Considering a realistic motor functioning environment, the functioning of motors is quite crucial under varying loads of current, temperatures and voltages. The life of motors is mostly affected by the damage introduced to its windings and bearings. Due to the design of variable frequency drives, Electro-magnetic interface is introduced in the system which gives rise to variable currents. These currents cause great damage to motor bearings and windings in case they are not able to surpass the functioning circuit and reach the ground.
Most of the times, vibration analysis is used to check the faults that arise in the bearings of the motor, but the VFD induced damages are sure to grow too large till the time such tests can be initiated. Checking the motor operating voltages and measuring its vibration while the motor is functional are the two possible solutions for analyzing the life of motors. An oscilloscope can be used for measuring the currents flowing in the circuit by simply touching its ends with the running shaft. If the induced currents continue to cause damage over a long-span of time, the race wall erodes and the motor becomes quite vulnerable to risks.
The unplanned or unpredictable failure of motors can sometimes lead to great financial losses. Ground shafting ensures that the excess currents introduced through the vibrations and variable frequency drives are grounded so as not to disturb the cycle of seamless flow of current. This is a method of placement of equipment so that any halt in the process due to motor bearing damage may not affect the other running parts of the production chain. The concept behind this methodology is that when bearing gets damaged, the path of current will be blocked and thus, the current will find an alternative pathway to reach the ground.
The alternate path that the currents can choose in case of a damaged motor can go through a pipe, tachometer, pump, brake motor or encoder. For this purpose, the currents usually choose a path with low impedance. The ground shafting methodology is helpful in letting these currents flow to the Earth by creating a low impedance path that would protect the equipment. The setup of industrial equipment along with proper design considerations for grounding the currents is thus an essential. Also, the motors should be well rated for their compatibility with all the other chained processes. With properly engineered structure and in-flow systems, the running life of motors can be drastically improved.
Our friends at AEGIS provide a solution to avoid damage from shaft voltage. AEGIS® SGR Bearing Protection Ring is the most effective solution to protect bearings in motors and attached equipment from EDM currents and high frequency circulating currents.
For more information, contact L&S Electric!