When restarting an elevator that has been off for a long time, what could cause the generator to trip the overload?

When restarting an elevator that has been off for a long time, a dry sleeve bearing can lead to the generator tripping the overload due to increased friction and resistance. In a dormant state, lubrication in bearings may degrade or evaporate, resulting in a dry condition. When power is restored, the generator must work harder to overcome this friction, leading to higher startup currents. If these currents exceed the generator's capacity or the rated limits, it will cause the overload protection to trip to prevent damage to the generator and electrical components.

The dry condition of the sleeve bearing is crucial, as it can create substantial resistance that generates heat and can potentially lead to overheating. This is especially pertinent when an elevator is designed to carry a specific weight; additional resistance from mechanical components leads to increased demand on the electrical system. Proper lubrication is essential to ensure the elevator operates smoothly and efficiently from the start.

In contrast, while other factors like faulty circuit breakers, excessive loads, or voltage fluctuations can also impact system performance, they may not be as directly responsible for the unique challenges presented when restarting machinery that has been inactive for an extended period.