# Relationship between speed and armature current

### Methods of Speed Control of DC Motor – Edgefx

İf you know please tell me the relationship between speed-torque and armature current-field current or give me the address where I can find. With increased armature current maximum speed, could be controlled up to rated speed, from zero speed as V= Eb+IaRa, where V the rated voltage and Ia the. DC shunt Motor Connection Diagram Hence the armature current differs and the speed of a DC Shunt motor will continue constant which is.

A portion of the main current is diverted through a variable resistance Rd. Thus, the function of a diverter is to reduce the current flowing through the field winding. The reduction in field current reduces the amount of flux and as a result the speed of the motor increases. Tapped Field Control The second method used in a series motor for the variation in field current is by tapped field control.

The connection diagram is shown below.

Here the ampere turns are varied by varying the number of field turns. This type of arrangement is used in an electric traction system. The speed of the motor is controlled by the variation of the field flux. The speed-torque characteristic of a series motor is shown below. Advantages of Field Flux Control The following are the advantages of the field flux control method.

This method is easy and convenient. As the shunt field is very small, the power loss in the shunt field is also small.

The flux cannot usually be increased beyond its normal values because of the saturation of the iron. Therefore, speed control by flux is limited to the weakening of the field, which gives an increase in speed. This method is applicable over only to a limited range because if the field is weakened too much, there is a loss of stability. The arrangement of this system is as required in the figure shown below.

M1 may be any AC motor or DC motor with constant speed. G is the generator directly coupled to M1.

### Characteristics of DC Shunt Motor - My Tech Info

In this method the output from the generator G is fed to the armature of the motor M2 whose speed is to be controlled. The generator output voltage can be connected to the motor M2 and it can be varied from zero to its maximum value, and hence the armature voltage of the motor M2 is varied very smoothly.

Hence very smooth speed control of motor can be obtained by this method. A Rheostart is connected parallel to the series field as shown in fig a. Hence flux can be decreased to desired amount and speed N can be increased.

For a given constant load torque, if armature current is reduced, then flux must increase.

### Speed Control of DC Motor: Armature Resistance Control and Field Flux Control - Circuit Globe

In this method, field coil is tapped dividing the number of turns. These characteristics are determined by keeping the following two relations in mind. For a DC motor, magnitude of the back emf is given by the same emf equation of a dc generator i. In DC series motors, field winding is connected in series with the armature, i.

Therefore, the Ta-Ia curve is parabola for smaller values of Ia. Therefore, after magnetic saturation, Ta-Ia curve becomes a straight line.

## Characteristics of DC Shunt Motor

The shaft torque Tsh is less than armature torque Ta due to stray losses. Hence, the curve Tsh vs Ia lies slightly lower. In DC series motors, prior to magnetic saturation torque increases as the square of armature current, these motors are used where high starting torque is required.

As we know, flux is directly proportional to Ia, speed is inversely proportional to Ia. Therefore, when armature current is very small the speed becomes dangerously high.