Motor Failures & Conditions
Excessive heat, noise, or vibration in a motor is an indication of this issue.
What are worn bearings?
This common term refers to the back-and-forth movement of a motor shaft along its axis.
What is end play?
The two typical flexible couplings for direct-drive motors are the jaw coupling and this.
What is a splined coupling?
This condition is a winding coming into contact with the motor frame.
What is a grounded winding?
The specific term for momentarily starting a motor to check its direction of rotation.
What is bumping?
The electrical fault that occurs when one phase of a three-phase system is lost.
What is single-phasing?
This test instrument uses a high test voltage to measure resistance values in the megohm range.
What is a megohmmeter (or megger)?
The specific term for frame distortion that occurs when a motor's feet are anchored to an uneven surface.
What is soft foot?
This instrument is used to measure the rotation speed of the motor shaft.
What is a tachometer?
The motor should be run for this amount of time, unloaded, during the first-time startup before connecting the load.
What is one hour?
According to the NEMA standard, this is the maximum allowable percentage of voltage imbalance.
What is 5%?
When performing an insulation test with a megohmmeter, the motor frame must be connected to this.
What is ground?
These mechanical fasteners are installed in the motor feet and base to allow the motor to be returned to the exact same position after removal for repair.
What are dowel pins?
This insulation class includes organic materials like cotton, paper, and enamel-coated wire.
What is Class A?
A primary electrical check to be performed during the first coupled startup, besides checking for excess vibration.
What is checking the operating current on each phase?
This is the maximum voltage variation from the nameplate voltage that a motor is typically built to withstand.
What is 10%?
This predictive test is performed with the motor stopped and power locked out and tagged.
What is an offline (or static) test?
The only part of a motor that is intended to be used for lifting the motor frame.
What are the eyebolts (on the motor frame)?
The type of motor analysis that is performed while the motor is running (dynamic).
What is online motor analysis (or online testing)?
A key step in establishing the motor shaft’s electrical center after loosening the bearings and before shimming or repositioning.
What is marking the shaft position?
Starting methods like primary resistor, autotransformer, and wye-delta are used to reduce this high electrical event.
What is starting current (or inrush current)?
This minimum value is recommended for the Polarization Index (PI) of AC and DC motors and generators.
What is 2.0?
During bearing lubrication, the motor must be run for 5 to 10 minutes to purge excess grease before reinstalling this component.
What is the relief plug?
The test that compares the insulation resistance after 10 minutes to the insulation resistance after 1 minute.
What is the Polarization Index (PI) test?
This configuration of motor is the most common type in commercial and industrial use.
What is a three-phase, squirrel-cage induction motor?