Two types of DC Series Motor Speed Control are there:
- Armature-controlled method.
- Field-controlled method.
1). Armature-Controlled Method
The armature controlled approach is further defined into three types:
- Armature-controlled resistance
- Shunted armature control
- Armature terminal voltage
Armature-Controlled Resistance
This method is most frequently used in applications when the motor supply and regulating resistance are connected in series.
Since this regulating method is typically employed for an extended period of time to reduce the speed during light loading conditions, the power loss that occurs in the DC series motor’s controlling resistance can be disregarded. It is mostly used to drive cranes, trains, & other vehicles and is an economical method for maintaining torque.
Shunted Armature Control
In this type, the rheostat will be connected to the armature in both series & shunting configurations. By adjusting the series rheostat, the voltage level applied to the armature will change.
The change in excitation current is accomplished by adjusting the shunt rheostat. Because of high power losses in speed regulation resistances, this method of controlling speed in a DC motor is rather inexpensive. The speed can be controlled to some amount, but it cannot be increased above the standard level.
Armature Terminal Voltage
A DC series motor’s speed can also be controlled by powering the motor with a variable supply voltage, although this method is expensive and not often used.
2). Field-Controlled Method
The field-controlled method is divided into two types:
- Field Diverter
- Tapped Field Control - Controlling of the Tapped Field
Field Diverter
This technique is employed by use of a diverter. The flux rate which is across the field can be decreased by short circuiting some part of the motor current through the series field. The lesser is the resistance of the diverter the field current is low hence showing lesser amount of current. This technique is employed beyond the typical range of speeds and is employed across the electric drives whereby there is an increase in the speed when the load is low.
Tapped Field Control
Here also, with the decrease of flux, the speed will be higher and it is done by redevelopment of turns of field winding from where current flows. Here, the number of tapping’s in the field winding is reduced and this technique is applied on electric tractions.
IEC 60034 & NEMA MG 1 for performance & design, IEEE 112 for efficiency testing, & UL 1004 for safety are DC Series Motor standards. In industrial applications, these standards ensure safety, compliance, and reliability.
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