efficiency of maximum power transfer theorem for D.C circuits? Maximum power is transferred in the circuit when load resistance is equal to the source resistance. For DC circuits power transfer is 50% at max power condition 6. State thevenin’s theorem Thevenin’s theorem states that any two terminal linear network having a number of voltage current sources and resistances can be replaced by a simple equivalent circuit consisting of a single voltage source in series with a resistance 7. Write Faraday’s laws of Electro magnetic induction Faraday’s first law : This law states that when ever magnetic flux changes with respect to an electrical conductor or a coil ,an emf is induced in the conductor Faraday’s second law : This law states the magnitude of the emf induced in the conductor by Electromagnetic induction is directly proportional to the time rate of change of the flux linkage i.e
8.State lenz’s law This law states that direction of the induced emf is always such that it tends to establish a current which opposes the change of flux responsible for inducing that emf ‘-‘ sign due to lenz’s law
9.Star to Delta and Delta to Star transformation
10. What are the units of charge and energy?
Units of charge: coulombs Units of energy: joules.
11 .Why an inductive circuit should not be opened when carrying a current?
When the switch is opened ,Current is changing in short duration ,i.e t =0 , ↑ Then Voltage across the inductor is very high , For this reason inductive circuit is not opened when carrying current
12.Write the expressions for energy stored in L & C
UNIT-II
Magnetic Circuits & Alternating Quantities
- What is ‘J’ operator? The J operator causes the phasor to rotate through 90^0 in the anticlockwise direction without affecting its magnitude
- What is coefficient of coupling (k)?
Where K is coefficient of coupling ,When 100% of the flux lines link each coil ,then K=
- Draw the magnetizing characteristics (B-H Curve)
- What is the relation between Frequency (f),synchronous speed(N (^) S)and Number of poles **(P)?
- What are the values of Form factor and Peak factor?
- What is the power factor of an RLC circuit at Resonancee? Unity** ,why Because at resonance condition ,inductive reactance (X (^) L ) is equal to capacitive reactance (Xc) 7. What is active power and reactive power? The product of RMS values of voltage and current with the Cosine of the angle between them is Called the reactive power in A.C circuit and is denoted by P
- What are the assumptions of ideal transformer? 2.)a No losses in the transformer 2.)b No leakage flux in the transformer 2.)c (^) Transformer core offers high conductivity and low reluctance 2.)d Winding resistance is zero
- What is the condition for maximum efficiency?
Variable losses( ) are equal to the Constant losses() i.e
- What is the principle of D.C generator? Electromagnetid induction principle: When ever a conductor cuts the flux an emf is induced in the conductor ,the current direction is found by using fleming’s right hand rule
- (^) What is the principle of D.C motor? Lorent’z law: When ever a current carrying conductor is placed in the magnetic field, conductor experiences a force .The direction of force found by using fleming’s left hand rule
- What are the different losses present in the transformer?
a) Copper losses b) Iron losses or Core loss c) Stray load losses d) Dielectric losses
7.What is the purpose of generator and motor? Generator converts mechanical energy into electrical energy Motor converts electrical energy into mechanical energy
- (^) Why starter is required in D.C motor?
Starter is used to limit the starting current , why because at starting Eb
- What are the difference between lap winding and wave winding?
Lap Winding Wave winding No of parallel paths(A)= P No of parallel paths(A)= Finishing end of one coil is connected to the beginning of another coil under same pole
Finishing end of one coil is placed to the beginning end of another coil under different pole
- Write the emf equation of a D.C generator.
- What is the purpose of commutator? Commutator is used to convert AC in the armature winding into DC
- Define Efficiency and Voltage regulation of a transformer. Efficiency is defined as the ratio of output power to the input power Voltage regulation is defined as the change in terminal voltage from no load to full load at some specific power factor of the load ,it is expressed as a fraction of no load voltage
- What is the purpose of conducting O.C test and S.C test? The purpose of O.C test is to determine the constant losses (iron losses)and parameters of noload branch(R 0 and X (^) 0) The purpose of S.C test is to determine the variable losses (copper losses) and total resistance and reactance of transformer(R 02 and X^02 )
13.Why transformer rating is always rated in KVA instead of KW?
Copper lossses depends upon the current and Core losses depends upon the voltage
14.What are the different types of transformers based on construction? a)Core type transformer b) Shell type transformer
15. How to reduce hysteresis losses and eddy current losses in a transformer? To reduce the hysteresis loss in a transformer ,choose the material as low hysteresis coefficient To reduce the eddy current losses in a transformer ,transformer core is divided into Different laminations
(ii) Controlling system to control the deflection of the moving mechanism
