Wound rotor motors
Wound rotor motors
(OP)
Does the added resistance in these motors on start up improve power factor. And also how is the inrush current limited I know that the as the rotors EMF passes the motor windings a counter EMF is produced decreasing the line current but how is inrush current different in these compared to squirrel cage motors?
RE: Wound rotor motors
This fig does shows steady state torque. Inrush depends on the resistance inserted. Inrush will be approximately proportional to percent full loss torque at zero speed.
RE: Wound rotor motors
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Wound rotor motors
If the contacts close simultaneously
(Torque) = (Tlockrotor) + (lock rotor current)*(rotor leakage reactance/(stator leakage reactance + rotor leakage reactance)) * (factor) + sin(2*pi*line hz*time)
where
(factor) = e^((-1)*(2*pi*line hz)*(Stator cct resistance)*(rotor cct resistance) / (magnetizing reactance * (stator cct resistance + rotor cct resistance)))*time
Note: calculated torque, lock rotor torque, lock rotor current, leakage and magnetizing reactance, and all resistances are in PER UNIT.
As any added resistance (e.g. a liquid rheostat or a switched resistor bank) in the rotor circuit becomes part of the rotor circuit during the start, it can be seen that the addition of resistance will have an effect on both the starting torque and the lock rotor current. More resistance in the circuit reduces inrush current (because there's only so much voltage to go around) and consequently the torque developed will also be less than a full-voltage condition.
Converting energy to motion for more than half a century
RE: Wound rotor motors
Torque doesn't go down, the breakdown peak just shifts around.
RE: Wound rotor motors
=====================================
(2B)+(2B)' ?