Mechanical Vibration Analysis of Induction Motors Using Wireless Sensors

Induction machines like induction motors have widespread applications. Due to their simplicity and robustness, the induction motors are prefered machines in many industrial as well as household applications. These machines are often operated under heavy-duty and with minimal downtime. Yet there are common faults that can affect the induction motors in many ways.

Irregular radial and tangential forces.
irregular mechanical behaviour.
bearing faults, rotor bar and end ring faults in case of squirrel cage induction motor
Stator faults and air gap eccentricity in rotors.

These faults can lead to abnormal vibrations in the machine. These irregular vibrations can result in faster degradation of the machine, Noise and can affect the mechanical behaviour of the machine. The vibration analysis at different rotational speed frequency can help us in finding different faults and overcome the failures caused by these faults.

In this Instructable we will be using Wireless Vibration Sensor to overcome this problem. These sensors are industrial grade sensors and have been successfully deployed in many application like Structural analysis of civil infrastructures , vibration analysis of wind turbine , vibration analysis of the hydro turbine . Here we will be demonstrating the following-

Wireless Vibration and Temperature Sensors.
Vibration analysis using these Sensors.
Gathering and analysing the data using Wireless gateway device
Publishing and Subscribing to Sensor data using Ubidots

Step 1: Hardware and Software Specifications

Software Specification

Hardware Specification

Step 2: Guidelines to Check Vibration in Induction Motor

Vibrations at a rotational speed frequency are characteristic of different faults. Vibration at this frequency can occur due to the unbalanced rotor, coupling misalignment or even a broken rotor bar. Rotor eccentricity(air gap between rotor and stator) leads unbalanced magnetic pull. This unbalanced magnetic pull excites the vibration at rotation speed frequency. In order to segregate the fault and fault identifying vibration we are using the following guidelines:

speed rotation frequency is given by- f = RPM/60
pole passing frequencies due to rotor eccentries given by-
f= 2ps (where p= number of poles and s=slip frequency of machine)

Experiments conducted on 1500 RPM (1493.4 RPM) motor with speed rotation frequency of 24.89 Hz with the load. The following guidelines have to be followed:

0.01g or Less - Excellent condition - The machine is properly working.
0.35g or less - Good condition. The machine is working fine. No action required unless the machine is noisy. There can be a rotor eccentricity fault.
0.75g or more - Rough Condition- Need to check the motor there can be rotor eccentricity fault if the machine is making too much noise.
1g or more - Very Rough condition - There can be a severe fault in a motor. The fault might be due to bearing fault or bending of the bar. Check for the noise and temperature
1.5g or more- Danger Level- Need to repair or change the motor.
2.5g or More -Very High Danger Level-Shut down the machinery immediately.

Step 3: Getting the Vibration Sensor Values

The vibration values, that we are getting from the sensors are in milis. These consists of the following values.

RMS value- root mean square values along all three axes. The peak to peak value can be calculated as

peak to peak value = RMS value/0.707

Min value- Minimum value along all three axes
Max values- peak to peak value along all three axes. The RMS value can be calculated using this formula

RMS value = peak to peak value x 0.707

Earlier when the motor was in good condition we got the values around 0.002g. But when we tried it on a faulty motor the vibration we examined was about 0.80g to 1.29g. The faulty motor was subjected to high rotor eccentricity.

So, we can improve the fault tolerance of the motor using the Vibration sensors.

Step 4: Publishing the Values to Ubidots

Now to visualize the published data in Ubidots dashboard . We need to add the variables and the widgets to it

Click '+' sign on the top right corner
Select the Widget, There are many ways to visualize sensor data using these widgets. Ubidots gives us the option to make a Line Chart, Bar Graph, Histogram and many more.
Add the variable, by selecting Add Variable option.
Now select the device and then Add variable
Now visualize and analyse the sensor data present in the dashboard

Step 5: Visualizing the Sensor Data on UbiDots

Step 6: Email Notification Using Ubidots

Ubidots gives us another tool to send an email notification to the user. We have created an event of temperature alert that is whenever the temperature goes beyond 30 degrees an automated mail will be sent to the user. We also have created an event for vibration. If there is any kind of vibration examined by the Wireless Sensors. An automated email notification will be forward to the user. When it comes back to the normal state another automated mail is sent to the user to notify him/her.

Step 7: Overall Code

The firmware of this setup can be found in this GitHub repository

Introduction: Mechanical Vibration Analysis of Induction Motors Using Wireless Sensors