- #1
Michael Neo
- 49
- 3
- Homework Statement
- A 250 V shunt motor has an armature resistance of 0.4 Ω and runs at a speed of 750 rev min –1 when taking a full load current of 25 A.
Estimate the speed of the motor at no load when the armature current is 3 A, assuming that the flux per pole remains constant.
- Relevant Equations
- Back EMF:
E=V-Ia*Ra
Field Current:
If=Il-Ia
Field Resistance:
Rf=V/If
Change in Speed:
Old speed = (New speed)*(V-If*Ia)/E
Field Current
If=25-3
If=22 A
Field Resistance
Rf=250/22
Rf=11.36363636 Ohms
Back EMF
E=250-3x0.4
E=248.8 V
New Speed
New Speed = (Old speed)*(V-If*Ra))/E
New Speed = (750)*(250-22*0.4)]/248.8
New Speed = 727.0900322 rpm
Where can I find the appropriate formula for the change in speed in this scenario?
I have searched several books.
If=25-3
If=22 A
Field Resistance
Rf=250/22
Rf=11.36363636 Ohms
Back EMF
E=250-3x0.4
E=248.8 V
New Speed
New Speed = (Old speed)*(V-If*Ra))/E
New Speed = (750)*(250-22*0.4)]/248.8
New Speed = 727.0900322 rpm
Where can I find the appropriate formula for the change in speed in this scenario?
I have searched several books.