Question

Write down the reasons why motors draw overcurrent from the mains and the names and protection types of motor protection relays used against this risk.
COMMAND AND POWER CIRCUIT IS A WHOLE IN QUESTIONS
The control circuit of the three asynchronous motors by answering the following requests
A) The second engine will not operate while the first or third engine is running
B) While the first or second engine is running, the third engine will not work.
C) When the first motor is stopped due to over current or by pressing the stop button, all
engines will stop.
D) Each engine can be operated separately.

Answer 1

The Main 5 reasons for motor draw over current are

1. Electrical overload.
2. Low Resistance
3. Over heating.
4. Contamination.
5. Vibration

Electrical overload.

Excessive current than the designed level flowing through the motor windings. This can be caused because of low voltage supply.

Prevention.

An over currene detector can be installed which detects the over current and cutoff the supply.

Low resistance

The overcurrent caused is mainly because of the insulation failure.  Low resistance is caused by the degradation of the insulation of the windings due to conditions such as overheating, corrosion, or physical damage. This leads to insufficient isolation between the conductors or motor windings, which can cause leakages and short circuits, and eventually motor failure.

Prevention

Preventive maintenance and constant check for insulation damage is the main method.

Over heating

Poor power quality can lead to over heating of coils and hence the insulation.

For every 10^oC increse then the rated temperature a 50% chance of increased possibility of damage of windigs.

prevention

Provide proper cooling.

Contamination

Contamination by foreign materials especially oil, sand particles, and metal powder cause damage to coils as well as the bearings of motor. which inturn draw overcurrent and stalls.

Prevention

Preventing contamination is relatively easy. Keep work areas, tools and fixtures as clean as possible to help eliminate the chance of contamination entering the motor. Also, when laying out the workspace, try to position motors away from grinding machines which produce large amounts of contaminants.

Vibration

Vibration is often caused by the motor being positioned on an uneven or unstable surface. However, vibration can also be a result of an underlying issue with the motor, such as loose bearings, misalignment, or corrosion.

Prevention

Proper mounting of Motor to the ground.

Check for any unusual noises.