Electrical Machines 101 · DC Machines

Torque–speed characteristic and equivalent circuit

Operating speed n — —

Operating mode — —

Torque T_e = ΣT_R — —

Armature current I_a — —

Field current I_f — —

Back EMF E_g — —

No-load speed n₀ — —

Stall torque T_p — —

Machine settings

Armature supply V_a 240 V

0300 V

sets ω₀ and T_p together

Field supply V_f 240 V

40300 V

independent of V_a — that is the point

Field resistance R_f 160 Ω

90480 Ω

I_f = 1.500 A

Mechanical load ΣT_R

Load torque at rated speed 57 N·m

−80 (overhauling)240 N·m

1.00 × rated torque

Load type

hoist, conveyor, kiln — torque does not change with speed

Equivalent circuit

Torque–speed characteristic

Torque–current characteristic

Operating point — numeric view

Steady state, linear magnetics. Speeds in rev/min with rad/s alongside — the equations use ω_m in rad/s. The sign convention is motoring-positive, so I_a < 0 means the machine is generating.

Quantity	Symbol	Value	Unit	Note