6.5.2. Direct current series motor
The direct current series motor is a direct current motor whose exciter windings (D1, D2) have been series-switched to the rotor winding.
1 Clockwise, 2 Anti-clockwise
Dependence of current take-up on the torque (load)
Current take-up by the motor depends on the load. As curve I = f (M) indicates, during idling the motor only takes up minimal current. Current take-up increases through greater load. Thereby, however, the increase in current intensity is greater than the load growth.
1 Rated current, 2 Rated torque
Dependence of speed on the torque (load)
The speed-torque curve (Figure 109) shows that the speed depends to a considerable extent on the load. Whilst idling speed assumes greater values. Given reduction the motor may “race” under certain circumstances.
1 Rated speed, 2 Rated torque
The considerable centrifugal power which then arises can destroy the motor. Therefore the motor must be securely attached to the drive machine. Speed declines markedly as the load increases. The direct current series motor develops a considerable initial torque during starting. It can, therefore, also start given excessive load.
Speed can be controlled by
- a series resistor
Direct current series motors are used where considerable speed ranges and excessive torques are in evidence and “racing” is not possible (e.g. for driving electric railways, cranes, escalators).
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