Reserve Bank of India
RBISB (Manager Grade B Electrical)
Descriptive Type Paper II
2010 Question Paper
1. (a) An LC parallel circuit has an applied voltage = 50 Cos (3000t+450) volts and
a total current iT = 2 cos (3000t – 450) amperes. It is also known that the current in the L branch is five times greater than the current in the C branch. Find L and C of this circuit.
(b) The Circuit constants R and L of a coil are to be determined by connecting the coil in series with a resistor of 25 and applying a 120 V, 60 Hz source and then reading the voltages across the resistor and the coil. Find R and L if VR = 70. 8 Volts and VCoil = 86 Volts.
2. (a) Explain the principle of transformer action and derive an expression for the emf induced in a transformer winding. Show that the emf per turn in primary is equal to emf per turn in the secondary.
(b) Develop a phasor diagram of a single phase transformer under load for a lagging power factor.
3. (a) Find an expression for the magnetic force developed in a doubly excited translational magnetic system.
(b) Two air-cored coils have their magnetic axes coincident. Their parameters are :—
L1 =0.4 H L2 = 0.2H
M12 = M21 = 0.1e– 4x H, and where x is the distance between the two Coils.
For steady state current of I1 = 10A and I2 = 5A, calculate the magnetic force developed. Calculate the magnitude of force for x = 2.5 cm.
4. (a) Discuss the effect of pitch and distribution factors is an alternator.
(b) A 3-ph. Star connected alternator has a rating of 810 kVA at 2.5 kV and has 12 poles. Rated speed is 500 r.p.m. There are three slots per pole per phase and the number of conductors per slot are 5. For a full pitched winding, compute the flux per pole to give the rated terminal voltage at no load.
5. (a) What is the effect of excitation, speed and load on the losses of a d.c. machine ?
(b) A 230 V d.c. shunt motor is taking 5A when running at no load. The armature
resistance including brushes is 0.2 and field circuit resistance is 115 . For and input current of 72A, calculate the shaft output and efficiency. Also calculate the armature current at which the efficiency is maximum.
6. A 6 pole, 50 Hz, 3-phase induction motor has a rotor resistance of 0.2 per phase and a maximum torque of 160 Nm at 875 r.p.m. Calculate the following :—
(a) The torque for full load slip of 4%.
(b) The resistance to be added to the rotor to obtain 80% of full load torque at starting.
7. (a) A synchronous motor is operating at 0.6 pf lag at half-full load. With Ef , Vt, Xs remaining constant, explain whether its power factor will be worsened or improved when it is made to operate at full load.
(b) A 433 – V, 3-phase, star-connected synchronous motor has a synchronous reactance of 5 per phase. For a power output of 15 kW, find its minimum armature current, excitation voltage and the power-angle. Armature resistance is negligible.
8. (a) Derive expressions for the inductance per phase of a 3 phase line with equilateral and unsymmetrical spacings, both, separately.
(b) The 3 conductors of a 3-phase line are arranged in a horizontal plane and are 4 meters apart. The diameter of each conductor is 2 cm. Calculate the capacitance between conductors.
9. (a) Discuss the advantages and disadvantages of transmitting large amounts of power over long distances using high voltage dc as compared to 3 phase ac transmission.
(b) What is the percentage saving in feeder conductor if the line voltage in a dc 2 wire system is raised from 220 volts to 500 volts for the same power to be transmitted.
10. Derive an expression for the resistance to be provided across circuit breaker contacts for critical damping when :—
(a) Circuit breaker is located at the sub-station and followed by a transmission line.
(b) The circuit breaker is located at the end of a long transmission line and with fault occuring on it.
————
Note: = Pie Symbol
RBISB (Manager Grade B Electrical)
Descriptive Type Paper II
2010 Question Paper
1. (a) An LC parallel circuit has an applied voltage = 50 Cos (3000t+450) volts and
a total current iT = 2 cos (3000t – 450) amperes. It is also known that the current in the L branch is five times greater than the current in the C branch. Find L and C of this circuit.
(b) The Circuit constants R and L of a coil are to be determined by connecting the coil in series with a resistor of 25 and applying a 120 V, 60 Hz source and then reading the voltages across the resistor and the coil. Find R and L if VR = 70. 8 Volts and VCoil = 86 Volts.
2. (a) Explain the principle of transformer action and derive an expression for the emf induced in a transformer winding. Show that the emf per turn in primary is equal to emf per turn in the secondary.
(b) Develop a phasor diagram of a single phase transformer under load for a lagging power factor.
3. (a) Find an expression for the magnetic force developed in a doubly excited translational magnetic system.
(b) Two air-cored coils have their magnetic axes coincident. Their parameters are :—
L1 =0.4 H L2 = 0.2H
M12 = M21 = 0.1e– 4x H, and where x is the distance between the two Coils.
For steady state current of I1 = 10A and I2 = 5A, calculate the magnetic force developed. Calculate the magnitude of force for x = 2.5 cm.
4. (a) Discuss the effect of pitch and distribution factors is an alternator.
(b) A 3-ph. Star connected alternator has a rating of 810 kVA at 2.5 kV and has 12 poles. Rated speed is 500 r.p.m. There are three slots per pole per phase and the number of conductors per slot are 5. For a full pitched winding, compute the flux per pole to give the rated terminal voltage at no load.
5. (a) What is the effect of excitation, speed and load on the losses of a d.c. machine ?
(b) A 230 V d.c. shunt motor is taking 5A when running at no load. The armature
resistance including brushes is 0.2 and field circuit resistance is 115 . For and input current of 72A, calculate the shaft output and efficiency. Also calculate the armature current at which the efficiency is maximum.
6. A 6 pole, 50 Hz, 3-phase induction motor has a rotor resistance of 0.2 per phase and a maximum torque of 160 Nm at 875 r.p.m. Calculate the following :—
(a) The torque for full load slip of 4%.
(b) The resistance to be added to the rotor to obtain 80% of full load torque at starting.
7. (a) A synchronous motor is operating at 0.6 pf lag at half-full load. With Ef , Vt, Xs remaining constant, explain whether its power factor will be worsened or improved when it is made to operate at full load.
(b) A 433 – V, 3-phase, star-connected synchronous motor has a synchronous reactance of 5 per phase. For a power output of 15 kW, find its minimum armature current, excitation voltage and the power-angle. Armature resistance is negligible.
8. (a) Derive expressions for the inductance per phase of a 3 phase line with equilateral and unsymmetrical spacings, both, separately.
(b) The 3 conductors of a 3-phase line are arranged in a horizontal plane and are 4 meters apart. The diameter of each conductor is 2 cm. Calculate the capacitance between conductors.
9. (a) Discuss the advantages and disadvantages of transmitting large amounts of power over long distances using high voltage dc as compared to 3 phase ac transmission.
(b) What is the percentage saving in feeder conductor if the line voltage in a dc 2 wire system is raised from 220 volts to 500 volts for the same power to be transmitted.
10. Derive an expression for the resistance to be provided across circuit breaker contacts for critical damping when :—
(a) Circuit breaker is located at the sub-station and followed by a transmission line.
(b) The circuit breaker is located at the end of a long transmission line and with fault occuring on it.
————
Note: = Pie Symbol
0 comments:
Pen down your valuable important comments below