Electrical Technology

(a) Derive an expression for the deflecting of a moving iron movement in terms of the rate of change of inductance with position of the movement.

(b) A 600 KVA, 1-phase transformer has an efficiency of 92% both at full load and half load at unity power factor. Determine its efficiency at 60% of full load at 0.8 power factor lag.

(a) Describe with suitable sketch, the main parts of DC machine. Explain the main function of each part.

(b) What is the significance of back emf in DC motor?

Find the current through 2 ohm resistor using nodal analysis and Thevenin's theorem for the circuit shown in fig 2.  

(a) Verify the reciprocity theorem in the circuit shown in fig. 3, w.r.t. the voltage source and the current I.  

(a) In the circuit shown in Fig. 5, Is = cos 1000 t. Determine the frequency domain circuit and determine the phasors Iand 12. Draw the phasor diagram for V1, V2, V3 and V4 in the same figure.

(b) Using superposition theorem determines the current through the branch AB, for the circuit shown in fig. 4. 

(b) A balanced star connected load of (4 + j6) ohm per phase is connected to a balanced 3-phase, 400v supply. Find the line current, power factor and total power. 

For a parallel RLC circuit define resonant frequency, damped resonant frequency and Q. Obtain exact expressions for half power frequencies in terms of resonant frequency and Q.

(a) Explain electric and magnetic circuits. Give analogy between them.

(b) A moving coil instrument has a resistance of 3 ohm and gives full scale reading of 25 mA.

(i). The shunt resistance for full scale deflection corresponding to 125 amp.

(ii) The resistance for full scale reading with 625v.

Also find power consumption in the shunt and multiplier 

(a) A 250v, 10A dynamometer type wattmeter has resistance of current and pressure coil are 0.5 ohm and 12500 ohm respectively. Find the percentage error when:

(i) The pressure coil is connected on the supply side.

(ii) The pressure coil on the load side. •

Assume unity power factor load at 250v, 4A.

(b) Discuss working of electronic energy meter.

(a) Prove that single phase induction motor is not self starting.

(b) Describe phasor diagram on no load and on load of a transformer.

(a) Explain types of DC motors.

(b) explain voltage regulation and efficiency of single phase transformer.

(a) Find the equivalent resistance across AB in the Fig. 1, all the resistances are equal and 5 ohm. 

(b) Explain the physical significance of power factor in AC system.

(c) Explain working of digital voltmeter.

(d) Describe controlling torque in indicating type instruments.

(e) Explain the effect of variation in load on the magnitude of flux in the core of single phase transformer. 

(a) Resistance of 209 and inductance of 0.2H and a capacitance of 150F are connected in series across 230V, 50 Hz mains. Determine X_L, X_C, z, and Y, p.f., active power and reactive power. 

(b) An alternating voltage is represented by e = 150 sin 100t. Determine amplitude, time period and frequency, angular velocity, form factor and peak factor of voltage.

(c) (i) Why a series RLC circuit is also called accepter circuit?

     (ii) Give the relationship between phase and line voltages and currents in three phase     star connected circuit.

(d) What are the essential torques of indicating instruments? Explain their necessity. 

(e) Explain the basic principle of operation of single phase transformer and draw the phasor diagram of ideal transformer on no load?

(a) State and Explain Maximum Power Transfer Theorem.

(b) For the circuit shown below, what will be the value of R_L to get the maximum power? What is the maximum power delivered to load?

(a) Derive the relationship between resistances connected in star and equivalent delta system. 

(b) Three resistances of 20, 25 and 30 are connected in delta.Calculate the corresponding resistances in an equivalent star connection.

(c) State and explain superposition theorem.

(a) Define (i) active and passive elements (ii) unilateral and bilateral elements (iii) linear and non linear elements. 

(b) Three similar resistors are connected in star across 400V, 3-phase line. The line current is 10A. Calculate the value of each resistor. To what value should the line voltage be changed to obtain the same line current with the resistors delta connected?

(a) Explain Series Resonance. Derive the condition of resonance in series RLC circuit.

(b) Determine the RMS value, average value and form factor of half wave rectified alternating current.

(a) Discuss in detail principle, construction and working of PMMC instruments.

(b) A moving coil instrument has a resistance of 10 2 and gives full scale deflection when carrying a current of 50mA. Show how it can be adopted to measure voltage up to 750 V and current upto 1000A.

(a) Explain the terms: Apparent power, Active power and Reactive power of an ac circuit.

(b) Explain the two wattmeter method used for measurement of power in three phase circuit.

(c) Why is eddy current damping not possible in moving iron instruments?