blob: c074420493d425bc765ae3c8d65fee9f5375c2b2 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
|
//Chapter 5:Dc Motor Drives
//Example 17
clc;
//Variable Initialization
//Ratings of the separately excited motor
V=220 // rated voltage in V
N=1500 // rated speed in rpm
Ia=50 // rated current in A
Ra=0.5 // armature resistance in ohms
Vl=440 // line voltage inV with 3-phase ac supply
f=50 //frequency of the source voltage in Hz
//Solution
//(i) Tranformer ratio
alpha=0 //firing angle in degrees
Va=V //motor terminal voltage is equal to the rated voltage when the firing angle is 0 degrees
Vm=%pi/3*Va/cos(alpha)
Vrms=Vm/sqrt(2) //rms value of the converter input voltage
a=(Vl/sqrt(3))/Vrms //required transformer ratio
//(ii)Value of the firing angle
E=V-Ia*Ra //back emf at the rated speed
//(a)When the speed of the motor is 1200 rpm and rated torque
N1=1200 //speed of the motor i rpm
E1=N1/N*E //back emf at the given speed N1
Va=E1+Ia*Ra //terminal voltage at the given speed N1
alpha=acos(%pi/3*Va/Vm) //required firing angle in radians
alpha1=alpha*180/%pi //required firing angle in degrees
//(b)When the speed of the motor is -800 rpm and twice the rated torque
N1=-800 //speed of the motor in rpm
E1=N1/N*E //back emf at the given speed N1
Ia=2*Ia //torque is directly proportional to the current hence twice the rated current
Va=E1+Ia*Ra //terminal voltage at the given speed N1
alpha=acos(%pi/3*Va/Vm) //required firing angle in radians
alpha2=alpha*180/%pi //required firing angle in degrees
//Results
mprintf("(i)Hence the required transformer ratio is :%.3f",a)
mprintf("\n(ii)(a)Hence the required firing angle is :%.2f °",alpha1)
mprintf("\n(b)Hence the required firing angle is :%.2f °",alpha2)
|
