FFT Applications
FFT Other analysis (special purpose usage)
O-1-2 Breakage diagnosis of rotor bar in squirrel cage induction motor
- If an abnormality such as breakage caused by stress due to aging occurs on the rotor of an induction motor, unbalanced current flows in the rotor and load current of the motor pulsates as a result. When unbalanced current flows, sideband waves ±2sf are generated with respect to the fundamental wave f on the current spectrum as shown in the following figure. This pulsation current ratio is almost proportional to the extent of rotor abnormality. By measuring pulsation current with a clamp type ammeter and analyzing frequency spectrum variation of the pulsation current with an FFT analyzer, breakage of a bar or a rotor can be diagnosed.
This diagnosis method can be used for the following induction motors.
| ■ Induction motor for an electric power plant | ■ Induction motor for a petro- chemical plant | ■ Induction motor for a railroad car |
| ■ Induction motor for a semi-conductor production plant | ■ Induction motor for a metal production plant | ■ Induction motor for an iron and steel production plant |
| ■ Induction motor for a paper manufacturing plant | ■ Induction motor for a water and wastewater disposing facility | ■ Induction motor for an LNG pump |
Product list
| Model | Product name | Remarks | Qty | |
|---|---|---|---|---|
| 1 | CF-9200A | Portable 2-ch FFT Analyzer | 10.4-inch LCD touch panel, 2-channel input, wide dynamic range 120 dB or more, compact and light weight, high spec FFT analyzer with mobility | 1 |