Anna University Chennai 2005 B.E Electrical and Electronics Engineering SOLID STATE DRIVES - Question Paper

B.E / B. Tech. Degree Examination, APRIL / MAY-2005

VII – SEMSTER
Electrical and Electronics Engineering

EE432-SOLID STATE DRIVES


Time: 3hrs Max. Marks: 100
ans all ques.
PART – A (10 x two = 20 Marks)

1. Classify the mechanical loads based on their speed- torque characteristics

2. elaborate the disadvantage of using a motor of wrong rating?

3. Mention 2 advantage of a dual converter fed DC drive when compared to conventional
Ward – scheme.

4. Why thyristors are not preferred now a days for chopper fed DC drives?

5. What happens to the performance of AC motor if the stator voltage control technique is
adopted with frequency being constant?

6. Constant torque loads are not suitable for AC voltage controller fed inductor motor drive. Why?

7. List the demerits of the rotor resistance control using SCR switching with external resistance

8. Why the power factor of the slip power recovery scheme of speed control of inducting motor is low?

9. elaborate the modes of speed control of a synchronous motor?

10. elaborate the applications of cycle converter fed synchronous motor drive?

PART – B (5 x 16 = 80 Marks)

11. (i) explain the different factors to be considered for selection of drive motor. (8)

(ii) The load cycle of a motor operating a lift for nine minutes is as follows.

(1) Load period at the bottom – four minutes – one kw
(2) Load going top – one minute – 20 kw
(3) Loading period at the top – three minutes – one kw
(4) load coming down – one minute – 15 kw
Regenerative braking takes place when the load is descending. The cycle is repeated continuously.Estimate a suitable rating of the motor. (8)

12. (a) (i) discuss the operation of a single phase fully controlled converter fed separately excited DC
motor with neat wave forms and derive the speed torque characteristics. (8)

(ii) A separately excited DC motor operating from a single phase half controlled bridge
at a speed of 1450 rpm, has input voltage of 330 sin 314 t and a back emf of 75 V.
The SCRs are fired symmetrically at ?????????in every half cycle and the armature
has resistance of 5???Neglecting armature inductance compute the avg. armature
current and the developed torque. (8)
(or)

(b) (i) Explain the operation of the 2 quadrant chopper fed de drive system. (8)

(ii) The speed of a separately excited dc motor is controlled by a chopper. The dc supply
voltage is 120 V, armature circuit resistance is 0.5 ???armature circuit inductance is 20 mH, and back emf constant 0.05 V/rpm. The motor drives a constant torque load requiring an avg. armature current of 20 A. Assuming the motor current to be continuous, determine
the range of speed control and the ranger of duty cycle. (8)

13. (a) Explain in detail the speed control scheme for a 3 phase inducting motor using
PWM inverter.Provisions are to be made in the scheme for speed control as well as
regenerative braking in the both directions. (16)
(or)

(b) (i) Compare voltage source inverter fed drive with a current source inverter fed drive. (6)

(ii) Discuss briefly the different braking methods for inductions motors. (10)

14. (a) Explain how the slip of slip ring induction motor can be altered by extracting power from
the rotor and dissipating it in the external circuit through a switching device. explain the
principle with neat sketch. (16)
(or)
(b) Explain how slip power recovery scheme helps to achieve sub synchronous speed control
of slip ring induction with an improvement in overall efficiency. (16)

15. (a) Explain how 3 phase synchronous motor fed by a 3 phase inverter can be made to
behave like a simple DC motor . Hence is it proper to call them as a commutator
less DC motor. (16)
(or)
(b) Write short notes on the following:

(i) Power factor control of synchronous motor drive. (8)

(ii) actual synchronous mode of operation. (8)

Earning:   Approval pending.