CHAPTER 4: DC DYNAMO TORQUE RELATIONS-DC MOTORS

Example 4.1, Page number 100

In [1]:
import math

#Variable declaration
d = 0.5        #Diameter of the coil(m)
l = 0.6        #Axial length of the coil(m)
B = 0.4        #Flux density(T)
I = 25.0       #Current carried by the coil(A)
theta = 60.0   #Angle between the useful force & the interpolar reference axis(degree)

#Calculation
F = B*I*l                             #Force developed on each coil side(N)
f = F*math.sin(theta*math.pi/180)     #Useful force at the instant the coil lies at an angle of 60° w.r.t the interpolar ref axis(N)
r = d/2                               #Radius of the coil(m)
T_c = f*r                             #Torque developed(N-m)
T_c1 = T_c*0.2248*3.281               #Torque developed in lb-ft by first method
T_c2 = T_c*0.737562                   #Torque developed in lb-ft by second method

#Result
print('Case(a): Force developed on each coil side , F = %.f N' %F)
print('Case(b): Useful force at the instant the coil lies at an angle of 60° w.r.t the interpolar ref axis , f = %.1f N' %f)
print('Case(c): Torque developed , T_c = %.1f N-m' %T_c)
print('Case(d): Torque developed by first method , 1.3 N.m * 0.2248 lb/N * 3.281 ft/m = %.2f lb-ft' %T_c1)
print('         Torque developed by second method , 1.3 N.m * 0.737562 lb.ft/N.m = %.2f lb-ft' %T_c2)
Case(a): Force developed on each coil side , F = 6 N
Case(b): Useful force at the instant the coil lies at an angle of 60° w.r.t the interpolar ref axis , f = 5.2 N
Case(c): Torque developed , T_c = 1.3 N-m
Case(d): Torque developed by first method , 1.3 N.m * 0.2248 lb/N * 3.281 ft/m = 0.96 lb-ft
         Torque developed by second method , 1.3 N.m * 0.737562 lb.ft/N.m = 0.96 lb-ft

Example 4.2, Page number 100

In [1]:
import math

#Variable declaration
d = 18.0       #Diameter of the coil(inches)
l = 24.0       #Axial length of the coil(inches)
B = 24000.0    #Flux density(lines/sq.inches)
I = 26.0       #Current carried by the coil(A)
theta = 60.0   #Angle between the useful force & the interpolar ref axis(degree)

#Calculation
F = (B*I*l*10**-7)/1.13             #Force developed on each conductor(lb)
f = F*math.sin(theta*math.pi/180)   #Useful force at the instant the coil lies at an angle of 60° w.r.t the interpolar ref axis(lb)
r = d/2                             #Radius of the coil(inches)
T_c = f*(r*1.0/12)                  #Torque developed(lb.ft/conductor)

#Result
print('Case(a): Force developed on each conductor , F = %.3f lb' %F)
print('Case(b): Useful force , f = %.2f lb' %f)
print('Case(c): Torque developed , T_c = %.3f lb-ft/conductor' %T_c)
Case(a): Force developed on each conductor , F = 1.325 lb
Case(b): Useful force , f = 1.15 lb
Case(c): Torque developed , T_c = 0.861 lb-ft/conductor

Example 4.3, Page number 102

In [1]:
#Variable declaration
Z = 700.0       #Number of conductors
d = 24.0        #Diameter of the armature of the dc motor(inches)
l = 34.0        #Axial length of the coil(inches)
B = 50000.0     #Flux density(lines/sq.inches)
I = 25.0        #Current carried by the coil(A)
per = 0.7       #Conductors lying directly under poles

#Calculation
F_av = (B*I*l*10**-7)/1.13*(Z*per)   #Average total force tending to rotate the armature(lb) 
r = d/2                              #Radius of the coil(inches)
T_av = F_av*(r/12)                   #Armature torque(lb-ft)

#Result
print('Case(a): Average total force tending to rotate the armature , F_av = %.f lb' %F_av)
print('Case(b): Armature torque , T_av = %.f lb-ft' %T_av)
Case(a): Average total force tending to rotate the armature , F_av = 1843 lb
Case(b): Armature torque , T_av = 1843 lb-ft

Example 4.4, Page number 102

In [1]:
#Variable declaration
slots = 120.0                #Number of armature slots
conductors_per_slot = 6.0    #Number of conductors per slot
B = 60000.0                  #Flux density(lines/sq.inches)
d = 28.0                     #Diameter of the armature(inches)
l = 14.0                     #Axial length of the coil(inches)
A = 4.0                      #Number of parallel paths
span = 0.72                  #Pole arcs span 72% of the armature surface
I = 133.5                    #Armature current(A)

#Calculation
Z_Ta = slots*conductors_per_slot*span     #Number of armature conductors
F_t = (B*I*l)/(1.13*10**7 *A)*Z_Ta        #Force developed(lb)
r = (d/2)/12                              #Radius of the armature(feet)
T = F_t*r                                 #Total torque developed(lb-ft)

#Result
print('Total developed armature torque , T = %.f lb-ft' %T)
Total developed armature torque , T = 1500 lb-ft

Example 4.5, Page number 103

In [1]:
#Variable declaration
slots = 120.0                #Number of armature slots
conductors_per_slot = 6.0    #Number of conductors per slot
B = 60000.0                  #Flux density(lines/sq.inches)
d = 28.0                     #Diameter of the armature(inches)
l = 14.0                     #Axial length of the coil(inches)
A = 4.0                      #Number of parallel paths
span = 0.72                  #Pole arcs span 72% of the armature surface
T_a = 1500.0                 #Total armature torque(lb-ft)

#Calculation
Z = slots*conductors_per_slot         #Number of armature conductors
r = (d/2)/12                          #Radius of the armature(feet)
I_a = T_a*A*1.13*10**7/(B*l*Z*r*span) #Total external armature current(A)

#Result
print('Total external armature current , I_a = %.1f A' %I_a)
Total external armature current , I_a = 133.5 A

Example 4.6, Page number 104

In [1]:
#Variable declaration
phi_orig = 1.0    #Original flux
Ia_orig = 1.0     #Original armature current
T_orig = 150.0    #Original torque(N-m)
phi_new = 0.9     #New flux
Ia_new = 1.5      #New armature current

#Calculation
T_new = T_orig*(phi_new/phi_orig)*(Ia_new/Ia_orig)     #New torque produced(N-m)

#Result
print('New torque produced , T = %.1f N-m' %T_new)
New torque produced , T = 202.5 N-m

Example 4.7, Page number 105

In [1]:
#Variable declaration
R_a = 0.25    #Armature resistance(ohm)
BD = 3.0      #Brush contact drop(V)
V = 120.0     #Applied voltage(V)
E_ca = 110.0  #counter EMF at a given load(V)
E_cb = 105    #Counter EMF due to application of additional load(V)

#Calculation
I_a_a = (V-(E_ca+BD))/R_a            #Armature current(A)
I_a_b = (V-(E_cb+BD))/R_a            #Armature current(A)
del_Ec = ((E_ca-E_cb)/E_ca)*100      #Change in counter EMF(percent)
del_Ia = ((I_a_b-I_a_a)/I_a_a)*100   #Change in armature current(percent)

#Result
print('Case(a): Aramature current , I_a = %.f A' %I_a_a)
print('Case(b): Aramature current due to additional load , I_a = %.f A' %I_a_b)
print('Case(c): Change in counter EMF , δE_c = %.2f percent' %del_Ec)
print('         Change in armature current , δI_a = %.1f percent' %del_Ia)
Case(a): Aramature current , I_a = 28 A
Case(b): Aramature current due to additional load , I_a = 48 A
Case(c): Change in counter EMF , δE_c = 4.55 percent
         Change in armature current , δI_a = 71.4 percent

Example 4.8, Page number 106

In [1]:
#Variable declaration
V_a = 120.0       #Rated terminal voltage of the DC motor(V)
R_a = 0.2         #Armature circuit resistance(ohm)
R_sh = 60.0       #Shunt field resistance(ohm)
I_l = 40.0        #Line current at full-load(A)
BD = 3.0          #Brush voltage drop(V)
S_orig = 1800.0   #Rated full-load speed(rpm)
per = 125.0/100   #Overload speed

#Calculation
#Case(a)
I_f = V_a/R_sh                     #Field current(A)
I_a_fl = I_l-I_f                   #Armature current at full-load(A)
E_c_orig = V_a-(I_a_fl*R_a+BD)     #Back EMF at full-load(V)
I_a_nl = I_a_fl/2                  #Armature current at half-load(A)
E_c_final = V_a-(I_a_nl*R_a+BD)    #Back EMF at half load(V)
S_a = S_orig*(E_c_final/E_c_orig)  #Speed at full load(rpm)
#Case(b)
I_a_b = I_a_fl*per                 #Armature current at 125% overload(A)
E_c_b = V_a-(I_a_b*R_a+BD)         #Back EMF at 125% overload(V)
S_b = S_orig*(E_c_b/E_c_orig)      #Speed at 125% overload(rpm)

#Result
print('Case(a): Speed at half load , S = %.f rpm' %S_a)
print('Case(b): Speed at an overload of 125 perecent , S = %.f rpm' %S_b)
Case(a): Speed at half load , S = 1863 rpm
Case(b): Speed at an overload of 125 perecent , S = 1769 rpm

Example 4.9, Page number 106

In [1]:
#Variable declaration
I_l_orig = 40.0         #Original line current(A)
I_l_final = 66.0        #Final line current(A)
phi_orig = 1.0          #Original flux
phi_final = 112.0/100   #Final flux
V_a = 120.0             #Rated terminal voltage of the DC motor(V)
R_sh_orig = 60.0        #Original Field circuit resistance(ohm)
R_sh_final = 50.0       #Decreased final field circuit resistance(ohm)
R_a = 0.2               #Armature circuit resistance(ohm)
BD = 3.0                #Brush voltage drop(V)
S_orig = 1800.0         #Rated full-load speed(rpm)

#Calculation
I_f_orig = V_a/R_sh_orig                              #Original Field current(A)
I_a_orig = I_l_orig-I_f_orig                          #Original Armature current at full-load(A)
E_c_orig = V_a-(I_a_orig*R_a+BD)                      #Back EMF at full load(V)
I_f_final = V_a/R_sh_final                            #Final field current(A)
I_a_final = I_l_final-I_f_final                       #Final Armature current(A)
E_c_final = V_a-(I_a_final*R_a+BD)                    #Final EMF induced(V)
S = S_orig*(E_c_final/E_c_orig)*(phi_orig/phi_final)  #Final speed of the motor(rpm)

#Result
print('Speed of the motor , S = %.f rpm' %S)
Speed of the motor , S = 1532 rpm

Example 4.10, Page number 108

In [1]:
#Variable declaration
I_a_1 = 38.0      #Armature current at full-load(A) from example 4-8a
E_c_1 = 109.4     #Back EMF at full-load(V)
S_1 = 1800.0      #Speed at full-load(rpm)
I_a_2 = 19.0      #Armature current at half-load(A) from example 4-8a
E_c_2 = 113.2     #Back EMF at half-load(V)
S_2 = 1863.0      #Speed at half-load(rpm)
I_a_3 = 47.5      #Armature current at 125% overload(A) from example 4-8b
E_c_3 = 107.5     #Back EMF at 125% overload(V)
S_3 = 1769.0      #Speed at 125% overload(rpm)
I_a_4 = 63.6      #Armature current at overload(A) from example 4-9
E_c_4 = 104.3     #Back EMF at overload(V)
S_4 = 1532.0      #Speed at overload(rpm)

#Calculation
P_d_1 = E_c_1*I_a_1    #Armature power developed at full-load(W)
P_d_2 = E_c_2*I_a_2    #Armature power developed at half-load(W)
P_d_3 = E_c_3*I_a_3    #Armature power developed at 125% overload(W)
P_d_4 = E_c_4*I_a_4    #Armature power developed at overload(W)

#Result
print(' Example \t I_a \t E_c \t Speed \t P_d or (E_c*I_a)')
print(' _______________________________________________________________________')
print(' 4-8a \t\t %d \t %.1f \t %d \t %d W at full-load' %(I_a_1,E_c_1,S_1,P_d_1))
print('      \t\t %d \t %.1f \t %d \t %.f W at half-load' %(I_a_2,E_c_2,S_2,P_d_2))
print(' 4-8b \t\t %.1f \t %.1f \t %d \t %d W at 125 percent overload' %(I_a_3,E_c_3,S_3,P_d_3))
print(' 4-9  \t\t %.1f \t %.1f \t %d \t %d W at overload' %(I_a_4,E_c_4,S_4,P_d_4))
print(' _______________________________________________________________________')
 Example 	 I_a 	 E_c 	 Speed 	 P_d or (E_c*I_a)
 _______________________________________________________________________
 4-8a 		 38 	 109.4 	 1800 	 4157 W at full-load
      		 19 	 113.2 	 1863 	 2151 W at half-load
 4-8b 		 47.5 	 107.5 	 1769 	 5106 W at 125 percent overload
 4-9  		 63.6 	 104.3 	 1532 	 6633 W at overload
 _______________________________________________________________________

Example 4.11, Page number 110

In [1]:
#Variable declaration
T_a = 6.5     #Torque(dyne-centimeters)
T_b = 10.6    #Torque in (gram-centimeters)
T_c = 12.2    #Torque in (ounce-inches)

#Calculation
T_a_Nm = T_a*1.416*10**-5*7.0612*10**-3    #Torque(N-m)
T_a_lbft = T_a*1.416*10**-5*5.208*10**-3   #Torque(lb-ft)
T_b_Nm = T_b*(1/72.01)*7.0612*10**-3       #Torque(N-m)
T_b_lbft = T_b*(1/72.01)*5.208*10**-3      #Torque(lb-ft)
T_c_Nm = T_c*7.0612*10**-3                 #Torque(N-m)
T_c_lbft = T_c*5.208*10**-3                #Torque(lb-ft)

#Result
print('Case(a): Torque , T = %.1e N-m' %T_a_Nm)
print('         Torque , T = %.1e lb-ft' %T_a_lbft)
print('Case(b): Torque , T = %.2e N-m' %T_b_Nm)
print('         Torque , T = %.2e lb-ft' %T_b_lbft)
print('Case(c): Torque , T = %.3e N-m' %T_c_Nm)
print('         Torque , T = %.2e lb-ft' %T_c_lbft)
Case(a): Torque , T = 6.5e-07 N-m
         Torque , T = 4.8e-07 lb-ft
Case(b): Torque , T = 1.04e-03 N-m
         Torque , T = 7.67e-04 lb-ft
Case(c): Torque , T = 8.615e-02 N-m
         Torque , T = 6.35e-02 lb-ft

Example 4.12, Page number 110

In [1]:
#Variable declaration
V_a = 120.0    #Rated terminal voltage of dc shunt motor(V)
R_a = 0.2      #Armature resistance(ohm)
BD = 2.0       #Brush drop(V)
I_a = 75.0     #Full-load armature current(A)

#Calculation
I_st = (V_a-BD)/R_a           #Current at the instant of starting(A)
percentage = I_st/I_a*100     #Percentage at full load

#Result
print('Current at the instant of starting , I_st = %.f A (Counter EMF is zero)' %I_st)
print('Percentage at full load = %d percent' %percentage)
Current at the instant of starting , I_st = 590 A (Counter EMF is zero)
Percentage at full load = 786 percent

Example 4.13, Page number 111

In [1]:
#Variable declaration
V_a = 120.0          #Rated terminal voltage of dc shunt motor(V)
R_a = 0.2            #Armature resistance(ohm)
BD = 2.0             #Brush drop(V)
I_a = 75.0           #Full-load armature current(A)
I_a_new = 1.5*I_a    #Armature current at 150% rated load(A) 
E_c_a = 0            #Back EMF at starting(V)
E_c_b = 0.25* V_a    #Back EMF is 25% of Va at 150% rated load(V)
E_c_c = 0.5*V_a      #Back EMF is 50% of Va at 150% rated load(V)

#Calculation
R_s_a = (V_a-E_c_a-BD)/I_a_new-R_a   #Starting resistance at starting(ohm)
R_s_b = (V_a-E_c_b-BD)/I_a_new-R_a   #Starting resistance 25% of Va(ohm)
R_s_c = (V_a-E_c_c-BD)/I_a_new-R_a   #Starting resistance 50% of Va(ohm)
E_c_d = V_a-(I_a*R_a+BD)             #Counter EMF at full-load without starting resistance(V)

#Result
print('Case(a): Starting resistance at the instant of starting , R_s = %.2f Ω' %R_s_a)
print('Case(b): Starting resistance at 25 percent of armature voltage , R_s = %.3f Ω' %R_s_b)
print('Case(c): Starting resistance at 50 percent of armature voltage , R_s = %.3f Ω' %R_s_c)
print('Case(d): Counter EMF at full-load without starting resistance , E_c = %.f V' %E_c_d)
Case(a): Starting resistance at the instant of starting , R_s = 0.85 Ω
Case(b): Starting resistance at 25 percent of armature voltage , R_s = 0.582 Ω
Case(c): Starting resistance at 50 percent of armature voltage , R_s = 0.316 Ω
Case(d): Counter EMF at full-load without starting resistance , E_c = 103 V

Example 4.14, Page number 115

In [1]:
#Variable declaration
T_orig = 160.0          #Original torque developed(lb-ft)
I_a_orig = 140.0        #Original armature current(A)
phi_f_orig = 1.6*10**6  #Original field flux(lines)
T_final_a = 190.0       #Final torque developed when reconnected as a cumulative compound motor(lb-ft)
I_a_b = 154.0           #Final armature current(A)

#Calculation
phi_f = phi_f_orig*(T_final_a/T_orig)                  #Field flux(lines)
percentage = (phi_f/phi_f_orig)*100-100                #Percentage increase in flux
phi_f_final = 1.1*phi_f                                #Final field flux(lines)
T_f = T_final_a*(I_a_b/I_a_orig)*(phi_f_final/phi_f)   #Final torque developed(lb-ft)

#Result
print('Case(a): Flux increase due to series field , Φ_f = %.1f percent' %percentage)
print('Case(b): Final torque , T_f = %.f lb-ft' %T_f)
Case(a): Flux increase due to series field , Φ_f = 18.8 percent
Case(b): Final torque , T_f = 230 lb-ft

Example 4.15, Page number 115

In [1]:
#Variable declaration
I_a_orig = 25.0    #Original armature current(A)
I_a_final = 30.0   #Final armature current(A)
T_orig = 90.0      #Original torque developed(lb-ft)
phi_orig = 1.0     #Original flux
phi_final = 1.1    #Final flux

#Calculation
T_a = T_orig*(I_a_final/I_a_orig)**2   #Final torque developed if field is unsaturated(lb-ft)
T_b = T_orig*(I_a_final/I_a_orig)*(phi_final/phi_orig) #Final torque developed when current rises to 30A and flux increases by 10%

#Result
print('Case(a): Torque when field is unsaturated , T = %.1f lb-ft' %T_a)
print('Case(b): Torque when current rises to 30 A and flux increases by 10 percent , T = %.1f lb-ft' %T_b)
Case(a): Torque when field is unsaturated , T = 129.6 lb-ft
Case(b): Torque when current rises to 30 A and flux increases by 10 percent , T = 118.8 lb-ft

Example 4.16, Page number 119

In [1]:
#Variable declaration
V_a = 230.0   #Rated armature voltage(V)
P = 10.0      #Rated power(hp)
S = 1250.0    #Rated speed(rpm)
R_A = 0.25    #Armature resistance(ohm)
R_p = 0.25    #Interpole resistance(ohm)
BD = 5.0      #Brush voltage drop(V)
R_s = 0.15    #Series field resistance(ohm)
R_sh = 230.0  #Shunt field resistance(ohm)
I_fl = 55.0   #Line current at rated load(A)
I_ol = 4.0    #No-load line current(A)
S_o = 1810.0  #No-load speed(rpm)

#Calculation
#Case(a)
R_a = R_A+R_p                          #Effective armature resistance(ohm)
I_f = V_a/R_sh                         #Field current(A)
I_a = I_ol-I_f                         #Armature current at no-load(A)
E_c_o = V_a-(I_a*R_a+BD)               #No-load back EMF(V)
I_a_fl = I_fl-I_f                      #Armature current at full-load(A)
E_c_full_load = V_a-(I_a_fl*R_a+BD)    #Back EMF at full-load(V)
S_r = S_o*(E_c_full_load/E_c_o)        #Speed at rated load(rpm)
#Case(b)
P_d = E_c_full_load*I_a_fl             #Internal power(W)
hp = P_d/746.0                         #Internal horse power(hp)

#Result
print('Case(a): Speed at rated load , S_r = %.f rpm' %S_r)
print('Case(b): Internal power in watts , P_d = %.f W' %P_d)
print('         Internal horse-power developed , P_d = %.1f hp' %hp)
Case(a): Speed at rated load , S_r = 1603 rpm
Case(b): Internal power in watts , P_d = 10692 W
         Internal horse-power developed , P_d = 14.3 hp

Example 4.17, Page number 119

In [1]:
#Variable declaration
V_a = 230.0    #Rated armature voltage(V)
P = 10.0       #Rated power(hp)
S = 1250.0     #Rated speed(rpm)
R_A = 0.25     #Armature resistance(ohm)
R_p = 0.25     #Interpole resistance(ohm)
BD = 5.0       #Brush voltage drop in volt
R_s = 0.15     #Series field resistance in ohm
R_sh = 230.0   #Shunt field resistance in ohm
phi_1 = 1.0    #Original flux per pole
I_fl = 55.0    #Line current at rated load(A)
phi_2 = 1.25   #Flux increased by 25% due to long-shunt cumulative connection
I_ol = 4.0     #No-load line current(A)
S_o = 1810.0   #No-load speed(rpm)

#Calculation
R_a = R_A+R_p                          #Effective armature resistance(ohm)
I_f = V_a/R_sh                         #Field current(A)
I_a = I_ol-I_f                         #Armature current at no-load(A)
E_c_o = V_a-(I_a*R_a+BD)               #No-load back EMF(V)
I_a_fl = I_fl-I_f                      #Armature current at full-load(A)
#Case(a)
E_c_o1 = V_a-(I_a*R_a+I_a*R_s+BD)      #No-load back EMF for long shunt cumulative connection(V)
S_n1 = S_o*(E_c_o1/E_c_o)              #Speed at no-load(rpm)
#Case(b)
E_c_full_load_lsh = V_a-(I_a_fl*R_a+I_a_fl*R_s+BD )       #Back EMF at full-load for long-shunt cumulative motor(V)
S_r_lsh = S_n1*(E_c_full_load_lsh/E_c_o1)*(phi_1/phi_2)   #Speed at rated load for long shunt connection(rpm)
#Case(c)
E_c_full_load = V_a-(I_a_fl*R_a+BD)                       #Back EMF at full-load(V)
S_r = S_o*(E_c_full_load/E_c_o)                           #Speed at rated load for shunt connection(rpm)
P_d = E_c_full_load*I_a_fl                                #Internal power(W)
hp = P_d/746.0                                            #Internal horse power(hp)
T_shunt = hp*5252/S_r                                     #Internal torque at full-load for shunt motor(lb-ft)
I_a1 = I_a_fl                                             #Armature current for shunt motor(A)
I_a2 = I_a_fl                                             #Armature current for long-shunt cumulative motor(A)
T_comp = T_shunt*(phi_2/phi_1)*(I_a2/I_a1)                #Internal torque at full load for long-shunt cumulative motor(lb-ft)
#Case(d)
Horsepower = (E_c_full_load_lsh*I_a_fl)/746               #Internal horsepower of compound motor based on flux increase(hp)

#Result
print('Case(a): Speed at no-load , S_n1 = %d rpm' %S_n1)
print('Case(b): Speed at rated-load , S_r = %d rpm' %S_r_lsh)
print('Case(c): Internal torque at full-load with series field , T_comp = %.2f lb-ft' %T_comp)
print('         Internal torque at full-load without series field , T_shunt = %.2f lb-ft' %T_shunt)
print('Case(d): Internal horsepower of the compound motor , Horsepower = %.1f hp' %Horsepower)
print('Case(e): The internal hp exceeds the rated hp because the power developed in the motor must also overcome the internal mechanical rotational losses')
print('\nNOTE: The change in obtained answer from that of textbook is due to more precision i.e more number of decimal places in this case')
Case(a): Speed at no-load , S_n1 = 1806 rpm
Case(b): Speed at rated-load , S_r = 1230 rpm
Case(c): Internal torque at full-load with series field , T_comp = 58.68 lb-ft
         Internal torque at full-load without series field , T_shunt = 46.94 lb-ft
Case(d): Internal horsepower of the compound motor , Horsepower = 13.7 hp
Case(e): The internal hp exceeds the rated hp because the power developed in the motor must also overcome the internal mechanical rotational losses

NOTE: The change in obtained answer from that of textbook is due to more precision i.e more number of decimal places in this case

Example 4.18, Page number 120

In [1]:
#Variable declaration
P = 25.0      #Power rating of a series motor(hp)
V_a = 250.0   #Rated voltage(V)
R_a = 0.1     #Armature circuit resistance(ohm)
BD = 3.0      #Brush voltage drop(V)
R_s = 0.05    #Series field resistance(ohm)
I_a = 85.0    #Armature current(A)
I_a1 = 100.0  #Armature current(A)(case a)
I_a2 = 40.0   #Armature current(A)(case b)
S_1 = 600.0   #Speed(rpm)
R_d = 0.05    #Diverter resistance(ohm)

#Calculation
#Case(a)
E_c2 = V_a-I_a1*(R_a+R_s)-BD       #Back EMF when Ia = 100 A(V)
E_c1 = V_a-I_a*(R_a+R_s)-BD        #Back EMF when Ia = 85 A(V)
S_2 = S_1*(E_c2/E_c1)*(I_a/I_a1)   #Speed(rpm)
#Case(b)
E_c3 = V_a-I_a2*(R_a+R_s)-BD       #Back EMF when Ia = 40 A(V)
S_3 = S_1*(E_c3/E_c1)*(I_a/I_a2)   #Speed(rpm)
#Case(c)
R_sd = (R_s*R_d)/(R_s+R_d )        #Effective series field resistance(ohm)
E_c2_new = V_a-I_a1*(R_a+R_sd)-BD  #Back EMF when Ia = 100 A(V)
S_2_new = S_1*(E_c2_new/E_c1)*(I_a/(I_a1/2))  #Speed(rpm) 
E_c3_new = V_a-I_a2*(R_a+R_sd)-BD  #Back EMF when Ia = 40 A(V)
S_3_new = S_1*(E_c3_new/E_c1)*(I_a/(I_a2/2))  #Speed(rpm) 

#Result
print('Case(a): Speed when current is 100 A , S_2 = %.f rpm' %S_2)
print('Case(b): Speed when current is 40 A , S_3 = %d rpm' %S_3)
print('Case(c): Speed when current is 100 A and using a diverter , S_2 = %.f rpm' %S_2_new)
print('         Speed when current is 40 A and using a diverter , S_3 = %.f rpm' %S_3_new)
Case(a): Speed when current is 100 A , S_2 = 505 rpm
Case(b): Speed when current is 40 A , S_3 = 1311 rpm
Case(c): Speed when current is 100 A and using a diverter , S_2 = 1021 rpm
         Speed when current is 40 A and using a diverter , S_3 = 2634 rpm

Example 4.19, Page number 121

In [1]:
#Variable declaration
S_n1 = 1810.0    #No-load speed(rpm) From Ex. 4-16
S_f1 = 1603.0    #Full-load speed(rpm)
S_n2 = 1806.0    #No-load speed(rpm) From Ex. 4-17
S_f2 = 1231.0    #Full-load speed(rpm)
S_n3 = 1311.0    #No-load speed(rpm) From Ex. 4-18
S_f3 = 505.0     #Full-load speed(rpm)

#Calculation
SR_1 = (S_n1-S_f1)/S_f1*100   #Speed regulation for shunt motor(%)
SR_2 = (S_n2-S_f2)/S_f2*100   #Speed regulation for compound motor(%)
SR_3 = (S_n3-S_f3)/S_f3*100   #Speed regulation for series motor(%)

#Result
print('Case(a): Speed regulation , SR(shunt) = %.1f percent' %SR_1)
print('Case(b): Speed regulation , SR(compound) = %.1f percent' %SR_2)
print('Case(c): Speed regulation , SR(series) = %.1f percent' %SR_3)
Case(a): Speed regulation , SR(shunt) = 12.9 percent
Case(b): Speed regulation , SR(compound) = 46.7 percent
Case(c): Speed regulation , SR(series) = 159.6 percent

Example 4.20, Page number 121

In [1]:
import math

#Variable declaration
SR = 0.1                    #Speed regulation of a shunt motor 
omega_f1 = 60.0*math.pi     #Full-load speed(rad/s)

#Calculation
omega_n1 = omega_f1*(1+SR)             #No-load speed(rad/s)
S = omega_n1*(1/(2*math.pi))*(60.0/1)  #No-load speed(rpm) 

#Result
print('Case(a): No-load speed , ω_n1 = %.fπ rad/s' %(omega_n1/math.pi))
print('Case(b): No-load speed , S = %.f rpm' %S)
Case(a): No-load speed , ω_n1 = 66π rad/s
Case(b): No-load speed , S = 1980 rpm

Example 4.21, Page number 122

In [1]:
#Variable declaration
S_int = 1603.0    #Internal rated speed(rpm)
S_ext = 1250.0    #External rated speed(rpm)
hp_int = 14.3     #Internal horsepower
hp_ext = 10.0     #External horsepower

#Calculation
T_int = hp_int*5252/S_int   #Internal torque(lb-ft)
T_ext = hp_ext*5252/S_ext   #External torque(lb-ft)

#Result
print('Case(a): Internal torque , T_int = %.2f lb-ft' %T_int)
print('Case(b): External torque , T_ext = %.1f lb-ft' %T_ext)
print('Case(c): Internal hp developed due electromagnetic torque is used internally to overcome mechanical losses of the motor reducing the torque available at its shaft to perform work')
Case(a): Internal torque , T_int = 46.85 lb-ft
Case(b): External torque , T_ext = 42.0 lb-ft
Case(c): Internal hp developed due electromagnetic torque is used internally to overcome mechanical losses of the motor reducing the torque available at its shaft to perform work

Example 4.22, Page number 123

In [1]:
#Variable declaration
P = 50.0    #Power rating of the servo motor(W)
S = 3000.0  #Full-load speed of the servo motor(rpm)

#Calculation
T_lbft = (7.04*P)/S          #Output torque(lb-ft)
T_ounceinch = T_lbft*192     #Output torque(ounce-inches)

#Result
print('Output torque available at the motor pulley , T = %.1f oz-in' %T_ounceinch)
Output torque available at the motor pulley , T = 22.5 oz-in

Example 4.23, Page number 123

In [1]:
import math

#Variable declaration
P = 50.0    #Power rating of the servo motor(W)
S = 3000.0  #Full-load speed of the servo motor(rpm)

#Calculation
S_rad_per_sec = S*2*math.pi/60         #Full-load speed of the servo motor(rad/s)
omega = 314.2                          #Angular frequency(rad/s)
T_Nm = P/omega                         #Output torque(N-m)
T_ounceinch = T_Nm*1/(7.0612*10**-3)   #Output torque(oz-in)

#Result
print('Case(a): Motor speed in radians per second = %.1f rad/s' %S_rad_per_sec)
print('Case(b): Output torque in newton-meters , T = %.4f N-m' %T_Nm)
print('Case(c): Output torque in ounce-inches , T = %.1f oz-in' %T_ounceinch)
print('Case(d): Both answers are the same')
Case(a): Motor speed in radians per second = 314.2 rad/s
Case(b): Output torque in newton-meters , T = 0.1591 N-m
Case(c): Output torque in ounce-inches , T = 22.5 oz-in
Case(d): Both answers are the same