Does a turbine need to undergo an overspeed test before being started up?

Safety considerations must be taken into account; it is also possible to conduct tests with the overspeed protection set at a relatively low speed.

When testing a piece of equipment individually, an overspeed test must definitely be conducted to check its overspeed protection system and emergency shutdown function.

What if the plant shuts down for a week? Provided that the turbine has not been overhauled

In my opinion, the overspeed test is primarily a form of protection for the unit, enabling an interlocked shutdown. Since the unit has not been overhauled, there is no need to repeat this experiment. If you are worried, you can conduct a simulated test to check whether the instruments are functioning properly.

1 From a safety management perspective, it is necessary to conduct various tests and adjustments before starting up, including speed tests; however, different users adopt different approaches. 2 There are various methods for over-speed protection, such as electronic systems, mechanical systems that utilize centrifugal force, and hydraulic systems that rely on the relationship between rotational speed and oil pressure. 3 In both mechanical and hydraulic systems, as long as the hardware is not damaged, the relationship with speed remains constant; what is unreliable are the measuring instruments used during the transition process. Electronic systems, on the other hand, are more affected by instrument inaccuracies. Therefore, one approach is to conduct simulation tests, using over-speed signals to observe whether the protection mechanism functions effectively. 4 It is still necessary to conduct regular actual overspeed tests to verify the effectiveness of various protections.

However, some users are concerned about the risks associated with speed tests and fear accidents, so they refrain from conducting such tests

1. Therefore, determining what “regularly” means is up to each user’s interpretation. For example: first commissioning, rotor modification or structural changes, operation for a long period of time, etc. 2. Mechanical over-speed operation is carried out within the range permitted by the design strength; the materials must be able to withstand the stress generated by the high rotational speeds of the rotor, with a safety margin ； Furthermore, the strength of metal materials decreases as temperature rises; operating at subcritical speeds in a cold state is safer than doing so at subcritical speeds in an operational state, so the subcritical speed itself remains within a controllable range. 3. The user’s concerns actually relate to speed control; that is, what if the speed exceeds the limit and the protection system does not activate? Conversely, this concern also exists at normal speeds: what if the speed gets out of control during operation? 4. Due to the concerns outlined in Article 3, even if mechanical overspeed is to be implemented, it is done after testing the instrumentation system first by sending an overspeed signal to see whether the protection mechanisms will activate. Only after the simulation test is passed can the actual overspeed test be conducted.

An overspeed test needs to be conducted before starting the turbine