in d.c motor T is directly proportional to I current and speed is inversely proportional to current. if we increase the current the torque is increases, speed is decreases, but here torque is twisting moment or force so speed is also increases. but here is decreases why?

 

Electrical...

are you asking for general information, or are you experiencing a problem with a specific machine?

Regards,
Phil Corso

 

Torque is directly proportional to current - but speed is directly proportional to voltage.

In a simple separately-excited machine, the rotor will generate an emf that is sufficient to match the applied armature voltage. Voltage is proportional to the product of field flux density and speed.

Torque is developed by the interaction of the current with the flux, and is proportional to the product of current and flux density.

If the field is connected to the armature in some way, the flux depends on the other electrical parameters - with shunt excitation, the field current and hence flux density will be proportional to the armature voltage, while with series excitation the field current is equal to the armature current. The effect you have described where torque increases and speed decreases sounds like a series-excited motor.