The field rheostat reduces the shunt field current( Ish). As flux is directly proportional to current,So the flux also get reduced. By this method the speed can be raised above normal speed as shown in figure. Generally, this method permits to increase the speed in the ratio 3:1.
How do you control the speed of a DC shunt motor?
In this method, speed variation is accomplished by means of a variable resistance inserted in series with the shunt field. An increase in controlling resistances reduces the field current with a reduction in flux and an increase in speed. This method of speed control is independent of load on the motor.
Which method we adopt to control the speed of DC shunt motor above the base speed?
The field flux control method is used when the speed is above the base speed. In this mode of operation, the armature current is maintained constant at its rated value, and the generator voltage Vt is kept constant. The motor field current is decreased and as a result, the motor field flux also decreases.
How does a DC drive change the speed of a motor?
A DC motor with a constant field voltage increases its speed when the voltage across its armature circuit increases, and vice versa. Above the motor’s base speed (maximum rated speed with rated load, armature, and field voltage), speed can be increased by reducing field voltage.
How do you calculate the speed of a DC shunt motor?
- I− × – n rps. V (supply) If. TL. …
- = 71000 rpm. × thus, n2. = 881.9 rpm. Initially a d.c shunt motor having ra = 0.5 Ω and Rf = 220 Ω is running at 1000 rpm drawing 20 A from 220 V supply. If the field resistance is increased by 5%, calculate the new steady state armature current and speed of the motor.
Why DC shunt motor is constant speed?
Since torque is proportional to armature current, torque also increases. Finally, this increased torque allows the motor to increase its speed and compensate for the slowdown due to loading. Hence, a DC shunt motor is able to self-regulate its speed, and can be referred to as a constant speed motor.
What are the advantages of DC shunt motor?
Advantages of DC Shunt Motors
- direct current machines can use for heavy industrial applications where torque and speed wider range.
- Shunt wound motor able to runs at a predetermined speed.
- The power supply of DC motor is any way cheap.
Can we change the direction of rotation of DC shunt motor?
shunt field connections. series field connections. … The direction of rotation of a DC compound motor may be conveniently reversed by reversing the connection of both series and shunt field winding or may be reversing the armature connection but not both at the same time.
How do you change the speed of a motor?
AC motors are constant speed devices but their speed can vary if you change the input voltage or frequency or the windings that make the motor rotate. The most common and efficient way of changing the speed is to vary the frequency by using an inverter as the power supply.
Can you control the speed of a single phase motor?
The two primary ways to control the speed of a single-phase AC motor is to either change the frequency of the line voltage the motor sees or by changing the voltage seen by the motor, thereby changing the rotational speed of the motor.
Which motor is used for variable speed?
What are the characteristics of DC shunt motor?
Characteristics of a DC Shunt Motor:
- Speed-Armature Current Characteristic: …
- Torque-Armature Current Characteristic: …
- Speed-Torque Characteristic: …
- Break in Field Circuit of a DC Motor:
Why DC shunt motor is started on no load?
For DC shunt motor the field resistance is high and armature resistance is low so the variation of flux is very less when rated voltage is applied to the motor and motor speed does not exceeds rated speed at no load. So we can start the DC shunt motor with no load.
What is the speed of dc motor?
DC controls adjust speed by varying the voltage sent to the motor (this differs from AC motor controls which adjust the line frequency to the motor). Typical no load or synchronous speeds for an AC fractional horsepower motor are 1800 or 3600 rpm, and 1000-5000 rpm for DC fractional hp motors.7 мая 2018 г.