JNTU B.Tech II FUNDAMENTALS OF ELECTRICAL ENGINEERING Previous Question Paper (April/May - 2018 - R13)

Explain the differences between Ideal and Practical Sources of Voltage and Current.

A delta connection contains three equal resistances R. Find the resistances of the equivalent star connection.

With the aid of a simple diagram, explain the j-notation method of phasor quantities.

Explain the significance of the root-mean-square value of an alternating current or voltage waveform. Define the form factor of such a waveform.

State Tellegen’s theorem.

Brief the superposition theorem with suitable example.

Why the armature core in d.c machines is constructed with laminated steel sheets instead of solid steel sheets?

How does d.c. motor differ from d.c. generator in construction?

Define rotating magnetic field.

Mention the difference between core and shell type transformers.

A 20V battery with an internal resistance of 5Ω is connected to a resistor of x ohms. If an additional 6Ω resistor is connected across the battery, find the value of x so that the external power supplied by the battery remains the same.

Determine the effective resistance between terminals A and B in the circuit of the given figure 1. If the current drawn at A is 9A, find the current in and the voltage drop across each element.

Derive expressions for equivalent star resistances for given delta and equivalent delta resistances for given star.

Two identical coils X and Y of 1000 turns each lie in parallel planes such that 80% of flux produced by one coil links with the other. If a current of 5A flowing in X produces a flux of 0.05mWb in it, find the mutual inductance between X and Y.

A coil of resistance 25 Ω and inductance 0.044 H is connected in parallel with a branch made up of a 50 μF capacitor in series with a 40 Ω resistor, and the whole is connected to a 200 V, 50 Hz supply. Calculate, using symbolic notation, the total current taken from the supply and its phase angle, and draw the complete phasor diagram.

The load taken from an a.c. supply consists of: (i) a heating load of 15 kW; (ii) a motor load of 40 kVA at 0.6 power factor lagging; (iii) a load of 20 kW at 0.8 power factor lagging. Calculate the total load from the supply (in kW and kVA) and its power factor. What would be the kvar rating of a capacitor to bring the power factor to unity and how would the capacitor be connected?

A series circuit consists of a non-inductive resistor of 10 Ω, an inductor having a reactance of 50 Ω and a capacitor having a reactance of 30 Ω. It is connected to a 230 V a.c. supply. Calculate: (i) the current; (ii) the voltage across each component. Draw to scale a phasor diagram showing the supply voltage and current and the voltage across each component.

A series a.c. circuit, ABCD, consists of a resistor AB, an inductor BC, of resistance R and inductance L, and a resistor CD. When a current of 6.5 A flows through the circuit, the voltage drops across various points are: VAB = 65 V; VBC = 124 V; VAC = 149 V. The supply voltage is 220 V at 50 Hz. Draw a phasor diagram to scale showing all the resistive and reactive volt drops and, from the diagram, determine: (i) the volt drop VBD and the phase angle between it and the current; (ii) the resistance and inductance of the inductor.

State your own interpretation of Thévenin’s theorem and use it to solve the following problem. Two batteries are connected in parallel. The e.m.f. and internal resistance of one battery are 120 V and 10 Ω respectively and the corresponding values for the other are 150 V and 20 Ω. A resistor of 50 Ω is connected across the battery terminals. Calculate (i) the current through the 50 Ω resistor, and (ii) the value and direction of the current through each battery. If the 50 Ω resistor were reduced to 20 Ω resistance, find the new current through it.

A circuit consists of a 10 Ω resistor, a 30 mH inductor and a 1 μF capacitor, and is supplied from a 10 V variable-frequency source. Find the frequency for which the voltage developed across the capacitor is a maximum and calculate the magnitude of this voltage.

For the network shown in Figure 2. Determine the Norton equivalent network.

For the network shown in Figure 3, determine the maximum power which can be dissipated by Z.

Derive the EMF equation of DC generator.

A 4-pole, lap connected DC machine has 540 armature conductors. If the flux per pole is 0.03 Wb and runs at 1500 RPM, determine the emf generated. If this machine is driven as a shunt generator with same field flux and speed, calculate the line current if the terminal voltage is 400V. Given the RSH=450Ω and RA=2Ω.

A 440 V D.C shunt motor takes 4A at no load. Its armature and field resistances are 0.4 ohms and 220 ohms respectively. estimate the kW output and efficiency when the motor takes 60A on full load.

Derive the expression for efficiency of D.C. machines.

Describe the construction and principle of operation of salient pole alternator with a neat sketch.

A 100kW, 330V, 50Hz, 3 phase, star connected induction motor has a synchronous speed of 500 rpm. The full load slip is 1.8% and full load power factor 0.85. Stator copper loss is 2440W, iron loss is 3500W, rotational losses is 1200W. Calculate (i) rotor copper loss, (ii) the line current.