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close this bookElectrical Machines - Basic Vocational Knowledge (IBE - Deutschland; 144 pages)
View the documentIntroduction
Open this folder and view contents1. General information about electrical machines
Open this folder and view contents2. Basic principles
Open this folder and view contents3. Execution of rotating electrical machines
Open this folder and view contents4. Synchronous machines
Open this folder and view contents5. Asynchronous motors
close this folder6. Direct current machines
View the document6.1. Constructional assembly
Open this folder and view contents6.2. Operating principles
Open this folder and view contents6.3. Operational behaviour of direct current machines
Open this folder and view contents6.4. Circuit engineering and operational features of customary direct current generators
close this folder6.5. Circuit engineering and operational features of customary direct current motors
View the document6.5.1. Direct current motor with permanent excitation
View the document6.5.2. Direct current series motor
View the document6.5.3. Direct current shunt motor
Open this folder and view contents7. Single-phase alternating current motors
Open this folder and view contents8. Transformer
 

6.5.3. Direct current shunt motor

The direct current shunt motor is a direct current motor whose exciter windings (E1, E2) have been series-switched to the rotor winding.


Figure 110 - Circuitry and terminal board of a direct current shunt motor

(1) Clockwise, (2) Anti-clockwise

Dependence of current take-up on the torque (load)

Current take-up is made up of rotor current IL and exciter current Ie : I = IL + Ie. The curve I = f (M) (Figure 111) shows that exciter current flows as M = 0. Current take-up increases as load increases. Very considerable current flows during overloading.


Figure 111 - I = f (M); Current take-up dependence on the torque of a direct current shunt motor

1 Rated current, 2 Rated torque, 3 Idling current (exciter current), 4 Idling torque

Dependence of speed on the torque (load)

Speed behaviour is characterised through minimal linear speed reduction as load increases.


Figure 112 - n = f (M); Speed dependence on the torque of a direct current shunt motor

1 Rated speed, 2 Rated torque, 3 Idling speed, 4 Idling torque

The unloaded motor runs at an idling speed of N0 and the rated speed of nn is less than 10 per cent.

The speed change between the idling speed n0 and the rated speed of nn is less than 10 per cent.

Speed control

Sound speed control is possible by altering the exciter flow with the aid of the strain field actuator and varying the applied mains voltage.

Application

The direct current shunt motor is used as a drive for machine tools and automation equipment because of its virtually constant speed.

Questions for repetition and control

1. Describe the construction and mode of operation of a direct current generator.

2. Differentiate between the different types of direct current machines.

3. How can the speed of a direct current shunt motor be changed?

4. Explain why a starter is required to start up a direct current motor?

5. How can one alter the rotational direction of a motor?

 

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