Why upon high axial displacement of steam turbine vacuum breaker opens?

The vacuum breaker in a steam turbine system opens upon high axial displacement to prevent damage to the turbine and maintain operational safety. High axial displacement can indicate abnormal operating conditions, such as excessive thermal expansion or load changes, which may lead to a vacuum forming in the turbine. By opening the vacuum breaker, it allows atmospheric pressure to equalize, thus protecting the turbine from cavitation and structural stress that could result from a vacuum condition. This mechanism ensures the turbine operates within safe limits and prolongs its lifespan.