GENERATOR VIBRATION PROTECTION

Vibration protection is also a part of the turbine protection system and is not normally supplied or specified by the electrical protection engineer. Still, as noted above, vibration detection is the backup for faults that cause unbalanced rotor heating due to rotor faults or negative-sequence rotor heating. It is important that there be coordination between the electrical protections and the mechanical backup.

Vibration detection equipment should always be in service on a turbine-generator system. It is not adequate, for example, to manually add the vibration detection recorder after having detected a field ground. The reason is that the second field ground may occur quite soon after the first one and before any manual action is possible. The vibration detector should at least provide an alarm, but preferably should issue a time-delayed trip of the generator and field breakers. As noted previously, it is preferable that the vibration detector not trip the turbine, but only the generator and field breakers.
This type of redundancy in protection is important. The electrical detection equipment is designed on the basis of the cause of problems that lead to rotor heating and possible unbalance. Vibration detectors, on the other hand, are based on the effect of the unbalance. Failure of one type of detector is not likely to cause failure of the other; hence, the protection system that includes both has good reliability.