When a synchronous motor starts, an excitation is imposed upon the torsional system due to field slippage. As the motor increases in speed, the torsional excitation frequency decreases toward zero. During this startup, the torsional system will be excited at its resonant frequencies below 120 Hz. The response amplitude and shaft stresses depend upon the resonant frequencies, the average and pulsating torque when the system passes through these resonant frequencies, the damping in the system, and the load torque of the driven equipment.
The analyses can be made for startup with the driven equipment loaded or unloaded. The transient response is also affected by the starting acceleration rate of the motor. For slower motor starts, the system will stay at a resonant frequency for a longer period of time allowing stresses to be amplified. If acceleration is rapid, then passing through the resonance quickly will minimize the amplification at resonant frequencies.
The main thing that sets EDI apart from other companies is our experience with analyzing and measuring vibration. This allows us to continually improve our analysis programs and verify that the calculated results are accurate. The plots below show torsional data measured with a strain gage telemetry system which closely matched the calculated torsional response.
