Table of Contents
- 1 Why is it necessary to cut out all the resistance in the field rheostat while stopping the motor?
- 2 What will happen if you reduce field current to minimum value?
- 3 What happens to motor speed when field resistance is decreased?
- 4 Why is motor field rheostat kept in minimum position?
- 5 What are the aims of performing a load test on DC shunt motor?
- 6 Why motor field rheostat kept in minimum position?
- 7 Why the armature rheostat kept in maximum position?
- 8 Why should the rheostat be adjusted to maximum resistance?
- 9 How do you estimate motor loads?
- 10 What is an acceptable load range for an electric motor?
Why is it necessary to cut out all the resistance in the field rheostat while stopping the motor?
Precaution While stopping the motor, all the resistance in the field rheostat is cutout, so that motor speed falls to its normal value; then the line switch is opened. This procedure ensures that, the next time the motor is started, it will be with a strong field and resultant strong starting torque.
What will happen if you reduce field current to minimum value?
On weakening of field current, flux of the field will reduced results in increase of speed. If we want to decrease the speed, firstly we should keep the field resistance at minimum value and then we will increase the armature resistance.
What does a field rheostat do?
rheostat, adjustable resistor used in applications that require the adjustment of current or the varying of resistance in an electric circuit. The rheostat can adjust generator characteristics, dim lights, and start or control the speed of motors.
What happens to motor speed when field resistance is decreased?
The connection of RC in the field reduces the field current, and hence the flux is also reduced. This reduction in flux increases the speed, and thus, the motor runs at a speed higher than the normal speed.
Why is motor field rheostat kept in minimum position?
Answer: At the time of starting of motor, the armature resistance is kept at maximum position to control and reduce the high starting current and field rheostat atminimum position to ensure that speed does not go beyond rated value and to have high starting torque.
Why should the field rheostat be kept?
What are the aims of performing a load test on DC shunt motor?
Readings with loading of DC Shunt Generator. AIM : To perform load test on a DC series generator and to draw the internal and external (Performance) characteristics . saturation of the machine iron & rapidly increasing voltage drop of armature and armature resistance.
Why motor field rheostat kept in minimum position?
Why does reducing the field current increase the motor speed?
Hence as we decrease field current below rated, the flux also reduces and hence speed increases(above rated speed). And Eb (back emf) is directly proportional to speed. Therefore, by reducing field current, the speed also increase which leads to increase in mechanical power output.
Why the armature rheostat kept in maximum position?
At the time of starting of motor, the armature resistance is kept at maximum position to control and reduce the high starting current and field rheostat atminimum position to ensure that speed does not go beyond rated value and to have high starting torque.
Why should the rheostat be adjusted to maximum resistance?
Set up the apparatus as show in the diagram above. Adjust the rheostat to the maximum so that the smallest possible current flows in the circuit. Adjust the rheostat to allow a larger current to flow in the circuit.
How to connect the motor field rheostat and generator?
PROCEDURE: 1. Make the connections as shown in the circuit diagram.Keep the motor field rheostat in the minimum position and the generator field rheostat in the maximum position at starting. 2. Start the MG set and bring it to the rated speed of the generator by adjusting the motor field rheostat.
How do you estimate motor loads?
Motor part-loads may be estimated through using input power, amperage, or speed measurements. This fact sheet briefly discusses several load estimation tech- niques. Most electric motors are designed to run at 50\% to 100\% of rated load. Maximum efficiency is usually near 75\% of rated load.
What is an acceptable load range for an electric motor?
Reasons to Determine Motor Loading Most electric motors are designed to run at 50\% to 100\% of rated load. Maximum efficiency is usually near 75\% of rated load. Thus, a 10-horsepower (hp) motor has an acceptable load range of 5 to 10 hp; peak efficiency is at 7.5 hp. A motor ’s efficiency tends to decrease dramatically below about 50\% load.
How do I perform a motor load and efficiency analysis?
You should perform a motor load and efficiency analysis on all of your major working motors as part of your preventative maintenance and energy conservation program. Use Attach- ment A, “Motor Nameplate and Field Test Data Form, ” to record motor nameplate data and field measurements.
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