hey,

i am after a bit of help on the question attached.

Okay so i figured out the torque and input power quite easily.

I then figured out Total current (before it has reached field or armature) by doing total power in divided by supply voltage of 48. This gave me 13.02 Amps

right so i tried re-arranging P = Tw = Eia (where w is angular velocity)

i messed around for a while rearranging torque into k If Ia and a few other things

i changed E to V - IaRa to try and get a constant etc etc.

I think perhaps part of the problem is i dont fully understand what rated and no load mean. I assumed rated was normal operating point and no load was full speed but no torque but i don't think that can be right because then armature current would b 0? (I have used it for other questions and it gives me the right answer but i don't know why)

anyways after searching for ages i found the equation V = IwL (L is inductance)

i assume this i only for AC but woteva i tried it for the field current using the mutual inductance and no load speed and i got the right answer for field current = 1.269

can somebody explain this? surly under DC, the field winding acts as a short no? the change in current with respect to time is zero?

so when i have this i can simply do 13.02 - 1.27 to get my armature current of 11.75

forpart b, i didn't really have many problems. I would like to know the whole idea of the transient equations tho. I know how to do them and what the voltages are for

for armature i got voltage over resistor (IaRa), over armature coil (Ldi/dt) and in rotor itself ( IfwLad)

i don't get the whole rotor bit itself, is this excited emf by movement of the rotor i assume?

so basically what this is saying i have voltage lost in resistor, voltage in rotor windings (when it is first switched on before steady state) and an extra bit of voltage caused by movement of conductor in the stators magnetic field. Surely this is going to create a voltage bigger than what i supply? Have i got summit wrong here? This (If w Lad) is screwing me over.

going back to the diagram does it mean i should have a armature resistor, armature coil and the emf circle thingy?

for field i got IfRf + Lfdi/dt

and i will worry about c when i know what is going on i parts a and b.

Thanks for your help and sorry if this is a bit mumbo jumbo,

Lee.

i am after a bit of help on the question attached.

Okay so i figured out the torque and input power quite easily.

I then figured out Total current (before it has reached field or armature) by doing total power in divided by supply voltage of 48. This gave me 13.02 Amps

right so i tried re-arranging P = Tw = Eia (where w is angular velocity)

i messed around for a while rearranging torque into k If Ia and a few other things

i changed E to V - IaRa to try and get a constant etc etc.

I think perhaps part of the problem is i dont fully understand what rated and no load mean. I assumed rated was normal operating point and no load was full speed but no torque but i don't think that can be right because then armature current would b 0? (I have used it for other questions and it gives me the right answer but i don't know why)

anyways after searching for ages i found the equation V = IwL (L is inductance)

i assume this i only for AC but woteva i tried it for the field current using the mutual inductance and no load speed and i got the right answer for field current = 1.269

can somebody explain this? surly under DC, the field winding acts as a short no? the change in current with respect to time is zero?

so when i have this i can simply do 13.02 - 1.27 to get my armature current of 11.75

forpart b, i didn't really have many problems. I would like to know the whole idea of the transient equations tho. I know how to do them and what the voltages are for

for armature i got voltage over resistor (IaRa), over armature coil (Ldi/dt) and in rotor itself ( IfwLad)

i don't get the whole rotor bit itself, is this excited emf by movement of the rotor i assume?

so basically what this is saying i have voltage lost in resistor, voltage in rotor windings (when it is first switched on before steady state) and an extra bit of voltage caused by movement of conductor in the stators magnetic field. Surely this is going to create a voltage bigger than what i supply? Have i got summit wrong here? This (If w Lad) is screwing me over.

going back to the diagram does it mean i should have a armature resistor, armature coil and the emf circle thingy?

for field i got IfRf + Lfdi/dt

and i will worry about c when i know what is going on i parts a and b.

Thanks for your help and sorry if this is a bit mumbo jumbo,

Lee.