NCCER Millwright Practice Exam

The over speed trip device is usually actuated when the turbine reaches what percentage above normal full-load speed?

1. 5%

2. 10%

3. 15%

4. 20%

The correct answer is: 10%

The over speed trip device is a crucial safety mechanism in turbine operations. It is designed to prevent damage to the turbine by shutting it down if it exceeds safe operational speed. Generally, this device is set to actuate when the turbine reaches approximately 10% above its normal full-load speed. This threshold is selected because it provides a balance between allowing sufficient operational flexibility and protecting the turbine from potentially damaging over-speed conditions. When the turbine approaches this 10% margin, the over speed trip device activates to ensure that the turbine can be safely controlled without risking mechanical failure, which could result in catastrophic consequences for both the machinery and personnel. This standard is widely recognized in the industry and aligns with best practices for turbine safety and reliability, which reinforces the choice of 10% as the correct answer.