Download D.C. Machine a) Explain the different methods of excitation system of

D.C. Machine
1) a) Explain the different methods of excitation system of a D.C. machine. [ 5 ]
b) A 250 volt shunt motor has an armature resistance of 0.5 ohm and runs at 1200 rpm.
When the armature current is 80 A. If the torque remain unchanged, find the speed and armature current when
the field is strengthened by 25%.
[5]
2) a) Why D.C. series motor is not started with no load ?
b) What is the significance of back e.m.f. in a D.C. motor ?
[3]
[3]
c) A 4 pole D.C. motor takes an armature current of 150A at 440 volt. If its armature circuit has
a resistance of 0.15 ohm. What will be the value of back e.m.f. at this load ?
3) . a)
[4]
Derive the expression of e.m.f of a d.c machine. What is the significance of back e.m.f?
Write the applications of a d.c shunt and series motor with reasons .
[3+1+2=6]
b) A 220v d.c machine has an armeture resistance of 0.5. If the full load armeture current is 20A, find the
induced e.m.f when the machine acts as (i)generator, (ii) motor.
[4]
4) a) Draw the speed-torque, Torque-current, & speed-current characteristics of a d.c shunt motor and series motor.
[6]
b) A 6-pole lap wound armature is required to generate a total e.m.f of 432 volt when revolving at 360 r.p.m. If the
flux per pole entering the armature be 0.08 Wb. Calculate the required number of armature conductor.
[4]
5) a) derive an expression for the torque developed in a d.c. motor.
b) The armature of a D.C. machine has a resistance of 0.2 ohm and is connected to a 220 V supply.
Calculate the generated e.m.f. when it is running
(i)
(ii)
6) Write short notes on:
As a generator giving 60A.
As a motor taking 40A
a) Speed control of DC motor
Single Phase Transformer
1) a) Derive the e.m.f. equation of a single phase Transformer.
[5]
b) A 6000/400V,50 Hz, single phase core type transformer has a net cross sectional area of the core 428 cm 2. The
maximum flux density in the core is 1.5 Tesla. Calculate the number of turns in the primary and secondary windings.
[5]
2) a) What is the significance of regulation of a Transformer ?
[3]
b) What is efficiency of a Transformer ?
[2]
c) A 25 KVA Transformer with a ratio of 2000/ 250 volt has a primary resistance of 1.15 ohm
and a secondary resistance of 0.016 ohm.Find out
[5]
i)
The total resistance refered to secondary.
ii)
The total resistance drop on full load.
iii)
The total copper loss on full load .
3. a) What is a transformer ? Draw the equivalent circuit of ideal transformer and the vector diagram of a transformer
on no load condition .
[1+2+2=5]
b) A 10 kvA, 200/400v,50 HZ single phase transformer gave the following test results:
o.c test: 200V, 1.3A, 120W (on l.v.side)
s.c test:
22V, 30A, 200W(on h.v.side)
Find the parameters of equivalent circuit as referred to l.v.winding.
[5]
4) a) Define efficiency of a single phase transformer.
b)Deduce the condition for maximum voltage regulation of a single phase transformer.[1+3=4]
c) Consider a 20KVA,2200/220V,50Hz, transformer. The open circuit &short circuit test results are as follows:
O.C Test:
220V 4.2A 148W (L. V side)
S.C Test:
86V
10.5A 360W (H.V side)
Determine the regulation at 0.8 p.f lagging and at full load.
[6]
5) a) Define efficiency of a single phase transformer.
b)Deduce the condition for maximum voltage regulation of a single phase transformer.[1+3=4]
c) Consider a 20KVA,2200/220V,50Hz, transformer. The open circuit &short circuit test results are as follows:
O.C Test:
220V 4.2A 148W (L. V side)
S.C Test:
86V
10.5A 360W (H.V side)
Determine the regulation at 0.8 p.f lagging and at full load.
[6]
6) a) Explain what will happened if D.C. supply is connected to the primary of the Transformer ?
b) In short-ckt. And open-ckt. Test data of a 4KVA, 200/400 volt ,50 Hz single phase transformer
are :
(i)
O.C. test on the primary side : v=200 v, I=0.8 SA, W= 70 W.
(ii)
S.C. test on the secondary side : V=17.5 V, I=9A, W=50W.
Find the parameter of the equivalent circuit.
7) Write short notes on: a) Hysteresis and Eddy current loss
b) Core and shell type Transformer
Induction Motor
1) a) Why induction motor never achieve the speed equals to synchronous speed ? [3]
b) What is “ Slip” ?
[2]
c) A 4 pole , 3 phase, 275 KW, 440 volt, 50Hz induction motor has a speed of
1460 rpm on full load. Calculate the slip.
[5]
2) a) Explain the production of rotating field in a 3 phase induction motor.
b)Explain the Torque-Slip curve of a 3 phase Induction motor considering all three mode.
3) a)
b)
[5]
[5]
Describe the Direct On Line (D.O.L) starting of squirrel cage induction motor with diagram.
[6]
What do you mean by slip?
A 3-phase induction motor having 2 poles is connected to 400V,50HZ supply . Calculate the actual rotor
speed . When the slip is 4%.
[1+3=4]
4) a) Explain the working principles of a 3-phase induction motor. What will happen if the slip of the motor becomes
zero.
[4+1=5]
b) The electromagnetic force in the stator of an 8-pole induction motor has a frequency of 50Hz, and that in the rotor is
1.5Hz. Calculate the speed of the motor and slip.
[5]
5) a) What is ‘slip’ ? Establish the relationship among the motor frequency ,Slip and supply frequency
of a 3 phase Induction motor.
b) A 6 pole, 3 phase, 373KW, 440 volt, 50 Hz Induction motor has a speed of 940 r.p.m. on full
load. Calculate the slip.
Three Phase System
1) a) Derive the relationship between phase and line voltages for a Star and Delta connected circuit. [5]
b) A balanced star connected load has impedance 6+j8 in each phase. If the supply is 3 phase, 230 volt, 50 Hz, find
the line current, power factor, active and reactive power.
[5]
2) a) Explain the method of measurement of balanced three phase power by two wattmeter method Under different
power factor conditions.
[7]
b) Draw single line diagram for power transmission and distribution.
[3]
3) a)
A 3-phase system is supplying 20 KW load on 0.8 p.f and 200 volts to a factory. Find out its line current and
phase current when the load is connected in (1)star ,(2) delta.
[4]
b) Draw single line diagram of transmission and distribution system .
What do you mean by balanced load and unbalanced load.
4) a) State some advantages of three phase a.c. system over single phase a.c. system.
b) Explain in brief “ phase sequence “ in relation to three phase a.c. system.
c) State the relation between line and phase voltages and current in a delta connection
and draw the complete phasor diagram for voltages and current in star connection.
[4+2=6]